The terrible fossil record of sea otters, part 1: What do we know about modern sea otters?

You can find the second part here, and the third part here.

Introduction

Sea otters are perhaps my favorite marine mammal, for several reasons. They’re adorable, endangered, ecologically fascinating, and simultaneously the smallest marine mammal and the largest member of the weasel family (Mustelidae). When I was a kid, I would see the sea otters at the Monterey Bay Aquarium and out on the rocky Northern California coast, especially in Monterey Bay – to the point where I actually got a bit bored of them. Once I got into marine mammal research as a twentysomething, however, I realized that 1) they’re only in the North Pacific, 2) endangered, and 3) sort of a success story. I realized that if I traveled to anywhere in the world other than central California, Kamchatka, Alaska, or British Columbia, I would not be seeing any sea otters. This post is going to go through some older ideas of sea otter evolution, what we know, and what we don’t know, and summarize some of the major findings of a paper I published back in 2017.

A few years back, I slowed down with blog writing. But I have realized one thing, especially with this paper: often just writing a scientific article is not enough. In the four years since my otter paper first appeared online, I’ve read multiple articles by ecologists, molecular biologists, and review articles that have either ignored it or misinterpreted the findings (e.g. Pacific invasion of Enhydra 1-3 million years off of my estimation). I think that my blog historically gets more readers than my actual papers, and many scientists outside my narrow discipline have stumbled across these posts and used them as a bridge to our paleontological literature. So, it is in the hope of clarifying what we do and do not know about the evolution of the sea otter that I am writing this more palatable version of one of my papers (with a much larger background review).

A large raft of northern sea otters; photo by Milo Burcham.

A brief and totally non-comprehensive review of relevant see otter biology

All otters are members of the subfamily Lutrinae (=otters) and are the only major aquatic clade of the weasel family (Mustelidae). Mustelids used to include badgers and skunks, now split out into their own families - but weasels, minks, fishers, martens, and the wolverine are still in the Mustelidae. Mustelids are members of the dog-like carnivores, the Caniformia; canids (dogs) are the first diverging branch, followed by bears (Ursidae), raccoons (Procyonidae), pinnipeds (Pinnipedia), and the red panda (Ailuridae), and eventually the mustelid-skunk-badger clade (pinnipeds occasionally are recognized as sister to bears, or at least traditionally were, and their origins now are somewhat murkier - though clearly not derived from mustelids). That means that there are at least five completely disparate lineages of marine carnivores that independently returned to the ocean: the pinnipeds, the polar bear, the sea otter, and the extinct sea mink, and the south american marine otter (same genus as the North American river otter, Lontra). Historically, there have been two ecomorphs of otters, not necessarily forming monophyletic groupings: the "fish eating" otters, and the "crab eating" otters. The fish eating otters tend to have longer snouts/toothrows and the crab eating otters tend to have shorter snouts with larger posterior crushing teeth (=carnassials of terrestrial carnivores) positioned closer to the jaw joint for greater mechanical advantage (Timm-Davis et al., 2015).

There are three named subspecies of modern sea otters, which seem to be anatomically differentiated from one another Enhydra lutris is quite large for a mustelid (20-40 kg) but still quite a bit smaller than fur seals (60-270 kg in males, depending upon the species). They tend not to stray into deep water and while they are typically considered to be associated with kelp forests, they are not bound to the presence of kelp forests; instead, they seem to be tied to rocky shore environments. All Enhydra have large, blunt, clam-cracking teeth, whereas all other mustelids (even river otters) have quite sharp cusps on their teeth; they have sagittal crests and large temporalis muscles, and thus have a powerful bite. Nevertheless, not all sea otter individuals put this bite force to equal use: some specialize on softer prey items (fish, cephalopods, sea cucumbers), and others specialize on mollusks, crustaceans, and echinoderms. In other words, the seemingly specialized feeding adaptations of Enhydra are not manifested as ecological specialization – in fact, the opposite: it allows individual otters to be specialized on different foods in a diverse rocky shore habitat – a sort of interspecific niche partitioning. This likely allows otters to inhabit geographically restricted rocky shore habitats in a higher population density. Otters starve if the shoreline freezes, which explains why sea otters live no further north than the southern limit of seasonal sea ice.

Skull of a sea otter, illustrated by N.N. Kondakov.

            A famous college statistics problem involves the asymmetry of the sagittal crest in sea otters, as otters express handedness in chewing, and with regards to their forepaws, Kenyon (1969) concluded that sea otters were typically right-handed. Roest (1993) is likely the origin of the statistics exercise, and investigates the frequency of various aspects of asymmetry in the skulls of Enhydra. Growth studies show that full biting ability is delayed during growth, and that males develop structures associated with powerful bite force more quickly than females, likely to gain a competitive advantage against other males (Law et al., 2017). Sea otters bite at an unusually wide gape angle in order to use their posteriormost enlarged teeth - upper p4 and the lower m1 - to crush hard prey with the greatest mechanical advantage (just like a lever-style nutcracker). They have unusually wide zygomatic arches to provide a longer distance for contraction of the masseter muscles (Timm-Davis et al., 2017) along with unusually high and long sagittal crests and nuchal crests. The bite of Enhydra lutris is quite a bit different from the only other major marine durophagous carnivore, the extinct "oyster bear" Kolponomos. It hasn't really been the focus of any particular study, but I've observed that the coronoid process (which the temporalis muscle attaches to - the major jaw closing muscle) is comically big and dorsally very elongate with respect to many terrestrial carnivores - including other otters. Enhydra has a loose mandibular symphysis (jaw joint at the chin), and so there is a bit of flexibility between the mandibles; Kolponomos instead has a fused mandibular symphysis and high mandibular stiffness - so its bite is more like a sabertooth cat than a sea otter, despite sharing the enormous rounded molars. Sea otters instead have low mandibular stiffness, allowing for a crushing bite on one side, a bit more like a hyena. Kolponomos probably did not have tactile paws like a sea otter, and therefore relied on its canines and front of the jaws to pry mollusks off of rocks, prior to crushing (Tseng et al., 2016).

Sea otters are famous for their tool use – often keeping a favored anvil stone in a famous armpit ‘pouch’ – rather, there’s a bit of loose skin that keeps the hammer stone from falling out if the otter holds it in place with its forelimb. Sea otters are often credited with carrying around ‘favorite’ anvil stones, and though I’ve seen this claim repeated endlessly across the web, I’ve never seen it credited to an actual biological observation in nature. It’s not mentioned by Kenyon (1969) nor is it mentioned in any more recent papers on tool use. If anyone knows of the origin of this claim, please share it! The one documented case of repeated use of the same rock I know of are stationary boulders in Elkhorn Slough where otters smash bivalves against, leaving little deposits of mussel shells with consistent fractures (a fascinating “archaeological” study of otter anvil stones by Haslam et al. 2019). Otters apparently do not use hammer stones; they use rocks, or occasionally bivalve shells, on their stomach and slam the bivalve downwards into the rock. I’ve witnessed it many times but always while fossil collecting on the cliffs in Santa Cruz, so I’ve been within earshot but never close enough to see what was being slammed into what.

Sea otters with an anvil stone and a stationary anvil boulder, from Haslam et al. 2019.

The tiny, mitten-like forepaw of the sea otter, from Strobel et al. 2018.

We know thanks to some careful genetic work (Ralls et al., 2017) that 1) not all otters use tools, but those that do are not closely related to one another; and 2) tool use is taught by mothers to their pups. This distributed tool use behavior suggests that the common ancestor of all sea otters, which likely lived during the last glacial maximum, was capable of tool use. Possibly correlated with tool use are the hilariously tiny forelimbs and mitten-like paws which frequently lack individual divisions between the fingers. For some reason, sea otters ended up reducing rather than lengthening their fingers, likely for heat retention (see below). Unfortunately, there is no obvious expression in brain endocast topography that distinguishes tool using Enhydra from the clawless otters, which use their paws extensively for prey manipulation.

Skeleton of a sea otter showing the disproportionate fore and hind limbs, from twitter user @seaottersavvy

A sea otter drying out its hindfeet while rafting. Photo by Shetzers Photography.

The hindlimbs of sea otters are quite long, and the hindfeet are developed into rudimentary flippers much like pinnipeds, with the outermost digits being very elongated, and extensive webbing along the entire length of the digit. Pinniped hindflippers have elongated outer (5) and innermost (1) digits with digit 3 being the shortest, whereas in Enhydra, digit 5 is longest and digit 1 is shortest; the hindflipper of Enhydra looks startlingly like the foreflipper of a phocid seal. All other otters instead have five toes with incomplete webbing that look nearly identical to the forepaw. Sea otters swim by dorsoventral undulation of these hindflippers as well as the elongate, muscular tail – but unlike other lutrines, most of the propulsive force comes from the feet. Opposite from the hindlimbs, the forepaws are highly reduced relative to the ancestral condition, and are not used in locomotion; the result are proportions not unlike many bipedal dinosaurs. Enhydra is quadrupedal, and the extreme disparity between forelimb and hindlimb length makes for an extremely strange and unsettling posture while walking around on land. Their reduced agility on land is probably a major contributing factor for haulout behavior by the southern sea otter, which appears to haul out less often than the northern sea otter in Alaska. This may also be a result of the extreme population bottleneck, and perhaps there is a greater fear of humans in the southern population.

Sea otters running on land; photo credit: seaottersavvy.org

Sea otters have no blubber, unlike other marine carnivores like pinnipeds. Pinnipeds have either blubber and no fur (sea lions, earless seals, walrus) or a combination (fur seals). Fur seals have some of the thickest fur in the animal kingdom – but fur is inadequate for diving at depth. Now, I just read a Scientific American article with a Q&A about fur and the first answer is “there’s no difference between fur and hair”, which from the perspective of homology may be true (both are cylindrical keratin growths from skin) but in terms of morphology and function is absolutely bullshit. Mammalian carnivores have basically two types of insulation: guard hairs, which are the longer, wider, and stiffer hairs you see externally on your dog or cat, and underfur, which is the really fine stuff that is often kind of wiggly. As I’m typing, I see a couple strands of my cat’s underfur right now. This is the stuff that you need to brush your dog or cat to remove. Hair does nothing for insulation underwater, but fur traps air bubbles. To help with this, it has a different scaly pattern under microscopy. This is only effective at shallow depths because once you go below the water pressure pushes the air bubbles out (Liwanag et al., 2012). So fur only works for shallow-diving, early marine invaders of aquatic lineages – once marine carnivores start to dive below 100 meters, they need to evolve blubber. Hair was lost independently within sea lions and earless seals, and more than likely a third time within walruses (and, if we ever had a way to test it, I’d wager it was lost a fourth time in the desmatophocids, based on body mass). Sea otters are shallow divers with a very tiny body mass – the smallest marine mammal – and rely completely on fur for insulation in the absence of blubber. The earliest pinnipeds, scarcely larger than Enhydra, very likely primitively had only fur and no blubber.

Map of modern sea otter populations, with original caption, from Kenyon (1969).

Sea otters nowadays have three very geographically disparate (and somewhat anatomically disparate; Wilson et al., 1991) subspecies populations: the western sea otter (Enhydra lutris lutris), today living in the Komandorskiye/Commander Islands and Kuril Islands south of Kamchatka, the northern sea otter (Enhydra lutris kenyoni) living throughout the Aleutians and east along the southern Alaska coast to Prince William Sound, and the southern sea otter (Enhydra lutris nereis), living only in central California from Santa Cruz County down to Ventura/LA counties and the channel islands. Historically, they lived continuously from Hokkaido and Sakhalin in the western North Pacific, eastward throughout the Aleutians and Alaskan panhandle as well as the Pribilof Islands, British Columbia, Washington, Oregon, California, and down to Baja California, at least as far south as Morro Hermoso on the Pacific side. The Spanish wrote that otters used to be seen frequently inside the San Francisco Bay as there used to be more kelp beds – now buried by the extensive silt deposits that filled in the bay and expanded the wetlands that make the area so famous for its natural history. These wetlands and buried rocky outcroppings mean that there is no longer very much kelp in the bay, and so there is little reason for otters to venture within. They also rarely venture further north than Point Ano Nuevo – though there are stray individuals occasionally as far north as Eureka; I saw one in 2017 at Pescadero State Beach (southern San Mateo county) and I lost my shit I was so excited.

A well-known graph showing the number of sea otter pelts (y axis in thousands - e.g. 1,000 to 8,500) sold in London (and only London) from the late 19th century to the early 20th century. Source: Wikimedia commons.  

Though hunted for thousands of years by indigenous peoples along the Pacific shores, sea otters were by westerners in the 1730s, leading to the first hunting expeditions by Russian fur traders in the Kuril Islands. Russian hunting extended ever further eastward, and the trade in sea otters decimated the populations in the Pacific Northwest so badly that kelp forests have vanished, a ghost of their former distribution – and severely limiting the carrying capacity for otter populations. Fort Ross, built in 1812 about a three hours’ drive north of San Francisco in Sonoma County, was built by the Russians to support otter hunting in northern California. Fort Ross marks the furthest outpost of Russian Imperialist expansion during the 19^th century – a high water mark – and it was abandoned in the 1840s. By this time the sea otter population in California had also been decimated. Southern sea otters were eventually considered extinct in the late 19^th century, and the species as a whole were commercially extinct throughout their range by the 1850s. In the early 20^th century, there were a handful of sightings kept secret by scientists, and thanks to the WPA construction of Highway 1 in the late 30s, otters were formally rediscovered to be very much alive in 1938. However, there was an estimated 50 individuals in this population (alternatively, I’ve read a raft of 50 individuals spotted by a couple testing a new telescope in 1938, presumably part of a larger but unquantified population). They have since rebounded to around 3,000 – though this is only a fraction of their pre-industrial population estimate of about 16,000.

Molecular phylogeny derived cladogram of lutrine relationships, from Koepfli et al. (2008).

Molecular phylogenetic work has focused on the genetic bottleneck of southern sea otters as well as the placement of Enhydra within the Mustelidae – it is typically recovered as the sister taxon to the old world clawless otters (Amblonyx + Aonyx). Molecular clock dating from a paper in the 90s suggests a rather broad (and predictable) range of dates for the common ancestor of all three modern subspecies, sometime about 20,000-200,000 years ago (Cronin et al., 1996). Clearly, more work is needed to refine this molecular divergence date. Morphometric studies (Wilson et al., 1991) seem to support the recognition of three subspecies (regardless of how one feels of the use of subspecies as taxonomic entities).

Next up: the fossil record of sea otters, and my desperate attempts to go out and find more.

References/Bibliography/Further Reading

Beichman et al. 2019. https://academic.oup.com/mbe/article-abstract/36/12/2631/5481008?redirectedFrom=fulltext

Haslam et al. 2019. https://www.nature.com/articles/s41598-019-39902-y

Kenyon, 1969. https://www.fwspubs.org/doi/abs/10.3996/nafa.68.0001

Larson et al., 2012. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0032205

Law et al. 2017. https://academic.oup.com/biolinnean/article/121/2/420/3045262

Liwanag et al. 2012. https://academic.oup.com/biolinnean/article/106/4/926/2452408

Ralls et al. 2017. https://royalsocietypublishing.org/doi/full/10.1098/rsbl.2016.0880

Roest, 1993. https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1748-7692.1993.tb00443.x

Sharpe, 1939. The discovery of the “extinct” sea otter. https://seaotters.org/pdfs/extinct.pdf

Strobel et al. 2018. https://jeb.biologists.org/content/221/18/jeb181347

Timm-Davis et al. 2015. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0143236

Timm-Davis et al. 2017. https://jeb.biologists.org/content/220/24/4703

Tseng et al. 2016. https://royalsocietypublishing.org/doi/full/10.1098/rspb.2016.0044

Wilson et al. 1991. https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1090&context=usdeptcommercepub

2019 in review: advances in marine mammal paleontology

Oi, it's been a long time since I've done this. We're five months late here, but let's just say 2019 was not a great year for me professionally and it's taken me about a year to mentally catch up, accept the new normal, and re-motivate me to do research. Have you ever seen Office Space? I was Peter Gibbons for quite a while (still am, and my students love it). Anyway, I'm going to get back into this blogging thing. Truth be told, winter was very busy for me, and so I genuinely did not have any time to write this post on time - all of December was spent working on getting a cast of a whale skeleton repaired and painted and ready for mounting. I reviewed like 16 manuscripts in 2019, and didn't submit a single one of my own! I finally, for the first time in my career, declined a few requests to keep my stress levels down. I taught my first giant lecture with about 100 students - which was not a whole lot harder than our typical 50 student lectures (more emails, though). And, now we're stuck in quarantine - and I've been catching up on various things in a big way, so without further ado, brought to you by Covid19, the very belated 2019 in marine mammal paleontology post!

Albright et al.: Cenozoic vertebrate biostratigraphy of South Carolina, U.S.A., and additions to the fauna. Bulletin of the Florida Museum of Natural History.

Link: https://digitalcommons.unf.edu/facultyshowcase/2020/Showcase/1/

Abstract: Study of vertebrate fossils from the South Carolina Coastal Plain played a significant role in the early history of vertebrate paleontology as a scientific discipline in North America. However, a clear understanding of the state’s vertebrate biostratigraphy has been greatly hindered by the paucity of well-exposed fossil-bearing stratigraphic sections and a complicated subsurface stratigraphy. Most units, particularly those of Neogene and Quaternary age, exist as thin veneers of marine or estuarine sediments that typically occur as infilled topographic lows or erosional remnants as determined primarily from borehole stratigraphy. Hence, lateral continuity can be difficult to confirm over broad geographic areas often resulting in confusion insofar as vertebrate fossil provenance is concerned. The evaluation of vertebrate fossils from the South Carolina Coastal Plain presented here, and of the geologic units from which they originated, or are thought to have originated, results in the first modern biostratigraphic framework for the known Cenozoic record of the state. Results provide (1) updated correlations of many units to the most recent, astronomically-tuned marine oxygen isotope stages; (2) the first viverravid from the Atlantic Coastal Plain, Didymictis proteus; (3) new information on the timing of certain Neotropical immigrants into the Southeast during the Great American Biotic Interchange, including the oldest record of Erethizon in this region and the oldest records of capybara in the USA; (4) the possible oldest record of the microtine rodent Allophaiomys pliocaenicus in the USA; (5) new details on the unit of origin for the type specimen of the archaeocete Dorudon serratus; and (6) new details on the ontogeny of the early odontocete Agorophius pygmaeus. New taxonomic records from South Carolina include Glyptotherium texanum, Holmesina floridanus, Ondatra idahoensis, Erethizon ?bathygnathum, Leopardus amnicola, Miracinonyx ?trumani, Canis lepophagus, Canis latrans, Phocanella pumila, Callophoca obscura, Monatherium sp., Anchippus texanus, Subhyracodon mitis, Aphelops ?malacorhinus, Teleoceras ?guymonense, and Perchoerus sp. New specimens of previously recorded taxa are also noted.

Comments: This behemoth of a paper has a LOT in it, and once I have barely had time to scratch the surface of - but discusses the South Carolina marine vertebrate fossil record in detail, including all sorts of obscure historical references I wasn't aware of. Also, it's worth noting that because South Carolina is so anomalously fossiliferous, and there are also no cliffs, that the history of paleontology here is dominated by tons and tons and tons of very neat but context-less ex situ fossils with uncertain ages and disagreements over provenance.

Bianucci et al: A new Monodontidae (Cetacea, Delphinoidea) from the lower Pliocene of Italy supports a warm-water origin for narwhals and white whales. Journal of Vertebrate Paleontology.

Link: https://www.tandfonline.com/doi/abs/10.1080/02724634.2019.1645148?journalCode=ujvp20

Abstract: A new taxon of monodontid cetacean, Casatia thermophila, gen. et sp. nov., is here described on the basis of a partial skull from lower Pliocene (5.1–4.5 Ma) marginal-marine deposits of Tuscany (central Italy). This new taxon belongs to Monodontidae based on the presence of a medial exposure of the maxillae anterior and lateral to the external bony nares; it mainly differs from all other named monodontids by the presence of a median depression of the premaxillae anterior to the premaxillary sac fossae and by a medial margin of the premaxillary-maxillary suture that does not parallel the anterolateral profile of the external bony nares. Our phylogenetic analysis, the first including all taxa of Monodontidae, recovers Casatia as a crown monodontid, more closely related to Delphinapterus than to Monodon and sister group of an unnamed taxon from the North Sea. The holotype of Casatia represents the first and only fossil monodontid from the Mediterranean Basin. Taking its place beside abundant fossils of strongly thermophilic marine vertebrates, such as the bull shark Carcharhinus leucas, the tiger shark Galeocerdo cuvier, and the extinct sirenian Metaxytherium subapenninum, Casatia thermophila represents the strongest evidence supporting the hypothesis that monodontids once thrived in low-latitude, warm-water habitats. On the basis of our phylogenetic reconstruction, early relatives of the extant monodontids might have adapted independently to the high-latitude, cold-water environments they currently master. The definitive disappearance of the Neogene thermophilic monodontids could be attributed to the cooling episode that accompanied the onset of long-term Northern Hemisphere glaciation around 3 Ma.

Comments: This paper is sort of a response to the 2018 paper by Ichishima et al. on Haborodelphis, a beluga-like monodontid from the Pliocene of Hokkaido. Previously reported temperate to subtropical latitude monodontids (e.g. Denebola, Bohaskaia) suggested that the earliest belugas were actually warm water cetaceans - but Ichishima et al. found a cold water invertebrate assemblage, and indicated that since there are some quite cold (albeit brief) periods in the Pliocene, greater care was needed to demonstrate paleoclimate aside from "ahhh, yeah it's from Mexico so it's gotta be warm". Casatia thermophila (great species name!) was recovered with a nice assemblage of warm water taxa, in the Mediterranean! Given the timing and incomplete preservation of Casatia I do wonder if Bianucci et al. saw the Ichishima paper and thought "well now is the perfect time to get this thing published" and wrote it up. Fascinating little back and forth. 

Bianucci et al. Rise of the titans: baleen whales became giants earlier than thought. Biology Letters.

Link: https://royalsocietypublishing.org/doi/10.1098/rsbl.2019.0175

Abstract: Baleen whales (Mysticeti) are major ecosystem engineers, thanks to their enormous size and bulk filter feeding strategy. Their signature gigantism is thought to be a relatively recent phenomenon, resulting from a Plio-Pleistocene mode shift in their body size evolution. Here, we report the largest whale fossil ever described: an Early Pleistocene (1.5–1.25 Ma) blue whale from Italy with an estimated body length of up to 26 m. Macroevolutionary modelling taking into account this specimen, as well as additional material from the Miocene of Peru, reveals that the proposed mode shift occurred either somewhat earlier, or perhaps not at all. Large-sized mysticetes comparable to most extant species have existed since at least the Late Miocene, suggesting a long-term impact on global marine ecosystems.

Comment: This paper is a response of sorts to earlier studies, chiefly Slater et al. 2017, which proposed that  baleen whales did not become gigantic (e.g. over 15 meters) until the last 2-3 million years - the analysis was based on skull size  and found that gigantism evolved independently and late in balaenids and balaenopteroids. How late, nobody was sure, because most Pliocene fossil mysticetes are still on the small side and our Pleistocene record is terrible. I always thought the Slater hypothesis was correct, based on the lack of large mysticete *crania*. This new study reported a nearly full size fossil blue whale skull from the middle Pleistocene of Italy, and a few gigantic mysticetes from the latest Miocene of Peru (Pisco Fm., of course) and it pulled the onset of gigantism back a few million years - same overall pattern, just slightly earlier. Now: I think a better way around this, to get a better sample size, is to get a regression for body length based on vertebral size (which, based on my last project, is eminently possible) and measure hundreds and hundreds of isolated vertebrae. Granted, vertebrae are non-diagnostic, so they will be devoid of phylogenetic context, but may show a very different pattern as I have seen gigantic vertebrae in cliffs, backyards, and museum collections from late Miocene and Pliocene localities, and I believe there is certainly collecting bias against large mysticetes (too big to excavate).

Bisconti et al. A new balaenopterid whale from the late Miocene of the Southern North Sea Basin
and the evolution of balaenopterid diversity (Cetacea, Mysticeti). PeerJ.

Link: https://peerj.com/articles/6915/

Abstract: Balaenopterid mysticetes represent the most successful family-rank group of this clade. Their evolutionary history is characterized by a rich fossil record but the origin of the living genera is still largely not understood. Recent discoveries in the southern border of the North Sea revealed a number of well preserved fossil balaenopterid whales that may help resolving this problem. In particular, skull NMR 14035 shares morphological characters with the living humpback whale, Megaptera novaeangliae and, for this reason, its characteristics are investigated here. The comparative anatomical analysis of the new specimen formed the basis of a new phylogenetic analysis of the Mysticeti based on a matrix including 350 morphological character states scored for 82 Operational Taxonomic Units. The stratigraphic age of the specimen was determined based on the analysis of the dinocyst assemblage recovered in the associated sediment. We assessed clade diversity in Balaenopteridae by counting the numbers of clades in given time intervals and then plotted the results. Nehalaennia devossi n. gen. et sp. is described for the first time from the late Tortonian (8.7–8.1 Ma) of the Westerschelde (The Netherlands). This new taxon belongs to Balaenopteridae and shows a surprisingly high number of advanced characters in the skull morphology. Nehalaennia devossi is compared to a large sample of balaenopterid mysticetes and a phylogenetic analysis placed it as the sister group of a clade including the genus Archaebalaenoptera. The inclusion of this fossil allowed to propose a phylogenetic hypothesis for Balaenopteridae in which (1) Eschrichtiidae (gray whales) represents a family of its own, (2) Balaenopteridae + Eschrichtiidae form a monophyletic group (superfamily Balaenopteroidea), (3) Cetotheriidae is the sister group of Balaenopteroidea, (4) living Balaenoptera species form a monophyletic group and (5) living M. novaeangliae is the sister group of Balaenoptera. Our work reveals a complex phylogenetic history of Balaenopteridae and N. devossi informs us about the early morphological transformations in this family. Over time, this family experienced a number of diversity pulses suggesting that true evolutionary radiations had taken place. The paleoecological drivers of these pulses are then investigated.

Comments: An interesting new study reporting the new genus and species Nehaelennia devossi - an Archaebalaenoptera-like early rorqual. When I started working on fossil baleen whales, we were in a state of 'taxonomic paralysis' because of good ole P.J. Van Beneden, who, bless him, named a lot of fossil species of mysticetes from Belgium in the late 19th century - based on chimaeric assemblages of non-associated fossils that he arranged to fit pre-imagined 'archetypes' (e.g. the modern Atlantic fauna has a small minke whale, so all these small bones go to the Pliocene version of the minke whale and surely all go together... right?) and then like, went ahead and fucking renamed a bunch of his own species and genera! Anyway, nobody had the gall to start fixing the problem until 2010 when Bosselaers and Post shit-canned all of his balaenopterids as nomina dubia with the possible exception of "Balaenoptera" borealina. Since then a number of new discoveries of Belgian and Dutch mysticetes have finally been able to be studied without being mired in the taxonomic web of Van Beneden. This new paper says a lot of things, including a very different placement of my own species Balaenoptera bertae which I very much doubt. Regardless, the new specimen is nice.

Boessenecker and Boessenecker. Paleontology of the "Ashley Phosphate Beds" of Charleston: insights from Northbridge Park, Charleston, South Carolina. GSA Field Guidebooks.

Link: https://pubs.geoscienceworld.org/books/book/2152/chapter/120859059/Paleontology-of-the-Ashley-Phosphate-Beds-of

Abstract: A man-made deposit at Northbridge Park near Charleston, South Carolina, consists of phosphatic nodules, fossils, and mud dredged from the bottom of the Ashley River; nodules and fossils lay strewn across the banks of the river. This artificial deposit is likely representative of deposits mined extensively in the late nineteenth century and widely referred to as the “Ashley Phosphate Beds.” Many of the taxa discovered at Northbridge Park were historically reported from the phosphate beds, and include sharks, rays, bony fish, sea turtles, giant birds, whales, dolphins, sea cows, and land mammals. Some of these bear adhering matrix indicating origin from the Oligocene Ashley Formation. Others lack matrix but have short geochronologic ranges and are derived from the Ashley Formation, Lower Miocene Marks Head Formation, Lower Pliocene Goose Creek Limestone, and Pleistocene Wando Formation.

Comments: This paper hilariously started out as a blog post (elsewhere on this very blog) and as the result of many recreational fossil collecting trips to a fossil site near my old apartment. This was the first fossil site I was able to visit now that quarantine closures are easing. GSA publications are notoriously hard to get a hold of, so email me if you want a pdf. This was my only paper in 2019! Coauthored with my lovely wife and coworker.

Bosio. Integrated chronostratigraphy and taphonomic studies in Miocene sedimentary successions of the East Pisco Basin (Peru). Plinius.

Link: http://www.socminpet.it/Plinius2019/bosio.pdf

Abstract: (no abstract, so here's the introduction) Along the western side of the Ica River (Ica Desert, Peru), the Miocene Chilcatay and Pisco formations of the East Pisco Basin crop out. These units are characterized by an extraordinarily preserved marine vertebrate fossil assemblage, especially cetaceans. This work has the purpose of making chronostratigraphic and taphonomic studies on these formations, cropping out in the Ica River valley. The Pisco Basin, in southern Peru, is one of the fault-bounded Cenozoic sedimentary basins along the Peruvian coast, located at 14°30’ S of latitude. Along the coast, the most easterly Outer Shelf High separates the forearc Pisco Basin into an offshore and an onshore portion, referred to as the West Pisco Basin, still submerged, and East Pisco Basin (Fig. 1a). The sedimentary infill of the East Pisco Basin has been described by Dunbar et al. (1990) and DeVries (1998), and consists of five lithostratigraphic units: the Eocene Caballas Formation, the
middle to upper Eocene Paracas Formation (subdivided in Los Choros and Yumaque members), the uppermost Eocene-lower Oligocene Otuma Formation, the uppermost Oligocene to lower Miocene Chilcatay Formation, and the upper Miocene to Pliocene Pisco Formation (Fig. 1b) (e.g., Dunbar et al., 1990; DeVries, 1998; DeVries & Jud, 2018).

Comments: I think there will be a longer followup paper later - I always look forward to taphonomic research!

Buono et al. Eocene Antarctica: a window into the earliest history of modern whales. Advances in Polar Science.

Link: http://www.aps-polar.org/paper/2019/30/03/A190617000001

Abstract: The Eocene–Oligocene Southern Ocean is thought to have played a major role in cetacean evolution. Yet, fossils from its heart—Antarctica—are rare, and come almost exclusively from the Eocene La Meseta and Submeseta formations of Marambio (Seymour) Island. Here, we provide a summary and update of this crucial fossil assemblage, and discuss its relevance in the broader context of cetacean evolution. To date, Eocene specimens from Antarctica include basilosaurids, a group of archaic stem cetaceans that had already fully adapted to life in water; and the archaic toothed mysticete Llanocetus, the second oldest crown cetacean on record (ca. 34 Ma). This Eocene co-occurrence of stem and crown cetaceans is highly unusual, and otherwise only observed in Peru. Though related, at least some of the Antarctic species appear to be different from, and notably larger than their Peruvian counterparts, suggesting an early differentiation of the high latitude cetacean fauna.

Comments: This interesting new paper is a summary of recent papers on basilosaurids and the toothed mysticete Llanocetus from the Priabonian La Meseta Formation of Seymour Island, Antarctica. This unit is an important window into mid-Cenozoic marine vertebrate evolution in the southern ocean. This paper does report some interesting new specimens including a beautifully preserved mysticete pelvis *probably* (but not certainly) belonging to Llanocetus.

Churchill and Uhen. Taxonomic implications of morphometric analysis of earless seal limb bones. Acta Palaeontologica Polonica.

Link: https://www.app.pan.pl/article/item/app006072019.html

Abstract: Fossil Phocidae (earless seals) are mostly known from isolated postcranial material, forcing researchers to rely upon humeri and femora for the diagnosis of taxa and reconstruction of phylogeny. However, the utility of these elements has never been rigorously tested. Here, we provide the first quantitative analysis of morphometric data from the humerus and femur, incorporating measurement data from all extant genera as well as several fossil taxa. Principle components analysis (PCA) found that genera clustered together on PC1 and PC2, although there was poor segregation of taxa and extensive overlap with genera in adjacent regions of the morphospace. Discriminant function analysis (DFA) was able to sort fossil taxa into different subfamilies, but performed poorly at lower taxonomic levels. A preliminary review of phylogenetic characters found that while some characters performed well at distinguishing different subfamilies, many characters were poorly defined and not quantified, possessed greater individual variation than past studies suggested, or were more variable in fossil taxa. Our analyses suggest that the utility of isolated humeri and femora for diagnosis of new taxa has been greatly exaggerated, and that extreme caution should be applied to interpretations of taxonomy of fossil material based on isolated elements. Future research should instead focus on study of associated skeletons and cranial material. A thorough revision of fossil phocid taxonomy is needed, and many described taxa are likely to be nomina dubia and of limited use in phylogenetic analysis.

Comments: This sorely needed paper is a first stab at actually resolving the hopelessly confused study of fossil seal postcranial bones. Lots of noise has been made about limb bones being diagnostic and paleoecologically informative, with non-associated bones being jumbled together into discrete "ecomorphotypes". This paper critically evaluates these claims and finds that there is not much statistical support for the diagnostic value of isolated limb bones.

Collareta et al. A new kogiid sperm whale from northern Italy supports psychrospheric conditions in the early Pliocene Mediterranean Sea. Acta Palaeontologica Polonica.

Link: https://app.pan.pl/article/item/app005782018.html

Abstract: Among living cetaceans, dwarf and pygmy sperm whales (Kogia) are the only members of the family Kogiidae, regarded as diminutive and elusive relatives of the great sperm whale Physeter. Kogiids are known as fossils by several skulls, teeth, and ear bones from Neogene deposits of the Northern Hemisphere and Peru. We report on a fossil kogiid specimen collected at Sant’Andrea Bagni (northern Italy) from Zanclean marine mudstone; these deposits also yielded a rich deep-water elasmobranch assemblage depicting the presence of Atlantic-derived psychrospheric waters. The kogiid specimen, consisting of a partial cranium, one detached tooth, one vertebra, and one fragmentary rib, is here referred to Pliokogia apenninica gen. et sp. nov. Pliokogia is mostly characterised by a long and dorsally flattened rostrum and by the presence of two well-distinct fossae on the right side of the supracranial basin, including an elongated peripheral maxillary fossa on the posterior portion of the right maxilla. Our phylogenetic analysis recovers Pliokogia as a member of the subfamily Kogiinae, which includes Kogia, Koristocetus, Nanokogia, and Praekogia. A low temporal fossa and the absence of dental enamel suggest that, like extant Kogia, Pliokogia was a suction feeder. Since living kogiids do not inhabit the Mediterranean waters, and considering that they feed on deep-water prey in open-sea areas, the association of Pliokogia with a psychrospheric elasmobranch assemblage with Atlantic affinities is noteworthy. Indeed, in early Pliocene times, the Gibraltar connection was controlled by estuarine dynamics, thus allowing the entrance of deep-water organisms (including the putative prey of Pliokogia) in the Mediterranean Basin. The subsequent abandonment of the Mediterranean Sea by kogiids might therefore be related to the definitive establishment of the present-day antiestuarine circulation at Gibraltar, which likely led to a limited deep nutrient supply and resulted in the strong depletion of most Mediterranean deep-water ecosystems.

Cortes et al. Shark‑cetacean trophic interactions during the late Pliocene in the Central Eastern Pacific (Panama). Palaeontologia Electronica.

Link: https://palaeo-electronica.org/content/2019/2652-pliocene-whale-from-panama

Abstract: We provide a description of the remains of a fossil whale from western Panama. The record consists of appendicular remains of a mysticete, which has been assigned to Balaenopteridae. These remains, found in the sediments of the late Pliocene Burica Formation, represent the first record of a marine mammal in the Neogene sedimentary succession of the Burica Peninsula. Two different types of shark bite marks, serrated and deep-unserrated, found on the radius and phalanges suggest scavenging by at least two white shark (Carcharodon) individuals. The deep, unserrated marks were possibly caused by continual biting by sharks. Both the morphology of the shark bite marks and their relative location on the whale limb bones constitute evidence of shark-cetacean trophic interaction. Although the specimen lacks diagnostic features that would allow a species-level identification, it does provide new information on the vertebrate fauna of a very poorly prospected Central Eastern Pacific exposure, thus opening an opportunity for exploring the marine fauna during a critical episode in Earth history, the Plio-Pleistocene transition.

Cuitino et al. Factors affecting the preservation and distribution of cetaceans in the lower Miocene Gaiman Formation of Patagonia, Argentina. Palaeogeography, Palaeoclimatology, Palaeoecology.

Link: https://www.sciencedirect.com/science/article/abs/pii/S0031018218306904

Abstract: Factors affecting cetacean preservation and distribution in ancient sedimentary successions are not well understood. Actualistic studies have focused on coastal and deep marine examples, and little is known about taphonomic processes occurring within shelf environments. In this paper, we integrate sedimentological, taphonomic and palaeontological data for the cetacean-bearing lower Miocene Gaiman Formation from Patagonia, Argentina, to analyse which factors affected the distribution and preservation of cetaceans in several localities of the Southwestern Atlantic. Facies analysis shows that the formation represents a transgressive-regressive stratigraphic cycle, with palaeoenvironments including coastal, storm-dominated shoreface, inner shelf embayment and open inner shelf. Cetacean remains show preservation styles varying from isolated elements to articulated specimens, with nearly all remains restricted to both embayment and open marine inner shelf settings. Two fossil cetacean assemblages are recognized: Assemblage A comprises small-sized odontocetes dominated by Platanistoidea, preserved mostly in inner shelf embayment deposits; and Assemblage B comprises large-sized odontocetes and mysticetes, dominated by Physeteroidea and Balaenopteroidea, preserved mostly in open inner shelf deposits. Cetacean preservation style is controlled by a combination of palaeoenvironmental conditions, such as energy and sedimentation rate, and by biological factors, such as cetacean body plan and its impact on carcass buoyancy. Ecological factors may also explain the stratigraphic distribution of cetaceans between coastal and oceanic assemblages. This novel integrative and multidisciplinary analyses improves our knowledge of cetacean taphonomy in shelf environments.

Comments: This study claims to show evidence of habitat preference in ancient cetacean assemblages - I am skeptical owing to the process of bloat and float, and wonder what a larger sample of additional assemblages would show. Nevertheless, it is an interesting taphonomic study and food for thought.

Davydenko et al. The earliest record of a marine mammal (Cetacea: Basilosauridae) from the Eocene of the Amazonia. Journal of Vertebrate Paleontology.

Link: https://www.tandfonline.com/doi/full/10.1080/02724634.2018.1549060

Abstract: The Amazon region is known by its rich Cenozoic mammalian diversity; however, fully aquatic mammals (cetaceans and sirenians) appear in its fossil record only from the Miocene, and solely as freshwater forms (Antoine et al., 2017). Meanwhile, during the Eocene, there were marine basins deeply intruding into the South American continent and reaching its inner regions (Louterbach et al., 2014); therefore, marine mammals could have inhabited Amazonia during that time. Here, we report the first record of an Eocene marine mammal, namely, a cetacean of the family Basilosauridae, from the northwestern Amazon region and discuss its taxonomic and morphological affinities, as well as its environment in the context of the geographic distribution of basilosaurids during the Eocene.

Diaz-Berenguer et al. The Hind Limbs of Sobrarbesiren cardieli (Eocene, Northeastern Spain) and New Insights into the Locomotion Capabilities of the Quadrupedal Sirenians. Journal of Mammalian Evolution.

Link: https://link.springer.com/article/10.1007%2Fs10914-019-09482-9

Abstract: In the transition from a terrestrial to an aquatic environment, sirenian marine mammals reduced and lost their hind limbs and developed a horizontal caudal fin, the main propulsive organ in extant sirenians. Quadrupedal forms are only known from the Eocene and are represented by three different clades: the amphibious “prorastomids,” the aquatic quadrupedal protosirenids, and Sobrarbesiren cardieli, a four-legged sirenian from the middle Eocene of Spain, considered the sister taxon of the fully aquatic Dugongidae. This ecological shift from terrestrial to an aquatic environment was naturally associated with adaptations, among others, of the skeleton. However, sirenian hind limb bones have been poorly studied because of the scarce material available in the fossil record. Here, we describe in detail the hind limb bones of Sobrarbesiren, analyzing their functional morphology and comparing them with other basal sirenians and cetaceans, and with related terrestrial mammals such as proboscideans and hyracoids. The hind limbs of Sobrarbesiren were capable of a great variety of movements. Based on the presence of a strong sacroiliac articulation, we propose that it swam by dorsoventral pelvic undulation combined with pelvic paddling analogous to extant otters and the “prorastomid” Pezosiren. We also conduct the first microanatomical analysis of hind limb bones of an Eocene sirenian. Data reveal extreme inner compactness in the Sobrarbesiren innominate and femur, with the first description of osteosclerosis in an amniote innominate combined with the highest degree of osteosclerosis observed in amniote femora. The results confirm that the microanatomical changes precede the external morphological changes in such ecological transitions. The process of adaptation of sirenians to an aquatic life was thus a more complex process than previously thought.

Di Celma et al. Allostratigraphy and paleontology of the lower Miocene Chilcatay Formation in
the Zamaca area, East Pisco basin, southern Peru. Journal of Maps.

Link: https://www.tandfonline.com/doi/full/10.1080/17445647.2019.1604439?af=R

Abstract:  Based on mapping of laterally traceable stratigraphic discontinuities, we propose a high-resolution allostratigraphic scheme for one of the world’s foremost fossil marine vertebrate Lagerstätten: the lower Miocene strata of the Chilcatay Formation exposed along the Ica River near Zamaca, southern Peru. Measured sections combined with 1:10,000 scale mapping of a 24 km² area provide an overview of the stratal architecture, as well as a general facies framework and interpretation of the various depositional settings. As a whole, the Chilcatay alloformation is bounded by the CE0.1 unconformity at the base and the PE0.0 unconformity at the top. An internal Chilcatay surface, termed CE0.2, splits the alloformation into two distinct allomembers (Ct1 and Ct2). The Ct1 allomember comprises three facies associations recording deposition in shoreface, offshore, and subaqueous delta settings. The Ct2 allomember comprises two facies associations, recording deposition in shoreface and offshore settings. Using these data, we place the rich marine vertebrate assemblage in a precise spatial and stratigraphic framework. The well-diversified vertebrate assemblage is dominated by cetaceans (mostly odontocetes) and sharks (mostly lamniforms and carcharhiniforms); rays, bony fish, and turtles are also present. Taxonomic novelties include the first records of baleen whales, platanistids, and eurhinodelphinids from the Chilcatay Formation.

Dominici et al. The awkward record of fossil whales. Earth Science Reviews.

Link: https://www.sciencedirect.com/science/article/abs/pii/S0012825219304301

Abstract: The habitat, actuopaleontology and global fossil record of crown cetaceans, today occupying apex positions in the marine ecosystem, is reviewed. A large Neogene- Quaternary dataset is built, covering the time span of the evolutionary radiation of crown Odontoceti and Mysticeti and including updated information on whale taxonomy, chronostratigraphy, geography, paleoenvironment, taphonomy and size. We outline an uneven chronostratigraphic and geographic distribution of fossils, which influences our understanding of global diversity trends. Notwithstanding the vast majority of whale carcasses sinks to bathyal depths, the fossil record is mainly associated with shelf paleoenvironments. The evolution of gigantic whales triggered the radiation of whale-fall communities, including a global bone-eating fauna that hampers the preservation of carcasses at bathyal depths. This “Osedax” effect may explain the unexpected distribution of the fossil record, particularly in the Pleistocene, when baleen whales became gigantic and the ecosystem engineers they are today. A review of the relative thickness of Pleistocene marine strata rules out artefacts of the rock record. The distribution of taphonomic grades suggests that the average skeletal completeness decreases during the Neogene and Quaternary, consistently with an increased efficiency of bioeroders. The frequency of complete and articulated skeletons is time-independent, suggesting a control by sedimentation rates. Quality of the record is expected to improve particularly from taxonomic studies dedicated to the rich, but unexplored South american record, documenting the record of little known productive regions, such as Africa, the Arctic and Antarctica, and the taphonomy and stratigraphic paleobiology of old and new findings.

Domning and Beatty. Fossil Sirenia of the West Atlantic and Caribbean region. XII. Stegosiren macei, gen. et sp. nov. Journal of Vertebrate Paleontology.

Link: https://www.tandfonline.com/doi/abs/10.1080/02724634.2019.1650369

Abstract: Stegosiren macei, a new genus and species of halitheriine dugongid from the mid-Oligocene of South Carolina, U.S.A. (Ashley and Chandler Bridge formations, late Rupelian–late Chattian), represents a stage of halitheriine evolution more derived than that of the Old World early Oligocene Eosiren imenti and Halitherium schinzii, but slightly less derived than the West Atlantic late Oligocene Metaxytherium albifontanum. It is more comparable in stage of evolution to its early Oligocene contemporaries Caribosiren turneri and Priscosiren atlantica and may be a sister taxon of these two. It is distinguished autapomorphically from all other sirenians by a notably broadened frontal roof and a thickened anterior tip of the frontal, which formed a butt joint with the premaxilla. Analogous (independently evolved) joints in several other sirenians (principally dugongines) are correlated with enlarged upper tusks thought to be used for excavating seagrass rhizomes. This suggests that large tusks also may have been present (although not preserved) in Stegosiren, which is only the second halitheriine in which such a feature has been observed. Stegosiren macei brings to at least seven the number of potentially sympatric sirenian species lineages known from the West Atlantic-Caribbean Oligocene (six or more from South Carolina alone). This extraordinary sirenian diversity, unmatched elsewhere in the world, poses problems for ecomorphology and feeding-niche partitioning.

Comments: This marks the fourth named holotype specimen from the collections at our museumm, the Mace Brown Museum of Natural History. This is yet another goddamn sirenian from the Oligocene deposits here - we're already full - Priscosiren, Metaxytherium albifontanum, Crenatosiren, Dioplotherium manigaulti - all of these are known from the Oligocene here! The world's most diverse sea cow assemblage.

Freschi et al. Chronostratigraphic distribution of cetaceans in the Pliocene of Northern
Apennines (Italy): palaeoecological implications. Palaeogeography, Palaeoclimatology, Palaeoecology.

Link: https://www.sciencedirect.com/science/article/abs/pii/S0031018218307156

Abstract: A large number of cetacean fossils have been recovered through the time from the Pliocene deposits in Northern Apennines thrust belt, on both the Padan-Adriatic and the Tyrrhenian side. In this work, the cetaceans of Castell'Arquato Basin (Padan-Adriatic side) have been placed within a high-resolution chronostratigraphic framework available for this area. This results in a better assessment of their evolutionary history and of the palaeoecologic factors controlling their diversity and abundance through the time. Our results document a greater diversity between 3.1 and 2.7 Ma time interval, likely due to the development of eutrophic conditions during precessionally-driven insolation maxima at 400 ka eccentricity maxima, which are recorded in deeper depositional settings by sapropel clusters. Eutrophic conditions kept a complex trophic chain, as currently observed in the Ligurian Sea (Corsican-Ligurian-Provençal Basin), an area characterized also by upwelling. A reduction in both number and ecological diversity of cetacean taxa is observed along the Pliocene-Pleistocene transition; this trend, related to the onset of the Quaternary icehouse conditions, appears in good agreement with the recently recognized extinction event that affecting the marine megafauna at the end of the Pliocene.

Comments: The merger of vertebrate paleontology and stratigraphy at its finest. This is one of my favorite papers from the past few years. Just... a model paper for discussing fossils, environments, and time. 

Gaetan et al. Prosqualodon australis (Cetacea: Odontoceti) from the Early Miocene of Patagonia, Argentina: Redescription and Phylogenetic Analysis. Ameghiniana.

Link:https://bioone.org/journals/ameghiniana/volume-56/issue-1/AMGH.21.11.2018.3208/Prosqualodon-australis-Cetacea--Odontoceti-from-the-Early-Miocene-of/10.5710/AMGH.21.11.2018.3208.short

Abstract: We re-describe the holotype and referred specimen of Prosqualodon australis, from the early Miocene of Gaiman Formation (Chubut Province, Argentina), and analyse its phylogenetic position. Our study shows that this taxon is presently represented by an adult and a juvenile individuals and we provide the first diagnosis of the species based on the morphology of the anterior projection of the antorbital process along with plesiomorphic dental features (such as well-marked heterodont teeth, with posterior double rooted teeth in the maxilla, large, lateromedially compressed teeth with long crowns and denticulated enamel). The total body length of P. australis is estimated to be 2 m in the juvenile and 3 m in the adult specimen. We included for the first time this species in a phylogenetic analysis as an operational taxonomic unit itself, recovering P. australis as a stem-odontocete and Prosqualodon as a paraphyletic genus.

Comment: A much needed re-description of Prosqualodon with new specimens. Sadly, no earbones are known. The original fossils of the other species, Prosqualodon davidis from Tasmania, have been tragically lost. 

  

Gibson et al. Tupelocetus palmeri, a new species of protocetid whale (Mammalia, Cetacea)
from the middle Eocene of South Carolina. Journal of Vertebrate Paleontology.

Link: https://www.tandfonline.com/doi/full/10.1080/02724634.2018.1555165

Abstract: We describe Tupelocetus palmeri, a new genus and species of archaeocete whale, based on a single specimen from the Cross Member of the middle Eocene Tupelo Bay Formation (Bartonian). The holotype consists of a partial cranium with complete petrosals, posterior processes of tympanics, the posterior ends of the nasals, a part of the right orbit, and what are interpreted as the right and left P2s. The incomplete skull was collected from the Martin Marietta Cross Quarry (Berkeley County, South Carolina), which has also furnished the holotype of Carolinacetus gingerichi. The new species differs from all other protocetids in having a deep cavity on the occiput, as well as having the following combination of features: large nasal processes of frontals, single-cusped P2, and premaxilla terminates at level of P2 or P3. A phylogenetic analysis places T. palmeri in a large polytomy along the cetacean stem, more closely related to crown Cetacea than Maiacetus, Artiocetus, and Rodhocetus, but more basal than Georgiacetus, Babiacetus, and Eocetus. Another member of this polytomy is Natchitochia jonesi, and although specimens of Natchitochia and T. palmeri do not share any elements, what is preserved suggests that they are similar in size and among the largest of all protocetids. Although we are unable to differentiate these two species, we outline future data that could resolve this question.

Comment: Not the most complete protocetid ever, but these poorly known whales are rare as hen's teeth outside the Middle East - and this one has some of the best preserved and prepared earbones of any protocetid. Also, from right here in the Charleston area!

  

Gingerich et al. Aegicetus gehennae, a new late Eocene protocetid (Cetacea, Archaeoceti) from Wadi
Al Hitan, Egypt, and the transition to tailpowered swimming in whales. PLoS One.

Link: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0225391

Abstract: Aegicetus gehennae is a new African protocetid whale based on a partial skull with much of an associated postcranial skeleton. The type specimen, Egyptian Geological Museum, Cairo [CGM] 60584, was found near the base of the early-Priabonian-age (earliest late Eocene) Gehannam Formation of the Wadi Al Hitan World Heritage Site in Egypt. The cranium is distinctive in having ventrally-deflected exoccipitals. The vertebral column is complete from cervical C1 through caudal Ca9, with a vertebral formula of 7:15:4:4:9+, representing, respectively, the number of cervical, thoracic, lumbar, sacral, and caudal vertebrae. CGM 60584 has two more rib-bearing thoracic vertebrae than other known protocetids, and two fewer lumbars. Sacral centra are unfused, and there is no defined auricular surface on the ilium. Thus there was no weight-bearing sacroiliac joint. The sternum is distinctive in being exceptionally broad and flat. The body weight of CGM 60584, a putative male, is estimated to have been about 890 kg in life. Long bones of the fore and hind limbs are shorter than expected for a protocetid of this size. Bones of the manus are similar in length and more robust compared to those of the pes. A log vertebral length profile for CGM 60584 parallels that of middle Eocene Maiacetus inuus through the anterior and middle thorax, but more posterior vertebrae are proportionally longer. Vertebral elongation, loss of a sacroiliac articulation, and hind limb reduction indicate that Aegicetus gehennae was more fully aquatic and less specialized as a foot-powered swimmer than earlier protocetids. It is doubtful that A. gehennae had a tail fluke, and the caudal flattening known for basilosaurids is shorter relative to vertebral column length than flattening associated with a fluke in any modern whale. Late protocetids and basilosaurids had relatively long skeletons, longer than those known earlier and later, and the middle-to-late Eocene transition from foot-powered to tail-powered swimming seemingly involved some form of mid-body-and-tail undulation.

Comment: This new protocetid is a fairly derived one, and a very late one at that: it is Priabonian, and overlaps in age with many basilosaurids. We don't know much about the transition from four-legged protocetids to fully marine basilosaurids, and ironically this whale may not tell us a whole lot since it post-dates many basilosaurids anyway. That being said, it's got slightly smaller hindlimbs than other protocetids

Govender. Fossil cetaceans from Duinefontein (Koeberg) an early Pliocene site on the southwestern Cape, South Africa. Palaeontologia Electronica.

Link: https://palaeo-electronica.org/content/2019/2398-koeberg-early-pliocene-cetacea

Abstract: Koeberg is a Zanclean, subsurface locality on the west coast of South Africa, which was unearthed during the excavations of the Koeberg Power Station foundations. Mysticetes and odontocetes have been identified from this locality ca. 12 m below the surface. The preservational nature prevents species level identification in some instances. The balaenopterids are represented by specimens assigned to ‘Balaenoptera’ borealina, Diunatans sp. 1 and Fragilicetus sp. while other specimens are only identified as balaenopterids. The odontocetes have been referred to Odontoceti indet. (possibly delphinids), a beaked whale (cf. Izikoziphius) and a single phocoenid, cf.Australithax. There is undescribed odontocetes most likely physeterids. The balaenopterids and odontocetes suggest a connection of the west coast of South Africa to north Atlantic of Europe and North America, and eastern South Pacific.

Kapur et al. A Middle Miocene (~14 Ma) vertebrate assemblage from Palasava, Rapar Taluka, Kutch (Kachchh) District, Gujarat State, western India. Historical Biology.

Link: https://www.tandfonline.com/doi/full/10.1080/08912963.2019.1648451

Abstract: The present article aims to record a recently discovered middle Miocene vertebrate assemblage (including marine and terrestrial mammals) from Palasava, Kutch (Kachchh) District, Gujarat State, western India. The faunal assemblage comprising fishes, chelonians, crocodiles, snakes, birds and mammals is significant in terms of palaeoecology, palaeoenvironment and biostratigraphy of the region and yields evidence concerning its biogeographic affinities linked to Neogene Eustatic history. Palasava fauna together with previously known Neogene (particularly Miocene) vertebrate assemblages from the Kutch region indicates the presence of a riverine-estuarine system(s) linked to the sea, i.e. the depositional centres were quite close to the sea. Furthermore, the Palasava vertebrate assemblage (recorded herein) points towards a prevalence of warm, humid/wet, tropical to sub-tropical environmental conditions. The terrestrial mammalian assemblage from Palasava represents at least seven families with six of the terrestrial mammalian taxa identified herein to the genus level, namely: Sanitherium, Sivameryx, Brachypotherium, Zygolophodon, Gomphotherium, and Deinotherium. The overall assemblage (including Zygolophodon and Deinotherium) is indicative of a Middle Miocene, 14 ± 2 Ma (Langhian to Serravallian) age for the sedimentary succession at Palasava. Furthermore, a ~ 14 Ma age for the Palasava fauna indicates a correlation to regression cycle R5 in the Tagus Valley succession of Portugal.

Kienle and Berta. The evolution of feeding strategies in phocid seals (Pinnipedia, Phocidae).

Link: https://www.tandfonline.com/doi/full/10.1080/02724634.2018.1559172

Abstract: Adaptations for feeding underwater were crucial to the success of pinnipeds (seals, sea lions, and walruses) in their transition from terrestrial to aquatic habitats. Extant phocids (true seals) use multiple feeding strategies—biting, filter, and suction feeding—to capture and consume prey, and each strategy is associated with cranial, mandibular, and dental adaptations. However, little is known about feeding strategies in stem pinnipeds. The objectives of this study were to investigate feeding strategies used by some extinct pinnipeds based on cranial and mandibular morphologies and use this framework to examine the evolution of phocid feeding strategies. Three-dimensional cranial and mandibular landmark data were collected from 249 extant and fossil pinnipeds. Principal component analysis and canonical variate analysis were performed to describe the major axes of variation and compare overlap of fossil and extant taxa in morphospace. Stem pinnipeds had morphologies associated with biting and filter feeding. Several fossil taxa were most similar to extant biters, suggesting that biting was a common and important feeding strategy for early phocids. One fossil taxon, Homiphoca capensis, was potentially a filter feeder, because it consistently overlapped with extant filter feeders in cranial morphospace. No fossil taxa had morphological adaptations for suction feeding, indicating that suction feeding is a more derived strategy in phocids. Extant phocids and their ancestors have cranial and mandibular adaptations for multiple feeding strategies, which allowed these animals to move into diverse aquatic niches and likely contributed to their successful transition from terrestrial to aquatic ecosystems.

Kimura. First squalodelphinid from the early Miocene of the Pacific realm in the Northern Hemisphere. Journal of Vertebrate Paleontology.

Link: https://www.tandfonline.com/doi/full/10.1080/02724634.2018.1493595

Abstract: Squalodelphinidae are moderately long-snouted dolphins from the late Oligocene to middle Miocene epochs (Marx et al., 2016). This family includes only six species in six genera. Recent studies have confirmed that Squalodelphinidae belong to the superfamily Platanistoidea (e.g., Lambert et al., 2014, 2017; Tanaka and Fordyce, 2015, 2016; Kimura and Barnes, 2016; Boersma et al., 2017; Tanaka et al., 2017; Bianucci et al., 2018). The only surviving Platanistoidea species, the South Asian river dolphin (Platanista gangetica), is distributed in the Ganges, Brahmaputra-Megna, and Karnaphuli-Sangu river systems of South Asia (Jefferson et al., 2008). Several recent studies have described fossil platanistoids from Japan (e.g., Kimura et al., 2009, and references therein; Kimura et al., 2013; Kimura and Barnes, 2016), which shed light on the group’s paleobiogeography and evolution in this area. However, the Platanistoidea fossil record from the wider Asian region is limited, and their evolutionary history remains unclear. This is especially true for Squalodelphinidae

because their fossil record is relatively rare and diagnostic material of squalodelphinids has been exclusively reported from the Atlantic and Pacific coasts of South America, the eastern coast

of North America, and Europe (Tanaka and Fordyce, 2014; Bianucci et al., 2015, 2018). Here, I report the first squalodelphinid from the Pacific region of the Northern Hemisphere: beautifully

preserved ear bones recovered from the lower Miocene Iwamura Group, Gifu Prefecture, Japan. This new fossil expands our knowledge of the paleobiogeography and evolution of the enigmatic odontocete family Squalodelphinidae.

Comments: See also the paper by Margot Nelson et al., reporting a partial squalodelphinid skull from the Clallam Formation of Washington USA: https://bioone.org/journals/Journal-of-Vertebrate-Paleontology/volume-38/issue-2/02724634.2017.1428197/First-Occurrence-of-a-Squalodelphinid-Cetacea-Odontoceti-from-the-Early/10.1080/02724634.2017.1428197.short

Kimura and Hasegawa. New specimen of Joumocetus shimizui from the Miocene Haraichi Formation, Annaka Group, Gunma Prefecture, Japan. Bulletin of the Gunma Museum of Natural History.

Link: http://www.gmnh.pref.gunma.jp/research_no23

Abstract: A new mysticete fossil was recovered from the Haraichi Formation, Annaka Group, Gunma Prefecture, Japan. The specimen includes incomplete cranium with periotics and tympanic bulla. The specimen represents the following morphological characters and here we describe the specimen as Joumocetus shimizui: parietals are widely exposed at vertex, supraoccipital shield is triangular in outline with a pointed apex, anterior process of the periotic is short and compressed transversely, and, although it is unclear due to brakeage, nasal is possibly located in part anterior to the level of the preorbital angle of the supraorbital process of the frontal. The horizon from which the specimen was found is stratigraphically between the Kitamura and Baba tuffs. In previous study, the geological ages of the Kitamura and the Baba tuffs was dated as 11.79 ± 0.08 Ma (biotite) and 11.26 ± 0.09 Ma (biotite)/11.29 ± 0.12 Ma (sanidine) respectively. This new specimen elucidates the morphology of J. shimizui which was not preserved in the holotype specimen of the species.

Comments: In Japanese, but well-illustrated as is always the case with Kimura's work, and adds some new character codings to the early cetotheriid Joumocetus.

Kimura and Hasegawa. A new species of Kentriodon (Cetacea, Odontoceti, Kentriodontidae) from the Miocene of Japan.

Link: https://www.tandfonline.com/doi/full/10.1080/02724634.2019.1566739

Abstract: Kentriodontids are small- to medium-sized odontocetes with a wide geographic range that flourished during the Miocene. They are closely related to crown Delphinida. Seven fossil kentriodontid specimens have been recovered from the Haraichi Formation, Annaka Group (latest middle/earliest late Miocene, Serravallian/Tortonian), Gunma Prefecture, Japan. We describe and diagnose a new species of the genus Kentriodon. Kentriodon nakajimai, sp. nov., has a larger fossa for the hamular and preorbital lobes of the pterygoid sinuses, which suggests that the species was more highly adapted for diving than other Kentriodon species. Asymmetric development of left and right maxillary crests indicates asymmetric development of the facial muscles attached to the melon. If this is the case, it suggests that K. nakajimai possessed a more sophisticated echolocation system than other kentriodontids. Phylogenetic analysis suggests that K. nakajimai is most closely related to K. obscurus and the genus Kentriodon may have originated in the Pacific and then dispersed into the Atlantic several times.

Comments: What a spectacular collection of fossils - quite a sample size! The second species of Kentriodon reported from Japan, and very likely the best known species to date.

Lambert and Bianucci. How to break a sperm whale’s teeth: dental damage in a large Miocene physeteroid from the North Sea basin. Journal of Vertebrate Paleontology.

Link: https://www.tandfonline.com/doi/full/10.1080/02724634.2019.1660987

Abstract: In contrast to the suction-feeding, predominantly teuthophagous extant sperm whale, several Miocene physeteroids display proportionally larger teeth, deeply embedded in both upper and lower jaws. Together with other osteological features, these differences lead to the functional interpretation of these taxa as macroraptorial predators, using their teeth to capture and process large marine vertebrates. However, the assumption that strong forces applied to macroraptorial physeteroid teeth during powerful bites and contacts with bone material should result in major dental damage has not yet been tested. In the present work, we analyzed a large collection of physeteroid teeth with an enameled crown from the Miocene of the North Sea Basin. We especially focused on a set of 45 teeth of Scaldicetus caretti discovered in Antwerp (Belgium, southern North Sea Basin) and tentatively dated to the Tortonian (early late Miocene). Visual inspection and computed tomography (CT) scans revealed dental damage, including wear and breaks. The latter could be interpreted as chipping fractures, occurring along the crown, and vertical root fractures, observed along the apical part of the massive root. Chipping fractures are most likely due to contacts with hard material, whereas vertical root fractures may result from the application of strong and repetitive bite forces and/or contacts with hard material. Such results further support the interpretation of a series of Miocene physeteroids with proportionally large teeth as macroraptorial (rather than suction-feeding) top predators. Considering the size of the teeth of S. caretti, its most likely prey items were other large marine vertebrates.

Comments: Every paleocetologist is familiar with tooth breakage and feeding - macropredatory whales bite down on a bony prey item like a turtle or a seal and the tooth crown breaks. There's a little bit of that in here, which is what I was expecting. What I was not expecting was breakage of the tooth roots during biting!!!

Lambert et al. An Amphibious Whale from the Middle Eocene of Peru Reveals Early South Pacific Dispersal of Quadrupedal Cetaceans. Current Biology.

Link: https://www.cell.com/current-biology/fulltext/S0960-9822(19)30220-9?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0960982219302209%3Fshowall%3Dtrue

Abstract: Cetaceans originated in south Asia more than 50 million years ago (mya), from a small quadrupedal artiodactyl ancestor. Amphibious whales gradually dispersed westward along North Africa and arrived in North America before 41.2 mya. However, fossil evidence on when, through which pathway, and under which locomotion abilities these early whales reached the New World is fragmentary and contentious. Peregocetus pacificus gen. et sp. nov. is a new protocetid cetacean discovered in middle Eocene (42.6 mya) marine deposits of coastal Peru, which constitutes the first indisputable quadrupedal whale record from the Pacific Ocean and the Southern Hemisphere. Preserving the mandibles and most of the postcranial skeleton, this unique four-limbed whale bore caudal vertebrae with bifurcated and anteroposteriorly expanded transverse processes, like those of beavers and otters, suggesting a significant contribution of the tail during swimming. The fore- and hind-limb proportions roughly similar to geologically older quadrupedal whales from India and Pakistan, the pelvis being firmly attached to the sacrum, an insertion fossa for the round ligament on the femur, and the retention of small hooves with a flat anteroventral tip at fingers and toes indicate that Peregocetus was still capable of standing and even walking on land. This new record from the southeastern Pacific demonstrates that early quadrupedal whales crossed the South Atlantic and nearly attained a circum-equatorial distribution with a combination of terrestrial and aquatic locomotion abilities less than 10 million years after their origin and probably before a northward
dispersal toward higher North American latitudes.

Comments: Not only is this new protocetid the first named protocetid from the Pacific, but it's also got pretty great limb material!

Lambert et al. Yaquinacetus meadi, a new latest Oligocene–early Miocene dolphin (Cetacea, Odontoceti, Squaloziphiidae, fam. nov.) from the Nye Mudstone (Oregon, U.S.A.). Journal of Vertebrate Paleontology.

Link: https://www.tandfonline.com/doi/full/10.1080/02724634.2018.1559174

Abstract: Represented by a nearly complete cranium with associated mandible, teeth, and vertebrae, Yaquinacetus meadi is a new genus and species of archaic homodont odontocete from the latest Oligocene–early Miocene (24–19.2 Ma) of Oregon, U.S.A. The new species is characterized by a moderately elongated rostrum bearing approximately 51 alveoli per tooth row and a knob-like, rectangular vertex. Together with Squaloziphius emlongi from the early Miocene of Washington State, Y. meadi constitutes a new odontocete family, Squaloziphiidae, fam. nov., diagnosed by a unique combination of characters, including transversely wide dorsal opening of the mesorostral groove at base of rostrum, followed posteriorly by an abrupt narrowing; thickened lateral margin of the maxilla in the antorbital region making a long and laterally concave crest; and massive, anteroposteriorly and ventrally long postglenoid process of the squamosal. Although sharing with Ziphiidae the presence of transverse premaxillary crests on the vertex, Squaloziphiidae differs in the pterygoid sinus fossa being shorter anteriorly and ventrally; the tubercule of the malleus being less reduced; and lacking a pair of enlarged alveoli for mandibular tusks. Our phylogenetic analysis confirms the sister-group relationship between S. emlongi and Y. meadi, either as late diverging stem odontocetes or as early crown odontocetes, but distant from Ziphiidae. These results confirm the northeastern Pacific as a center of diversification for several groups of archaic homodont odontocetes during the late Oligocene–early Miocene.

Comments: This is only the second species of squaloziphiid named since Squaloziphius was first named in 1991. it's also got the first earbones for the family (and, the clade Squaloziphiidae is named). Based on a beautiful skull collected by Doug Emlong from the Nye Mudstone of Oregon.

Leslie et al. Norrisanima miocaena, a new generic name and redescription of a stem balaenopteroid mysticete (Mammalia, Cetacea) from the Miocene of California. PeerJ.

Link: https://peerj.com/articles/7629/

Abstract: Rorqual whales are among the most species rich group of baleen whales (or mysticetes) alive today, yet the monophyly of the traditional grouping (i.e., Balaenopteridae) remains unclear. Additionally, many fossil mysticetes putatively assigned to either Balaenopteridae or Balaenopteroidea may actually belong to stem lineages, although many of these fossil taxa suffer from inadequate descriptions of fragmentary skeletal material. Here we provide a redescription of the holotype of Megaptera miocaena, a fossil balaenopteroid from the Monterey Formation of California, which consists of a partial cranium, a fragment of the rostrum, a single vertebra, and both tympanoperiotics. Kellogg (1922) assigned the type specimen to the genus Megaptera Gray (1846), on the basis of its broad similarities to distinctive traits in the cranium of extant humpback whales (Megaptera novaeangliae (Borowski, 1781)). Subsequent phylogenetic analyses have found these two species as sister taxa in morphological datasets alone; the most recent systematic analyses using both molecular and morphological data sets place Megaptera miocaena as a stem balaenopteroid unrelated to humpback whales. Here, we redescribe the type specimen of Megaptera miocaena in the context of other fossil balaenopteroids discovered nearly a century since Kellogg’s original description and provide a morphological basis for discriminating it from Megaptera novaeangliae. We also provide a new generic name and recombine the taxon as Norrisanima miocaena, gen. nov., to reflect its phylogenetic position outside of crown Balaenopteroidea, unrelated to extant Megaptera. Lastly, we refine the stratigraphic age of Norrisanima miocaena, based on associated microfossils to a Tortonian age (7.6–7.3 Ma), which carries implications for understanding the origin of key features associated with feeding and body size evolution in this group of whales.

Comments: A much needed redescription of "Megaptera" miocaena, originally published by Kellogg in the 1920s. Many more fossils of Norrisanima, perhaps not N. miocaena, are present in collections at UCMP, SDNHM, and LACM, so it's nice to finally apply a genus name other than "Megaptera". I find the images of the skull - derived from 3D models - washed out and difficult to see, however.

Loch et al. Enamel Microstructure in Eocene Cetaceans from Antarctica (Archaeoceti and Mysticeti). Journal of Mammalian Evolution.

Link: https://link.springer.com/article/10.1007/s10914-018-09456-3

Abstract: Modern baleen whales have no adult teeth, whereas dolphins and porpoises have a homodont and polydont dentition, with simplified enamel microstructure. However, archaic cetaceans (archaeocetes and early mysticetes and odontocetes) had a complex and ornamented dentition, with complex enamel microstructure as in terrestrial mammals. This study describes the morphology of teeth and enamel microstructure in two fossil cetaceans from Antarctica: a basilosaurid archaeocete from the La Meseta Formation (middle Eocene); and Llanocetus sp. from the Submeseta Formation (late Eocene), one of the oldest mysticetes known. The two teeth analyzed were lower premolars, with transversely compressed triangular crowns composed of a main cusp and accessory denticles. The enamel microstructure of the basilosaurid and Llanocetus sp. is prismatic with Hunter-Schreger bands (HSB) and an outer zone of radial enamel. In the basilosaurid, the enamel is relatively thin and measures 150–180 μm, whereas in Llanocetus sp. it is considerably thicker, measuring 830–890 μm in the cusp area and 350–380 μm near the crown base. This is one of the thickest enamel layers among cetaceans, extinct and living. Structures resembling enamel tufts and lamellae were observed in both fossils at the enamel-dentine junction (EDJ) and extending along the thickness of the enamel layer, respectively. The presence of HSB and biomechanical reinforcing structures such as tufts and lamellae suggests prominent occlusal loads during feeding, consistent with raptorial feeding habits. Despite the simplification or absence of teeth in modern cetaceans, their ancestors had complex posterior teeth typical of most mammals, with a moderately thick enamel layer with prominent HSB.

Comments: There is a raging debate as to what toothed mysticetes ate, and this paper adds some fuel to that fire. This paper reports enamel features of Llanocetus, which has unusually thick enamel - suggestive of powerful bite force rather than reduction of tooth function related to either suction feeding or filter feeding.

Marx et al. Like phoenix from the ashes: How modern baleen whales arose from a fossil “dark age”. Acta Palaeontologica Polonica.

Link: https://www.app.pan.pl/article/item/app005752018.html

Abstract: The evolution of baleen whales (Mysticeti), the largest animals on Earth, was punctuated by a pivotal turnover event. Following their emergence around 36 million years (Ma), mysticetes diversified into a disparate range of toothed and toothless species until 23 Ma, but then nearly vanished from the global fossil record for the next five million years. Following this early Miocene “dark age”, toothless mysticetes spectacularly reappeared around 18–17 Ma, whereas toothed mysticetes had gone entirely extinct. Here, we suggest that this turnover event reflects a change in mysticete habitat occupancy. Using the well-sampled record of Australasia as a case study, we show that Oligocene pre-“dark age” mysticetes formed distinct coastal and offshore assemblages, dominated by small (2–4 m), ecologically disparate toothed species, and larger (5–6 m) toothless filter feeders, respectively. Environmental change around the Oligocene–Miocene boundary led to the decline of the endemic coastal assemblages, leaving nearshore deposits virtually devoid of mysticetes. Filter feeders persisted offshore and subsequently re-invaded coastal habitats during the mid-Miocene Climatic Optimum, thus establishing the modern, cosmopolitan mysticete fauna.

Comments: One of Felix's corniest paper titles by far (we love you Felix). A quirky paper on a very poorly understood hitherto underappreciated aspect of the baleen whale fossil record: it sort of ceases to exist for about a 3-4 million year period (Aquitanian stage) yet dolphins are quite common in this interval, so it can't readily be explained away by time/rock bias. Felix started talking my ear off about this problem when we were Ph.D. students at Otago, and I'm glad to see it published. Don't forget the Supp Info though: they report the first eomysticetids from Australia!

Marx et al. Gigantic mysticete predators roamed the Eocene Southern Ocean. Antarctic Science.

Link: https://www.cambridge.org/core/journals/antarctic-science/article/gigantic-mysticete-predators-roamed-the-eocene-southern-ocean/0EEFC32753A8909BC4E7C134F5AEA6AE

Abstract: Modern baleen whales (Mysticeti), the largest animals on Earth, arose from small ancestors around 36.4 million years ago (Ma). True gigantism is thought to have arisen late in mysticete history, with species exceeding 10 m unknown prior to 8 Ma. This view is challenged by new fossils from Seymour Island (Isla Marambio), Antarctica, which suggest that enormous whales once roamed the Southern Ocean during the Late Eocene (c. 34 Ma). The new material hints at an unknown species of the archaic mysticete Llanocetus with a total body length of up to 12 m. The latter is comparable to that of extant Omura's whales (Balaenoptera omurai Wada et al. 2003), and suggests that gigantism has been a re-occurring feature of mysticetes since their very origin. Functional analysis including sharpness and dental wear implies an at least partly raptorial feeding strategy, starkly contrasting with the filtering habit of living whales. The new material markedly expands the size range of archaic mysticetes, and demonstrates that whales achieved considerable disparity shortly after their origin.

Comments: Tantalizing evidence in the form of huge teeth of Llanocetus, suggesting an even larger species than Llanocetus denticrenatus ranging up to 12 meters in length. However, since these are just isolated teeth, it's admittedly possible that this was a much larger-toothed species of Llanocetus. We don't have a skull for this taxon, so it's difficult to really say much about its size or feeding ecology.

Marx et al. A large Late Miocene cetotheriid (Cetacea, Mysticeti) from the Netherlands clarifies the status of Tranatocetidae.

Link: https://peerj.com/articles/6426/

Abstract: Cetotheriidae are a group of small baleen whales (Mysticeti) that evolved alongside modern rorquals. They once enjoyed a nearly global distribution, but then largely went extinct during the Plio-Pleistocene. After languishing as a wastebasket taxon for more than a century, the concept of Cetotheriidae is now well established. Nevertheless, the clade remains notable for its variability, and its scope remains in flux. In particular, the recent referral of several traditional cetotheriids to a new and seemingly unrelated family, Tranatocetidae, has created major phylogenetic uncertainty. Here, we describe a new species of Tranatocetus, the type of Tranatocetidae, from the Late Miocene of the Netherlands. Tranatocetus maregermanicum sp. nov. clarifies several of the traits previously ascribed to this genus, and reveals distinctive auditory and mandibular morphologies suggesting cetotheriid affinities. This interpretation is supported by a large phylogenetic analysis, which mingles cetotheriids and tranatocetids within a unified clade. As a result, we suggest that both groups should be reintegrated into the single family Cetotheriidae.

Comments: Another welcome discovery from the North Sea - Trantocetidae, erected only a few years ago, is now found to be synonymous with the Cetotheriidae - something I suspected for a while. this study has one of the best resolved phylogenies of Mysticeti yet (though I'm not sure about Caperea).

 Matsui and Tsuihiji. The phylogeny of desmostylians revisited: proposal of new clades based on robust phylogenetic hypotheses.

Link: https://peerj.com/articles/7430/

Abstract: Desmostylia is a clade of extinct aquatic mammals with no living members. Today, this clade is considered belonging to either Afrotheria or Perissodactyla. In the currently-accepted taxonomic scheme, Desmostylia includes two families, 10 to 12 genera, and 13–14 species. There have been relatively few phylogenetic analyses published on desmostylian interrelationship compared to other vertebrate taxa, and two main, alternative phylogenetic hypotheses have been proposed in previous studies. One major problem with those previous studies is that the numbers of characters and OTUs were small. In this study, we analyzed the phylogenetic interrelationship of Desmostylia based on a new data matrix that includes larger numbers of characters and taxa than in any previous studies. The new data matrix was compiled mainly based on data matrices of previous studies and included three outgroups and 13 desmostylian ingroup taxa. Analyses were carried out using five kinds of parsimonious methods. Strict consensus trees of the most parsimonious topologies obtained in all analyses supported the monophyly of Desmostylidae and paraphyly of traditional Paleoparadoxiidae. Based on these results, we propose phylogenetic definitions of the clades Desmostylidae and Paleoparadoxiidae based on common ancestry.

Comments: Perhaps the best phylogenetic analysis of desmos to date. Sadly, my favorite genus name for the clade, Vanderhoofius is no more: now recombined as Desmostylus coalingensis. Fortunately, Cornwallius, my second favorite genus name is still accepted.

McCurry et al. The repeated evolution of dental apicobasal ridges inaquatic-feeding mammals and reptiles.

Link: https://academic.oup.com/biolinnean/article/127/2/245/5427318

Abstract: Since the Permian, Earth’s aquatic ecosystems have been ecologically dominated by numerous lineages of predatory amniotes. Many of these groups evolved elevated ridges of enamel that run down the apical–basal axis of their teeth, referred to here as apicobasal ridges. This trait is commonly used as a taxonomic tool to identify fossil species and higher groupings, but the function of the ridges and their associated ecological significance are poorly understood. Here, we aim to clarify the phylogenetic distribution of apicobasal ridges among amniotes and to examine how the morphology of apicobasal ridges varies across species. We show that these ridges have evolved independently numerous times and are almost exclusively found in aquatic-feeding species. Ridge morphology varies, including tall, pronounced ridges, low, undulating ridges and interweaving ridges. Their internal structure also varies from tooth crowns with locally thickened enamel to undulating enamel–dentine interface. We assess the relative merits of different hypothetical functions of the ridges and propose that although apicobasal ridges might provide some strengthening of the tooth, their morphology and pattern of evolution do not indicate that this is their primary function. Instead, we suggest that apicobasal ridges serve to increase the efficiency of puncture, grip and/or removal.

Comments: I was not expecting tooth shape/texture to be apparently decoupled from internal structure - though this study does not examine enamel ultrastructure, which is a necessary test of the central hypothesis: that enamel "fluting" as a shape is important for piercing the tissues of prey animals and not, for example, distributing stress from point loading. Regardless, an interesting and thought provoking study.

Muizon et al. Mystacodon selenensis, the earliest known toothed mysticete (Cetacea, Mammalia) from the late Eocene of Peru: anatomy, phylogeny, and feeding adaptations. Geodiversitas.

Link: https://bioone.org/journals/Geodiversitas/volume-41/issue-1/geodiversitas2019v41a11/Mystacodon-selenensis-the-earliest-known-toothed-mysticete-Cetacea-Mammalia-from/10.5252/geodiversitas2019v41a11.short

Abstract: Mystacodon selenensis Lambert, Martínez-Cáceres, Bianucci, Di Celma, Salas-Gismondi, Steurbaut, Urbina & Muizon, 2017 is a toothed mysticete that represents the earliest member of the suborder in the current state of knowledge. Its holotype is a relatively complete skeleton from the upper Eocene (early Priabonian, c. 36.4 Ma) Yumaque Member of the Paracas Formation from the southern coast of Peru. The thorough description of this specimen is presented here and reveals numerous similarities with the contemporaneous basilosaurids including the retention of an innominate that originally articulated to the unpreserved hind limb. However, several characters of M. selenensis clearly relate this taxon to the mysticetes, such as the large palate with a dorsoventrally flattened rostrum, the posterior extension of the palate with an infraorbital plate of the maxilla, the shortening of the premaxillary part of the rostrum, the zygomatic process of the squamosal being closely apposed to the postorbital process of the frontal, and the humeral head being oriented more proximally than posteriorly. A parsimony analysis retrieves Mystacodon as the earliest diverging branch of the Mysticeti with no close phylogenetic relationship with Llanocetus the second oldest known mysticete (c. 34.2 Ma). The dental formula of M. selenensis is that of basilosaurids (I 3/3, C 1/1, P 4/4, M 2/3). The anterior teeth (incisors and canine) are distinctly proportionally smaller than in basilosaurids, whereas the cheek teeth are very close in relative length, but are relatively larger than in most other toothed mysticetes (except Coronodon). The large cheek teeth of Mystacodon suggest a raptorial feeding strategy, probably assisted with some degree of suction, as indicated by the large size of the palate. The anterior teeth of the holotype display a subhorizontal apical wear facet and the cheek teeth a moderately sloping wear surface, differing from the subvertical attrition facets of basilosaurids. This pattern suggests an efficient dental abrasion resulting from feeding upon abrasive food items or/and from the ingestion of sediment during prey capture, which could indicate some degree of bottom feeding. On the forelimb, the size and orientation of the acromion, the great length of the deltopectoral crest, the massiveness of the olecranon of the ulna, and the strong radial anterior process indicate powerful shoulder movements, which suggest an active use of the forelimb when foraging for food on the sea floor. The robustness of digits and the pachyosteosclerosis of ribs with pestle-like distal end corroborate such a scenario. Mystacodon selenensis represents a first step in the evolutionary history of feeding adaptations of early mysticetes; the latter are likely to have experimented an abundant set of feeding strategies and were probably very eclectic in prey choice and capture before hyperspecialized filter feeding became widespread in the suborder.

Comments: Great followup to the initial publication of the earliest toothed mysticete Mystacodon in 2017 - well illustrated, exhaustive paleobiological investigation.

Orihuela et al. First cranial endocasts of early Miocene sirenians (Dugongidae) from the West Indies. Journal of Vertebrate Paleontology.

Link: https://www.tandfonline.com/doi/full/10.1080/02724634.2019.1584565

Abstract: We report and describe the first sirenian endocranial casts from the West Indies based on three specimens collected from two quarries of the upper Oligocene–lower Miocene Colón Formation, in the province of Matanzas, western Cuba. We assign them to Dugongidae incertae sedis, based on a phylogenetic analysis of fossil and extant sirenians. Thus, these new specimens provide a unique opportunity to describe the endocranial neuroanatomy of this family. The endocasts are suggestive of dugongids with limited vision and olfaction, based on the diminished olfactory and optic nerves. Additionally, we provide a geological reinterpretation of the Colón Formation and its paleoecological setting. Altogether, these data provide further insight into the diversity and evolution of sirenians, especially Caribbean dugongs.

Paolucci et al. Diaphorocetus poucheti (Cetacea, Odontoceti, Physeteroidea) from Patagonia, Argentina: one of the earliest sperm whales. Journal of Systematic Palaeontology.

Link: https://www.tandfonline.com/doi/full/10.1080/14772019.2019.1605544 

Abstract: Sperm whales (Physeteroidea) are the basal-most surviving lineage of odontocetes, represented today by just three highly specialized, deep-diving suction feeders. By contrast, extinct sperm whales were relatively diverse, reflecting a major Miocene diversification into various suction feeding and macroraptorial forms. The beginnings of this diversification, however, remain poorly understood. The Atlantic coast of South America provides a crucial window into early physeteroid evolution and has yielded some of the oldest species known from cranial material, Idiorophus patagonicus and Diaphorocetus poucheti – both of which are in need of re-description and phylogenetic reappraisal. Here, we re-examine Diaphorocetus in detail and, in light of its complex taxonomic history, declare it a nomen protectum. Phylogenetically, the species forms part of a polytomy including ‘Aulophyseter’ rionegresis and the two crown lineages (Physeteridae and Kogiidae) and demonstrates that facial asymmetry and a clearly defined supracranial basin have characterized this lineage for at least 20 Ma. With a total body length of 3.5–4 m, Diaphorocetus is one of the smallest physeteroids yet known. Its cranial morphology hints at an intermediate raptorial/suction feeding strategy and it has a moderately developed spermaceti organ and junk.
Comments: Hot on the heels of other papers redescribing critical early Miocene cetaceans from Patagonia - Phoberodon, Morenocetus, Prosqualodon - and now this early sperm whale.

Peri et al. An Inticetus-like (Cetacea: Odontoceti) postcanine tooth from the Pietra leccese (Miocene, southeastern Italy) and its palaeobiogeographical implications, Neues Jahrbuch fur Geologie und Palaontologie.

Link: https://www.ingentaconnect.com/content/schweiz/njbgeol/2019/00000291/00000002/art00007

Abstract: We report on an isolated cetacean postcanine tooth that was collected close to the village of Melpignano (Lecce Province, Apulia region) from the Miocene "Pietra leccese" formation of southeastern Italy. This tooth exhibits a transversely compressed and roughly semi-circular crown featuring several large, broad-based accessory denticles that are arranged radially. Dental enamel ornamentation is limited to faint subvertical grooves, and a slight subvertical incision just below the base of the crown suggests that it was double-rooted. Our comparisons allow us to identify the Melpignano specimen as belonging to a heterodont dolphin close to Inticetus vertizi, the only named member of the archaic odontocete family Inticetidae, which has been recently described from Burdigalian (early Miocene) strata of the Chilcatay Formation of southern Peru. This find highlights the elusive presence of Inticetus-like toothed whales in the Mediterranean region during the Miocene. We then review the geographic distribution of fossil remains of Inticetus-like cetaceans, which includes records from the Miocene of Peru, North Carolina (eastern U. S. A.), the Atlantic coast of France, and south-eastern Italy. We hypothesise that inticetids dispersed via the Central American Seaway, which allowed faunal interchanges between the south-eastern Pacific and the northern Atlantic/Mediterranean realms until latest Miocene times. In conclusion, the finding of an Inticetus -like tooth in Miocene beds in Italy suggests that our knowledge on the past distribution of inticetid cetaceans is far from being exhaustive.

Comments: One of the only papers to cite my paper on Phococetus teeth from North Carolina! Sigh...

Peri et al. Reduction of olfactory and respiratory turbinates in the transition of whales from land to sea: the semiaquatic middle Eocene Aegyptocetus tarfa. Journal of Anatomy.

Link: https://onlinelibrary.wiley.com/doi/full/10.1111/joa.13088

Abstract: Ethmoturbinates, nasoturbinates, and maxilloturbinates are well developed in the narial tract of land‐dwelling artiodactyls ancestral to whales, but these are greatly reduced or lost entirely in modern whales. Aegyptocetus tarfa is a semiaquatic protocetid from the middle Eocene of Egypt. Computed axial tomography scans of the skull show that A. tarfa retained all three sets of turbinates like a land mammal. It is intermediate between terrestrial artiodactyls and aquatic whales in reduction of the turbinates. Ethmoturbinates in A. tarfa have 26% of the surface area expected for an artiodactyl. These have an olfactory function and indicate that early whales retained a sense of smell in the transition from land to sea. Maxilloturbinates in A. tarfa have 6% of the surface area expected for an artiodactyl. These have a respiratory function and their markedly reduced size suggests that rapid inhalation and exhalation was already more important than warming and humidifying air, in contrast to extant land mammals. Finally, the maxilloturbinates of A. tarfa, although greatly reduced, still show some degree of similarity to those of artiodactyls, supporting the phylogenetic affinity of cetaceans and artiodactyls based on morphological and molecular evidence.

Powell et al. Geology and Paleontology of the Late Miocene Wilson Grove Formation at Bloomfield Quarry, Sonoma County, California. USGS Professional Publications.

Link: https://pubs.usgs.gov/sir/2019/5021/sir20195021.pdf

Abstract: An extensive fauna of at least 77 taxa is reported from the basal Wilson Grove Formation in a small quarry just north of the town of Bloomfield, Sonoma County, California. The fauna represents intertidal to shallow subtidal water depths and water temperatures interpreted from the fauna, consistent with the latitude of the fossil locality (37° north) during the late Miocene. The fauna from Bloomfield Quarry is unusually large and diverse from such a small area. It consists of thousands of specimens of 4 brachiopod, 42 mollusk (28 bivalves and 14 gastropods), 6 arthropod (1 crab, 1 shrimp, and 4 barnacles), and 25 vertebrate (3 sharks, 1 ray, 8 bony fishes, 9 marine mammals, and 4 birds) taxa. Unusual in the fauna is the abundant and diverse brachiopod fauna, the diverse barnacle fauna, which was described previously, and the extensive and diverse vertebrate fauna. Most significant among the vertebrates is the walrus fauna, which is the most diverse assemblage of walrus yet reported worldwide from a single locality. A single strontium (Sr) isotope age determination of about 8 million years (megaannum, Ma) from a pectinid mollusk is consistent with a new age determination of the overlying, informally named Roblar tuff as described by SarnaWojcicki in 1992 (6.203±0.011 Ma) and previously reported age determinations (recalculated here) from basalt (9.27±0.06 Ma) underlying these deposits. The Roblar tuff at Bloomfield Quarry can be correlated with other sites, including the Delgada Fan offshore northern California and the Coalinga anticline in California’s Central Valley. These age determinations conform with the “Jacalitos” California provincial molluscan stage age, the Hemphillian North American Land Mammal age determined from the fossils, and is part of the International Tortonian Stage of the Miocene.

Comments: This paper was a long time coming - I wrote the descriptions for this the month before I got married to Sarah back in 2011. Nevertheless it boasts the most diverse walrus fossil assemblage in the world: five taxa! Imagotaria, Dusignathus, Gomphotaria, Pontolis, and an odobenine. This is also one of the most exhaustive reports on a fossil site from the west coast: stratigraphy, geochronology, invertebrate and vertebrate paleontology, you name it. Everything we know about this locality.

Racicot et al. Evidence for convergent evolution of ultrasonic hearing in toothed whales (Cetacea: Odontoceti). Biology Letters.

Link: https://royalsocietypublishing.org/doi/full/10.1098/rsbl.2019.0083

Abstract: Toothed whales (Cetacea: Odontoceti) are the most diverse group of modern cetaceans, originating during the Eocene/Oligocene transition approximately 38 Ma. All extant odontocetes echolocate; a single origin for this behaviour is supported by a unique facial source for ultrasonic vocalizations and a cochlea adapted for hearing the corresponding echoes. The craniofacial and inner ear morphology of Oligocene odontocetes support a rapid (less than 5 Myr) early evolution of echolocation. Although some cranial features in the stem odontocetes Simocetus and Olympicetus suggest an ability to generate ultrasonic sound, until now, the bony labyrinths of taxa of this grade have not been investigated. Here, we use µCT to examine a petrosal of a taxon with clear similarities to Olympicetus avitus. Measurements of the bony labyrinth, when added to an extensive dataset of cetartiodactyls, resulted in this specimen sharing a morphospace with stem whales, suggesting a transitional inner ear. This discovery implies that either the lineage leading to this Olympicetus­-like taxon lost the ability to hear ultrasonic sound, or adaptations for ultrasonic hearing evolved twice, once in xenorophids and again on the stem of the odontocete crown group. We favour the latter interpretation as it matches a well-documented convergence of craniofacial morphology between xenorophids and extant odontocetes.

Comment: This paper started out from the first completely prepared dolphin from the James Goedert collection at the Mace Brown Museum of Natural History to have a periotic- which we offered to Dr. Rachel Racicot to CT scan, just to see if there was anything interesting. Then it turned out that this dolphin had none of the hallmark features that are a requirement for echolocation - and based on its phylogenetic position, requires either 1) a single loss of echolocation in this lineage or 2) independent derivation or elaboration of echolocation within xenorophids and main-line odontocetes. For various reasons we laid out, the latter option is more likely - but awaits testing by study of other simocetid-grade odontocetes. A surprising reward for four months of acid preparation in a rubbermaid bin in our lab, and 5 minutes of scrubbing a week!

Ramasammy and Lauridsen. A new specimen of Ziphiidae (Cetacea, Odontoceti) from the late Miocene of Denmark with morphological evidence for suction feeding behaviour. Royal Society Open Science.

Link: https://royalsocietypublishing.org/doi/10.1098/rsos.191347

Abstract: A new fossil of Ziphiidae from the upper Miocene Gram Formation (ca 9.9–7.2 Ma) is described herein. Computed tomographic scanning of the specimen was performed to visualize the mandibles and to obtain a three-dimensional digital reconstruction. It possesses several characters of the derived ziphiids, such as the dorsoventral thickening of the anterior process of the periotic, the dorsoventral compression of the pars cochlearis and the short unfused symphysis. The specimen cannot be identified beyond the family level, because of the unusual nature of the preserved parts consisting of the mandibles, earbones and postcranial remains. It differs from other ziphiid species from the Gram Formation, Dagonodum mojnum, in its larger size and the more derived morphology of its mandibles and earbones. Its long and thickened stylohyal, combined with its reduced teeth, suggests that this new specimen relied primarily on suction feeding. By contrast, the other ziphiid species from the Gram Formation, D. mojnum, shows adaptations for a more raptorial feeding strategy. Assuming the two species were coeval, their co-occurrence at the same locality with two different feeding strategies, may represent a case of niche separation. They may have hunted different types of prey, thus avoiding direct competition for the same food resource.

Samonds et al. New Miocene sirenians from Nosy Makamby, northwestern Madagascar. Journal of Vertebrate Paleontology.

Link: https://www.tandfonline.com/doi/abs/10.1080/02724634.2019.1570223

Abstract: The near lack of vertebrate fossils from the Cenozoic of Madagascar has left many of the details regarding the origin and evolution of the island’s extant faunas unknown. However, recent fossil discoveries from Madagascar’s nearshore marine deposits have begun to elucidate this mystery. These finds include sharks, bony fish, turtles, crocodylians, a middle Eocene sirenian (Eotheroides lambondrano), and the island’s first fossil dolphin. We report here at least three (possibly four) different early (or possibly later) Miocene dugongid sirenians recovered from the island of Nosy Makamby, Mahajanga Basin, northwestern Madagascar. These include (1) a fragmentary braincase originally attributed to the genus Halitherium but here reidentified as a previously named species known only from Libya (Rytiodus heali; Dugonginae); (2) a newly named genus and species (Norosiren zazavavindrano) interpreted as a primitive relative of Xenosiren (Dugonginae); (3) a probable dugongine not yet identified with any known species; and (4) a taxon reported here as Metaxytherium cf. krahuletzi (Halitheriinae), the first Neogene halitheriine credibly reported from the Indian Ocean basin. This pattern of shallow marine environments harboring multispecies sirenian paleofaunas is seen elsewhere in the world, and these three or four contemporaneous sirenians represent the first glimpse into Madagascar’s sea cow diversity during the Miocene. This specific time period is a poorly known and critical interval for interpreting Madagascar’s past, and these specimens are potentially highly significant for reconstructing sirenian evolutionary and biogeographic history. Surprisingly, this sirenian fauna, so far, shares no genera with the roughly contemporaneous and relatively nearby one from Kutch, western India.

Schipps et al. Borealodon osedax, a new stem mysticete (Mammalia, Cetacea) from the Oligocene of Washington State and its implications for fossil whale-fall communities. Royal Society Open Science.

Link: https://royalsocietypublishing.org/doi/10.1098/rsos.182168

Abstract: Baleen whales (mysticetes) lack teeth as adults and instead filter feed using keratinous baleen plates. They do not echolocate with ultrasonic frequencies like toothed whales but are instead known for infrasonic acoustics. Both baleen and infrasonic hearing are separately considered key innovations linked to their gigantism, evolutionary success and ecological diversity. The earliest mysticetes had teeth, and the phylogenetic position of many so-called toothed mysticetes remains debated, including those belonging to the nominal taxonomic groups Llanocetidae, Mammalodontidae and Aetiocetidae. Here, we report a new stem mysticete, Borealodon osedax gen. et sp. nov., from the Oligocene of Washington State, USA. Borealodon preserves multi-cusped teeth with apical wear; microCT scans of the inner ear indicate that the minimum frequency hearing limit of Borealodon was similar to mammalodontids. Borealodon is not recovered within a monophyletic Mammalodontidae nor a monophyletic Aetiocetidae; instead, it represents an unnamed lineage of stem Mysticeti, adding to the diversity of stem mysticetes, especially across the Rupelian–Chattian boundary. Furthermore, the presence of a putative chemosynthetic bivalve along with Osedax, a bone-boring annelid, found in association with the type specimen of Borealodon, offer more insights into the evolution of deep-sea whale-fall communities.

Comments: An interesting albeit fragmentary toothed mysticete - I first saw the specimen, expertly prepared by the discoverer - James L. Goedert - in 2016. It was originally presented as a mammalodontid in an SVP abstract a few years ago, an affinity not supported in this paper (their analysis places it outside Mammalodontidae and outside Aetiocetidae), so I suspect the name - Borealodon - was a nod to Mammalodon but kept regardless of the affinity. More complete fossils currently under study will shed light on the affinities of this poorly understood toothed mysticete.

Serio et al. Macroevolution of Toothed Whales Exceptional Relative Brain Size. Evolutionary Biology.

Link: https://link.springer.com/article/10.1007%2Fs11692-019-09485-7

Abstract: Toothed whales (Odontoceti, Cetacea) are well-known for their ability to produce complex vocalizations, to use tools, to possess self-recognition, and for their extreme behavioural plasticity. The toothed whale intelligence is said to compete with that of primates, so does their extremely large brain to body size ratio. Common explanations for the acquisition of such large brains over the evolutionary time (encephalization) in toothed whales range from their demanding, complex social lives, to their feeding habits, to echolocation. Yet, several studies found no macroevolutionary trend in Odontoceti encephalization, which casts doubts on its selective advantage. We applied a recently developed phylogenetic comparative method to study macroevolutionary trends in relative brain size (RBS) and brain size evolutionary rates in cetaceans, comparing toothed whales to the other cetaceans and contrasting groups of species as ascribed to different feeding categories. We found that cetaceans as a whole followed a trend for increased encephalization over time, starting from small-brained archaeocete ancestors. Toothed whales do not show this same trend in RBS but have possessed larger RBS than any other cetacean ever since the beginning of their existence. The rate of RBS evolution in Odontoceti is significantly slower than in other Cetacea and slower than the rate of Odontoceti body size evolution. These results suggest that toothed whales’ history is characterized by high and conservative relative encephalization. Feeding lifestyle does not explain these patterns, while the appearance of echolocation within stem group Odontoceti remains a viable candidate for them.

Shinmura and Matsui. Life appearances of Desmostylia using a three-dimensional computer graphics (3D CG). Fossils.

Link: http://www.palaeo-soc-japan.jp/publications/106_FrontPage_Shinmura_Matsui.pdf

Abstract: In Japanese (can't copy/paste).

Tanaka and Taruno. The First Cetacean Record from the Osaka Group (Middle Pleistocene, Quaternary) in Osaka, Japan. Paleontological Research.

Link: https://bioone.org/journals/Paleontological-Research/volume-23/issue-2/2018PR016/The-First-Cetacean-Record-from-the-Osaka-Group-Middle-Pleistocene/10.2517/2018PR016.short

Abstract: A new partial skeleton consisting of a left mandible and five caudal vertebrae, OMNH-QV 282 from the Osaka Group (Middle Pleistocene, about 0.3 million years ago) of Osaka City is reported as the first cetacean record from the group. The skeleton is identified as Balaenopteridae gen. et sp. indet. based on the combination of mandibular characters, such as having a small mandibular foramen, reflected neck in dorsal view and lack of a satellite process of the mandible. OMNH-QV 282 expands diversity for the local fauna, and also adds evidence for the existence of large-sized balaenopterids from a poorly known epoch, the Middle Pleistocene.

Tanaka et al. A Large Fossil Baleen Whale from the Shikiya Formation (Early Middle Miocene) of Wakayama, Japan. Paleontological Research.

Link: https://bioone.org/journals/Paleontological-Research/volume-23/issue-3/2018PR020/A-Large-Fossil-Baleen-Whale-from-the-Shikiya-Formation-Early/10.2517/2018PR020.short

Abstract: A new large Chaeomysticeti indet., WMNH-Ge-1140240005 from the Shikiya Formation of Kumano Group (early middle Miocene; about 16 to 15 Ma) of Wakayama, Japan is described here. It preserves a large rostrum (about 50 cm width at the base of the rostrum), which has gently tapered lateral margins of the rostrum, narrow mesorostral groove at the level of the narial fossa, and wide premaxillae and maxillae. There are no diagnostic features pertaining to the specimen at the family level, but it is comparable to “cetotheres” sensu lato such as Pelocetus calvertensis and Diorocetus hiatus by having wide premaxillae that occupy 1/3 width of the rostrum anterior to the narial fossa in dorsal view, which implies that WMNH-Ge-1140240005 is a possible member of “cetotheres” sensu lato. Its size is possibly between the two large species Pelocetus calvertensis and Diorocetus hiatus of the early middle Miocene, and larger than the reported middle Miocene mysticete specimens from Japan (“Diorocetus” chichibuensis, “Diorocetus” shobarensis, Parietobalaena sp. (SMNH-VeF-62)). The rostral width of WMNH-Ge-1140240005 suggests that this animal was medium-sized compare to extant species, but the largest in the class of baleen whales of its time.

Tanaka and Watanabe: An early and new member of Balaenopteridae from the upper Miocene of Hokkaido, Japan. Journal of Systematic Palaeontology.

Link: https://www.tandfonline.com/doi/full/10.1080/14772019.2018.1532968

Abstract: The family Balaenopteridae includes the modern blue whale, which is the largest animal on Earth. Our knowledge of the early members of Balaenopteridae, especially during the late Miocene and earlier periods, has recently increased, but this family is still poorly understood. A fossil balaenopterid (including the frontals, squamosals, parietals, vomer, pterygoid, basisphenoid, basioccipital, exoccipitals, right periotic and presternum) from the lower part of the Horokaoshirarika Formation, late Miocene (6.5–6.8 Ma) of Hokkaido, Japan is named as a new genus and species Miobalaenoptera numataensis, and is placed in a phylogenetic context. As a result, Miobalaenoptera numataensis is placed among the stem balaenopterids. The periotic of Miobalaenoptera numataensis shows a deeper suprameatal fossa and a shorter caudal tympanic process than extant species, incipient lateral tuberosity and a sharp anteroposteriorly long ridge on the ventral side of the anterior process. Miobalaenoptera numataensis adds information on the early morphology of the family including the periotic.

Tanaka et al. Crown beaked whale fossils from the Chepotsunai Formation (latest Miocene) of Tomamae Town, Hokkaido, Japan. Palaeontologia Electronica.

Link: https://palaeo-electronica.org/content/2019/2544-ziphiid-from-japan

Abstract: In the last decades, our knowledge of ziphiid evolution has increased dramatically. However, their periotic morphology is still poorly known. A fossil ziphiid (TTM-1) including the periotic, bulla, isolated polydont teeth and vertebrae from the Chepotsunai Formation (latest Miocene) of Tomamae Town, Hokkaido, Japan, is identified as a member of a clade with crown ziphiids of Bianucci et al. (2016) by having three periotic synapomorphies; a posteriorly wide posterior process, transversely thick anterior process, and laterally elongated lateral process. The specimen adds morphological information of the periotic. Among the Ziphiidae from the stem to crown, the periotic morphologies were changed to having a more robust anterior process, wider anterior bullar facet and posterior process. The crown Ziphiidae shares a feature; enlarged medial tubercle on the anterior process. Among the crown Ziphiidae, TTM-1 does not have a swollen medial tubercle not like Tasmacetus, Nazcacetus and others. This new morphological information might represent useful future phylogenetic comparisons.

Taylor et al. - Isotopes from fossil coronulid barnacle shells record evidence of migration in multiple Pleistocene whale populations. Proceedings of the National Academy of Sciences.

Link: https://www.pnas.org/content/116/15/7377

Abstract: Migration is an integral feature of modern mysticete whale ecology, and the demands of migration may have played a key role in shaping mysticete evolutionary history. Constraining when migration became established and assessing how it has changed through time may yield valuable insight into the evolution of mysticete whales and the oceans in which they lived. However, there are currently few data which directly assess prehistoric mysticete migrations. Here we show that calcite δ18O profiles of two species of modern whale barnacles (coronulids) accurately reflect the known migration routes of their host whales. We then analyze well-preserved fossil coronulids from three different locations along the eastern Pacific coast, finding that δ18O profiles from these fossils exhibit trends and ranges similar to modern specimens. Our results demonstrate that migration is an ancient behavior within the humpback and gray whale lineages and that multiple Pleistocene populations were undertaking migrations of an extent similar to those of the present day.

Tsai and Chang. A right whale (Mysticeti, Balaenidae) from the Pleistocene of Taiwan. Zoology Letters.

Link: https://zoologicalletters.biomedcentral.com/articles/10.1186/s40851-019-0153-z

Abstract: Current patterns of biological distribution result from the deep past. Of particular interest, some closely related species appear at high latitudes of both hemispheres, but not in between, a pattern known as antitropical distribution. However, the timing, pathway, and drivers of antitropical distributions remain mostly unknown. Here we describe a new fossil, a left tympanic bulla (part of the ear bones), from the Middle/Late Pleistocene (0.78–0.01 mya, but not excluding the possibility of Holocene in age, as the specimen was dredged from the sea bottom and the geological horizon remains uncertain) of Taiwan. The tympanic bulla is diagnostic in baleen whales, and this specimen shows morphological features that are identical to extant Eubalaena, including: relatively large size (the anteroposterior length is 117 mm); rectangular outline in medial view; short anterior lobe, judging from the remaining of the lateral furrow; squared anterior margin; prominent transverse crease on the involucrum; transversely compressed in anterior view; well-developed and rounded outer lip; and parallel involucral and main ridges. Although incomplete, the morphological characters and overall similarity to extant Eubalaena allow a reliable taxonomic assignment to Eubalaena sp. The occurrence of a Pleistocene Eubalaena on the southern margin of the western North Pacific is the first balaenid fossil evidence indicative of the biotic interchange between two hemispheres leading to the origin of antitropical distribution in the Pleistocene; alternatively, this specimen might merely represent an extra-limital record of the North Pacific Eubalaena. Furthermore, this find suggests that the Eubalaena interchange, being one of the largest species displaying antitropical distribution pairs in the history of life, likely took place along the western Pacific. Notably, this does not preclude the Eubalaena interchange from other routes, such as the eastern Pacific or the Atlantic Ocean, and future finds should test the scenario for the biotic interchange between Northern and Southern Hemispheres of Eubalaena.

Comments: CH Tsai and I have already published a couple of papers on isolated yet quite critical Pleistocene mysticete bullae from northern California - so it was nice to see him continuing the practice on the opposite side of the Pacific! Let's just say there are many more surprising fossils yet to be reported from the Penghu Channel and elsewhere in Taiwan. Cheers to Tsai for reinvigorating the study of marine mammal evolution in Taiwan.

Valenzuela-Toro and Pyenson. What do we know about the fossil record of pinnipeds? A historiographical investigation. Royal Society Open Science.

Link: https://royalsocietypublishing.org/doi/10.1098/rsos.191394

Abstract: The fossil record of pinnipeds (seals, fur seals and walruses) is globally distributed, spanning from the late Oligocene to the Holocene. This record shows a complex evolutionary history that could not otherwise be inferred from their extant relatives, including multiple radiations and iterative ecomorphological specializations among different lineages, many of which are extinct. The fossil record of pinnipeds is not uniformly represented in space and time, however, leaving some gaps in our knowledge. We performed a historiographical investigation of the published fossil record of pinnipeds based on the information available in the Paleobiology Database, with the aim to broadly characterize and evaluate it from a taxonomic, geographical and temporal perspective. We identified major trends, strengths and weaknesses of the pinniped fossil record, including potential biases that may affect our interpretations. We found that 39% of the record corresponds to extant taxa, which are essentially from the Pleistocene and Holocene. There is a larger record from the Northern Hemisphere, suggesting biases in sampling and collection effort. The record is not strongly biased by sedimentary outcrop bias. Specifically, for extinct species, nearly half of them are represented by a single occurrence and a large proportion have type specimens consisting of single isolated postcranial elements. While the pinniped fossil record may have adequate temporal and taxonomic coverage, it has a strong geographical bias and its comparability is hindered by the incompleteness of type specimens. These results should be taken into account when addressing patterns of their past diversity, evolutionary history and paleoecology.

Vautrin et al. From limb to fin: an Eocene protocetid forelimb from Senegal sheds new light on the early locomotor evolution of cetaceans. Palaeontology.

Link: https://onlinelibrary.wiley.com/doi/full/10.1111/pala.12442

Abstract: Cetaceans constitute a textbook example of the secondary adaptation of tetrapods to aquatic life. This major event in the evolutionary history of mammals is often linked in the literature to the limb‐to‐fin transition. Paradoxically, limb bones are scarce in the fossil record of early cetaceans, and the transition from a limb‐adapted morphology for an amphibious life in shallow water to a fin‐adapted morphology for a pelagic lifestyle remains poorly documented. Here, we describe new protocetid remains from the upper Lutetian of Senegal, including a nearly complete articulated forelimb. A cladistic analysis including 24 taxa and 137 morphological characters recovers the new African specimen close to Carolinacetus. It also confirms that cetacean dispersal to the New World was not the result of a single colonization event. A 3D model of the forelimb was reconstructed. Anatomical comparisons suggest that it is unlikely that the Senegalese forelimb was used as a rigid pectoral flipper for steering as in basilosaurids and modern cetaceans. Instead, we suggest that the hand was actively used during swimming. This challenges previous reconstructions of protocetids as mainly foot‐powered swimmers, and suggests that swimming specializations of early cetaceans were probably more diverse than previously considered.

Velez-Juarbe and Valenzuela-Toro. Oldest record of monk seals from the North Pacific and biogeographic implications. Biology Letters.

Link: https://royalsocietypublishing.org/doi/10.1098/rsbl.2019.0108

Abstract: True seals (crown Phocidae) originated during the late Oligocene–early Miocene (approx. 27–20 Ma) in the North Atlantic/Mediterranean region, with later (middle Miocene, approx. 16–11 Ma) dispersal events to the South Atlantic and South Pacific. Contrasting with other pinnipeds, the fossil record of phocids from the North Pacific region is scarce and restricted to the Pleistocene. Here we present the oldest fossil record of crown phocids, monachines (monk seals), from the North Pacific region. The specimens were collected from the upper Monterey Formation in Southern California and are dated to 8.5–7.1 Ma, predating the previously oldest known record by at least 7 Ma. This record provides new insights into the early biogeographic history of phocids in the North Pacific and is consistent with a northward dispersal of monk seals (monachines), which has been recognized for other groups of marine mammals. Alternatively, this finding may correspond with a westward dispersal through the Central American Seaway of some ancestor of the Hawaiian monk seal. This record increases the taxonomic richness of the Monterey pinniped assemblage to five taxa, making it a fairly diverse fossil assemblage, but also constitutes the oldest record of sympatry among all three extant pinniped crown clades.

Comments: This surprising discovery reports a couple of very fragmentary but distinctive teeth of monachine seals from a bonebed in the Monterey Formation. These teeth would be typical for Peru or even here in South Carolina - but the story up until this (told even in my own papers) was that phocid seals did not arrive in the eastern North Pacific until the middle Pleistocene, with the dispersal of harbor seals through the Arctic and elephant seals northward across the equator from the southern ocean. These rare specimens, and the lack of skulls or obvious monachine limb bones, suggests to me that these may represent vagrants rather than a resident breeding population of monk seals.

Velez-Juarbe and Wood. An early Miocene dugongine (Sirenia: Dugongidae) from Panama. Journal of Vertebrate Paleontology. 

Link: https://www.tandfonline.com/doi/full/10.1080/02724634.2018.1511799

Abstract: Herein, we describe a new early Miocene dugongine from marine deposits of the Culebra Cut (Gaillard Cut) of the Panama Canal. The new taxon, Culebratherium alemani, gen. et sp. nov., represents one of the few records of late Aquitanian–early Burdigalian sirenians and the oldest sirenian from Central America. A phylogenetic analysis places Culebratherium in a clade with Dioplotherium cf. D. allisoni (Miocene of Brazil), Dioplotherium allisoni (Miocene of Baja California Sur, Mexico, and California, U.S.A.), and Dioplotherium sp. (Pliocene of Yucatan, Mexico). Similar to these taxa, Culebratherium is characterized by the presence of large incisor tusks, a premaxillary symphysis without a boss, a premaxilla-frontal suture forming a butt joint, and a moderately downturned rostrum. In addition, Culebratherium exhibits prominent occipital-cervical attachment sites for enlarged neck musculature. These features taken together are interpreted as adaptations for uprooting large, deeply buried seagrass rhizomes. Other dugongines with similar, yet convergent, dental and facial adaptations are known from earlier or coeval deposits in Puerto Rico, Florida, South Carolina, California, Baja California Sur, Brazil, and India and were constituents of sympatric paleocommunities of sirenians. Only fragmentary evidence of a second smaller and unidentifiable sirenian species is known from the Culebra Formation, but future discoveries may reveal a similar sympatric paleocommunity during the early Miocene of Panama. Finally, we used the results of the phylogenetic analysis to propose the new clade Pan-Sirenia as the most inclusive group consisting of stem and crown groups and redefine the Sirenia, Dugongidae, and Dugonginae clades.

 

Voss et al. - Stomach contents of the archaeocete Basilosaurus isis: Apex predator in oceans of the late Eocene. PLoS One.

Link: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0209021

Abstract: Apex predators live at the top of an ecological pyramid, preying on animals in the pyramid below and normally immune from predation themselves. Apex predators are often, but not always, the largest animals of their kind. The living killer whale Orcinus orca is an apex predator in modern world oceans. Here we focus on an earlier apex predator, the late Eocene archaeocete Basilosaurus isis from Wadi Al Hitan in Egypt, and show from stomach contents that it fed on smaller whales (juvenile Dorudon atrox) and large fishes (Pycnodus mokattamensis). Our observations, the first direct evidence of diet in Basilosaurus isis, confirm a predator-prey relationship of the two most frequently found fossil whales in Wadi Al-Hitan, B. isis and D. atrox. This extends our understanding of their paleoecology. Late Eocene Basilosaurus isis, late Miocene Livyatan melvillei, and modern Orcinus orca are three marine apex predators known from relatively short intervals of time. Little is known about whales as apex predators through much of the Cenozoic era, and whales as apex predators deserve more attention than they have received.

 Comments: Earlier studies by Julia Fahlke demonstrated bite marks on juvenile Dorudon atrox skulls, presumed to be made by Basilosaurus isis. This awesome discovery reports the gut contents of Basilosaurus - including Dorudon bones and teeth, and fish/shark remains. Gut contents were reported for Dorudon atrox as well by Mark Uhen in his 2004 monograph, and fish bones were reported as gut contents in Basilosaurus isis ages ago in a still-unpublished SVP abstract.

Werth et al. Enamel Microstructure in Cetacea: a Case Study in Evolutionary Loss of Complexity. Journal of Mammalian Evolution.

Link: https://link.springer.com/article/10.1007/s10914-019-09484-7

Abstract: Enamel microstructure of 34 species in eight odontocete families is described and categorized according to structural complexity (from no or prismless enamel to highly arranged enamel in decussating layers), then correlated with parameters of ecology, life history, and occlusal function. Overall, more complex dental structure in extant and extinct cetaceans is associated with smaller, more numerous teeth in taxa that bite or grasp smaller, harder prey with longer, narrower jaws and have more oral processing. Enamel complexity loosely correlates with mechanical properties, but measurement of compressive strength is complicated by the presence of cementum overlying or in place of crown enamel. Given the presence of Hunter-Schreger bands and other indices of high microstructural complexity in archaic cetaceans (with presumed plesiomorphic characters), the absence of complex enamel, as well as more generally of gross dental form, signals a loss of complexity in various cetacean lineages. Nonetheless, it is difficult to draw robust or reliable inferences regarding either cetacean phylogeny or dental function given the pattern of presumed loss of tooth complexity, and the confounding presence of numerous exceptions (taxa with complex teeth despite limited use, or with thin, weakly developed enamel and soft, simple teeth despite high occlusal function). Although retention of a complex feature implies its continued adaptive value, and thus selection for the underlying genetic and developmental bases for that complexity, loss of complexity can simply follow absence of function. Loss of complex traits presumably relates to accumulated mutations and economic efficiency, but unfolds with no distinct pattern of distribution.

 

Woolley et al. Microanatomy and histology of bone pathologies of extant and extinct phocid seals. Historical Biology.

Link: https://www.tandfonline.com/doi/abs/10.1080/08912963.2019.1689238

Abstract: This study investigates three presumed fractured phocid seal bones: An isolated metapodial and an ulna belonging to different individuals of the extinct phocid, Homiphoca capensis, from Langebaanweg and a mandible of a juvenile elephant seal (Mirounga leonina), which was included to assess the validity of the assumption that changes to bones caused by fractures are consistent across extant and extinct members of the same groups. The bones were studied using a multi-method approach, including gross morphology, microcomputed tomography (micro-CT) and histology. Micro-CT showed that the metapodial was not fractured and information drawn from other analyses suggested that the pathology was an osteosarcoma. Histology of normal and fractured regions of the mandible and ulna permitted an estimate about the fracture healing stage, and showed the bone tissue at the fracture sites to be histologically similar. A birth line found on the lateral surface of the elephant seal mandible emphasised its young age and marked the first example of a birth line in a bone of a semi-aquatic mammal. A large scope of information was obtained using this multi-method approach, which could permit insight into the life events and lifestyles of modern and extinct individuals, such as H. capensis.