Saturday, March 15, 2014

Science Fiction Double Feature: Two new papers on the same day – a strange new fossil porpoise, and vertebrate taphonomy of the Purisima Formation

Yesterday saw the publication of two new papers: the first of which is about a new genus and species of bizarre porpoise from the Pliocene of California, and the second is the published version of my master’s thesis.

The first paper is a collaboration with Rachel Racicot, Brian Beatty, and Tom Deméré and finally describes the extinct odontocete informally known as the “skimmer” or “half-beaked” porpoise. The new fossil phocoenid is named Semirostrum ceruttii, the genus name referring to the dramatically shorter rostrum, and is also an homage to the half-beak fish, Hemiramphus. The species name is in honor of Richard Cerutti, longtime field paleontologist and preparatory for the San Diego Natural History Museum. Mr. Cerutti collected the holotype in the early 90’s from the Pliocene San Diego Formation – I met him during a 2012 visit to the SDNHM.

The holotype skull, earbone, and mandible of Semirostrum ceruttii, and a composite skeletal reconstruction from three specimens. From Racicot et al. (2014); skeletal reconstruction by yours truly.

The new fossil porpoise has a somewhat longer rostrum than modern phocoenids, and is slightly more delphinid-like than modern porpoises as well. Most obviously, Semirostrum has a bizarre lower jaw with an elongate, fused mandibular symphysis that is developed into a laterally flattened and expanded, paddle-shaped process that juts far beynd the edge of the rostrum. The teeth in the mandible do not extend past the rostrum, so the majority of the symphysis is edentulous. The preserved teeth have labial wear facets, which we interpret as being the result of substrate abrasion – the observed patterns of tooth wear differ from extant phocoenids in lacking apical wear facets. When articulated, the wear facets do not match up with occluding upper teeth – indicating that regular tooth wear does not account for the observed pattern. We hypothesize that the elongate mandibular symphysis is a benthic probe, and that Semirostrum pushed its “chin” through the substrate, with sediment streaming along the lateral sides of the toothrow – snatching up any burrowing prey that came into contact with the “chin” or rostrum. In my life restoration, I illustrated Semirostrum as using it’s mandibular symphysis like a benthic plough, ploughing through the uppermost layer of the sediment in its search for burrowing invertebrates. The type specimen consists of a complete skull and mandible with periotic, tympanic bulla, and postcrania – an absolutely gorgeous set of fossils which I first had the opportunity to examine on my first visit to the SDNHM back in 2007.

Life restoration of Semirostrum ceruttii, from Racicot et al. (2014) - by yours truly.
My contribution to the paper was describing fossil material of Semirostrum from the Purisima Formation. Although the holotype specimen of Semirostrum ceruttii is from the San Diego Formation, multiple specimens of Semirostrum have been collected from contemporaneous sections of the Purisima Formation. In fact, one of the earliest known specimens of Semirostrum – collected in the mid 1980s by local collector Wayne Thompson – consists of a pair of fused mandibles. The specimen still unpublished and is now at LACM, but I was not able to see it on my last museum visit in November 2013. Material from the Purisima Formation includes a nearly complete skull and isolated mandible, a partial rostrum, and a couple of isolated periotics. None of the material is associated – it’s all scattered material preserved in bonebeds and other inner shelf sediments, presumably scattered across the seafloor by currents or from drifting carcasses. Nevertheless, every referred element exhibits morphological features unique to Semirostrum. Some specimens – including the periotics and the mandible – are morphologically indistinguishable from and identical in age to Semirostrum ceruttii. However, the skull and partial rostrum are somewhat older, from about the Mio-Pliocene boundary; furthermore, the skull exhibits a slightly asymmetrical facial region – which is a bit more primitive than extant phocoenids, and Semirostrum ceruttii. For these reasons, we interpreted this slightly older material as representing an as yet unnamed, slightly older species, and chose to simply identify it as Semirostrum sp.

Examples of different preservational features on shark teeth (A), odontocete vertebrae (B), auk (Alcidae) humeri (C), and odontocete periotics (D) - specifically, the top periotic is Parapontoporia wilsoni, and the bottom periotic is a referred periotic of Semirostrum ceruttii figured by Racicot et al. (2014:figure 2).

The second paper is the publication derived from my master’s thesis research at Montana State University. My master’s thesis dealt with the taphonomy of Miocene and Pliocene marine vertebrates preserved in the Purisima Formation of Northern California. I initially got hooked on taphonomy – the science of fossil preservation – thanks to my undergraduate adviser Dave Varricchio, who did his Ph.D. on the formation of “Jack’s Birthday Site”, a multispecies bonebed assemblage from the late Cretaceous Two Medicine Formation. I took his taphonomy course in fall 2005, and read a few articles on the taphonomy of modern whales. At that time, I had just returned from my first summer season of permitted field work in the Purisima Formation, so I was naturally interested in looking into the taphonomy of the unit. Further piquing my interest was marine reptile researcher Pat Druckenmiller’s return to MSU to teach for a year. Pat did his master’s thesis at MSU, where he published the short necked plesiosaur Edgarosaurus from the Thermopolis Formation near Bridger, Montana. Pat had an interest in marine vertebrate taphonomy – and we talked quite a bit about it.

Histograms of taphonomic characteristics of bones, teeth, and cartilage from different lithofacies of the Purisima Formation. In general, highest energy conditions are on left, lowest energy on right.

As it turns out, the Purisima Formation had already been the focus of a taphonomic study of fossil invertebrates in the 1980’s. The Purisima Formation is rather unique in that, unlike most rock units which have received taphonomic study, it preserves invertebrate and vertebrate fossils in a number of different depositional environments. This provided Norris (1986) with the unique opportunity of examining across-shelf trends in preservation of marine invertebrate fossil concentrations. Even with such an expansive shelly fossil record, similar studies have been few and far between. No studies investigating across-shelf trends in marine vertebrate taphonomy had ever really been attempted. My own limited field experience at the time indicated that a study of similar scope as Norris’s original paper – but analyzing marine vertebrates from the Purisima Formation instead – would uniquely permit the examination of cross-shelf changes in vertebrate preservation. All previous studies had sampled vertebrates from a single marine unit reflecting a single depositional environment, or a single fossil bed, or a single skeleton. These studies are of course necessary and make up the bread and butter of marine vertebrate taphonomy, but investigating larger scale processes that control or influence the spatial distribution and preservation of vertebrate bones and teeth in the marine environment is (or, was) virgin territory.

I’ll discuss the highlights later on in a dedicated series of posts, but these are takeaway points:
1) vertebrate material is most abundantly concentrated along time-rich hiatal or erosional surfaces – namely, bonebeds and shell beds.

2) taphonomic damage – abrasion, phosphatization, fragmentation, polish – are all positively correlated with both high-energy, shallower water deposits, and time-rich surfaces.

3) this indicates a systematic relationship between sedimentary architecture and marine vertebrate preservation, and that the sheer majority of the marine vertebrate fossil record is controlled by physical sedimentary processes, rather than biotically controlled. From a paleoecological perspective, there is not much hope that using any sort of specimen counting methods (e.g. relative abundance) for faunal analysis will be able to backstrip the rather severe taphonomic overprint.

Friday, March 7, 2014

Megachasma applegatei: A new megamouth shark from the Oligocene and Miocene of California and Oregon

In 1976, a strange large bodied shark with a wide mouth and a multitude of tiny, unicuspate teeth was discovered after being entangled in an anchor of a US Navy ship off the coast of Hawaii. Preliminary examination indicated it was an entirely new genus and species of filter feeding shark, not similar or closely related to basking sharks (Cetorhinus) and whale sharks (Rhincodon). It was named several years later as Megachasma pelagios – the megamouth shark. Megachasma is approximately 4-6 meters in length, inhabits temperate waters of the Atlantic, Pacific, and Indian Oceans, and extraordinarily rare – only 55 specimens have been observed since its discovery, explaining why this shark took so long to discover (in contrast, most other large bodied sharks at temperate latitudes have been known to science since the 18th century).

The modern megamouth shark, Megachasma pelagios.

This week, a new species of fossil megamouth – named Megachasma applegatei after the late paleoichthyologist Shelton Applegate – was described by Kenshu Shimada, Bruce Welton, and Doug Long. Fossil teeth of M. applegatei occur in the late Oligocene-early Miocene Pyramid Hill member of the Jewett Sand near Bakersfield (California), the Skooner Gulch Formation in Mendocino County (California), and the Yaquina Formation and Nye Mudstone of coastal Oregon. Oddly enough, despite being named recently, the first fossils of this new species were discovered (at the Pyramid Hill locality) fifteen years prior to the discovery of the modern megamouth shark – which sort of makes the modern megamouth shark a living fossil.

The holotype and some paratypes of Megachasma applegatei.

Shimada et al. (2014) describe in total a series of 67 teeth (see above) – virtually every specimen present in museum collections. Many more specimens are present in private collections, but are useless to paleontologists interested in publishing as they are not publishable specimens. Private specimens include many published in an earlier study by de Schutter (2009), who unfortunately published photographs and descriptions of specimens in private collections. The 67 specimens reported by Shimada et al. (2014) include all publishable specimens, and constitutes a fairly large sample set. Other Cenozoic sharks are represented by tens of thousands of specimens – but a fair amount of variation is recorded in this sample. This large sample demonstrates two primary morphological differences between Megachasma applegatei and extant Megachasma pelagios: relatively shorter crowns (relative to root size) and the primitive retention of lateral cusplets in M. applegatei. The lateral cusplets and overall morphology of the teeth of M. applegatei are reminiscent of sand tigers (Odontaspididae), and appear to retain some primitive lamniform tooth morphology.

The rather large sample size of Megachasma applegatei. Serious kudos to the authors for figuring every single specimen!

The authors also review the rest of the published fossil record of Megachasma, and demonstrate that most Cenozoic teeth fall into two categories: Megachasma applegatei and similar teeth from Belgium from Mio-Pliocene deposits, and younger Pliocene specimens much more similar to extant Megachasma pelagios (e.g., Pliocene Yorktown Formation, Lee Creek Mine, North Carolina). The third species, Megachasma comanchensis, was described earlier by Shimada (2007) from the Cretaceous of the western interior (USA) but has been challenged by other authors as not genuinely representing a Cretaceous megamouth shark.

Proportional differences between M. applegatei and M. pelagios. Note the overlap between the two. From Shimada et al. (2014).

This study and two recent papers on fossil basking sharks mark the return of paleoichthyologist Bruce Welton, who published quite a bit during the 1970’s and 1980’s, but was less productive prior to his retirement from the petroleum industry. I’m truly pleased that this paper is finally out, and am eagerly looking forward to more papers on fossil sharks from the North Pacific. On that note, I will conclude that I have just submitted my own paper on fossil sharks from the region – with Dana Ehret, Doug Long, Evan Martin, and my wife Sarah – so, there will be more to read in the somewhat distant future!


De Schutter, P. 2009. The presence of Megachasma (Chondrichthyes: Lamniformes) in the Neogene of Belgium, first occurrence in Europe. Geologica Belgica, 12: 179–203.

Shimada, K. 2007. Mesozoic origin for megamouth shark (Lamniformes: Megachasmidae). Journal of Vertebrate Paleontology, 27: 512–516.

Shimada, K., Welton, B.J., and Long, D.J. 2014. A new fossil megamouth shark (Lamniformes, Megachasmidae) from the Oligocene-Miocene of the western United States. Journal of Vertebrate Paleontology 34:281-290.

Monday, March 3, 2014

Radio interview on Radio Live NZ - fossil marine mammals from Northern California

Last weekend I was interviewed by Graeme Hill for the New Zealand station Radio Live, which broadcasted here over the weekend. For those of you who live elsewhere and probably missed it, you can listen to a podcast [9:55 min], linked below:

The interview covers the results of a recently published paper in Geodiversitas regarding fossil marine mammals from the Pliocene Purisima Formation of California. It covers some of the behind the scenes stuff - the discovery of the fossil site, some details of the ten years of laboratory work involved, in addition to discussing the broader implications of the fossilized fauna, and potential insights into the appearance of modern marine mammal species in the North Pacific.

Friday, February 28, 2014

Sexual dimorphism in pinnipeds - comments on two new studies in the journal Evolution

Two newly published articles in the journal Evolution investigate the evolution of sexual dimorphism in pinnipeds (seals, sea lions, and walruses). One paper by Kruger et al. (2014) examines it largely from a modern biological perspective, while the other paper by Cullen et al. (2014) incorporates fossil data. We’ll start with Kruger et al., and then move on to Cullen et al.

But first, some introductory remarks. Sexual dimorphism, for the uninitiated, is the condition where males and females of a particular species are of different sizes, color pattern, or proportion (or, all of the above). Naturally this doesn’t apply to anatomical differences in sex organs, as that is something that characterizes practically all vertebrates. Humans are somewhat sexually dimorphic – generally males are taller and more robust than females, and are characterized by some subtle skeletal differences (wider pelves in females, for example). As compared to humans, gorillas are a bit more extremely dimorphic – the males are quite a bit larger, and sport large sagittal crests for jaw muscle attachment on their skulls. Extreme sexual dimorphism has often been linked with reproductive behavior – in particular, “harem” size. In pinnipeds, the males of the least sexually dimorphic species tend to mate with only one female, while males of the most extremely sexually dimorphic species tend to arrange and defend large harems (dozens to hundreds of females) and engage in male-male combat, such as the dramatic fighting commonly seen in elephant seals.

The paper by Kruger et al. (2014) analyzed data on modern pinnipeds including male and female body size, harem size, latitude of breeding, and the length of breeding and lactation, using several phylogenetic comparative methods including phylogenetic independent contrasts and phylogenetic confirmatory path analysis (neither of which I am very familiar with). Their analysis reconstructed ancestral pinnipeds as non-dimorphic and polar in distribution (e.g. Arctic). They further found that sexual dimorphism probably preceded increases in harem size (polgyny); in their words, sexual dimorphism originated first and facilitated polygyny, rather than being a consequence of it. They identify ice breeding as the ancestral reproductive behavior for pinnipeds, rather than aquatic or terrestrial breeding.

Hypothesized sequence of events in the evolution of sexual dimorphism and polygyny in pinnipeds, from Kruger et al. (2014).

There are a few problems with this hypothesis, and most of them revolve around the lack of fossils incorporated into the analysis. Of course, many of the data categories are unknown in fossils (e.g. length of breeding period). However, many fossils indicate that early pinnipeds were in fact sexually dimorphic (Berta 1994; also, see remarks upon Cullen et al., 2014 below). Secondly, simply because many modern pinnipeds breed on ice now doesn’t necessarily mean that they always have, and suggest that this trait is probably unreliable to work with. Tusked walruses, for example, were until only one or two million years ago nearly completely temperate and even subtropical in distribution – only with the evolution of Odobenus rosmarus have walruses been confined to the arctic. Furthermore, Pliocene fossils of Odobenus sp. from Japan indicate that even Odobenus was only cold temperate in distribution roughly 2-3 million years ago. The majority of the walrus fossil record not only reflects sexual dimorphism but also ~20 million years of temperate distribution – in other words, no ice. The early Miocene – the period of pinniped diversification – was substantially warmer than present with smaller icecaps; it makes me wonder if the abundance of modern ice breeding seals is due to recent (Pliocene-Holocene) diversifications into Arctic and Antarctic niches alongside rapidly expanding ice caps. Consider this: the basalmost phocids – monk and elephant seals – are all terrestrial breeding, and several members of the Phoca-Pusa-Halichoerus species complex are terrestrial breeders. It makes much more sense to me that Antarctic lobodontines and Arctic phocines evolved ice breeding habits since the Pliocene during rapid cooling and ice cap growth, rather than all pinnipeds evolving from an ice breeding ancestor and retaining that behavior for 27 million years (in fact, the complex distribution of ice and terrestrial breeding within phocines suggests that if anything, this behavior is really flexible at a macroevolutionary level). A further problem is that the most primitive known fossil pinnipeds, the enaliarctines, are all known from temperate ice-free latitudes. The moral of this story: fossils are important!

New specimen of Enaliarctos emlongi described by Cullen et al. (2014) and interpreted as an adult female.

The new study by Cullen et al. (2014), on the other hand, does incorporate fossil data. They report on a new skull of the early pinniped Enaliarctos emlongi from the Nye Mudstone of coastal Oregon, and performed a geometric morphometric analysis of sexual dimorphism in modern and fossil pinniped skulls. The skull was in fact initially tentatively referred to Enaliarctos emlongi by Annalisa Berta in her 1991 paper on Enaliarctos material from the Emlong collection. The skull is a bit squashed, but appears to be smaller and a bit more gracile than the adult male holotype. Berta (1991) originally considered this specimen to represent a juvenile, although Cullen et al. argue that the sutures are fully closed in the referred specimen, although it’s not immediately obvious from the photographs (a common problem with material in the Emlong collection is that it is consistently dark in color; generally it’s a good idea to coat specimens with ammonium chloride, as has been done by Barnes, Fordyce, Deméré, Berta, and others working on that collection). Sexually dimorphic features they highlight include a narrower rostrum in females, more strongly pronounced nuchal and sagittal crests in males, a proportionally wider palate in males (this probably goes hand in hand with a narrower/broader rostrum in general), and more widely flaring mastoid processes of the squamosal.

Sexually dimorphic features in modern and fossil pinnipeds: Enaliarctos emlongi (left) and Arctocephalus (right); first and third columns are females, second and fourth columns are males.

Morphometric analysis indicated strong sexual dimorphism both in skull size and shape for most pinnipeds, with the exception of numerous extant phocids (true seals - Pusa, Monachus, Erignathus, and Leptonychotes) – of the phocids analyzed, only the gray (Halichoerus) and hooded seals (Cystophora) were strongly dimorphic (Elephant seals, although extraordinarily dimorphic, were not part of the analyzed data set). All otariids, the walrus, and all fossil pinnipeds investigated were dimorphic. When plotted on a cladogram of modern pinnipeds, the ancestral character state is ambiguous owing to widespread lack of dimorphism in the true seals. However, when they incorporated fossil taxa – Enaliarctos and Desmatophoca only – it indicated that sexual dimorphism was primitive for all pinnipeds, and secondarily lost in phocids – and secondarily regained in gray and elephant seals.

Ancestral character state reconstruction of sexual dimorphism in pinnipeds; black=extreme dimorphism, white=little to no dimorphism. Top tree includes extant pinnipeds only, and bottom tree shows the influence of the inclusion of fossil taxa.
Overall, this publication by Cullen et al. is vastly superior in its treatment of sexual dimorphism in pinnipeds, particularly for its inclusion of fossils – which is unsurprising, since the authors are all paleontologists. I strongly suspect that Cullen et al. are correct, and this paper serves to reinforce earlier suggestions that enaliarctines were sexually dimorphic. However, there are a few minor nitpicky things that bear mentioning.

First, it is important to note that this study is not the first to propose that enaliarctines were sexually dimorphic. In fact, the first study to demonstrate sexual dimorphism was the reevaluation of Pteronarctos by Annalisa Berta (1994) – in that paper, she examined a large collection of material from the Emlong collection and concluded that Pteronarctos piersoni and Pacificotaria hadromma were prematurely named, and fall within the range of variation expected for a single species of pinniped (based on examination of variation in extant Callorhinus ursinus), and synonymized both species with Pteronarctos goedertae (regardless, later works by Barnes have been uncharitably dismissive of this hypothesis). Berta (1994) ascribed much of the variation between species to sexual dimorphism, and identified the holotypes of P. piersoni and P. hadromma as females (also dismissed by recent work by Barnes), in addition to figuring and describing additional female specimens of Pteronarctos goedertae from the Emlong collection. Curiously, this acknowledgement of sexual dimorphism in Pteronarctos was not mentioned or cited by Cullen et al. (2014), despite citing the paper. Sexual dimorphism in enaliarctines has also been suggested in various papers by Larry Barnes (1989, 1990, 1992, 2008), and demonstrated in the enaliarctine-like proto-walrus Proneotherium repenningi (Deméré and Berta 2001).

Secondly, the entire crux of this paper hinges upon the identification of the referred skull, USNM 314290 as being conspecific with Enaliarctos emlongi. I’ve never seen the specimen (it was on loan in Canada when I visited the USNM to examine their pinnipeds in 2012), but a few things struck me with the description. For starters, it was only compared with Enaliarctos emlongi, Enaliarctos barnesi, and Enaliarctos tedfordi. What about Pteronarctos? Pteronarctos is, after all, known from really low down in the Astoria Formation – around the same level as some Enaliarctos material reported by Berta (1991). No comparisons with Pinnarctidion are made, and most problematic, no comparisons with Enaliarctos mitchelli are made – Enaliarctos mitchelli is tiny, with a transversely narrow rostrum (consistent with USNM 314290) and known from the Nye Mudstone of Oregon (Berta 1991) in addition to Pyramid Hill in California. I could easily see this specimen representing another E. mitchelli specimen – but that possibility was not evaluated.

This study by Cullen et al. (2014) is certainly an excellent contribution, and a great starting point. Future analyses can (and, should) utilize other fossil pinnipeds for which males and females are known: Allodesmus gracilis/kernensis, Dusignathus seftoni, Imagotaria downsi, Neotherium mirum, Proneotherium repenningi, Pteronarctos “spp.”, Thalassoleon mexicanus, and Valenictus chulavistensis (some of these are known from male and female mandibles only (e.g. Neotherium). And of course, there’s also canines, postcrania, and that curious baculum.

A parting comment is necessary, and this should not be misconstrued as further criticism, but a word of caution for any study regarding the phylogenetic position of fossil pinnipeds: We currently do not have a robust up-to-date phylogeny for modern and fossil pinnipeds. It’s now been twenty years since Berta and Wyss (1994) published their seminal analysis of modern and fossil pinniped phylogeny, and nobody has taken up the challenge of adding more characters and taxa to that dataset (or, even putting together a new dataset of equivalent breadth). Most subsequent studies have incorporated taxa only from a single family (and this is something I am definitely guilty of). Although not stated by the authors, the phylogenetic position of Enaliarctos and Desmatophoca are probably from Berta and Wyss (1994). Morgan Churchill and I have talked about these issues at length, and we wouldn’t be surprised if 1) desmatophocids were more closely related to otarioids than phocids, 2) morphological evidence could be mustered to support an odobenid-otariid clade, and 3) enaliarctines might actually be more closely related to otarioids than to phocoids. What can be done about this? Cullen et al. (2014) rightfully point out that enaliarctines are greatly in need of a taxonomic enema (my paraphrasing): they are probably greatly oversplit, and a detailed comprehensive study of enaliarctine morphology is in order – this is especially true if Berta’s (1991) lumping of Pteronarctos goedertae, Pteronarctos piersoni, and Pacificotaria is any indication. In addition to a better treatment of enaliarctines, we need a larger analysis of pinniped phylogeny, with more taxa. Morgan and I started a such a project several years ago and presented it at SVP, and then decided it would be best to treat each family one at a time before doing anything comprehensive – but, more on that in the future.

References and further reading:

L. G. Barnes. 1989. A new enaliarctine pinniped from the Astoria Formation, Oregon, and a classification of the Otariidae (Mammalia: Carnivora). Contributions in Science 403:1-26

L. G. Barnes. 1990. A new Miocene enaliarctine pinniped of the genus Pteronarctos (Mammalia: Otariidae) from the Astoria Formation, Oregon. Contributions in Science 422:1-20

L. G. Barnes. 1992. A new genus and species of middle Miocene enaliarctine pinniped (Mammalia, Carnivora, Otariidae) from the Astoria Formation in Coastal Oregon. Contributions in Science 431:1-27

L. G. Barnes. 2008. Otarioidea. In C. M. Janis, G. F. Gunnell, M. D. Uhen (eds.), Evolution of Tertiary Mammals of North America 2:523-541

A. Berta. 1991. New Enaliarctos* (Pinnipedimorpha) from the Oligocene and Miocene of Oregon and the role of "enaliarctids" in pinniped phylogeny. Smithsonian Contributions to Paleobiology 69:1-33

A. Berta. 1994. New specimens of the pinnipediform Pteronarctos from the Miocene of Oregon. Smithsonian Contributions to Paleobiology 78:1-30

A. Berta and A. R. Wyss. 1994. Pinniped phylogeny; pp. 33–56 in A. Berta and T. A. Deméré (eds.), Contributions in Marine Mammal Paleontology Honoring Frank C. Whitmore, Jr. Proceedings of the San Diego Society of Natural History 29.

T.M. Cullen, D. Fraser, N. Rybczynski, and C. Schroder-Adams. 2014. Early evolution of sexual dimorphism and polygyny in Pinnipedia. Evolution DOI: 10.1111/evo.12360

T.A. Deméré and A. Berta. 2001. A reevaluation of Proneotherium repenningi from the
Miocene Astoria Formation of Oregon and its position as a basal odobenid
(Pinnipedia: Mammalia). Journal of Vertebrate Paleontology 21: 279–310.

N. Kohno, L. G. Barnes, and K. Hirota. 1995. Miocene fossil pinnipeds of the genera Prototaria and Neotherium (Carnivora; Otariidae; Imagotariinae) in the North Pacific Ocean: Evolution, relationships and distribution. The Island Arc 3:285-308

O. Kruger, J.B. Wolf, R.M. Jonker, J.I. Hoffman, and F. Trillmich. 2014. Disentangling the contribution of sexual selection and ecology to the evolution of size dimorphism in pinnipeds. Evolution DOI: 10.1111/evo.12370

Tuesday, February 25, 2014

When will we find more Eocene odontocetes and mysticetes?

Baleen whales (Mysticeti) and toothed whales (Odontoceti) are nearly universally considered to share a sister-group relationship, and constitute a monophyletic clade termed Neoceti (also known as Autoceta). Odontocetes and mysticetes are generally considered to have diverged and diversified during the Oligocene, and neither group really has an extensive fossil record prior to the Oligocene. On the other hand, archaeocetes – a paraphyletic assemblage of stem cetaceans leading up to neocetes – generally are considered to be restricted to the Eocene. For paleocetologists, the Eo-Oligocene boundary is colloquially thought of as the archaeocete-neocete split. However, many early Oligocene neocetes are relatively derived, and few are really archaeocete-like – in other words, few appear to exhibit archaeocete-like morphology with only a couple of acquired neocete synapomorphies. This begs the question of when exactly Neoceti evolved.

The early Oligocene dolphin Simocetus rayi.

Early Oligocene Neoceti

Although the majority of the Oligocene record of fossil cetaceans is limited to the late Oligocene (owing to generally low sea levels and widespread erosion of early Oligocene strata), a few notable records of early Oligocene cetaceans are worth discussing. In particular are the fossil cetaceans of the Alsea Formation in west central Oregon. Although considered by Fordyce (2002) to be late Oligocene, paleomagnetic data indicate it is probably early Oligocene in age (Prothero, 2001). First and foremost is Simocetus rayi – the only formally described cetacean from this unit, a bizarre agorophiid-grade dolphin described by Fordyce (2002). Simocetus is pretty derived, and not really archaeocete-like in many regards. Another agorophiid-grade dolphin is an unnamed tusked odontocete, preliminarily reported by Fordyce et al. (2012) at the Society of Vertebrate Paleontology meeting in Raleigh, North Carolina. This undescribed dolphin is also fairly derived and fairly removed from the odontocete stem. A third cetacean from the Alsea Formation is the world’s earliest toothless mysticete (an eomysticetid in my personal opinion), which remains undescribed and was preliminarily reported by Mark Uhen (2007). A fourth cetacean which I spotted at the USNM in 2012 is an undescribed aetiocetid with a complete braincase and somewhat basilosaurid-like mandible. The Alsea Formation demonstrates that the early Oligocene was populated by the same sorts of cetaceans known from the late Oligocene. Most notably, the presence of an early chaeomysticete – in my opinion an eomysticetid – indicates that mysticete evolution is telescoped into a 5 million year interval (or less), given our current understanding of the timing of mysticete origins.

Holotype mandible fragment of the late Eocene mysticete Llanocetus denticrenatus from the La Meseta Formation of Seymour Island. There is much more material awaiting description.

Known records of neocetes in the Eocene

As could be surmised from the presence of relatively derived Neoceti in the early Oligocene, a few – but only a few – records of latest Eocene mysticetes and odontocetes exist. First and foremost, the only named Eocene neocete is the earliest known baleen whale, Llanocetus denticrenatus from the La Meseta Formation of Seymour Island in Antarctica. It was named by Ed Mitchell in 1989, and the miserable scraps he designated as the holotype were originally collected in the mid 1970’s. My Ph.D. adviser, Ewan Fordyce, returned to the locality in 1986 and collected the rest of the specimen, which is a rather large skull and mandible in addition to some postcrania. The type specimen dates from just below the Eo-Oligocene boundary and is approximately ~34 Ma in age. Accordingly, Llanocetus is perhaps one of the most basilosaurid-like mysticetes. There is also an undescribed odontocete preliminarily reported from about the Eo-Oligocene boundary within the Lincoln Creek Formation in Washington state, U.S.A. (Barnes and Goedert, 2000). These specimens – although only barely scraping into the Eocene – do demonstrate that odontocetes and mysticetes did evolve before the end of the Eocene.

Phylogenetic relationships and stratigraphic ranges of Basilosauridae, from Gol'Din and Zvonok 2013.

The earliest Basilosauridae – middle Eocene

One problem inherent with a late or even latest Eocene origin of Neoceti is that it would telescope the majority of basilosaurid evolution into a 5 Ma period during the Priabonian and late Bartonian stages of the Eocene. The oldest records of traditionally identified basilosaurids are only about 40 Ma, only 5-6 Ma older than Llanocetus. However, a recent discovery of a basilosaurid from the Bartonian (late Middle Eocene) of Ukraine suggests a reinterpretation of “Eocetuswardii from similarly aged strata in the eastern USA. Gol’din and Zvonok (2013) named a new genus and species, Basilotritus uheni – which has vertebrae like “Eocetuswardii with the tympanic bulla of a basilosaurid. Gol’Din and Zvonok (2013) transferred “Eocetuswardii to Basilotritus, recombining it as Basilotritus wardii. In additition to the recognition of both species of Basilotritus as early basilosaurids, a couple other middle Eocene basilosaurids have been reported, including a braincase from the Bartonian of New Zealand identified as Zygorhiza sp. (Kohler and Fordyce, 1997), and Ocucajea and Supaycetus from the Bartonian of Peru (Uhen et al., 2011). Unfortunately, the protocetid-basilosaurid transition is poorly known, although several protocetids exhibit derived basilosaurid-like features, including Georgiacetus, Babiacetus, and Eocetus, and the earlier basilosaurids like Basilotritus and Supaycetus are a bit more plesiomorphic than other basilosaurids.

In summary, there are numerous derived Neoceti from the early Oligocene, a couple of genuine records of Neoceti from the latest Eocene – and lastly, the expanded fossil record of basilosaurids now ameliorates the problem of a formerly telescoped record of the family. More records of early odontocetes and mysticetes from the Eocene does not sound like such an strange idea anymore, but is in fact now predicted by the fossil record. We have little evidence of it, but improved sampling of late Eocene marine rocks – especially from poorly sampled areas (in terms of Eocene rocks) like the Pacific Northwest and the west coast of South America – may yield more records of early Neoceti.

References Cited

L. G. Barnes and J. L. Goedert. 2000. The world's oldest known odontocete (Mammalia, Cetacea). Journal of Vertebrate Paleontology 20(3):28A.

R. E. Fordyce. 2002. Simocetus rayi (Odontoceti, Simocetidae, new family); a bizarre new archaic Oligocene dolphin from the eastern North Pacific. Smithsonian Contributions to Paleobiology 93:185-222.

R.E. Fordyce, E.M.G. Fitzgerald, G. Gonzalez Barba. 2012. Long-tusked archaic odontocetes from Oregon and Baja California Sur, eastern Pacific Margin. Journal of Vertebrate Paleontology 32:3:95.

P. Goldin and E. Zvonok. 2013. Basilotritus uheni, a New Cetacean (Cetacea, Basilosauridae) from the Late Middle Eocene of Eastern Europe. Journal of Paleontology 87(2):254-268.

R. Kohler and R. E. Fordyce. 1997. An archaeocete whale (Cetacea: Archaeoceti) from the Eocene Waiho Greensand, New Zealand. Journal of Vertebrate Paleontology 17(3):574-583.

E. D. Mitchell. 1989. A new cetacean from the late Eocene La Meseta Formation, Seymour Island, Antarctic Peninsula. Canadian Journal of Fisheries and Aquatic Sciences 46(12):2219-2235.

Prothero DR, Bitboul CZ, Moore GW, Niem AR. 2001. Magnetic stratigraphy and tectonic rotation of the Oligocene Alsea, Yaquina, and Nye formations, Lincoln County,
Oregon. In: Prothero DR, ed. Magnetic stratigraphy of the Pacific coast Cenozoic. Pacific Section SEPM (Society for Sedimentary Geology) 91:184–194.

M. D. Uhen (2007): The earliest toothless mysticete: A chaeomysticetan from the early Oligocene Alsea Formation, Toledo, Oregon. – Journal of Vertebrate Paleontology 27/3 Suppl.: 161A.

M. D. Uhen, N. D. Pyenson, T. J. DeVries, M. Urbina, and P. R. Renne. 2011. New middle Eocene whales from the Pisco Basin of Peru. Journal of Paleontology 85(5):955-969.

Thursday, February 6, 2014

Coastal Paleontology in the News: recent press coverage, new publication in Geodiversitas

It's been about four weeks since I posted something on here last, but I've got some new stuff coming up. To kick it off, I have finally gotten around to submitting a press release about my new publication in Geodiversitas (in all actuality, published on December 27 of last year). What took me so long? I needed a suitable image for the press release, so I waited until I had completed a new piece of artwork. More on that below.

The new paper in Geodiversitas is concerned with a fossil assemblage of marine mammals from a relatively young section of the Purisima Formation. Most marine mammal fossils from the Purisima Formation are a bit younger, being from the latest Miocene; few well-preserved specimens are known from the Pliocene sections. Plenty of other latest Miocene marine mammal assemblages in California and Baja California exist, including the Capistrano and San Mateo Formations of Orange and San Diego Counties, and the Almejas Formation of Cedros Island off the Baja California Peninsula. However, pretty much only one Pliocene marine mammal assemblage exists for comparison - the San Diego Formation.

With this in mind, I began digging up marine mammal fossils over two two-year periods, each covered by a paleontological collections permit from California Parks and Rec. It took years to complete preparation, curation, and study the hundreds of fossils uncovered during this study, but ultimately this project produced three separate publications. The first covered the sharks, bony fish, and marine birds, while the second reported on the youngest fossil of a bony toothed bird from the Pacific basin. Although titled "A new marine vertebrate assemblage from the Late Neogene Purisima Formation in Central California, part II: Pinnipeds and Cetaceans", technically speaking the pelagornithid article was really the second part, but my coauthor Adam Smith wasn't too keen having such a long title.

One fossil in particular, the skull that would eventually become the holotype specimen of Balaenoptera bertae named in this paper, was collected when I was 19 years old. It was my first real excavation, and the first time I had ever made a plaster jacket. I'll have a longer post about the collection of the holotype later on down the line.

The fossil assemblage eventually yielded 21 marine mammals, for a total of 34 marine vertebrates. The assemblage includes fur seals (Callorhinus), walruses (Dusignathus), a "river" dolphin (Parapontoporia sternbergi) related to the recently extinct (ca. 2007) Baiji, several porpoises (Phocoenidae, unnamed genus 1, unnamed genus 2, cf. Phocoena sp.), a delphinid dolphin, a globicephaline pilot whale, two species of dwarf baleen whales (Herpetocetus bramblei, Herpetocetus sp.), the archaic balaenopterid "Balaenoptera" portisi, a possible Balaenoptera, the new species Balaenoptera bertae, and two right whales (Eubalaena spp.). Curiously absent from the fossil assemblage are tusked odobenine walruses and beluga-like monodontids (both present in other Pliocene sections of the Purisima, and will likely be found after further sampling) and hydrodamaline sirenians (e.g. Hydrodamalis cuestae), also absent from other Pliocene sections of the Purisima but abundant in coeval rocks further south in California, as well as basal late Miocene strata of the Purisima. Sirenian bones have an extraordinarily high preservation potential thanks to their large, pachyosteosclerotic (super dense) bones, and the complete absence of their fossils amongst hundreds of other marine mammal fossils suggests that this is a true absence, as their absence cannot really be argued from a taphonomic perspective. In other words, the same biases exist against other marine mammal groups, and even in intense taphonomic conditions sirenian bones are still just as common - if not more common - than cetacean bones.

The curious thing about this assemblage is that it shows that the marine mammal fauna of the Pliocene North Pacific was quite a bit different from the modern fauna. It includes numerous archaic species, such as "Balaenoptera" portisi, Herpetocetus, and a delphinid-like porpoise with a primitively asymmetrical skull, marine mammals with strange adaptations such as the as-yet unnamed "skimmer" or "half-beaked" porpoise with the elongate, edentulous "chin" that protruded beyond the upper jaw, the double-tusked walrus Dusignathus, and Herpetocetus (which counts again in this category as it had a strange feeding apparatus adapted for benthic filter feeding). The remaining marine mammals include species that are far removed with respect to modern relatives, such as Parapontoporia, the sister taxon to the recently extinct Yangtze river dolphin (Lipotes), and beluga-like monodontids and tusked odobenine walruses such as Valenictus (with modern relatives now restricted to the arctic), and early species within modern lineages, such as the newly described Balaenoptera bertae, the fur seal Callorhinus gilmorei, and an early harbor porpoise, Phocoena sp. (the Cuesta sea cow, Hydrodamalis cuestae, also counts towards this as it is known from other localities and is an early record of the recently extinct Steller's sea cow, Hydrodamalis gigas).

What explains the persistence of such a strange fauna, while modernized marine mammals were already abundant in the Atlantic? A warm-water equatorial barrier lay to the south, with the recently closed Panamanian isthmus to the east; the Bering strait had not yet opened, restricting dispersal to (and from) the north. After the Pliocene, climatic deterioration and associated oceanic cooling permitted dispersal across the equator, and the Bering strait opened up, allowing marine mammals to disperse through the arctic.

Life restoration of Balaenoptera bertae, a Pliocene species of rorqual from the Purisima Formation of Northern California. Artwork by RW Boessenecker.

Read more:

Official University of Otago Press Release. February 6, 2014.

Strange marine mammals of ancient North Pacific revealed. Science Daily, February 6, 2014.

Dwarf whales, twin-tusked walrus once swam West Coast., February 7, 2014.

Otago student's whale of a find. Otago Daily Times, February 7, 2014.

Balaenoptera bertae: new fossil whale species discovered. Sci-News, February 7, 2014. 

Fossils reveal eclectic ancient marine mammals of North Pacific. Redorbit, February 7, 2014.

Fossils show strange marine mammals lived in pre-Ice Age Pacific., February 6, 2014.

Pre-Ice Age whale found. Radio New Zealand, February 6, 2014.

Kiwi's key to ancient seas. New Zealand Herald, February 7, 2014.

New species of fossil whale excavated from San Francisco Bay Area's Purisima Formation. Science, Space, and Robots, February 6, 2014.

And of course, there's the original peer-reviewed article too:

Boessenecker, R.W. 2013. A new marine vertebrate assemblage from the Late Neogene Purisima Formation in Central California, Part II: Pinnipeds and Cetaceans. Geodiversitas 35:4:815-940.

Wednesday, December 25, 2013

2013 in review: Advances in marine mammal paleontology

Edit: as it turns out, there are still a few articles I need to include on here, including Koretsky and Rahmat (2013) on Pachyphoca, Flynn et al. (2013) on a pathologic dolphin tooth, Montgomery et al. (2013) on the evolution of brain size in modern and fossil cetaceans, and Uhen's (2013) review of the North American fossil record of Basilosauridae. I'll get these done soon, but have been "distracted" by dissertation eomysticetid research and a just-submitted manuscript on an Early Pleistocene gray whale earbone from California with my labmate Cheng-Hsiu Tsai.

Happy Holidays, Merry Christmas, Happy Hannukah, Kwanzaa, etc. – and happy Boxing Day from New Zealand. As an American, I’m not really sure what I’m supposed to do today, so other than recoup from consuming a disgusting amount of chicken, potatoes, cobbler, and berry pie, I’m completing my longest ever blog post. I’ve summarized every paper in marine mammal paleontology that has come out in 2013 (either published or appeared online as an in press manuscript). I did this last year for 2012, and it quickly became apparent that I left quite a few out. So, I’ve put this rather large body of text and images together, and I’m quite frankly a bit embarrassed with how much time I put into it, but to be fair – there were quite a few studies that came out this year, and it forced me to read or skim several that I had not yet had a chance to flick through. There are also several new papers I’ve put out this year which have also inflated the list a little bit (and there is one more yet to come this year). I hadn’t originally considered to include my own work, but my wife convinced me to at the last minute.

            This year’s only new species of fossil pinniped is a new species of monachine true seal from the latest Miocene Pisco Formation of Peru (Sud-Sacaco level). The material is pretty well preserved, and includes several complete skulls and mandibles, in addition to postcrania (much of which remains to be figured). Hadrokirus – meaning stout tooth – shares a sister-taxon relationship with another Pisco Formation phocid, Piscophoca pacifica. The cheek teeth of Hadrokirus are very robust, and owing to this – and some robust muscle attachments on the cervical vertebrae – Hadrokirus was interpreted as having durophagous diet, potentially feeding on hard shelled prey like crustaceans, or even other vertebrates. I’ll admit I was initially a bit skeptical of the feeding ecology hypothesis, since dental features were the rationale behind the “killer walrus” macrophagous apex predator hypothesis initially proposed for Pelagiarctos, and criticized in the PLOS One article published by Morgan Churchill and myself early this year. However, in the case of Hadrokirus, there are some peculiarities of the neck muscle attachments that add some credence to the hypothesis. Another interesting aspect of the study is that it recovered Acrophoca as sister to extant lobodontines (Antarctic phocids), and Hadrokirus, Piscophoca, and Homiphoca (South Africa) as a clade sister to the lobodontines. If this group gets further support in the future, we could very well see a “Piscophocinae” or “Homiphocinae”.

Subfossil bowhead whale remains from Sweden.

This study reports a latest Pleistocene bowhead whale skeleton from marine sediments along the coast of Sweden. The skeleton is approximately 13,800 years old based on radiocarbon dating, and includes mandibles, vertebrae, and ribs. Ancient DNA was recovered from the specimen, which indicated that the skeleton was in fact from a bowhead whale, Balaena mysticetus. Previously reported subfossil bowhead remains had been used to erect the fossil species Balaena swedenborgii; morphologically, the specimen did not appear to represent Balaena swedenborgii, but this fossil species has been interpreted by some to perhaps be a synonym of Balaena mysticetus or perhaps a subspecies of it (or alternatively Eubalaena glacialis). The new fossil is probably not complete enough to weigh in on the taxonomic distinctiveness of B. swedenborgii anyway. The authors also inspected the specimen for any evidence of colonization by the bone-eating worm Osedax – and found none. They concluded that this skeleton was deposited in at least 100 m water depth, but regardless – this specimen was certainly deposited on the Pleistocene shelf (…because the specimen was found 72 m above sea level). Modern studies of whale falls have demonstrated that Osedax has a difficult time colonizing carcasses on the continental shelf, owing to intermittent currents and sedimentation events. However, Anderung et al. speculate that rapid sedimentation caused by retreating ice pack along the saline front (where clay flocculation is accelerated). This is difficult to test, and to be fair – perhaps 1 out of 1,000 Neogene marine mammal fossils I have ever seen have convincing evidence of Osedax bioerosion, probably resultant from their deposition on the shelf – and I think this is a more likely reason for the lack of Osedax colonization.

Fossil ambergris from the Pleistocene of Italy.

One of the most fascinating taphonomic discoveries in years was the report of fossil ambergris from the early Pleistocene of Italy. Numerous large coprolites – a few dozen bearing cephalopod beaks and hooklets – were found in Pleistocene muddy strata. Admittedly, this was pretty unexpected – ambergris is known to be positively buoyant (although, admittedly – the buoyant examples are those we see – who knows what proportion sinks rather than floating) – and there is currently debate regarding how hard it is when it is inside the digestive tract; it is thought by some that while in the body it remains somewhat ‘compliant’ and only hardens after floating at sea for extended periods of time. Ambergris is only known to occur in giant sperm whale guts (Physeter macrocephalus), although in this case no cetacean body fossils exist to corroborate such an association. I've already discussed this exciting find.

Skeleton of the holotype of Neoparadoxia cecilialina.

Barnes, L.G. 2013. A new genus and species of Late Miocene paleoparadoxiid (Mammalia, Desmostylia) from California. Natural History Museum of Los Angeles County Contributions in Science 521:51-114. Direct link to pdf.

One of the studies published this year that is more geographically relevant to this blog is the new monograph on desmostylians by Larry Barnes (LACM). The main fossil in the paper is a new, absolutely gorgeous paleoparadoxiid from the Monterey Formation – this specimen includes a complete skull, mandibles, complete vertebral column, and appendicular elements. Barnes named this as a new genus – Neoparadoxia cecilialina. I had heard ahead of the publication that it would be named as a new genus, and I was unsure of the rationale prior to reading the paper. A quick skim of the paper revealed no solid rationale for splitting the genus Paleoparadoxia into three, cladistic or otherwise: all four species – the new species, and formerly P. repenningi, P. weltoni, and P. tabatai – all form a monophyletic group in Barnes’ cladistic analysis anyway, which Barnes named the Paleoparadoxiinae. Why not just keep things simpler and leave it as one genus? I haven’t read the entire monograph, so I’m not quite ready to judge whether or not this is a case of oversplitting. In addition to erecting a new genus name, Barnes also referred the Stanford skeleton – Paleoparadoxia repenningi – to the new genus, recombining it as Neoparadoxia repenningi. He also established a new genus for the latest Oligocene-earliest Miocene paleopardoxiid from the Skooner Gulch Formation, recombining it as Archaeoparadoxia weltoni. The paper includes many dozens of beautiful figures and illustrations, and certainly appears to be one of Barnes’ more significant contributions to our field. I think I’ll have to cover this study with a dedicated blog post in the future, after I have more time to read and digest the paper.

Phlogenetic and geographic placement of the Tunisian sea cow specimen.

Archaic sirenians are probably not my strong point. The only sirenians I’ve ever dug up are all hydrodamalines – which represent, I would say, the tragic pinnacle of sirenian evolution. So, as a result of reading mostly about crown sirenians, I’ve not strayed much into the literature on archaic sirenians – so this paper was a bit new to me. The problem with sirenians is that they are members of the Afrotheria – a group of mammals with African origins – but the earliest and most primitive known sirenian is Prorastomus from the early-middle Eocene of Jamaica. So, we’re missing the earliest representatives of the group from where they should be – Africa. The earliest known and most primitive sirenians – Prorastomus, Pezosiren – are quadrupedal sirenians that had not yet lost their hindlimbs (Pezosiren in particular, in terms of its phylogenetic placement and terrestriality, is a sirenian analog of Pakicetus). These two sirenians from Jamaica have been found in estuarine sediments. Benoit et al. report a new sirenian earbone from the late early Eocene (late Ypresian to early Bartonian) of Tunisia, in a lacustrine limestone. The anatomy of this earbone is relatively more primitive than Prorastomus from Jamaica, making the Tunisian specimen the most primitive known sirenian. Unfortunately, the new specimen is far too incomplete to be named – but the earbones of mammals – particularly of cetaceans – are very informative and isolated earbones such as this can often be accurately identified (for example, in some morphological cladistic analyses, up to 1/3 of all phylogenetic characters are periotic or tympanic bulla characters). In this study, Benoit et al. were able to conduct a phylogenetic analysis, corroborating the stem position of this taxon. They suggest that pachyostosis of the periotic is tied to aquatic adaptation in this early sirenian (as in other sirenians and cetaceans). Another study by Mark Clementz on isotopes suggested that sirenians took a direct route to marine life, instead of having a prolonged intermediate freshwater aquatic stage. The presence of the Tunisian specimen in freshwater settings, however, suggests that sirenians may have indeed adapted to a transitional freshwater environment before leaving Africa. On a humorous parting note, this paper has to have the record for the number of authors per single fossil bone in paleo literature.

Skull of the extremely strange ziphiid Globicetus from offshore Portugal.

In 2007, Giovanni Bianucci, Olivier Lambert, and Klaas Post published a large number of fossil beaked whales (Ziphiidae) trawled from offshore South Africa, which included multiple strange new genera and species. Most of these were found inside phosphorite nodules on the seafloor, and unfortunately because of this no detailed age data is known.
A new study published this year Is sort of a followup to that South African study, and reports many new – and also strange – ziphiids from offshore Portugal. These include a new species of Tusciziphius, known from Portugal and also South Carolina – that has a large ossification formed as a posteriorly-rising “fin” of bone on the rostrum, somewhat similar to Aporotus (although in Aporotus it is formed by the paired premaxillae and is transversely bilobed). Several new skulls are referred to Tusciziphius atlanticus. Another strange ziphiid, Imocetus, bears a strangely elongate facial region and a rostrum with a very wide, triangular base, vaguely reminiscent of the overall shape of a beluga skull in dorsal view; however, it bears elongate maxillary ridges, and a pair of short conical crests on the base of the rostrum. Other ziphiids include new records of Caviziphius, Ziphirostrum, and a new species of Choneziphius. Arguably the strangest new cetacean, however, is Globicetus – a robust beaked whale with a bizarre football-shaped ossification on the middle of the rostrum. I remember at the 2011 Aquatic Tetrapods conference in San Diego, Ted Cranford asked if the spherical structure could be a fossilized melon – unfortunately the chances of that happening are remarkably slim, although some soft tissue structures such as baleen and intervertebral disks have been preserved in Peruvian mysticetes. The structure is actually bone, and is formed by the medially fused premaxillae. Many ziphiids bear strange rostral ossifications and crests, and they probably have some function in reflecting sound (air is an effective acoustic barrier, but bone makes for a close second); the ossifications appear to be distinctive amongst various species, and are also known to arise via different developmental means (a paper by Olivier Lambert in Comptes Rendus Palevol reviews this nicely, and would be a good topic to cover on here at some point). In a way, Globicetus isn’t really any stranger than extant Hyperoodon (bottlenose whales), which has a pair of tall maxillary crests on either side of the melon; it’s just that Hyperoodon is “familiar” but strange, and Globicetus is “unfamiliar” and strange, so to speak.

Fossil platanistine periotic from Amazonian Peru.

This short communication presents a pretty surprising discovery, even if it’s just a single earbone: a record of a Platanista-like dolphin (identified to Platanistinae) from the Peruvian Amazon. Most of us probably think of the Pisco-Ica region on the Pacific side, which is dry and dusty and effectively a big desert; however, it’s easy to forget about the part of Peru on the other side of the Andes, which is technically part of Amazonia. A single periotic was collected from late middle Miocene fluvial rocks here, and the periotic shares numerous features in common with extant Ganges river dolphin, Platanista gangetica. For the geographically uninformed, this may not seem like anything huge: the Ganges river is in India, and Platanista is currently relegated to Pakistan, India, and Bangladesh, and is totally riverine in distribution. Although G.G. Simpson placed all river dolphins into a single subfamily Platanistoidea, it now appears that each river dolphin really needs its own family: Pontoporiidae (Franciscana/La Plata river dolphin), Iniidae (Amazon river dolphin/Boto), Lipotidae (Chinese river dolphin/Baiji), and Platanistidae (Ganges river dolphin/Susu), as these occur as a paraphyletic group in most molecular and many morphological cladistic analyses of odontocete relationships. So, this new record indicates that three of these families – Pontoporiidae, Iniidae, and Platanistidae – were all swimming around in coastal waters or rivers of South America during the Miocene. This has some curious biogeographic implications; it’s thought that these reflect independent adaptation to riverine life amongst archaic odontocetes, with many of their oceanic relatives going extinct and being replaced (passively or competitively) by more recently evolved delphinoids. This new find demonstrates that platanistines were not restricted to Asia, and an early Miocene specimen from Oregon indicates they were not uniformly riverine during the Miocene. Bianucci et al. hypothesized that platanistines had a marine, North Pacific origin, followed by invasion of rivers in South America and southern Asia, and subsequently going extinct in South America. Bianucci et al. also suggested that the long rostra of “platanistoids” (sensu Simpson) was a preadaptation for freshwater existence – perhaps suggesting a limited ability of delphinoids to colonize freshwater environments (although plenty of freshwater brevirostrine delphinoids exist: Orcaella spp., and Neophocaena, and a couple of other more longirostrine delphinids).

Holotype skull of the new Pliocene dolphin Septidelphis.

Giovanni Bianucci’s Ph.D. thesis and eventual publications in the late 1990’s dealt with a comprehensive reassessment of the Pliocene odontocete assemblage from Italy, which is a pretty sizeable assemblage and certainly no small feat. Of many of the historical specimens, there was one he was never able to track down and examine: a specimen of Stenella cf. frontalis reported in 1980; unfortunately the author of the study did not report where the specimen was reposited, and died before Bianucci could contact him about it. After recently learning the whereabouts of the specimen, Bianucci examined and reevaluated the specimen. Owing to some cranial differences, he named it Septidelphis morii – one peculiar feature is the presence of a fairly wide mesorostral groove, which is quite a bit wider than in other delphinids (elegantly shown graphically within the paper). Instead of conducting a dedicated morphological cladistic analysis of small bodied delphinine delphinids – no doubt a difficult undertaking thanks to the skulls of modern delphinines looking damned near identical (if I tried it, it would surely result in tears and hair being pulled out) – Bianucci used a molecular “scaffold”, constraining the tree topology and phylogenetic position of extant delphinids based on their occurrence in molecular phylogenies. 14 morphological characters were used to place the fossil taxa on the tree, with Pliocene fossil delphinids Astadelphis, Etruridelphis, and Septidelphis forming a paraphyletic stem group of delphinines. Each of these taxa were formerly identified as fossil Stenella; Bianucci suggests that, based on his results and the molecular phylogenetic results of others, that extant genera of delphinids probably did not arise until the Pleistocene, and that the majority of Pliocene delphinids are probably better attributed to extinct genera. Interestingly, given the recent proposal by William Perrin and others to combine Delphinus, Tursiops, Stenella, Lagenodelphis, and Sousa under Delphinus – which would no doubt make all of these extinct delphinine genera from Italy Delphinus as well. Is this a case – modern and fossil species alike - of taxonomic oversplitting, with recombining everything as Delphinus as the solution? I’m not sure, and certainly more morphological work on delphinines is necessary. To be fair, I have a hard time swallowing the idea that extant delphinid genera were not present at all during the Pliocene, but that’s just a gut opinion.

Holotype skull of the new baleen whale Parietobalaena campiniana.

During the late 19th century, a number of fossil baleen whales were named from the Miocene and Pliocene of Belgium. Many of these are of debatable utility and diagnosability, and many have been demonstrated to be chimaeras – collections of isolated, non-associated bones which the author interpreted to belong together. One of these fragmentary baleen whales was described as Isocetus depauwi – it includes a series of cervical and thoracic vertebrae, a partial mandible, a tympanic bulla, and an ulna. Reevaluation of the type specimen indicated that it is indeed a distinct genus and species, albeit difficult to compare with more complete fossil mysticetes; a nearly complete skull, periotic, tympanic bulla, mandible, and vertebrae was referred by the German paleontologist Abel to Isocetus depauwi. This specimen was described in detail and figured by Bisconti et al., who named it as a new species of ParietobalaenaParietobalaena campiniana. Interestingly, this study proposed some of the first synapomorphies for the genus Parietobalaena, including numerous earbone features. Two poorly known mysticetes which were transferred to Parietobalaena by Steeman in 2010 – Heterocetus affinus and Idiocetus laxatus – were concluded to likely be valid genera owing to periotic differences. Most significantly, a new clade of mysticetes was named: it includes all mysticetes crownward of right whales (Balaenidae), including Balaenopteridae (rorquals), Eschrichtiidae (gray whales), Cetotheriidae sensu stricto (true cetotheres), and cetotheres sensu lato, jokingly referred to as kelloggitheres (e.g. Kellogg’s cetotheres – Parietobalaena, Diorocetus, Aglaocetus, Thinocetus, Halicetus, Pelocetus, etc.). Admittedly, kelloggitheres are my least favorite group of mysticetes – they all look the same to me. There’s only one problem with the proposal of this new taxon – depending upon which phylogenetic result is achieved, it may or may not be equivalent (or mutually exclusive) with Balaenopteroidea, sensu Deméré et al. (2005). In Deméré et al. (2005), Cetotheriidae ss. appear on the stem relative to balaenids, but in this study, cetotheriids occur crownward of balaenids; in Deméré et al., everything crownward of balaenids belongs to Balaenopteroidea, whereas everything crownward of Balaenidae in this new study is termed Thalassotherii. By the way, I was pretty pleased and entertained to hear the term kelloggithere used in at least one SVP talk this year.

The Pliocene marine vertebrate assemblage from the San Gregorio section 
of the Purisima Formation.

Boessenecker, R. 2013. A new marine vertebrate assemblage from the Late Neogene Purisima Formation in central California, part II: Pinnipeds and Cetaceans. Geodiversitas 35:815-940.

This new study which came out on Dec. 27 was almost in time for Christmas. It marks the culmination of 8 of research on my part. In 2004 I received a tip to check out some bones at a beach by a local surfer, and when I got out there I found numerous bonebeds and hundreds of bones sticking out of the cliffs. It was my first summer home from college in Montana, and I had an idea for fieldwork – virtually nothing had been published on fossil marine mammals from the Purisima Formation, and literally nothing had been published on material outside the Santa Cruz area – so this was a ripe piece of fruit to pick. I received my first permit in 2005, had it renewed for 2006, and received another permit for 2010 to 2011. During these periods I collected a rather large number of marine vertebrate fossils, which would eventually represent over thirty species of sharks, bony fish, marine birds, pinnipeds, and cetaceans. Two earlier papers published all of the sharks, bony fish, and birds, including the embarrassingly large pelagornithid humerus which Adam Smith and I published in 2011 (the drawer label at UCMP is titled “Bobby’s big bird”). This new paper is concerned with the fossil marine mammals, and includes three pinnipeds, several baleen whales including Eubalaena (right whale), Herpetocetus, and a new species of Balaenoptera Balaenoptera bertae, which I’ve named in honor of Dr. Annalisa Berta. Odontocetes include delphinids, a globicephaline, an indeterminate sperm whale, Parapontoporia sternbergi, and several phocoenids including the strange “skimmer porpoise” as well as a harbor porpoise like fossil I’ve identified as cf. Phocoena. In addition to reporting all of these marine mammals, the paper includes a review of various Pliocene marine mammal assemblages from around the globe. Interestingly, I found that when I tallied up the proportion of extant to extinct genera in various assemblages, Pliocene marine mammal assemblages from the Pacific consistently had fewer extant genera than the North Atlantic. The Yorktown Formation of the eastern US, for example, is approximately 55% extant, whereas it is about 30-35% or so for the eastern North Pacific, and about 17% for the eastern South Pacific. This suggests that many extant marine mammals appeared earlier in the Atlantic than they did in the Pacific. Furthermore, many Pliocene assemblages seem to have all sorts of non-cosmopolitan “bizarre” species without modern ecological analogs in the region. All of these data, in concert with a Pleistocene marine mammal assemblage that is mostly comprised of extant taxa, indicate that a higher degree of faunal provinciality prevailed during the Pliocene and that various extinctions occurred amongst these groups sometime during the early Pleistocene.

Revised stratigraphic range of Herpetocetus with some other charismatic megafauna added for context.

This study published in Naturwissenschaften early this year reports a surprisingly late surviving example of the archaic mysticete Herpetocetus - the specimen may be as young as 700 thousand years. This has some interesting implications for how we think about marine mammal faunal change during the Pleistocene. Read about it here.

A collage initially intended for a cover image - barnacle encrusted sea lion bones and their locality.

This paper published earlier in the year in Journal of Paleontology is another taphonomic contribution of mine, and reports a new occurrence of barnacle encrusted marine mammal bones - and expands on the possible data we can squeeze out of the fossil record from encrusting invertebrates. Read about it here.

Life restoration of the extinct "killer" walrus Pelagiarctos.

This paper by myself and Morgan Churchill describes a new fossil of Pelagiarctos and reevaluates the problematic "killer walrus" hypothesis for the original Pelagiarctos thomasi material from Sharktooth Hill. Read more about it here, here, here, here, and here.

Life restoration of a globicephaline whale from the Purisima Formation.

This paper describes new records of globicephaline whales from the Purisima Formation of central/northern California. Read more about it here.

The holotype skull of the new beaked whale Notoziphius from Argentina.

This is one of the few papers published this year which I had the fortune to review. This study reports a new genus and species of beaked whale from the late Miocene of Argentina, collected by (late) local fossil collector Rodolfo Brunet. The specimen includes a relatively large skull, approximately Mesoplodon sized – missing the anterior part of the rostrum, and also some mandibular fragments. Monica Buono and Mario Cozzuol named this new genus Notoziphius, and named it after the collector – Notoziphius bruneti. Phylogenetic analysis indicates that this new ziphiid forms a clade with Messapicetus, Ziphirostrum, Beneziphius, and Aporotus. This new beaked whale is the first record of a fossil ziphiid from the southwestern Atlantic, and demonstrates that ziphiids were widely dispersed and diverse during the Miocene.

Fossil pygmy right whale mandible from the late Miocene of Argentina.

This new paper continues last year’s Caperea frenzy: this is the third fossil neobalaenid/neobalaenine to be reported in the last 16 months: the paper reports a partial mandible from the late Miocene of Argentina that is most similar to that of the extant pygmy right whale, Caperea marginata. It notably differs in having a larger coronoid process (reduced to absent in adult, modern Caperea, but retained in juveniles – see Marx et al., below), and in having a slightly less dorsally arched mandible; however, the features preserved are unique to neobalaenines. This specimen is the oldest known pygmy right whale, at approximately 9-10 million years old; it is about 3-4 million years older than the recently described Miocaperea from Peru. These attest to an old origin for pygmy right whales, and this specimen is just slightly younger, for example, than the oldest well-demonstrated fossil balaenopterids. Fossil balaenids, on the other hand, extend back to the early Miocene (~10 Ma).

Fossil skull of an undescribed kekenodontid from the Oligocene of New Zealand, currently being studied by labmate Josh Corrie.

Although published in 2013, this paper came out “online early” in 2012 and I covered it in last year’s post, which you can read here.

The strange taxonomic and phylogenetic framework for sharks in Diedrich 2013.

This paper by Cajus Diedrich is a followup to the 2011 paper on a supposed pinniped from the Eocene (a highly unlikely and poorly supported case which I summarized on this blog a couple years ago). This new paper reports the co-occurrence of the aforementioned “pinniped” in addition to a purported Protosiren rib, and a couple of bone fragments questionably identified as protocetid remains (which had been more appropriately identified by Diedrich as indeterminate mammalian remains in a previous paper); rationale for these identifications is not provided in the paper (which admittedly is not a solid foundation). Curiously, he uses a rather bizarre taxonomic framework for sharks, concluding – again without evidence – that the Carcharodon carcharias lineage can be traced back to the Eocene, and that both Carcharodon and Carcharocles were separate entities during the Eocene. The teeth identified as Carcharodon are clearly just small Carcharocles teeth that have been misidentified; the earliest taxon that can be reliably ascribed to Carcharodon is Carcharodon hastalis in the Miocene, as shown by Dana Ehret’s careful work. Diedrich argues that the co-occurrence of three marine mammals, and the earliest appearance of serrated Carcharodon and Carcharocles – is indirect evidence that the latter evolved after marine mammals first appeared in the North Sea. Is correlation = causation in this case, assuming for one moment the marine mammals are correctly identified (or even identifiable)? Or does the co-occurrence of these specimens in a time averaged, taphonomically concentrated horizon instead indicate a physical control on their occurrence simply by virtue of these sharing a calcium phosphate mineralogy which may be concentrated in certain sedimentological circumstances such as this? From a taphonomic perspective, any claim that there is a causal link is a bit of a stretch. It’s not really clear what the science was here aside from storytelling, and the puzzling taxonomic framework for sharks and lack of defense for marine mammal identifications undercuts this paper’s significance.
Full disclosure: I reviewed this paper twice for two different journals, and was more than a little surprised to see it published – effectively unabridged replete with all of its original typos – in a third journal, less than a month after it was rejected from the second journal. Despite not utilizing a shred of my constructive review comments, I was the only reviewer thanked in the published paper…

Hand-drawn speculative cladogram of diphyletic sirenian evolution by Diedrich.

This new study by Cajus Diedrich is a followup to the above study and the 2011 paper on a very dubious report of an Eocene pinniped fossil, and purports to document a new record of Protosiren from the proto-North Sea, and demonstrate evidence that sirenians are biphyletic (not monophyletic, and had two separate origins and is therefore not a biologically real group). The new fossil of Protosiren is just a rib – although ribs are diagnostic for sirenians as a whole, they are not exactly a rich treasure trove of morphological features, and I’m skeptical that such an identification is based on well-founded reasoning. Apparently Protosiren does have distinctive bone histology (thanks to Jorge Velez-Juarbe for the heads up), but no attempt at sectioning the specimen was made (in fact, the fossil remains in a private collection – which is not so good). Little morphological evidence is marshaled to support the identification as Protosiren. The central tenet of the paper – the identity of the main fossil reported within – is not solidly founded, in other words. The rationale behind the other point of the article – is not clearly accessible in the article – no attempt at conducting a phylogenetic analysis which reflects sirenian biphyly is made, although a pretty diagram showing sirenian diphyly is included. Importantly, no cladistic analysis was executed or reported upon – it is necessary to note here that the reported tree is a hand-drawn cladogram. That’s fine, it’s still a hypothesis, but not one that was tested by the author. It’s unclear after reading just where the “science” was in this study.

Cluster diagram of various fossil and modern marine and terrestrial mammals, grouped together based on microwear data.

This new paper by Julia Fahlke and colleagues investigates dental microwear on the teeth of archaeocete whales to document changes in diet during the land to sea transition in early cetaceans. Fahlke et al. investigated a pakicetid, several protocetids, and basilosaurids – fully bridging the terrestrial to marine transition. The habitat and locomotion of archaeocetes are already well known thanks to functional and isotopic studies, but it’s unclear exactly what archaeocetes were eating. For example: did aquatic feeding or adaptation for aquatic locomotion occur earlier in whale evolution? Or vice versa? The study of microwear is the microscopic analysis of damage to enamel, which is broadly correlated with diet. In extant herbivorous mammals, the number of pits and scratches is tied to how much silica is ingested and chewed – often in the form of phytoliths that grow in grass, and information like this can tell you whether or not a mammal was a browser or grazer. Dental microwear has historically been applied more frequently to herbivorous mammals, but recently a number of studies  by Brian Beatty and others have applied microwear to marine reptiles in order to evaluate feeding ecology – so there is scope for applying these methods to toothed marine mammals (sorry, chaeomysticetes). As it turns out, pakicetids and semiaquatic (pinniped equivalent semiaquatic-ness) protocetids share similar microwear patterns, suggesting that pakicetids were indeed feeding in the water. Basilosaurids, on the other hand, were found to have microwear indicating feeding on occasional harder prey – marine mammals, sea birds, etc., in addition to exhibiting extensive tooth damage related to contact with the bones of prey items. One protocetid, Qaisracetus, had microwear patterns similar to hyenas and killer whales, suggesting a large component of warm-blooded prey in its diet (e.g. other marine mammals, sea birds, large fish, etc.). In summary, they concluded that specialized piscivory and teuthophagy in extant odontocetes is derived from what was formerly a much more generalized diet during the Eocene – perhaps permitted by a dentition that could still shear, as opposed to modern odontocetes which predominantly swallow prey whole (killer whales being an exception).

Fossil sea cow as discovered in 1975 in a cave in New Guinea.

It’s always difficult finding vertebrate fossils in the tropics; carbonate rocks predominate in equatorial latitudes, and are not a great environment for preserving abundant marine vertebrate skeletal material – coastal carbonate systems tend to be characterized by relatively rapid, aggradational deposition, as opposed to vertebrate-rich low subsidence settings in siliciclastic basins where bones can be concentrated quite densely. As such, the marine vertebrate fossil record from Oceania – outside Australia and New Zealand – is quite limited. Occasionally, interesting gems are found though. A caving expedition in the mid 1970’s came across a series of bones in early-middle Miocene limestone in New Guinea (admittedly, not a very small island). As it turns out, this partial skeleton belongs to a small but indeterminate sirenian (sea cow). The extant Dugong currently inhabits Australasian, Indonesian, and Philippine waters, but has a crappy fossil record- it’s known from various Holocene localities in Australia and New Guinea, but only scraps of sirenians are known from earlier rocks in Australia. Eocene sirenians are plentiful further north and west in the Indian subcontinent as well as Java, but little evidence can be marshaled even to say that sirenians were present (or absent) during the intervening time. This new discovery suggests that sirenians indeed probably inhabited this region, and fossils of them from rocks of this time have so far gone undiscovered. Fitzgerald et al. suggest that this is due to incomplete sampling, and that other rocks in Australia may yet yield additional sirenian material.

Location and radiocarbon ages of fossil and subfossil Eubalaena (purple) and Balaena (blue) occurrences in the eastern North Atlantic.

This fascinating new study utilized ancient DNA from relatively young fossils of North Atlantic balaenids – bowhead whales (Balaena mysticetus) and right whales (Eubalaena glacialis) to examine evolutionary dynamics of the two whales during the late Pleistocene. They used about 44 samples from subarctic and cold temperate latitudes in the North SeaUnited Kingdom, Denmark, Sweden, and Norway. Specimens of late Pleistocene age turned out to all represent Balaena mysticetus, while those from the same latitudes – but from the Holocene – all represented Eubalaena glacialis. Currently, Balaena mysticetus is an arctic mysticete and is tied to ice-bound regions, whereas Eubalaena – all three putative species – are temperate water whales. The combination of identity (based on ancient DNA) and radiocarbon dates, in concert with paleoclimate suggests that during the last glacial period of the late Pleistocene, bowhead whales inhabited latitudes much further south than at present. During the Holocene, as icepack receded North and the earth recovered from the last glacial maximum, warmer water (note: still cold temperate and temperate – warmer, but still not “warm” or warm temperate) Eubalaena replaced the bowhead whale in those latitudes. This is a rather nice demonstration of habitat tracking in the fossil record of an extant mysticete.

The novel phylogenetic hypothesis of Caperea relationships.

Another paper from Caperea fever. This new paper by my adviser R. Ewan Fordyce and former labmate Felix Marx presents a provocative new hypothesis on the phylogenetic relationships of the pygmy right whale, positing that it is most closely related to extinct herpetocetine cetotheriids such as Herpetocetus and Nannocetus, which resurrects the Cetotheriidae from extinction. I’ve already covered this paper here.

Morphological changes in cetacea. There's a lot of labels here, so you can go ahead and consult the actual paper.

This large study is a review paper of sorts, and reviews various aspects of molecular and morphologic evolution of cetaceans. The study does reanalyze molecular and morphological data, but this is one of the more robust and up to date reviews of cetacean evolution and nicely summarizes current ideas on changes in locomotion, feeding ecology, sensory biology, sound production, brain size, diving adaptations, respiration, habitat (e.g. terrestrial v. aquatic v. marine), and other various aspects. There’s really too much to cover here, but if you’re looking for an excellent review of cetacean evolution within a phylogenetic framework, peppered with beautiful artwork by Carl Buell thrown to boot – look no further than this paper.

Partial skull attributed to Stromerius by Gingerich.

Historically collected specimens can often be problematic, even if they have been cited and discussed by various earlier researchers. There can be many changes in schools of thought and practice within a discipline over a century or so; as a result, many early specimens – types or otherwise – have a dramatically changed meaning to us relative to Victorian scientists. A new paper by Phil Gingerich illustrates quite nicely why old museum labels should never be trusted at face value. A skull and mandible of an archaeocete at the Field Museum in Chicago was historically identified as Prozeuglodon osiris (=Saghacetus osiris of current usage). It was sold to the Field Museum in 1914 or 1915 by Richard Markgraf. However, detailed study by Gingerich indicated that the two specimens differ in preservation and appear to represent two differently sized individuals. The skull is too small to represent Saghacetus or Dorudon, and Gingerich tentatively referred the specimen to the smaller basilosaurid Stromerius (the type specimen of which is represented by a vertebral column – albeit smaller than other basilosaurids). The mandible is in fact referable to Dorudon atrox. Gingerich points out that Richard Markgraf was not a paleontologist or a stratigrapher, and highlights problems with accepting museum labels at face value. This issue is familiar to me, and was hammered into my brain during the first few years of research, and as a result of questioning previous identifications while visiting various west coast museum collections, I developed a photographic and mental atlas of Neogene marine mammal fossils from UCMP, SDNHM, LACM, and others to construct a body of knowledge that I could use to evaluate and reidentify museum specimens (and, my own collected material).

Reconstructed olfactory apparatus of extinct protocetid archaeocete.

One of the most fascinating papers in marine mammal functional morphology this year was a paper by Stephen Godfrey, Erich Fitzgerald, and Jonathan Geisler on olfaction in archaeocetes and mysticetes. This study examined a fragmentary archaeocete skull from Virginia, mostly consisting of a frontal shield; they reasonably make the case that the specimen represents a protocetid rather than a basilosaurid. The specimen was found by a private collector who has been really generous in donating material from his collection to various institutions; it was found on a riverbank, with no adhering matrix, although its protocetid morphology suggests it is Eocene and may have been derived from the Piney Point Formation. The specimen includes well preserved olfactory structures. The olfactory apparatus of this protocetid is well-developed, in contrast to extant odontocetes – which appear to lack many of the structures found in this archaic whale and other “macrosmatic” mammals (macrosmatic means mammals with well-developed olfactory senses, such as dogs); odontocetes are widely considered to lack a sense of smell. The protocetid appears to have a well-developed sense of smell, probably far more sensitive than in humans. Interestingly, sectioned skulls of modern minke whales have an olfactory apparatus that is strikingly similar and functionally identical to the Eocene protocetid, leading Godfrey et al. to state that the protocetid had effectively modern olfactory anatomy. While it is clear that well-developed olfaction is probably primitively retained in some modern mysticetes (possibly all) and lost in odontocetes, the discovery of probable well-developed olfaction in mysticetes is somewhat surprising, given that when diving and foraging, the nostrils of cetaceans are closed off by the nasal plugs so as to prevent ingestion of water (and drowning). Godfrey et al. indicate that krill give off a particular odor, and it has recently been proposed that bowhead whales use their retained sense of smell to identify other whales, and locate “clouds” of planktonic prey; they suggest that olfaction – when the whales are at the surface, of course – could be used for finding dense accumulations of prey items.

Skull outlines of fossil squalodontids. The grayed area on the right hand side is the preserved portion of the partial skull described by Godfrey.

As a followup to the above article, Stephen Godfrey published another great paper on olfaction – but this time in an archaic odontocete – Squalodon, from the middle Miocene of Maryland. The cross-sectional area of the olfactory epithelium is about 7 times than the area of the ethmoid bone, whereas in most terrestrial mammals it’s about 16 times larger; this demonstrates that (unsurprisingly) Squalodon had an intermediate olfactory sense between archaeocetes and extant odontocetes – and, that olfaction was probably gradually lost within odontocetes during the Miocene.

Part of the holotype of the new basilosaurid Basilotritus uheni.

This new paper by Pavel Gol’Din and Evgenij Zvonok describes a new genus and species of basilosaurid archaeocete from the late Middle Eocene of Ukraine. This new fossil consists only of a partial tympanic bulla and several vertebrae. The vertebrae are grossly pachyosteosclerotic and inflated (vaguely resembling sirenian vertebrae), and bear a strange punctate texture on the external bone surface. This skeleton was given the name Basilotritus uheni, and named after archaeocete researcher Mark Uhen, and represents the oldest fossil cetacean from Eastern Europe. Phylogenetic analysis recovered Basilotritus uheni as an early diverging basilosaurid. Interestingly, Gol’Din and Zvonok noted the similarity between the vertebrae of Basilotritus uheni and “Eocetuswardii from the eastern USA, and recombined the latter as Basilotritus wardii. Several other fragmentary and problematic fossil cetaceans, such as Platyosphys, may have something to do with this new genus.

Sperm whale teeth from the late Miocene of Moldova.

Gol’Din, P. and V. Marareskul. 2013. Miocene toothed whales (Cetacea, Odontoceti) from the Dniester Valley: the first record of sperm whales (Physeteroidea) from the Eastern Europe. Vestnik Zoologii 47:21-26.

This short study reports several isolated teeth from an indeterminate physeteroid from the Tortonian (~9-12 Ma) of Moldova (a small country sandwiched between Ukraine and Romania). Two teeth apparently representing the same taxon are similar to teeth of the wastebasket taxon “Scaldicetus” in having a large enamel cap and swollen roots, and another tooth with an elongate and narrow root looks a bit like some “physeterines” (=Physeteridae of some workers), potentially indicating that two sperm whales were present. In the grand scheme of things, these are admittedly not very old, since there are plenty of examples of middle Miocene sperm whales (e.g. Aulophyseter from California), and Ferecetotherium from the Caucasus is potentially late Oligocene. These are, however, the first records of physeteroids from eastern Europe, a region which is becoming better known in terms of cetacean fossils thanks to recent efforts by the author, Pavel Gol’Din.

Skull and subantarctic locality of Africanacetus from the seafloor.

A second paper forms a followup to the 2007 paper on fossil ziphiids trawled from th seafloor off South Africa (This paper was covered last year as it was evidently online early in 2012 and only published this year, but I’ve typed up a longer and more fitting summary this year). This study by Pavel Gol’Din and Karina Vishnyakova reports two partial skulls of the beaked whale Africanacetus from offshore Antarctica, at a remarkably high latitude – approximately 60º south, and about midway (longitudinally speaking) between Australia and South Africa. The two skulls are slightly larger than the skulls reported from offshore South Africa, and differ in having a more well-developed mesorostral ossification of the vomer, leading the authors to simply identify the skulls as Africanacetus sp. These authors further hypothesize a circum-Antarctic distribution of Africanacetus, and also note that it is so far the highest latitude fossil ziphiid yet known; an interesting parallel is the Pliocene ziphiid-convergent delphinid Australodelphis from Antarctica named by Ewan Fordyce about a decade ago.

Articulated skeleton of the holotype of Cetotherium riabinini from the late Miocene of Ukraine. Scale bar = 1 meter.

It’s been a good year for Pavel Gol’Din – this study, also published this year in Acta Palaeontologica – reevaluates the skeletal anatomy of Cetotherium riabinini, a well preserved cetotheriid sensu stricto from the late Miocene of Paratethys (collected in Ukraine). I had the pleasure of reviewing this article last fall – and actually conducted my peer review during Hurricane Sandy when I was shuttered in my friend’s brownstone apartment in Washington D.C. (I was unable to go into the Smithsonian for about four days). Cetothrium riabinini is a more obscure species of Cetotherium from Paratethys; the genus is based on Cetotherium rathkei, which is known from a skull – but when Brandt described it initially, there was apparently a very narrow and tapering maxilla, which I and others did not really think was complete. As it turns out, the more complete skull of Cetotherium riabinini indicates that the narrow rostrum was in fact accurate as illustrated by Brandt. Cetotherium riabinini is small – about four meters body length, with a tiny skull with an elongate rostrum. The postcranial skeleton is well preserved, and includes Caperea-like platelike pachyosteosclerotic ribs. The rostrum is “bent” slightly anteroventrally, and it shares some peculiar features of the mandibular articulation with Herpetocetus. Owing to some of these features, Gol’Din and others argued that Cetotherium riabinini was adapted for benthic suction feeding much like today’s gray whale (Eschrichtius robustus). On a similar note, an in press article by Joe El Adli, Tom Deméré, and myself makes the same case for Herpetocetus from the Pliocene of California.

Bony tumor in the late Miocene balaenopterid "Megaptera" hubachi.

This new paper by German colleague Oliver Hampe and others is literally hot off the press, and came out just a couple of days ago in Alcheringa. This paper is concerned with large bony protrusions on the occipital shield of the skull of “Megapterahubachi, a fossil baleen whale from the late Miocene of Chile which was initially thought to be a fossil humpback whale relative. “Megapteramiocaena is generally plesiomorphic and shares various primitive characters with extant Megaptera, explaining why the original author placed it in the same genus. Regardless, it needs a new genus, as has been concluded by several researchers. The skull of “Megapteramiocaena has a strange bony lump on its occipital bone, in about the same position as small tubercles in rorquals (Balaenoptera) and even larger tubercles in the gray whale (Eschrichtius). In “Megapteramiocaena, it is only developed on the left side, whereas in gray whales it is bilaterally symmetrical – which Hampe et al. indicate is likely evidence that it is pathologic, and not a gray whale-like muscle attachment as suggested by Michelangelo Bisconti. Hampe et al. identify the strange structure as a benign bony tumor or osteoma – which apparently is the first known example of this in cetaceans. The inside of the structure is homogeneous and very dense. Previously reported pathologies identified as osteomas in extant cetaceans reported that the structures were very porous, and Hampe et al. suggest that these extant examples are probably not osteomas and represent some other type of abnormal bone growth such as spondylitis.           

Osteohistologic sections of fossil desmostylians.

Bone histology has been an excellent tool to gauge aquatic-ness of fossil marine tetrapods; multiple groups have acquired extremely dense bones upon invasion of the aquatic realm, thought to aid as ballast or to modify trim (orientation while swimming). This study by my Japanese friend and colleague Shoji Hayashi took postcranial bones of various desmostylian specimens from Japan. They found that the early desmostylian Ashoroa laticosta had pachyosteosclerotic bones – that is, bones with a reduced medullary cavity and an outwardly expanded cortex (e.g. inflated bones). The earlier diverging desmostylian Behemotops, and Paleoparadoxa both showed evidence of pachyostosis (inflated cortical bone). The most derived desmostylian, Desmostylus, on the other hand, showed evidence of osteoporosis – decreased bone density (the opposite of osteosclerosis). An increase in bone mass is tied to hydrostatic buoyancy and body trim and correlated with inefficient swimmers. However, decreased bone mass is related to hydrodynamic buoyancy control in active swimmers. This trend parallels that seen in cetaceans and pinnipeds, indicating all desmostylians have osteologic adaptations for aquatic life. Desmostylus in particular appears to have been a more active swimmer and more adapted for marine life than others – which does appear at odds with its inferred ecology as a seagrass or kelp grazer (i.e. since aquatic plants and algae grow in the photic zone and along the shoreline in shallow water). The spongy bone in Desmostylus parallels most modern cetaceans, in addition to elephant seals.

Referred skull of Haborophocoena toyoshimai.

This paper reports a new specimen of the fossil porpoise Haborophocoena toyoshimai. Haborophocoena is a porpoise that differs from extant porpoises in retaining an asymmetrical skull: the right premaxilla is wider than the left and extends further posterior to the left, in addition to the right maxilla being wider than the left, and the vertex being offset to the left side of the midline. A second species, Haborophocoena minutis, was reported by the same authors in 2009 from a different locality – and from this locality originated the new, second specimen of Haborophocoena toyoshimai. The new specimen yields additional insights into the skull anatomy of this porpoise.

Beautiful life restoration of the fossil ziphiid Ninoziphius from Peru.

Ninoziphius is an archaic beaked whale described by Christian de Muizon in the early 1980’s from the early Pliocene Pisco Formation of Peru. It was initially described in a brief article in French, and subsequently a longer description was published as part of a monograph on Pisco Fm. odontocetes – but again, in French. This new study redescribes the type specimen in even more detail (and in English!), and reports new skulls which preserve the vertex, which is damaged in the holotype. The cladistic analysis in this study confirms that Ninoziphius is the most archaic known fossil ziphiid. The feeding apparatus of Ninoziphius is less specialized for suction feeding than extant ziphiids, owing to the retention of a homodont dentition and elongate rostrum. Extensive tooth wear in Ninoziphius is interpreted to correspond to benthic feeding, or capture of prey near the sea floor. Based on facial cranial anatomy, Ninoziphius evidently was as capable of echolocation as extant ziphiids; it also exhibited relatively enlarged pterygoid sinuses, which appear to correspond to deep diving in ziphiids and physeteroids. Despite all this, the vertebral column of Ninoziphius is more flexible than extant ziphiids, with a longer cervical series; these suggest a less stiffened vertebral column that is less well adapted to deep diving than extant beaked whales.

The holotype skull of Brachydelphis jahuyaensis from the late Miocene of Peru.

This new study by Olivier Lambert and Christian de Muizon reports a new species of pontoporiid dolphin from the Pisco Formation of Peru. The dolphin is a new species of Brachydelphis. Brachydelphis mazeasi is a short-snouted relative of the extant La Plata River Dolphin Pontoporia blainvillei, notable for having an extremely short snout; it was described in the late 1980’s by Christian de Muizon. This new species is somewhat younger than B. mazeasi, and named Brachydelphis jahuayensis. Curiously, it has a somewhat longer rostrum than the older species – although it is still a notably short rostrum for a pontoporiid. If these two species belong in a single lineage, it implies that this lineage developed a short rostrum from a longirostrine ancestor (the primitive condition for pontoporiids), and subsequently evolved towards having a longer rostrum.

The ascending process of the maxilla and coronoid process of the mandible in various mysticetes.

Yet another paper from Caperea mania. This paper looked at juvenile and adult specimens of fossil and modern mysticetes to examine the ontogenetic polarity of a few characters that influence the phylogenetic position of the pygmy right whale. One feature is the lack of a coronoid process in adult Caperea, which it shares with right and gray whales to the exclusion of other mysticetes; however, juvenile specimens have a triangular coronoid, whereas juvenile balaenids – and juveniles of archaic balaenids – still lack one, suggesting that Caperea evolved from an ancestor with a triangular coronoid. The other character, lack of an ascending process of the maxilla, is shown to actually be present in juvenile Caperea, but absent in juvenile balaenids. Again, this suggests that Caperea evolved from an ancestor with an ascending process, which appears to have never been present in balaenids. Both features then are not really synapomorphic, and cloud our ability to effectively use them in phylogenetic analyses. As a bonus, there’s a figure of a mandible and skull of Herpetocetus bramblei provided by yours truly.

Periotics of the new albireonid from Japan (top) and Albireo whistleri from Cedros Island, Baja California (bottom).

Murakami, M., and Y. Koda. 2013. The first Pliocene albireonid (Cetacea, Delphinoidea) periotic from the western North Pacific and paleobiogeographic significance of fossil delphinoid ear bones of Na-arai Formation of Choshi, Chiba, central Japan. Japan Cetology 23:13-20.

This study by my colleague Mizuku Murakami reports the first record of an albireonid dolphin from Japan. Albireonids are thus far only known from two species in one genus – Albireo whistleri and Albireo savagei, from the late Miocene Almejas Formation of Baja California (Mexico) and late Pliocene Pismo Formation of California (respectively). Although the late Miocene species is represented by a beautiful skull, mandibles, earbones, and well preserved postcranial skeleton, the Pliocene species is represented only by a partial vertebral column and ribs. Albireo looks a bit like a cross between a phocoenid, monodontid, and a kentriodontid, and are some strange basal offshoot of delphinoids that didn’t quite make it to the modern day (but almost did). Murakami’s new study reports a diagnostic earbone – the periotic in particular – from the Pliocene of Japan. This new find establishes a circum North Pacific distribution for albireonids during the Pliocene. There are more complete remains of albireonids from Japan, but these have yet to be described. 

Vertebral columns of fossil and modern phocoenids.

Mizuki Murakami and colleagues report on another Pliocene porpoise (Phocoenidae) from Japan. This one, unfortunately, is too incomplete to be identified or named, but includes teeth, a strange rostrum, and quite a bit of the vertebral column. The phocoenid was relatively small, with an abnormally narrow rostrum for a phocoenid; sectioning of its teeth indicate that it was about four years old when it died. The young age and skeletal maturity of this specimen suggest that skeletal maturity was achieved quite early on during its ontogeny. The vertebral column of this specimen is morphologically intermediate between that of more primitive porpoises like Numatophocoena, and extant phocoenids like Phocoenoides. This finding suggests that postcranial evolution amongst phocoenids has been mosaic rather than gradual and ‘directed’.

Fossil gray whale mandible collected from the seafloor off Georgia.

This paper is a followup to a Palaeontologia Electronica article by Garrison et al. (2012), and reports on several fossil gray whale specimens recovered from the sea floor off of Georgia (U.S.A.). Two gray whale specimens are represented by mandibles with radiocarbon dates of about 30 Ka, and appear to represent juveniles, possibly under one year old. These fossils demonstrate that at about 30 Ka, Eschrichtius robustus was calving along the eastern coast of North America, in addition to being the oldest known specimens of the now-extinct North Atlantic population of gray whales (in the western North Atlantic, anyway).

Restricted distribution of sirenians during the Pliocene in Europe and North Africa (yellow spots).

This new study summarizes the known fossil record of sirenians (sea cows) in Europe and North Africa. This region is now totally devoid of sirenians, although they inhabited the Mediterranean from the Oligocene through to the Pliocene. The disappearance of sirenians is an interesting phenomenon, and one facet of late Neogene faunal change in marine mammal assemblages. Prista et al. concluded that sirenians became extinct in the eastern North Atlantic first, due to oceanic cooling and fragmentation of seagrass habitats. Seagrass habitats were inferred to persist in the Mediterranean, and extinction of Mediterranean sirenia was concluded to be caused by glacially induced cooling.

Mandibles and measurements - gigantic jaws of Balaenoptera.

This study examined the mandibles of balaenopterid whales (rorquals) to determine how they scaled with body size. They also point out that the mandible of the blue whale is the largest vertebrate skeletal element; perhaps an unremarkable finding, since blue whales are widely known to be the world’s largest vertebrate animal, fossil or modern (some dinosaur fan boys have proposed several sauropod dinosaurs that may be larger, but have produced insufficient evidence to dethrone Balaenoptera musculus). They report that a specimen of Balaenoptera musculus, USNM 268731, was from a 28 meter long female, and measure 6.8 meters in length. Damn, that’s huge. The more interesting aspect of this study was their use of scaling relationships to estimate body length from mandible size; many fossil balaenopterids are incomplete, few with skeletons or any postcrania, although isolated mandibles are abundant (they have a very high preservation potential owing to their large size). Mandible length corresponds to skull length, and skull length correlates well with body size in balaenopterids. They used three measurements – chord length (i.e. straight line from tip to tip), curvilinear length, and condyle to coronoid distance. They found that the relationship between mandibular length and body length is nearly isometric, and also that condyle-coronoid length decreases with increasing size. Although based on skeletal length and mandibular measurements of extant mysticetes, they tested their mandibular estimates with skull-based estimates for two fossil mysticetes with postcranial skeletons. Mandibular estimates were comparable with skull-based estimates, which is encouraging. Pyenson et al. then used two partial balaenopterid mandibles from the Purisima Formation (my favorite rock unit) to give examples of applying this method. The two mandibles from the Purisima Formation ended up being reconstructed as 3.26 and 4.83 meters in length, total – smaller than extant minke whales.

Physeteroid teeth from the Miocene of Spain.

This study reports some isolated teeth of a physeteroid sperm whale from the Late Miocene of southern Spain. They identify the teeth to the problematic genus Scaldicetus. Scaldicetus is supposedly diagnosed by having robust teeth with primitively retained enamel caps. However, teeth of the Scaldicetus morphotype have been found among various skull morphologies – and teeth of this morphotype belong to several extinct genera including Zygophyseter, Acrophyseter, Brygmophyseter, and Livyatan. Scaldicetus as a taxonomic entity is virtually meaningless. Admittedly, I only have a Spanish language version of the paper, and am unable to read the rest of the work.

Map of fossil cetacean localities in Taiwan.

Tsai, C., Fordyce, R., Chang, C., and L. Lin. 2013. A review and status of fossil cetacean research in Taiwan. Taiwan Journal of Biodiversity 15:113-124.

This new study by my labmate and fellow mysticete enthusiast Cheng-Hsiu Tsai and colleagues summarizes current and former research on fossil cetaceans from Taiwan. This study is derived in part from Tsai’s master’s thesis – the other half of which will be coming out in the Japanese journal Paleontological Research sometime next year on fossil gray whales from the Penghu Channel (along the western shore of Taiwan). Tsai et al. report the occurrence of numerous mysticetes including balaenopterids, balaenids, and Eschrichtius (again, to be considered in more depth in a following study) as well as delphinids, all from Miocene through Pleistocene rocks. A fossil pilot whale (Globicephala macrorhynchus) was trawled out of the Penghu Channel, and a well-preserved globicephaline skeleton which was previously named Pseudorca yuanliensis in an abstract-length publication. However, Tsai et al. pointed out that in the absence of a description this name is a nomen nudum. They also indicate that the taxon Balaenoptera taiwanica is based only on a tympanic bulla, meaning that some caution needs to be exercised when using the name. Tsai et al. conclude that although only a meager cetacean fossil record has been established in Taiwan in contrast to Japan, there has been very little research focus as well; preliminary field observations suggest a richer record than has been published, and that much more field work needs to be done in order to flesh out the cetacean fossil record of Taiwan.

Pinniped localities in South America and fossil southern sea lion remains from Chile.

This new paper marks Anita Valenzuela-Toro’s publishing debut, and describes several new pinniped fossils from the late Pliocene and Pleistocene of Chile. Most are fragmentary, but nonetheless tell an important story. The Pliocene specimens are a couple of ankle bones that are undoubtedly those of extinct true seals, several genera of which (like Hadrokirus mentioned above) inhabited the southeast Pacific during the Pliocene. However, the Pleistocene specimens – probably late Pleistocene at that – are all otariid specimens, most of which are identifiable to the extant South American sea lion, Otaria byronia. The modern pinniped assemblage in South America is entirely composed of otariids (Otaria, Arctocephalus) in addition to the southern elephant seal (Mirounga) – but none of these genera are known from the Pliocene marine mammal record there. Instead, we have extinct phocids like Hadrokirus, Piscophoca, and Acrophoca; these pinnipeds are known from both Peru and Chile (with the exception of Hadrokirus, which is so far only known from Peru). Numerous other strange late Neogene marine mammals that are now extinct are known from both Chile and Peru, including Brachydelphis (short snouted river dolphin - see above), Odobenocetops (walrus faced whale), and Thalassocnus (aquatic sloth). These faunal similarities attest to some sort of faunal turnover during the Pliocene-Pleistocene interval. Valenzuela-Toro et al. suggested that phocids were extirpated in this region as a result of sea level changes and changing coastal geomorphology, with otariids repopulating the region as rocky shorelines proliferated during the Pleistocene. I really enjoyed this paper, and this was one of my first reviews for a paper in JVP; additionally, I had the good fortune of meeting Anita in person at SVP in Los Angeles this year; we spent some time looking at pinniped fossils at the Cooper Center, something I ought to write some blog posts about.

Miocene seagrass and sea cow fossil records.

The fossil record of seagrasses is relatively limited, and little can be said directly from the fossil record of seagrasses regarding their paleogeographic distribution. Seagrasses are the primary food source of sirenians, and their modern distribution is tied to the distribution of seagrasses. This new study by Jorge Velez-Juarbe uses the fossil record and paleogeographic distribution of sea cows to reconstruct the paleogeography of seagrasses through Cenozoic history. The sirenian fossil record suggests that seagrasses were already distributed widely in the western North Atlantic and Caribbean by the middle Eocene. Oligocene cooling appears to have contracted the range of seagrasses and sea cows, which soon expanded again early in the Miocene. Later in the Miocene both groups expanded west and south into the eastern Pacific and the western South Atlantic. The distribution of seagrasses – as reconstructed from sea cow fossils – reached its modern pattern during the Miocene.