It's that time of year again! Somehow we made it through another year of the pandemic. This past semester happened to be the worst of my teaching career for a multitude of reasons, but all stemming from misbehaving students. It's over with now, and somehow I've managed to claw back some of my pre-pandemic research motivation. 2021 was not a great year for my publications, but a pretty good year for research - 2022 will be a decent year for me, publication-wise.
This year had only a few papers on archaeocete whales, though the papers on a new skull of Togocetus and the new genus Phiomicetus stand out; there were a few papers on fossil pinnipeds, including a preliminary article on a stunning new enaliarctine skull from Japan - loads of papers on Neoceti, and a couple papers on sirenians. The topic that really became the star of 2021 in marine mammal paleo, however, was taphonomy and paleoecology of fossil marine mammals - several assemblage-level studies of these topics, many papers on shark bites on marine mammal bones, some on ichnology - altogether a number of fantastic studies I only dreamt of being able to cite ten years ago when I was wrapping up my master's thesis research on the topic.
The usual disclaimers apply:
1) If you think I am missing an article, double check the post from last year. If it was published "online early" in 2020, and just has a formal 2021 publication date, then it counts for 2020. Please do not ask me to shift them from one post to the other - don't be daft.*
2) I have copied the authors (citation style) and the title, as well as the URL; I don't have time to include these all in a complete reference format. Please don't ask me to do that. Don't be daft.*
3) In order to qualify the paper MUST consider fossils, because this is a paleontology list. Marine mammal paleontologists frequently publish on the morphology of extant species. That's not paleontology, though. If a phylogenetic study doesn't incorporate fossil data, it also doesn't count.
4) None of the genus/species names are italicized. This is because I pasted directly into notepad to remove formatting. I will not be italicizing these names so please do not ask me to. Don't be daft.*
*Yes, these are all things [daft] randos have asked me to do in the past. I don't get it. If you want these things, do it yourself.
In spite of a continuously expanding physeteroid fossil record, our understanding of the origin and early radiation of the two modern sperm whale families Kogiidae Gill, 1871 (including the pygmy and dwarf sperm whales, Kogia spp.) and Physeteridae Gray, 1821 (including the great sperm whale, Physeter Linnaeus, 1758) remains limited, especially due to the poorly resolved phylogenetic relationships of a number of extinct species. Among those, based on fragmentary cranial material from the late early to middle Miocene of Antwerp (Belgium, North Sea basin), the small-sized Thalassocetus antwerpiensis Abel, 1905 has been recognized for some time as the earliest branching kogiid. The discovery of a new diminutive physeteroid cranium from the late Miocene (Tortonian) of Antwerp leads to the description and comparison of a close relative of T. antwerpiensis. Thanks to the relatively young ontogenetic stage of this new specimen, the highly modified plate-like bones making the floor of its supracranial basin could be individually removed, a fact that greatly helped deciphering their identity and geometry. Close morphological similarities with T. antwerpiensis allow for the reassessment of several facial structures in the latter; the most important reinterpretation is the one of a crest-like structure, previously identified as a sagittal facial crest, typical for kogiids, and here revised as the left posterolateral wall of the supracranial basin, comprised of the left nasal (lost in kogiids for which the postnarial region is known) and the left maxilla. Implemented in a phylogenetic analysis, the new anatomical interpretations result in the new Belgian specimen and T. antwerpiensis being recovered as sister-groups in the family Physeteridae. Consequently, the geologically oldest kogiids are now dated from the Tortonian, further extending the ghost lineage separating these early late Miocene kogiid records from the estimated latest Oligocene to earliest Miocene divergence of kogiids and physeterids.
Remarks: I've been waiting for such a paper for literally my entire career. Fossil balaenopterids (rorquals like humpbacks, minkes, blues, and fin whales) from Pacific basin deposits were once viewed as too daunting to study, given severe nomenclatural baggage from the taxonomic chaos and ensuing paralysis caused by Van Beneden. When I began doing background research in 2005/2006 for the work that would eventually culminate in the naming of Balaenoptera bertae, I was struck by the apparent laziness of early workers who would just identify primitive-looking balaenopterids as "Plesiocetus sp." Tom Demere and others cleared some of this up, but it wasn't until the revision of a number of Italian and Dutch fossil mysticetes that balaenopterids from California, Japan, and even Peru were able to be described properly. Major kudos to Michelangelo and Mark for undertaking this thankless task!
The evolution of gigantic body size represents a key to understand the ecological role of baleen whales in oceanic ecosystems. Many efforts have been devoted to the formulation of equations relating different body parts to total body length and mass in living and fossil mysticetes, mainly focusing on balaenopterid and balaenopterid-like mysticetes. Right whales (family Balaenidae) have a unique head-to-body length ratio, suggesting that their body proportions cannot be predicted effectively using equations based primarily on non-balaenid mysticetes. A new morphometric dataset of living and fossil balaenids is provided herein, and new regression equations allow one to predict the body length and mass of extinct species based on the expected head-to-body length ratio of extant balaenids. The reconstructed values are mapped on a new phylogenetic analysis of the Balaenidae, inferring body size and mass at ancestral nodes. The variations of body size and mass in Balaenidae since the early Miocene are reconstructed, revealing that: (1) a reduction in total body length occurred in the early Pliocene; (2) the origin of the gigantic body size in the bowhead whale (Balaena mysticetus) is probably related to invasion of the Arctic Ocean in the last 3 Myr; and (3) the origin of the gigantic body size in the right whales (genus Eubalaena) occurred since the latest Miocene, probably concomitant with pulses of nutrients sustaining large zooplankton populations. We suggest that the evolution of gigantism in Balaenidae occurred independently in two lineages and, probably, in response to different palaeoenvironmental drivers.
Remarks: We started this paper in early 2019, and it's sort of a sequel to my wife Sarah Boessenecker's paper on the Pleistocene survival of the extinct walrus Ontocetus emmonsi in South Carolina, and also builds on published and unpublished research on fossil walruses from California. Unfortunately it was accepted in final form in late 2019 and delayed over a year by the pandemic, and so there are no references to the paper on "imagotariine" walruses by Biewer et al. (2020). The main thrust of the paper is the more recent evolution of the odobenines and Odobenus itself, which is still very much up to date.
Microstructural and biomolecular preservation is reported in fossils as old as the Triassic. Such preservation suggests unusual taphonomic conditions. We collected fragments of fossil whale bone from silty, tuffaceous, and diatomaceous rocks of the middle-upper Miocene portion of the Pisco Formation. The whale fossils within the region are generally well-preserved and mostly articulated, including some specimens with in situ baleen. Due to the depositional setting associated with the preservation of these fossils, they could be expected to be favorable candidates for the preservation of cellular microstructures and/or original biomolecules. To test this hypothesis, fossil whale bone fragments were subjected to microscopic analysis and EDTA-mediated demineralization to release extractable materials. Microscopy of partially demineralized fossil bones revealed quartz-permineralized osteocyte-like and vessel-like structures. Protein assay (micro-Bicinchoninic Acid Assay) of the supernatants obtained from demineralized fossils yielded 12 to 19.5 μg of protein per gram of bone. MALDI-TOF analysis of the extracted protein demonstrated the presence of approximately 5 kD molecules in one fossil sample, consistent with the presence of highly fragmented polypeptides. An LC-MS/MS analysis of the fragmentation pattern of the tryptic digest of extracted protein was performed. However, attempted protein identification was unsuccessful. Nevertheless, this study first documents the microstructural preservation with some silicification of the fossil whale bones of the Pisco Formation, and then quantifies extractable protein from these bones. It adds to the growing body of reports of microstructural and organic preservation in fossils.
The global decline of megafauna is believed to have had significant and widespread ecological impacts. One such extinction of likely important consequence is the 18th century extinction of the Steller’s sea cow (Hydrodamalis gigas); however, little has been written about how the loss of this megaherbivore may have impacted coastal ecosystem dynamics. Drawing on historical evidence, sea cow biology, kelp forest ecology, and the ecology of extant sirenians, we propose several discrete hypotheses about the effects Steller’s sea cows may have had on kelp forest dynamics of the North Pacific.
The ichnogenus Thatchtelithichnus Zonneveld, Bartels, Gunnell & McHugh was created for ring-shaped, roughly circular grooves affecting the outer surface of plastral bones of Eocene geoemydid turtles. Such traces were assumed to be attachment scars of aquatic ectoparasites (possibly ticks, leeches or liver ﬂukes). Despite its well-distinctive aspect, Thatchtelithichnus has only been reported subsequently by few works and mostly from the plastron-bottom of freshwater turtles. Here we provide the first record of Thatchtelithichnus from a fossil mammal bone, namely, a partial grey whale mandible from the Belgian Pliocene. Thatchtelithichnus traces from this cetacean fossil commonly penetrate into the outermost portion of the cancellous bone, achieving a maximum depth of about 2 mm. The external margin of these grooves is sharply defined and commonly follows an elliptical, somewhat festooned path. A scrutiny of recent literature in palaeontological and forensic taphonomy as well as new first-hand observations reveal that Thatchtelithichnus-like structures can be produced by the attachment of barnacles on the surface of mammal bones that suffered long-lasting exposure on the seafloor. When encrusting bare bones in marine settings, barnacles can thus produce a variety of traces, including Anellusichnus Santos, Mayoral & Muñiz, Thatchtelithichnus and, possibly, Karethraichnus lakkos Zonneveld, Bartels, Gunnell & McHugh. The modes of trace formation are still largely to be understood, but observations on how barnacles damage paint coatings during growth might help us in envisaging how this kind of process works.
Extant baleen whales (Mysticeti) have a deciduous foetal dentition, but are edentulous at birth. Fossils reveal that the earliest mysticetes possessed an adult dentition. Aetiocetids, a diverse clade of Oligocene toothed mysticetes, have a series of small palatal foramina and associated sulci medial to the postcanine dentition. The openings have been homologized with lateral palatal foramina that transmit neurovascular structures to baleen in extant mysticetes, thereby implying a co-occurrence of teeth and baleen in aetiocetids. However, homology of the foramina and sulci have been questioned. Using CT-imaging, we report that the lateral palatal foramina of Aetiocetus weltoni are connected internally to the superior alveolar canal, which transmits neurovascular structures to baleen in extant mysticetes and to teeth in extant odontocetes. Furthermore, the lateral palatal foramina of Aetiocetus are separate from the more medially positioned canals for the greater palatine arterial system. These results provide critical evidence to support the hypothesis that the superior alveolar neurovasculature was co-opted in aetiocetids and later diverging mysticetes to serve a new function associated with baleen. We evaluate competing hypotheses for the transition from teeth to baleen, and explore the transition from raptorial feeding in early mysticetes to filter-feeding in extant species.
Remarks: I'm sure this won't be the last word as some folks can't seem to move on from this, but in my mind this is the silver bullet: excellent CT data from Eric Ekdale & Tom Demere indicate that the purported palatal foramina in Aetiocetus weltoni are homologous to those present in modern baleen whales, and therefore support the interpretation that aetiocetids possessed both teeth and baleen simultaneously.
Based on a shark-bitten partial skeleton of an immature sirenian (Metaxytherium cf. medium) from the middle Miocene of the Styrian Basin (Austria), we report on the oldest predator–prey interaction between tiger sharks and dugongs. The bite mark-bearing ribs and vertebrae are associated with seven teeth of Galeocerdo aduncus, which are otherwise rare in the fossil record of the Styrian Basin. The unique tooth morphology of the genus Galeocerdo is reflected by an unambiguous pattern of bite marks, which is repeatedly detected on one rib fragment. Similar bite marks were reproduced experimentally by using clay instead of bone. The obtained pattern is consistent with the observed bite marks on the sirenian rib fragment, which demonstrates that tiger sharks fed upon the Metaxytherium carcass. Furthermore, we also report on the first record of the angel shark Squatina sp. within the Styrian Basin.
A new monotypic genus of Neogene odontocete (Isoninia borealis) is named on the basis of a partial skull (CMM-V-4061). The holotype was found on the riverbed of the Meherrin River (North Carolina, USA) and probably originated from the Miocene marine Eastover Formation. Deep interdigitation of the cranial sutures indicates that this individual was mature. The new taxon differs from all other delphinidans in the unique combination of the following characters: anteriorly retracted premaxillae and maxillae; premaxillae not contacting nasals; thick nasals with ventrolateral margins deeply imbedded within corresponding troughs in the frontals (this is an apomorphy); nasals with transversely convex dorsal surface; nearly symmetrical vertex; os suturarum (or interparietal or extra folds of the frontals) at the vertex; large dorsal infraorbital foramen level with the posterior margin of the external bony nares; and a postorbital recess on the ventrolateral face of the frontal below and behind the postorbital process of the frontal. This odontocete exhibits two small but pronounced concavities on the cerebral face of the frontal/presphenoid that are presumed to have held vestigial olfactory bulbs in life. Inioidea is only diagnosed by a single unequivocal synapomorphy: width across nasals and nares subequal. Isoninia shares this feature with other inioids and forms the basis for the placement of Isoninia within this clade. A relatively high vertex coupled with a supraoccipital that is deeply wedged between the frontals suggests placement of this new inioid species within the family Iniidae. This is the second inioid described from the Eastover Formation (the other being Meherrinia isoni). This new species adds new cranial morphology and a new combination of cranial characters to this taxonomically small but growing group of mostly marine and mostly Western Hemisphere odontocetes.
A description and analysis is given of a single physeteroid tooth, from the Neogene of the Nutrien Aurora Phosphate Mine (formerly known as the Lee Creek Mine, Aurora, North Carolina, USA), that was bitten either by the extinct megatoothed shark Otodus chubutensis or Otodus megalodon. The tooth shows three gouges, one of which also preserves raking bite traces, made as the serrations on the Otodus sp. tooth struck and cut into its surface. We do not know if these bite traces came about as a result of scavenging or active predation. However, because the bite traces occur on part of the skull, this suggests a predatory interaction. This tooth preserves the first evidence in the fossil record of a predatory/antagonistic interaction between a sperm whale and a megatoothed shark.
Godfrey and Lowry: The ichnospecies Linichnus bromleyi on aMiocene baleen whale radius preserving multiple shark bite-shake tracessuggests scavenging
An isolated Miocene baleen whale left radius was marked repeatedly by shark bite-shake traces. The radius probably derives from the Plum Point Member of the Calvert Formation, Calvert Cliffs, Calvert County, Maryland, U.S.A. At least three successive bite-shake traces marking the radius, made by multiple teeth, are attributed to the trace fossil Linichnus bromleyi. These bite-shake traces consisting of shallow, thin arching gouges on a radius, likely indicate scavenging rather than active predation. The most likely means of producing the bundle of L. bromleyi within each of the three sets of traces would be through repeated biting as the shark re-positioned the prey in its mouth or, perhaps, by a shark species with multiple functional teeth within its tooth row. If the bite traces were produced by a non-serrated tooth (as they appear to have been), then the most likely candidate would be Carcharodon hastalis.
Over about 10 million years, the ancestors of whales transformed from herbivorous, deer-like, terrestrial mammals into carnivorous and fully aquatic cetaceans. Protocetids are Eocene whales that represent a unique semiaquatic stage in that dramatic evolutionary transformation. Here, we report on a new medium-sized protocetid, Phiomicetus anubis gen. et sp. nov., consisting of a partial skeleton from the middle Eocene (Lutetian) of the Fayum Depression in Egypt. The new species differs from other protocetids in having large, elongated temporal fossae, anteriorly placed pterygoids, elongated parietals, an unfused mandibular symphysis that terminates at the level of P3, and a relatively enlarged I3. Unique features of the skull and mandible suggest a capacity for more efficient oral mechanical processing than the typical protocetid condition, thereby allowing for a strong raptorial feeding style. Phylogenetic analysis nests Phiomicetus within the paraphyletic Protocetidae, as the most basal protocetid known from Africa. Recovery of Phiomicetus from the same bed that yielded the remingtonocetid Rayanistes afer provides the first clear evidence for the co-occurrence of the basal cetacean families Remingtonocetidae and Protocetidae in Africa. The discovery of Phiomicetus further augments our understanding of the biogeography and feeding ecology of early whales.
Remarks: I am very humbled to have participated in this research with Abdulla Gohar and the rest of the Mansoura paleo team! My first archaeocete research, jumping way down the tree to protocetids.
A study of the Mio-Pliocene marine palaeoenvironment on South Africa’s west coast revealed aspects of the biology and behaviour of fossil marine mammals. Close examination showed that seals from Langebaanweg suffered from pathologies and bore marks of marine carnivore activity. This study adds to our knowledge of shark feeding behaviour in the geological past and is one of a few studies of sharks feeding on seals in the fossil record. Two incomplete seal humeri with shark tooth marks are the first documented evidence from South Africa’s Mio-Pliocene of such behaviour. These injuries show no healing, which suggests that the animals were most likely scavenged.
The history of cetaceans demonstrates dramatic macroevolutionary changes that have aided their transformation from terrestrial to obligate aquatic mammals. Their fossil record shows extensive anatomical modifications that facilitate life in a marine environment. To better understand the constraints on this transition, we examined the physical dimensions of the bony auditory complex, in relation to body size, for both living and extinct cetaceans. We compared the dimensions of the tympanic bulla, a conch-shaped ear bone unique to cetaceans, with bizygomatic width—a proxy for cetacean body size. Our results demonstrate that cetacean ears scale non-isometrically with body size, with about 70% of variation explained by increases in bizygomatic width. Our results, which encompass the breadth of the whale fossil record, size diversity, and taxonomic distribution, suggest that functional auditory capacity is constrained by congruent factors related to cranial morphology, as opposed to allometrically scaling with body size.
A new species of an extinct dolphin belonging to the kentriodontids, i.e., Kentriodon sugawarai sp. nov., is described from the upper lower to lowest middle Miocene Kadonosawa Formation in Ninohe City, Iwate Prefecture, northern Japan. The holotype of Kentriodon sugawarai sp. nov., consists of a partial skull with ear bones, mandibular fragments, and some postcranial bones. This new species shares five unique characters with other species of Kentriodon. In addition, the new species differs from other species of the genus in displaying a narrow width of the squamosal lateral to the exoccipital in posterior view, the dorsolateral edge of the opening of the ventral infraorbital foramen that is formed by the maxilla and the lacrimal or the jugal, and at least three anterior dorsal infraorbital foramina. Our phylogenetic analysis based on 393 characters for 103 Odontoceti taxa yielded a consensus tree showing all previously identified kentriodontids as a monophyletic group that comprises the sister group of the crown Dephinoidea, which in turn include Delphinidae, Phocoenidae and Monodontidae. Our analysis also indicates that the distinct innovation of the acoustic apparatus (i.e., 13 out of 29 derived characters are from tympanoperiotic) would have occurred in the ancestral lineage of the Delphinoidea (sensu lato) including the monophyletic Kentriodontidae during their initial evolution and diversification.
Modern pinnipeds (true and eared seals) employ two radically different swimming styles, with true seals (phocids) propelling themselves primarily with their hindlimbs, whereas eared seals (otariids) rely on their wing-like foreflippers. Current explanations of this functional dichotomy invoke either pinniped diphyly or independent colonizations of the ocean by related but still largely terrestrial ancestors. Here, we show that pinniped swimming styles form an anatomical, functional, and behavioral continuum, within which adaptations for forelimb swimming can arise directly from a hindlimb-propelled bauplan. Within phocids, southern seals (monachines) show a convergent trend toward wing-like, hydrodynamically efficient forelimbs used for propulsion during slow swimming, turning, bursts of speed, or when initiating movement. This condition is most evident in leopard seals, which have well-integrated foreflippers with little digit mobility, reduced claws, and hydrodynamic characteristics comparable to those of forelimb-propelled otariids. Using monachines as a model, we suggest that the last common ancestor of modern seals may have been hindlimb-propelled and aquatically adapted, thus resolving the apparent contradiction at the root of pinniped evolution.
Remarks: This paper is definitely more of an extant biomechanics study, but it does discuss forelimb morphology and swimming adaptations in extinct pinnipeds such as Allodesmus and friends, thereby making the cut for this list.
Earliest cetaceans (whales) originated from the early Eocene of Indo-Pakistan, but the group dispersed through most of the oceans of the planet by the late middle to late Eocene. This late Eocene global distribution indicates that important dispersal events took place during the middle Eocene (Lutetian), a globally undersampled time interval that is well documented in the Togolese phosphate series. We report here the first discovery of a partial cetacean cranium from middle Eocene deposits of Togo (West Africa). A 3D model of the cranium and teeth was reconstructed in order to reveal hidden anatomical features. The dental and cranial characteristics of the Togolese specimen recall those of protocetid taxa described in Africa, Asia, and North America, but also display significant differences. In particular, we show that the new specimen shares a number of morphological features with the Togolese taxon Togocetus. Such a hypothesis is further supported by a cladistic analysis including 45 taxa and 167 morphological characters, which recovers the new specimen close to Togocetus as the first offshoot of protocetids. Phylogenetic analysis including all the protocetids remains of Kpogamé confirms the singular diversity of the Togolese phosphate basin, and enables to examine potential connections with faunas from contemporaneous localities in Africa.
A new species of a beaked whale that belongs to the extant genus Berardius is described from the Middle to Late Miocene boundary age Tsurushi Formation (ca 12.3–11.5 Ma) on the Sado Island, Niigata Prefecture, Japan. The new species, Berardius kobayashii sp. nov. represents the oldest record of this genus and provides a minimum age for the emergence of this extant genus. Berardius kobayashii sp. nov. has the following generic characters: the ratio between the width of the premaxillary crests and the width of the premaxillary sac fossae is 1.0–1.25, nodular frontals make isolated protuberance on the posterior part of the vertex. Among the species within the genus, B. kobayashii sp. nov. shares a unique character with B. minimus: the apices of the left and right hamular processes of the pterygoids contact medially, forming together a posteriorly directed medial point. In addition, B. kobayashii sp. nov. displays a unique combination of the following characters: it is extremely small in size, and the nasals are short, the ratio between the length of the medial suture of nasals on the vertex and the maximum width of nasals is less than 0.4. Berardius kobayashii sp. nov. fills the gap between the origin of the genus and later diversifications of the extant species. This discovery is also key to elucidate the process of the emergence and dispersal of the genus during the Middle to Late Miocene. Based on the distributional patterns of the fossil and extant species of the genus, the western North Pacific including the Sea of Japan may have been one of the areas for the evolution and radiation of this genus at the time before 11 Ma.
Sirenians are placental mammals that comprise the extant manatees (Trichechus manatus, T. inunguis, and T. senegalensis) and dugongs (Dugong dugon). Since the late 19th century, cranial endocasts of extinct sirenians have been employed to study the neurological evolution of these mammals during the Cenozoic. Here, we analyzed the endocranial morphology of Dioplotherium cf. allisoni (MPEG 63–V) from the middle Miocene of South America to gain insights on brain morphology and encephalization. This sirenian was ca. three meters long, weighed approximately 800 kg, and inhabited coastal marine environments of northern Brazil 14.2 to 12.7 million years ago. The cranial endocast of this animal is lissencephalic, with two smooth hemispheres divided by a deep median sulcus and presenting a weakly marked Sylvian fissure separating frontal and temporal lobes. The olfactory bulbs are small (compared to Paleogene stem sirenians as well as terrestrial mammals), and the optic nerves were thin but long. The sphenorbital fissure and mandibular canal are bulky, indicating the presence of large sensory trigeminal components that innervate the facial region, which was presumably covered by perioral bristles and facial hairs used to feed and explore the environment. The encephalization quotient is 0.36 (Jerison’s EQ) and 0.34 (Manger’s EQ). Ancestral character state reconstruction suggests that, despite an overall slight increase in the degree of encephalization of sirenians, except for the extant Dugong dugon, other analyzed taxa present values below 0.5. This is in accordance with previous studies that have maintained that sirenians have a relatively small brain size compared to other tethytherians, perhaps associated with their lifestyle.
Kimura and Hasegawa（2019a）described a cranium with periotics and right tympanic bulla of Joumocetus shimizu（i GMNH-PV-3456）, which was recovered from the Miocene Haraichi Formation, Annaka Group, Gunma, Japan. In this short paper, we describe newly discovered fossil bones of the same individual（ GMNHPV-3456）. It includes left mandible, left tympanic bulla, seven cervical vertebrae, and rib fragments. The present specimen reveals that the angle of the mandible of the basal member of the Cetotheriidae, J. shimizui, is markedly smaller than the other members of the Cetotheriidae（e.g., Herpetocetus spp.）.
Kohno et al.: A fossil pinniped from the lower Miocene Akeyo Formation, Mizunami Group at the construction site of the Togari-Tsukiyoshi City Road in Mizunami City, Gifu Prefecture, central Japan
A pinniped fossil was found at the construction site of the Togari-Tsukiyoshi City Road in Akeyo-cho, Mizunami City, Gifu Prefecture, Japan in September 2020. We briefly report this new discovery of a partial skeletal bones belonging to a single individual (MFM18009), which was recovered from the lowermost part of the Yamanouchi Member of the Akeyo Formation, the Mizunami Group (lower Miocene: ca 18 Ma). MFM18009 is consisted from a complete skull, distal half of the left mandible, the atlas, distal half of the left humerus, proximal half of the left ulna, the third metacarpus, thoracic vertebrae and ribs. MFM18009 seems to belong in the Pteronarctos-Pacificotaria species complex of pinnipediforms, and is provisionally identified as Enaliarctine genus and species undetermined.
Remarks: A preliminary report on an utterly gorgeous looking skull of something closely related to Pteronarctos, possibly Pacificotaria, if you believe that it exists. I am really looking forward to seeing this specimen being thoroughly prepared, described, and named.
Numerous Miocene fossil terrestrial mammals have been discovered at the Gritsev locality of Ukraine, but this is the first record of a fossil marine mammal found at this site. Dental morphology and morphometric analysis of the rostral portion of this middle-late Miocene (12.3-11.8 mya) partial skull suggests that it belongs to the subfamily Phocinae. The small size and cranial morphology of this partial skull is compared to Recent and fossil representatives of the extant subfamily Phocinae and the extinct subfamily Devinophocinae. Fossil and modern representatives of the extant subfamilies Cystophorinae and Monachinae were not incorporated in this study due to their extremely large size in comparison to this new finding. This newly described skull is a small-sized seal (likely similar in size to the modern sea otter based on the width of the rostrum) with an extremely short rostrum and several diagnostic characters that differ from all other fossil and extant phocines. Due to the lack of preservation and fragility of fossil seal skulls, less than 20 have been described so far. This new skull is yet another example of a small-sized ancestral seal, supporting the suggestion that modern seals have gotten larger over evolutionary history. Overall, any cranial information on fossil true seals is extremely vital to help resolve contentious phylogenetic relationships.
Hyper-longirostry, the character of having extremely elongated rostra, emerged in the early and middle Miocene among several different clades of echolocating toothed whales (odontocetes) followed by a rapid decline near the end of the middle Miocene, and postdated by a much lower number of occurrences in the late Miocene and Pliocene and a complete absence among extant odontocetes. New finds of unreworked fossils of Xiphiacetus cristatus (Eurhinodelphinidae) in the middle Tortonian Diest Formation in Belgium (9.54–8.8 Ma) allow for the documentation of the survival of a hyper-longirostrine dolphin into the early late Miocene. An extensive dataset of the rostral index (calculated as the ratio between rostral length and condylobasal length) of Neogene and extant odontocetes is compiled and presented here, which facilitates discussion of evolutionary trends of rostrum proportions during a time period spanning 23 million years. Of interest, the iterative survival into the late Miocene of a single different species of hyper-longirostrine dolphins in a number of paleogeographic regions (North Sea Basin, Atlantic Coastal Plain, and probably the southeastern Pacific) is noted, whereas hyper-longirostrine morphologies only seem to re-appear by the late Messinian in the Northeastern Pacific. A correlation between this pattern and a decrease in habitat size for coastal to estuarine dolphins linked to a major sea level drop is tentatively proposed; such a process may also have played a role in the ecological shift in several dolphin families to freshwater habitats.
Phylogenetic trees provide a powerful framework for testing macroevolutionary hypotheses, but it is becoming increasingly apparent that inferences derived from extant species alone can be highly misleading. Trees incorporating living and extinct taxa are needed to address fundamental questions about the origins of diversity and disparity but it has proved challenging to generate robust, species-rich phylogenies that include large numbers of fossil taxa. As a result, most studies of diversification dynamics continue to rely on molecular phylogenies. Here, we extend and apply a recently developed meta-analytic approach for synthesizing previously published phylogenetic studies to infer a well-resolved set of species level, time-scaled phylogenetic hypotheses for extinct and extant cetaceans (whales, dolphins, and allies). Our trees extend sampling from the ∼90 extant species to over 500 living and extinct species, and therefore allow for more robust inference of macroevolutionary dynamics. While the diversification scenarios, we recover are broadly concordant with those inferred from molecular phylogenies they differ in critical ways, notably in the relative contributions of extinction and speciation rate shifts in driving rapid radiations. The metatree approach provides the most immediate route for generating higher level phylogenies of extinct taxa and opens the door to re-evaluation of macroevolutionary hypotheses derived only from extant taxa.
Bowhead whales are a member of Balaenidae (right whales), an ancient lineage stretching back at least 20 million years. Despite this long history, the early evolution of right whales remains obscured by a notoriously patchy fossil record. This pattern only changes about 7–6 million years ago (Ma), when balaenids suddenly appear around the globe in a variety of shapes and sizes. Bowhead whales arose during this radiation and initially shared the oceans with several smaller balaenids, some of them a mere 6–7 m long. This diverse assemblage abruptly declined with the onset of the ice ages about 3 Ma, which hit small baleen whales (including balaenids) especially hard. Thanks to their larger size, bowhead whales persisted, and eventually turned into polar specialists found exclusively in the Arctic.
Cetaceans (whales and dolphins) have some of the largest and most complex brains in the animal kingdom. When and why this trait evolved remains controversial, with proposed drivers ranging from echolocation to foraging complexity and high-level sociality. This uncertainty partially reflects a lack of data on extinct baleen whales (mysticetes), which has obscured deep-time patterns of brain size evolution in non-echolocating cetaceans. Building on new measurements from mysticete fossils, we show that the evolution of large brains preceded that of echolocation, and subsequently followed a complex trajectory involving several independent increases (e.g. in rorquals and oceanic dolphins) and decreases (e.g. in right whales and ‘river dolphins’). Echolocating whales show a greater tendency towards large brain size, thus reaffirming cognitive demands associated with sound processing as a plausible driver of cetacean encephalization. Nevertheless, our results suggest that other factors such as sociality were also important.
Shark bite marks incising fragmentary ribs from a single specimen of the extinct sirenian Metaxytherium subapenninum are described from lower Pliocene shallow-water, marginal-marine (shoreface) deposits exposed at Arcille (Tuscany, Italy). Two of the bitten ribs display bite marks whose morphology matches that of juvenile teeth of the extant bluntnose sixgill shark Hexanchus griseus, which is known from the same site thanks to several dental remains. Our new finds comprise the second published occurrence of hexanchid bite marks on fossil marine mammal bones; furthermore, they represent the first piece of evidence documenting a trophic interaction between H. griseus and sirenians across both the fossil and the Recent records. In light of the environmental preferences of extant sirenians (which thrive in shallow-marine, nearshore seagrass meadows), and considering that the bitten skeleton takes its place in shoreface sands, our finds are seemingly at odds with the current understanding of hexanchids as deep-water sharks. Juveniles of H. griseus, however, are known for their diel vertical migrations, which result in frequenting relatively shallow waters at nighttime. Frequentation of the marginal-marine, shoreface Arcille palaeo-biotope by bluntnose sixgill sharks might have been facilitated by a steep morphology of the seafloor as well as by the presence of a bathymetrically high thermosphere-psychrosphere interface in the early Pliocene Mediterranean Sea.
Remarks: I've been waiting for fossil evidence of marine mammal feeding damage on mollusks - modern Odobenus doesn't chew or bite its molluscan prey, but it can break the shells during feeding, at least in experiments where walruses were fed on a hard surface. In this case, repetetive damage to gaper clams was found near the margin of the shell where the fleshy siphon comes out - and these authors, reasonably in my opinion, attribute this to walrus feeding by the extinct Pliocene-Pleistocene species Ontocetus emmonsi - which has a full set of incisors to nip with, unlike modern Odobenus rosmarus. Unfortunately, for some reason, no citation was made to Sarah Boessenecker et al.'s paper reviewing the geologic range and Pleistocene survival of Ontocetus emmonsi in the North Atlantic, which I found puzzling.
Sea cows are exceptional fossil vertebrates recently discovered in the deposits of the Qom Formation. Yet, the Sirenia-bearing limestones are still poorly understood in terms of detail paleoenvironmental and micropaleontological investigations. In order to distinguish the temporal and paleoenvironmental context of the Sirenia (sea cow) bearing deposits of the Qom Formation in central Iran, three stratigraphic sections were studied in Hamedan (Ivak and Shirinsu) and Isfahan (Chahriseh) provinces. A total number of 47 thin sections were studied for micropaleontology, biozonation and carbonate microfacies analysis, as well as sedimentary environment recounstruction. Biostratigraphical investigations suggest that the Sirenia-bearing deposits are Aquitanian/Burdigalian in age, which implies restriction of sea cows remains to the Lower Miocene. We recognized nine microfacies (n=8 correspond to carbonate; n=1 correspond to siliciclastic) in the study areas. They are systematically grouped into two microfacies settings, representing inner and middle ramp environments. This is based on the facies associations and the distribution of skeletal components and rock textures. The Sirenia-bearing limestone consists of peloid/algae bearing wackstone/packstone/floatstone. A carbonate (inner) ramp system under shallow water conditions is interpreted as the habitats of the Sirenian mammals during the Aquitanian/Burdigalian in Central Iran. This paleoenvironmental setting could be utilized for further exploration of Qom Formation deposits for discovering sea cows.
The highly productive waters of the Humboldt Current System (HCS) host a particular temperate ecosystem within the tropics, whose history is still largely unknown. The Pisco Formation, deposited during Mio-Pliocene times in the Peruvian continental margin has yielded an outstanding collection of coastal-marine fossils, providing an opportunity to understand the genesis of the HCS ecosystem. We present a comprehensive review, completed with new results, that integrates geological and paleontological data from the last 10 My, especially focusing on the southern East Pisco Basin (Sacaco area). We discuss the depositional settings of the Pisco Formation and integrate new U/Pb radiometric ages into the chronostratigraphic framework of the Sacaco sub-basin. The last preserved Pisco sediments at Sacaco were deposited ~ 4.5 Ma, while the overlying Caracoles Formation accumulated from ~ 2.7 Ma onwards. We identified a Pliocene angular unconformity encompassing 1.7 My between these formations, associated with a regional phase of uplift. Local and regional paleoenvironmental indicators suggest that shallow settings influenced by the offshore upwelling of ventilated and warm waters prevailed until the early Pliocene. We present an extensive synthesis of the late Miocene–Pleistocene vertebrate fossil record, which allows for an ecological characterization of the coastal-marine communities, an assessment of biodiversity trends, and changes in coastal-marine lineages in relation to modern HCS faunas. Our synthesis shows that: (i) typical endemic coastal Pisco vertebrates persisted up to ~ 4.5 Ma, (ii) first modern HCS toothed cetaceans appear at ~ 7–6 Ma, coinciding with a decline in genus diversity, and (iii) a vertebrate community closer to the current HCS was only reached after 2.7 Ma. The genesis of the Peruvian coastal ecosystem seems to be driven by a combination of stepwise transformations of the coastal geomorphology related to local tectonic pulses and by a global cooling trend leading to the modern oceanic circulation system.
Remarks: This might be one of the single most important papers on marine mammals out this year - a massive synthesis of the marine vertebrate fossil record from the Pisco Basin. I've only skimmed it, but it dovetails quite nicely with some of the papers I've written on Pliocene-Pleistocene faunal change in the North Pacific. Also... the first published recognition of southern hemisphere walruses (!!!).
Sperm whales (Physeteroidea) include today only two genera of morphologically disparate odontocetes: the largest toothed whale known (Physeter macrocephalus) and small sized forms (Kogia spp.). In contrast, their fossil record indicates a high diversity for the group during the Miocene, with over 20 species recognized. Miocene marine sediments from Patagonia (Argentina) record this diversity, including at least five species. Among them, Preaulophyseter gualichensis, from the Miocene of Gran Bajo del Gualicho Formation, has been one of the most enigmatic. Despite the fragmentary nature of the type and referred materials (isolated teeth and periotics), which casts some doubts on its validity, this species has not been revised since its original description. In this contribution, we re-describe the materials referred to P. gualichensis, revise the taxonomic status of the species and evaluate the phylogenetic signal of ear bones among Physeteroidea. Our results indicate that the physeteroid tympano-periotic complex morphology is poorly diagnostic at the species level. Intraspecific variation (including ontogeny and sexual dimorphism) and/or taphonomic processes cannot be ruled out as the causes of the minor differences observed among specimens. We suggest that sperm whale tympano-periotics retain many plesiomorphic characters and are diagnostic only between kogiids and non-kogiid physeteroids. Based on the fragmentary and isolated state of the studied specimens, and the lack of diagnostic characters in both teeth and periotics, we consider P. gualichensis as nomen dubium and we re-assign the referred specimens as Physeteroidea indet. A conservative morphology of the tympano-periotic and, to a lesser extent, the nasal complex in sperm whales, might result from the morpho-functional constraints imposed by a highly specialized but successful echolocation system.
The taphonomy of a partial skeleton of the fur seal Arctocephalus australis from the mid-Holocene of Miramar (southern Buenos Aires province, Argentina) comprising most of both hindlimbs and some vertebral elements is herein described and discussed. The main axis of the long bones is oriented perpendicular to the coastline, flexed and slightly disarticulated, while the vertebrae are somewhat arched, possibly suggesting rigor mortis. The specimen was probably transported from a nearby coastal area, and possibly died from starvation with subsequent stranding. Short weathering times, fragmentation and possible rotation of the pelvic region are the main factors affecting the remains. The material corresponds to a subadult individual, determined by the pattern of fusion of the epiphysis and size of long bones. This study adds important information on the taphonomy of Holocene marine mammals and paleoenvironmental conditions influencing the preservation of these pelagic pinnipeds along the Atlantic Ocean compared with the populations of the Pacific Ocean.
Differing from the extant physeteroids, macroraptorial sperm whales are currently regarded as apex predators of the Miocene seas based on several morphofunctional observations. Here, we estimate the bite force of Zygophyseter varolai, a macroraptorial physeteroid from lower upper Miocene strata of the Pietra leccese formation (Apulia, Italy) using the finite element analysis (FEA). To explore multiple bite scenarios, we set four different load cases on a 3D model of the cranium obtained via digital photogrammetry, considering the temporalis and masseter muscles as jaw adductors. Our FEA simulations indicate that Z. varolai exerted an anterior bite force of more than 4000 N and a posterior bite force of more than 10000 N. These values are similar to those estimated for other marine predators known for their powerful bite. This suggests that Z. varolai might have fed upon medium-sized marine vertebrates like other odontocetes. Considering the significant difference observed between the anterior and posterior bite forces, Z. varolai likely fed via ‘grip-and-shear’ feeding, snapping the food items with an anterior bite and then cutting them with a powerful posterior bite. Other macroraptorial sperm whales such as the roughly coeval Acrophyseter from Peru likely employed the same feeding technique.
The name “Cetartiodactyla” was proposed in 1997 to reflect the molecular data that suggested that Cetacea is closely related to Artiodactyla. Since then, that taxon has spread in popularity, even outside the scientific literature. However, the implications of the name are confusing, because Cetacea and Artiodactyla are not sister-taxa. Instead, the evidence clearly shows that cetaceans are a group embedded within Artiodactyla, not a sister-taxon of equal rank. It has long been accepted practice that systematists do not modify the names of higher groups when new subgroups are added to them. For example, Owen’s original concept of Artiodactyla did not change its name when more and more disparate taxa were added to it. Dinosauria did not become “Avedinosauria” when it became clear that birds are a subgroup of dinosaurs, nor did Reptilia become “Avereptilia”. In the interests of taxonomic priority and stability, and especially because the name is inherently misleading, we recommend that the name “Cetartiodactyla” be abandoned. If one wishes to make a reference to the fact that whales are now considered to be a subgroup of artiodactyls, they could be referred to informally as “whales and other artiodactyls” or “whales and terrestrial artiodactyls” without using a formal taxonomic name that is confusing and misleading.
To date, for the family Phocidae, only two fossil genera of the subfamily Monachinae (Monotherium and Terranectes) and two fossil genera of the subfamily Phocinae (Prophoca and Leptophoca) have been described from the Western Shore of the Chesapeake Bay (Maryland, USA). This study presents the first description of a new fossil partial seal skull from the St. Mary’s Formation (late Miocene, 8.5–7.5 MYA) in Maryland, USA. The new skull exhibits both primitive and derived features. Morphological assessment of this new skull supports classifying it within the subfamily Monachinae (based on numerous diagnostic characters). However, the presence of unique characters that do not match with any known genera of Monachinae led to the naming of a new genus and species, Magnotherium johnsii. This is now the third taxon of the subfamily Monachinae described from this locality. Some key characters of the Magnotherium johnsii (sp. nov.) skull include the presence of six incisors (similar to seals of the subfamily Phocinae), a long rostrum, and long concavity of the preorbital area of the maxilla.
Despite decades of research, the systematics of extinct true seals (Phocidae) is still overly reliant on morphological data from extant taxa. As a result, monk seals (Monachini) have been interpreted as ‘archaic’ despite an absence of fossil data to support this hypothesis. This has affected systematic hypotheses for extinct phocids, including fossils from Australasia. Recent finds from New Zealand indicate that the first seal fossils described from Australia, two temporal bones from the late Miocene–early Pliocene (6.24–4.35 Ma), need to be revisited. Here we re-describe these temporal bones and find them to represent monk seals. This places the oldest known fossils of this group in the Southern Hemisphere, implying monk seals had a longer history at southern latitudes. Our ancestral state estimation of the temporal bone morphology of monachines indicates that monk seal temporals may be derived, rather than plesiomorphic as has previously been assumed. This suggests that an over-reliance on the morphology of extant true seals may be obscuring the true diversity of both stem- and crown-phocids, and indicates that a rethink of the morphology underlying the taxonomic assessments of fragmentary true seal fossils is needed.
We report a single whale bone associated with many molluscan fossils from the Omma Formation, Lower Pleistocene shallow marine deposits, along the Sai-gawa River, Kanazawa City, in central Japan. Most molluscan species which are commonly found in the Omma Formation show disarticulated and/or damaged shells, indicating semi-autochthonous or allochthonous modes of occurrence. However, the assemblage contained chemosynthetic bivalves, such as lucinid, solemyid and thyasirid bivalves, which are rare in the Omma Formation. The lucinids and solemyids show a high articulation ratio, along with some predatory and scavenging gastropods, such as naticids, nassariids and borsoniids whose well-preserved shells indicate an autochthonous mode of occurrence. In addition, most of the lucinid bivalves show an umbo-upward position similar to the life position of Recent species. Recent lucinid, solemyid and most thyasirid bivalves harbor chemosymbiotic bacteria in their gills and are well known members of the chemosynthetic community. These lines of evidence indicate that the community, mainly comprising lucinid bivalves and other autochthonous molluscan species associated with the whale bone, is an ancient whale-fall community. This shallowest fossil whale-fall community differs from deep-water cases in the dominance of infaunal bivalves, such as lucinids, and in the lack of epifaunal and semi-infaunal chemosynthetic bivalves, such as bathymodiolins and vesicomyids. This community supports a previous suggestion that the difference in characteristic species of the whale-fall communities depends on the water depth.
The marine fossil assemblages of the Pliocene of south Spain constitute the record of the marine fauna that colonised the western part of the Mediterranean after the Messinian Salinity Crisis. This work focuses on the analysis of lithofacies and fossil assemblages including trace fossils, invertebrates, and vertebrates with special attention to taphonomic features, for interpreting palaeoenvironmental conditions in the Vera Basin (SE Spain). The sedimentary sequences of the northern region of the Vera Basin display diverse stratigraphical, sedimentological, and palaeontological features that correspond to the evolution of a fan-delta in a narrow basin. The Vera Basin was characterised by shallow-marine shelf conditions during the early-mid Pliocene (Cuevas Formation). The basin emergence with the development of Gilbert-type fan deltas (Vera Member), and a protected, partially-enclosed marine embayment (Almanzora Member) occurred during the mid-late Pliocene due to regional uplift and movements of the Palomares strike-slip Fault along the eastern basin margin. The progradation of the central fan-delta lobes and the interaction with marginal fan-delta resulted in the partitioning of the basin that formed a small sub-basin with restricted stagnant conditions that favoured a Konservat Fossil-Lagerstätte. The high input of siliciclasts due to the uplift context of the margins of the basin favoured a high sedimentation rate and the fast burial of vertebrate remains. Fossil marine mammals occurs from shallow shelf deposits (Cuevas Formation) to bottomset (Cuevas Formation-Vera Member transition) and lower part of the clinoforms in the foreset (Vera Member). Cetacean remains are usually recorded not only in the relatively deep-water silty marls and sandy marls of the outer shelf and distal facies of the fan-delta (Espiritu Santo Formation), but also in the shallower coarse sands and conglomerates (Cuevas Formation and Espiritu Santo Formation). Sirenian remains, in contrast, are only recorded in coarse sand facies (Cuevas Formation and Espiritu Santo Formation) associated to charcoal wood fragments deposited in shallow waters near the shoreline. This narrow and relatively protected basin is interpreted as an area of reproduction and nursery of juveniles on the basis of the presence of cetaceans.
Smith et al.: Biogeographic, stratigraphic, andenvironmental distribution of Basilosaurus (Mammalia, Cetacea) in North America with a review of the late Eocene shoreline in thesoutheastern coastal plain
A new specimen of Basilosaurus cetoides was discovered on the banks of the Flint River in Albany, Georgia, USA, in 2010. This fossil, which was the most complete specimen of the species from Georgia to date, consisted of five nearly complete and two partial post-thoracic vertebrae, tentatively identified as S4 through Ca6. During excavation, however, the site was looted and most of the specimen was lost to science. Nonetheless, we use this discovery as an opportunity to update the current state of knowledge on the stratigraphic, biogeographic, and environmental distribution of Basilosaurus in North America, as well as the position of the late Eocene shoreline in the southeastern United States. The results show that Basilosaurus was most abundant across the southeastern coastal plain during the early to middle Priabonian, coincident with the late Eocene maximum marine transgression. The decline in Basilosaurus localities is associated with the retreating shoreline of the terminal Eocene. The majority of Basilosaurus localities fall well south of the position of the late Eocene shoreline hypothesized in this study, suggesting the genus favored middle to outer neritic zones of the epicontinental sea. The comparatively low number of Priabonian specimens in the Atlantic Coastal Plain versus the Gulf Coastal Plain, then, suggests the presence of shallow zones in the Atlantic Coastal Plain that may have limited the distribution of Basilosaurus across the region. The hypothesized shoreline of this study ultimately differs from earlier reconstructions by extending the Mississippi embayment at the Bartonian/Priabonian boundary farther north than previously noted.
Balaenopteroidae is a diverse superfamily within the mysticetes that consists of numerous recent fossil species. The publication of new taxa has increased, which improves the knowledge about this group. In this work, we name and describe Kennedycetus pericorum from the Late Miocene deposits of the Trinidad Formation in Baja California Sur, Mexico. Our phylogenetic results indicate that this is a step taxon, far from the balaenopterid crown group, that is closely related to Norrisanima miocaena from the Monterey Formation, California. The associated fauna of K. pericorum includes the internal molds of different mollusks attributable to Glycymeridae, Semelidae, and Lucinidae, which indicate a coastal environment of warm waters.
Potamosiren magdalenensis Reinhart, is an extinct species of manatee (Sirenia, Trichechidae, Trichechinae), which has only been recorded for the middle Miocene Honda Group, in the La Venta area (Huila Department, Colombia). A new specimen referable to Potamosiren cf. P. magdalenensis is reported herein, collected from the early Miocene Barzalosa Formation. This unit crops out in the Pubenza locality, at the Tocaima municipality of the Cundinamarca Department, Colombia. The material described here represents the first evidence of a mammal from the Barzalosa Formation, the earliest record of Potamosiren so far reported and one of the only two trichechid records for the early Miocene of South America. The new specimen adds to a small but growing record of extinct trichechids, increasing the fossil record of this group in South America and allowing us to further explore their evolutionary history. The early Miocene appearance of trichechines coincides geographically and temporally with the onset of the Pebas Mega-Wetland System, which likely provided favourable conditions for the invasion of freshwater ecosystems of this group of fully aquatic mammals. Finally, the depositional environments represented by the Barzalosa Fm and a review of the fossil record of trichechines further support the notion that manatees have had a close association with freshwater systems since early in their evolutionary history, and that reinvasion of marine ecosystems did not occur until much later.
This paper describes the fossil sharks associated with the skeleton of Eschrichtius akishimaensis （GMNH-PV 3210, so called“ Akishima-Kujira”） . The fossils consist of twelve isolated teeth（ GMNH-PV 3601 – PV 3607, PV 3609 – PV 3613） and one tooth tip（ GMNH-PV 3608） within an anterior rib fragment of“ Akishima-Kujira”. Eight fossil teeth（ GMNH-PV 3601-3608） are identified as great white shark, Carcharodon carcharias, based on their morphological characteristics. One fossil tooth （GMNH-PV-3609） is similarly identified as oceanic whitetip shark, Carcharhinus longimanus. And the remaining four teeth are identified as requiem sharks, Carcharhinus spp. These fossils mark the first record of shark fossils from the Komiya Formation and Akikawa-Tamagawa area of the Kazusa Group. Also these records are important as a clue to know the sedimentary environment and oceanographic condition of the paleo bay（ now called the Kanto Plain） in the late Pliocene to early Pleistocene. And GMNH-PV 3608 is recognized as direct evidence of shark-whale interaction and the marine food chain in the early Pleistocene of Japan.
The generic name of the humpback whale, Megaptera was named after their forelimb, which means a “large wing”. New whale remains (specimen number: OMNH-QV 60) including the right scapula, humerus, and radius from the Namba Formation, Holocene in Osaka, Japan is reported as a humpback whale, Megaptera novaeangliae based on diagnoses of the species; having reduced acromion and coracoid processes of the scapula, and long humerus and radius. The body length of the individual can be estimated as 13 m based on the proportion between forelimb elements and body length. It suggests that OMNH-QV 60 is adult. The specimen is a certain record of Megaptera novaeangliae from Holocene sediments in Japan with size estimation.
The present study describes a new specimen of a pinniped mandible from the lower Miocene Irino Sandstone Member of the Takami Formation (approximately 16.5 Ma), Shimane, western Japan, as a basal odobenid Neotherium mirum Kellogg, 1931. Our review of the basal odobenid records from Japan reveals that it is the first record of N. mirum and the western- and southernmost record in the western North Pacific. In addition, the present specimen is one of the oldest records of N. mirum around the world. The records clearly showed that Japan was one of the major habitats for the basal odobenids. The early evolution of odobenids occurred around the North Pacific; however, there is no record of basal odobenids with a trans-Pacific distribution. Our study demonstrates that N. mirum was widely distributed in the North Pacific, and suggests that the basal odobenids already had the mobility to expand their distribution.
A new specimen of a pinniped humerus was found from the middle Miocene Fujina Formation, Shimane, Japan. It was identified as Allodesminae gen. et sp. indet. based on morphological description and comparisons with allodesmine humeri. The results of the comparisons suggest that there is variation in morphological features within this group. This discovery that revealed allodesmines had already expanded along the north-to-south coastal regions from the early stage of the back-arc spreading of the Sea of Japan. According to the summary of Japanese allodesmines, these pinnipeds thrived in the Japanese coastal regions during the middle to late Miocene as well as in North America.
The inner ear of the two higher clades of modern cetaceans (Neoceti) is highly adapted for hearing infrasonic (mysticetes) or ultrasonic (odontocetes) frequencies. Within odontocetes, Platanistoidea comprises a single extant riverine representative, Platanista gangetica, and a diversity of mainly extinct marine species from the late Oligocene onward. Recent studies drawing on features including the disparate tympanoperiotic have not yet provided a consensus phylogenetic hypothesis for platanistoids. Further, cochlear morphology and evolutionary patterns have never been reported. Here, we describe for the first time the inner ear morphology of late Oligocene–early Miocene extinct marine platanistoids and their evolutionary patterns. We initially hypothesized that extinct marine platanistoids lacked a specialized inner ear like P. gangetica and thus, their morphology and inferred hearing abilities were more similar to those of pelagic odontocetes. Our results reveal there is no “typical” platanistoid cochlear type, as the group displays a disparate range of cochlear anatomies, but all are consistent with high-frequency hearing. Stem odontocete Prosqualodon australis and platanistoid Otekaikea huata present a tympanal recess in their cochlea, of yet uncertain function in the hearing mechanism in cetaceans. The more basal morphology of Aondelphis talen indicates it had lower high-frequency hearing than other platanistoids. Finally, Platanista has the most derived cochlear morphology, adding to evidence that it is an outlier within the group and consistent with a >9-Myr-long separation from its sister genus Zarhachis. The evolution of a singular sound production morphology within Platanistidae may have facilitated the survival of Platanista to the present day.
Most authors have identified two rapid increases in relative brain size (encephalization quotient, EQ) in cetacean evolution: first at the origin of the modern suborders (odontocetes and mysticetes) around the Eocene-Oligocene transition, and a second at the origin of the delphinoid odontocetes during the middle Miocene. We explore how methods used to estimate brain and body mass alter this perceived timing and rate of cetacean EQ evolution. We provide new data on modern mammals (mysticetes, odontocetes, and terrestrial artiodactyls) and show that brain mass and endocranial volume scale allometrically, and that endocranial volume is not a direct proxy for brain mass. We demonstrate that inconsistencies in the methods used to estimate body size across the Eocene-Oligocene boundary have caused a spurious pattern in earlier relative brain size studies. Instead, we employ a single method, using occipital condyle width as a skeletal proxy for body mass using a new dataset of extant cetaceans, to clarify this pattern. We suggest that cetacean relative brain size is most accurately portrayed using EQs based on the scaling coefficients as observed in the closely related terrestrial artiodactyls. Finally, we include additional data for an Eocene whale, raising the sample size of Eocene archaeocetes to seven. Our analysis of fossil cetacean EQ is different from previous works which had shown that a sudden increase in EQ coincided with the origin of odontocetes at the Eocene-Oligocene boundary. Instead, our data show that brain size increased at the origin of basilosaurids, 5 million years before the Eocene-Oligocene transition, and we do not observe a significant increase in relative brain size at the origin of odontocetes.
Historically, the Saqqara region of Egypt has been thought or treated as devoid of vertebrate fossil material. While the Eocene sequence in the Saqqara region is incompletely understood, elsewhere the Eocene of Egypt is better known, particularly from the multiple cetacean and sirenian genera of Wadi Al Hitan (better known as the Valley of the Whales) in the western desert of the Fayum region. Within the catacombs, the fossil bearing marlstone of the Eocene aged Maadi Formation (Priabonian, approximately 36 Ma ago), which here is up to 2.0m in thickness, is argillaceous with a high smectite content, and contains abundant gypsum veins. These features distinguish it from the other marlstones within the Maadi Formation. Within the Eocene of Egypt there are three known genera of Sirenia – Eosiren, Eotheroides and Protosiren. Throughout this analysis we shall refer to the catacomb specimen as the “Saqqara Sirenian”. Taphonomically the specimen appears to represent a “whale fall” assemblage consisting of numerous associated post-cranial (vertebrae, thoracic ribs, girdle) and possible cranial (basicranium) elements.
Evidence for the earliest invasion of the marine realm by mammals was previously restricted to Eocene (48.6–37.8 Ma) skeletal remains. We report incontrovertible ichnofossil evidence for brackish-water habitat use by at least two mammalian species in southern Wyoming during the late Paleocene (58 Ma). These are the first Paleocene mammal trackways recorded in the United States and only the fourth documented in the world. Multiple tracks preserved in restricted marine deposits represent animals repeatedly walking across submerged to partially emergent tidal flats. Hundreds of tracks are preserved in planform and cross-sectional exposure within five horizons along a 1032 m tracksite. Four prints exhibit five clear toe imprints, while two others distinctly display four toes. Some tracks penetrate beds populated by dwelling traces of marine bivalves and polychaetes in the upper layers and sea anemones at the base. Candidates for the five-toed tracemakers are pantodonts such as Titanoides, Barylambda, and Coryphodon, which have been recovered from late Paleocene strata throughout western North America. The four-toed tracks provide the earliest evidence of previously-undescribed large artiodactyls and/or tapiroids, mutually supporting recent molecular phylogenetic studies that place the origin of Cetartiodactyla near the Cretaceous-Paleogene boundary (~ 67.7 Ma). Collectively, these trackways irrefutably demonstrate the utility of ichnological data in reconstructing the evolutionary history and adaptive behaviors of extinct taxa beyond the evidence provided by body fossils alone.