The best known fossil pinniped, part 2: How many species (...and genera) are there of Allodesmus, anyway?

Last week I summarized the history of research on Allodesmus (and Atopotarus). How many species of Allodesmus exist? And how many genera of desmatophocids are there? On one extreme, one could take the view that there are only two genera – Allodesmus and Desmatophoca – and that Atopotarus, Megagomphos, and Brachyallodesmus are all synonyms of Allodesmus. On the other hand, a more diverse view of the Desmatophocidae would include as many as 10 species in the aforementioned 5 genera. We’ll start with genera – and then look at the species level.

How many genera of desmatophocids are there?

I won’t bother with Allodesmus and Desmatophoca, since these are both clearly “real” and the oldest available names for generic concepts.

Atopotarus – Atopotarus is largely diagnosed by the retention of primitive characteristics in comparison to Allodesmus spp. For example, Atopotarus lacks the prenarial shelf of more derived Allodesmus such as Allodesmus kernensis/kelloggi/gracilis, has a less inflated braincase, and retains double-rooted postcanine teeth (premolars and molars). In contrast, the teeth of Allodesmus are single rooted. All these features were listed by Barnes and Hirota (1995) as distinguishing A. courseni from Allodesmus at the generic level. Mitchell (1966) was the first to suggest that Atopotarus courseni was possibly a species of Allodesmus – prior to his description of Allodesmus kelloggi, insufficient cranial and postcranial material was known to really evaluate the generic validity of Atopotarus. This skepticism was echoed by Barnes (1972), Kohno (1996) and Deméré and Berta (2002) – although its generic distinctiveness was endorsed by Barnes and Hirota (1995). I’ve always been on the fence about Atopotarus – it’s barely distinguishable from Allodesmus as it is slightly more plesiomorphic and its morphology – with the exception of the possibly lost second lower molar – could reflect the ancestral morphology of the entire genus. Amongst extant pinnipeds, including phocids – closely related clusters of species (e.g. Zalophus, Arctocephalus, Monachus), with the exception of the Phoca-Pusa-Halichoerus complex – tooth rooting doesn’t vary this much between species, potentially suggesting that Atopotarus might be real. More fossil material of Atopotarus is necessary to further evaluate it, since the holotype is a somewhat flattened articulated specimen exposed in relief in a large slab.

The holotype specimen of Atopotarus courseni, from Downs (1956).

Brachyallodesmus: this genus was erected by Barnes and Hirota (1995) for Allodesmus packardi, the skull from Portola Valley in southern San Mateo County. Features used by these authors to distinguish it from other Allodesmus include canines with an oval cross section (rather than round), an inflated braincase lacking strong nuchal crests, enormous orbits with an extremely narrow intertemporal region, and some primitively retained characteristics such as bilobed premolar roots, a furrow on the side of the braincase marking the position of the pseudosylvian sulcus on the brain, and a less flattened tympanic bulla. This species is arguably much less primitive than Atopotarus courseni, and while I’m on the fence about the generic distinction of Atopotarus, the claim that Allodesmus packardi is generically distinct is spurious in my opinion, and in my preference for taxonomic conservatism (aka lumping), I’ve always held the consideration that this is a species of Allodesmus.

Megagomphos: This genus of desmatophocid was also erected by Barnes and Hirota (1995) for a fragmentary rostrum previously known as Allodesmus sinanoensis (originally erroneously placed in Eumetopias). This specimen is the same size as the largest specimens of Allodesmus from California. Characteristics used by Barnes and Hirota (1995) to elevate it to a separate genus include the lack of a prenarial shelf (like Atopotarus) and the presence of larger canines than other Allodesmus. Kohno (1996), however, identified several features of this specimen suggesting that it was immature, such as unworn teeth that have large pulp cavities and are not completely erupted. In contrast, Barnes and Hirota (1995) thought that this specimen was an adult because of the shape of the tooth roots and purported fusion of the premaxilla-maxilla suture, but didn’t discuss the ontogenetic stage of this specimen any further. In contrast, Kohno (1996) interpreted the specimen to have a large prenarial shelf, eliminating one purported feature excluding it from Allodesmus; similarly, it exhibits single rooted postcanine teeth and no features of the dentition preclude it from being Allodesmus. Furthermore, one Allodesmus synapomorphy – the prenarial shelf – unequivocally links this specimen with Allodesmus to the exclusion of all other pinnipeds. Although Barnes and Hirota (1995) considered this specimen to lack a shelf, it is present but since the specimen is bilaterally compressed and crushed, which has made the shelf appear less apparent than in life. While this specimen has a few minor differences with other described species of Allodesmus such as procumbent, large canines – no features suggest that establishment of Megagomphos was necessary.

In conclusion, evidence supporting the generic distinction of Megagomphos and Brachyallodesmus is limited to non-existent – but Atopotarus may be “real”, although more cranial material is necessary to evaluate Atopotarus.

How many species of Allodesmus?

Allodesmus from Japan: To date, four species of Allodesmus have been described from Japan. These include the aforementioned Allodesmus sinanoensis, the well-preserved Allodesmus sadoensis, and the more fragmentary Allodesmus naorai (the “Mito seal”) and Allodesmus megallos. Allodesmus sadoensis is known from a nearly complete skull and partial mandibles, and is readily distinguished from all other Allodesmus by having anteriorly crowded and procumbent (forward pointing) postcanine teeth, more vertically oriented mandibular symphysis, and lower postcanine teeth without gaps between them. Allodesmus naorai is similar to Allodesmus packardi, and differs only in a few minor features such as having a slightly wider interorbital region and supraorbital processes positioned further posterior – potentially diagnostic features. The fourth species, Allodesmus megallos, was also named by Barnes and Hirota (1995) and diagnosed based on its enormous size, procumbent tusk-like canines and proportionally larger incisors. However, Kohno (1996) independently referred this specimen to Allodesmus sinanoensis, based upon the shared large size, large procumbent canines, and enlarged incisors, and considered this specimen to be an adult – it is substantially larger than the holotype of A. sinanoensis, now recognized to be a juvenile. Furthermore, Kohno (1996) pointed out that both this specimen and the juvenile A. sinanoensis type specimen were from the same rock unit. This specimen, by the way, represents one of the most gigantic of all pinnipeds – it has an estimated skull length of 55-59 centimeters, just a hair smaller than the giant walrus Pontolis (60 cm), and even larger than the double tusked walrus Gomphotaria (40 cm). I think Kohno (1996) makes a reasonable case that this specimen is an adult of Allodesmus sinanoensis, and therefore that Allodesmus megallos is a junior synonym. In conclusion, three species of Allodesmus appear to be known from Japan.

A size comparison with casts of the partial gigantic rostrum of Allodesmus sinanoensis (=Allodesmus megallos) and the type specimen of Allodesmus kelloggi.

Allodesmus from Sharktooth Hill, California: Five species of Allodesmus are known from the middle Miocene of California, and three of them have all been named from the Round Mountain Silt: Allodesmus kernensis, Allodesmus kelloggi, and Allodesmus gracilis. As stated in the previous post, Allodesmus kernensis was described from a partial mandible with an erect canine, a deep mandibular symphysis, and a somewhat double-rooted lower molar. Mitchell (1966) originally drew attention to the observation that the mandibles of Allodesmus kelloggi and other mandibles from the Sharktooth Hill Bonebed consistently differed from Kellogg’s type specimen in having a shallower mandibular symphysis, having a more erect canine, and having a single rooted lower molar. Mitchell (1966) also pointed out that the locality data for the Allodesmus kernensis holotype actually pointed to two different, mutually exclusive localities, and suggested that the locality data indicated that the Allodesmus kernensis holotype was collected somewhat below the stratigraphic level of the Sharktooth Hill Bonebed, lower down within the Round Mountain Silt. Because of these perceived differences, Mitchell restricted A. kernensis to the type specimen, named his new skeleton A. kelloggi, and referred all known Allodesmus material from the bonebed to his new species.

 

The holotype skull of Allodesmus kelloggi. Check out the size of that orbit!

            Many of these claims were criticized by Barnes (1970, 1972). He pointed out that in the context of variation of modern Zalophus (California Sea Lion), the features identified by Mitchell as separating Allodesmus kernensis from the rest of the bonebed sample are within the range of variation expected for a pinniped species, with the exception of shape of the mandibular symphysis – which varies less within extant Zalophus than it does within the bonebed sample of Allodesmus. Regardless, Barnes (1970) pointed out that all of the morphologic features used by Mitchell (1966) to separate Allodesmus kernensis actually fell within the range of variation of Allodesmus mandibles from within the bonebed itself. Barnes (1970, 1972) then synonymized A. kelloggi with A. kernensis, and referred all known material from the bonebed to A. kernensis. Barnes further pointed out “no conclusive arguments that the holotype of A. kernensis was collected from some formation other than the Round Mountain Silt”. Although this does not really negate Mitchell’s suggestion that the holotype came from an older horizon, Barnes correctly points out that there is uncertainty regarding the A. kernensis type locality – which in my mind means that Mitchell’s hypothesis is speculative. In the context of known Allodesmus variation and the fact that the A. kernensis holotype falls within the range of variation reported for mandibles from the bonebed – I think the idea that the A. kernensis type is more primitive than the bonebed sample falls on its face, and that the hypothesis that A. kernensis was really collected from a lower, older horizon need not be invoked. After all, the type specimen was (thought to be) collected in 1911 by R.C. Stoner, according to the specimen label, or by Charles Morrice (according to Kellogg, 1922), in 1909-1912; locality data were not always accurate in those days. Given the two sets of contradictory data regarding the provenance of the type specimen, any argument being made about the locality of this specimen should be considered to be speculative at best. I speculate that, given how abundant vertebrate fossils are within the bonebed, and how rare they are outside the bonebed, that it is more likely that the specimen was in fact collected from the bonebed and that the locality data is inexact. This seems more reasonable to me, but I note that it is not falsifiable – and that Mitchell’s (1966) arguments are not falsifiable either (although perhaps less parsimonious than my suggestion).

 

Fifty years of taxonomic disagreement contained in a single photograph. How many species of Allodesmus are represented here? One? Two? or Three? From top to bottom, holotype mandible of Allodesmus kelloggi, cast of holotype of Allodesmus kernensis, and cast of referred mandible of Allodesmus gracilis.

Despite the rather sober arguments made earlier, Barnes and Hirota (1995) indicated that the wider variation within the “Allodesminae” resulted in the recognition that the seemingly minor differences between Allodesmus kernensis and the bonebed sample were in fact meaningful. In the absence of quantitative study (as Barnes, 1970, had done) they resurrected Allodesmus kelloggi – a name which they restricted to Mitchell’s type specimen – and went so far as to establish a third species, Allodesmus gracilis, for the remainder of material from the bonebed. Barnes and Hirota (1995) echoed many of Mitchell’s (1966) arguments and casually dismissed Barnes (1970, 1972) earlier, and in my opinion well-reasoned observations. They further pointed out that the holotype mandibles of Allodesmus kelloggi have a strange, widened flange of bone on the anterior part of the coronoid process, in addition to having a single-rooted lower molar, apparently unique amongst specimens from Sharktooth Hill. However, it is well known that modern pinnipeds have tooth roots that vary quite a bit – the short version is that arctoids primitively have triple or double-rooted premolars and molars, and that in the transition to aquatic life, many pinnipeds have lost their carnassial teeth in favor of simplified teeth for catching fish, roughly similar to what happened with dolphins. Dental simplification, in concert with crowding the teeth in the front of the jaw, has resulted in double rooted teeth of archaic pinnipeds fusing together, generally starting from the front of the jaw. In my 2011 paper on fossil Callorhinus, I noted that there is a fair amount of variation in the tooth roots of extant Callorhinus ursinus (Northern Fur Seal). In the context of extant pinniped dental variation (which is considerably more than terrestrial carnivores, probably because pinnipeds do not chew and thus do not require precise occlusion), this observation on Allodesmus kelloggi does not preclude it from being a member of Allodesmus kernensis.

 

The holotype skull of Allodesmus gracilis.

Deméré and Berta (2002), although not focused on Allodesmus taxonomy, noted that the occurrence of three species of Allodesmus within a narrow stratigraphic interval in the Round Mountain Silt is a bit hard to swallow, and I agree. I can understand the rationale behind restricting names to seemingly oddball specimens like the holotypes of Allodesmus kelloggi and Allodesmus kernensis – these are decisions done in spirit of taxonomic stability. However, any argument that these three perceived species are distinctive enough to be recognized as separate taxonomic entities needs to be done quantitatively – which has been done exactly once - by Barnes (1970). There is a huge discrepancy between the rather taxonomically conservative conclusions of Barnes (1970) and the rather optimistic splitting of Allodesmus into several genera.

 

The holotype mandible of Allodesmus gracilis - or a referred specimen of Allodesmus kernensis?

So, how many species and genera are there? I tend to be on the taxonomic lumping side of things, as modern pinnipeds show quite a bit of variation – and keeping this variation in mind, I think a bit of skepticism is in order regarding new taxonomic names for the densely sampled and well published record of pinnipeds from the eastern North Pacific. I think the following list best summarizes my opinions on which genera and species are real:

Atopotarus? Allodesmus? courseni

Allodesmus packardi (syn: Brachyallodesmus)

Allodesmus kernensis (syn: A. gracilis, A. kelloggi)

Allodesmus sadoensis

Allodesmus sinanoensis (syn: Megagomphos sinanoensis, Allodesmus megallos)

Allodesmus naorai

Next up: we still have at least two more parts to this, including the paleoecology of Allodesmus and the phylogenetic position of the family Desmatophocidae.

References

L. G. Barnes. 1970. A re-evaluation of mandibles of Allodesmus (Otariidae, Carnivora) from the Round Mountain Silt, Kern County, California. PaleoBios 10:1-24.

L. G. Barnes. 1972. Miocene Desmatophocinae (Mammalia: Carnivora) from California. University of California Publications in Geological Sciences 89:1-76.

L. G. Barnes and K. Hirota. 1995. Miocene pinnipeds of the otariid subfamily Allodesminae in the North Pacific Ocean: Systematics and relationships. The Island Arc 3:329-360.

Demere, T. A., and A. Berta. 2002. The Miocene pinniped Desmatophoca oregonensis Condon 1906 (Mammalia: Carnivora), from the Astoria Formation of Oregon; pp. 113–147 in R. J. Emry (ed.), Cenozoic
Mammals of Land and Sea: Tributes to the Career of Clayton E. Ray. Smithsonian Contributions to Paleobiology 93.

T. Downs. 1956. A new pinniped from the Miocene of southern California: With remarks on the Otariidae. Journal of Paleontology 30(1):115-131.

R. Kellogg. 1922. Pinnipeds from Miocene and Pleistocene deposits of California. University of California Publications in Geological Sciences 13(4):23-132.

N. Kohno. 1996. Miocene pinniped Allodesmus (Mammalia: Carnivora); with special reference to the "Mito seal" from Ibaraki Prefecture, Central Japan. Transactions and Proceedings of the Palaeontological Society of Japan, New Series 181:388-404.

E. D. Mitchell. 1966. The Miocene pinniped Allodesmus. University of California Publications in Geological Sciences 61:1-105.

The best known fossil pinniped, part 1: a review of research and taxonomy of the Miocene pinniped Allodesmus

 

 

What to call this animal? Allodesmus kernensis, kelloggi, or gracilis? This very topic remains one of the major bones of contention in marine mammal paleontology. Skeletal reconstruction (by yours truly, 2009) of a mounted skeleton at the San Diego Natural History Museum, and beautiful life reconstruction based on my skeletal illustration by Roman Yevseyev.

Four fossil pinnipeds were discovered from California and Oregon during the early 20^th century: Pontolis magnus, from the Empire Formation of Oregon, described by Frederick True in 1905, Desmatophoca oregonensis, from the Astoria Formation of Oregon, described by Thomas Condon in 1906, Pliopedia pacifica, from the Paso Robles Formation of Oregon, described by Remington Kellogg in 1921, and Allodesmus kernensis, from the Round Mountain Silt, named by Remington Kellogg in 1922. Desmatophoca and Pontolis were originally known from partial skulls, but neither specimen was well preserved or well-prepared, and hailed from localities with vertebrate fossils embedded largely within hard concretions – it would not be until the late 1980’s that more research on fossil pinnipeds from these localities would continue again. In short, neither specimen seriously influenced the early understanding of pinniped evolution. Pliopedia was only known from a partial forelimb, and it wasn’t until the late 1970’s that it was identified as an odobenine walrus. At the time of its discovery, Allodesmus was only known from a partial, not very well-preserved mandible. In 1931, Kellogg referred several mandibular and skull fragments and postcrania to Allodesmus.

 The fossil that started it all. The holotype mandible of Allodesmus kernensis.

            Elsewhere worldwide, few fossil pinnipeds had been discovered; the early seal Leptophoca had been named, in addition to a bunch of fragmentary fossil true seals (Phocidae) with problematic taxonomic history from the North Sea named by Van Beneden in the late nineteenth century. As a result, none of these fossils influenced the understanding of pinniped evolution much, either. And while Allodesmus at first was less completely known at the time of discovery, it would soon dominate discussions of pinniped phylogeny for decades. A problem facing these early workers in North America was that they were Otariidae-centric – many of these early fossils were assumed, a priori, to represent ancestors of sea lions, rather than featuring in walrus or true seal evolution – or representing completely extinct groups of pinnipeds.

            In the 1950’s, LACM paleontologist Theodore Downs reported a series of discoveries of new Allodesmus material. In 1953, he reported a nearly complete mandible from Sharktooth Hill, and then in 1955, he reported some associated postcrania from the Monterey Formation in Orange County. And then, in 1956, he reported an Allodesmus-like skeleton including a nearly complete skeleton, lacking parts of the hindlimbs. He named it Atopotarus courseni, and its distinction as a truly separate genus from Allodesmus has been controversial.

            A few years later, Earl Packard (1962) reported on a partial skull in a concretion collected from unnamed middle Miocene rocks of Portola Valley in southernmost San Mateo County, right near where I grew up – he tentatively referred this specimen to Atopotarus courseni.

 One of the first complete skulls of Allodesmus: the holotype specimen of Allodesmus/Brachyallodesmus packardi, from unnamed middle Miocene rocks of Portola Valley, San Mateo County, California.

 Life restoration of Allodesmus kelloggi from Mitchell (1966).

            In 1966, Ed Mitchell published a monograph on a newly discovered skeleton (actually collected in 1960) from Sharktooth Hill. This skeleton was nearly complete, missing only a few bones from the hindflipper. A baculum unequivocally indicates it was a male. This specimen represented the first good skull referable to Allodesmus (not including Atopotarus), and demonstrated how the postcranial skeleton was very convergent with extant otariids – but the skull was not. The skull of Allodesmus is about as different from an otariid as you can get – an elongate, narrow rostrum with a prenarial shelf, similar to elephant seals, an elongate palate, enormous orbits, a vertically expanded zygomatic arch, absent supraorbital shelves (a distinctive feature unique to fur seals and sea lions), a shallowly sloping mandibular symphysis, and a retained lower second molar (this tooth position has been lost in modern fur seals and sea lions). Many of these skull features occur in true seals – and aside from simplified teeth and a primitively otariid-like basicranium, few features are evocative of otariids. Mitchell admitted that these differences precluded Allodesmus from having an ancestral role in the evolution of the Otariidae. Regardless, Mitchell concluded that the holotype jaw of Allodesmus kernensis was collected from somewhat below the Sharktooth Hill Bonebed, but within the Round Mountain Silt – and also noted that Allodesmus specimens from the bonebed consistently had a shallower mandibular symphysis, lower incisors that were positioned differently, a less vertical canine, a single rooted lower first molar, and a slightly more robust mandible. Because of this, Mitchell restricted Allodesmus kernensis to the type specimen, named the skeleton from the bonebed as the holotype of Allodesmus kelloggi, and referred all material from the bonebed to this new species.

The modern mount of the holotype skeleton of Allodesmus kelloggi, as it can be seen today hanging in the hall of mammals at the Los Angeles County Museum. Unfortunately much of the actual skeleton is hanging there and totally inaccessible for study; cardinal elements, such as the skull, mandibles, scapula, humerus, femur, and baculum, are mounted as casts so that they may be studied.

The next two publications in the saga were published by Larry Barnes in 1970 and 1972. The first study was an analysis of mandibles, including the types of Allodesmus kernensis and Allodesmus kelloggi. Barnes (1970) concluded that the differences between these were minimal, and that they easily fell within the range of variation expressed by modern pinnipeds. Barnes (1972) described new skulls, mandibles, and postcrania of Allodesmus, and reiterated his earlier conclusion (based on quantitative analysis!) that Allodesmus kelloggi was a junior synonym of Allodesmus kernensis. He also transferred Atopotarus courseni to Allodesmus, recombining it as Allodesmus courseni, and reported on the skull reported earlier by Packard (1962) – which was now fully prepared, and designated it as the holotype specimen of Allodesmus packardi. For another 20 years, this study constituted the last word on Allodesmus taxonomy.

The first, and only quantitative study of morphological variation in Allodesmus - from Barnes (1970).

            In 1995, Larry Barnes and Kiyoharu Hirota published an article in the special volume (mostly marine mammal-themed) of The Island Arc on “allodesmine” pinnipeds from the North Pacific. In the intervening decades, Barnes changed his mind on Allodesmus from Sharktooth Hill – and (without executing any sort quantitative analysis using the large sample of Allodesmus mandibles) not only reaffirmed Mitchell’s (1966) conclusion that Allodesmus kernensis was different from those specimens from the bonebed, but also restricted Allodesmus kelloggi to Mitchell’s type specimen, and named a well-preserved skull and mandibles originally described by Barnes (1972) as a new species – Allodesmus gracilis – to which they referred the rest of known bonebed Allodesmus specimens. In addition to this decision, they also resurrected Atopotarus as a distinct genus, and named the new genus Brachyallodesmus to contain the Portola Valley skull – recombined as Brachyallodesmus packardi. Material from Japan was considered to represent three species in two genera. A large but fragmentary roustrum and mandible fragments, similar in size and morphology to Allodesmus kernensis, was named Megagomphos sinanoensis (originally named in the 1950’s as Eumetopias sinanoensis). A far more enormous snout – comparable in size to a steller’s sea lion or small elephant seal – was named as the holotype specimen of Allodesmus megallos. Lastly, a somewhat more complete specimen with skull and mandibles was named as the new species Allodesmus sadoensis. Their use of the subfamily name Allodesminae was necessitated by the splitting of the generic concept into eight named (and three unnamed) species in four genera.

 The holotype skull of Allodesmus gracilis, from Barnes (1972).

            A paper by Naoki Kohno that came out in 1996 was evidently submitted and accepted prior to publication of the Barnes and Hirota (1995) paper. This study by Kohno (1996) was a bit more sober in its taxonomic conclusions, considering the gigantic snout of Allodesmus megallos as an adult specimen of Allodesmus sinanoensis (=Megagomphos sinanoensis of Barnes and Hirota), and considered only one species of Allodesmus from the Round Mountain Silt to be valid (Allodesmus kernensis), following Barnes (1970, 1972). Kohno (1996) also considered Atopotarus courseni to be a species of Allodesmus. In this article, Kohno (1996) named the “Mito seal” – a partial skull thought to be lost due to Allied bombing of Japan during the second world war, but figured and discussed by Repenning and Tedford (1977) based on a cast at the Smithsonian. In fact, the specimen had not been destroyed but was rediscovered – and the specimen He named the “Mito seal” Allodesmus naorai, and considered it to be closely related to Allodesmus packardi. Kohno also summarized other fragmentary occurrences of Allodesmus from Japan.

An alternate view of desmatophocid/allodesmine diversity published by Kohno (1996); this idea was published in parallel and independent from Barnes and Hirota (1995).

In 1998, a paper by Kimura et al. reported a mandible of Atopotarus sp. from the middle Miocene of Hokkaido. It is very similar to the holotype of Atopotarus courseni - but under a different paradigm of Allodesmus taxonomy, it could also be identified as Allodesmus courseni rather than Atopotarus sp.

            The most recent paper weighing in on the subject was Deméré and Berta (2002), which actually focused on the closely related Desmatophoca oregonensis. They argued that Allodesmus was oversplit, and emphasized the problematic recognition of three species of Allodesmus from a narrow stratigraphic interval in a single rock unit in California – Allodesmus kernensis, Allodesmus kelloggi, and Allodesmus gracilis from the Round Mountain Silt. However, a discussion of Allodesmus taxonomy was clearly beyond the scope of the study, and they elected to not discuss the topic further.

Next up: How many species of Allodesmus are there, any way? I've given out a brief sketch of the history of work on Allodesmus, but there's quite a bit more to the story than this.

References

L. G. Barnes. 1970. A re-evaluation of mandibles of Allodesmus (Otariidae, Carnivora) from the Round Mountain Silt, Kern County, California. PaleoBios 10:1-24.

L. G. Barnes. 1972. Miocene Desmatophocinae (Mammalia: Carnivora) from California. University of California Publications in Geological Sciences 89:1-76.

L. G. Barnes and K. Hirota. 1995. Miocene pinnipeds of the otariid subfamily Allodesminae in the North Pacific Ocean: Systematics and relationships. The Island Arc 3:329-360.

T.A. Demere, and A. Berta. 2002. The Miocene pinniped Desmatophoca oregonensis Condon,
1906 (Mammalia: Carnivora) from the Astoria Formation, Oregon. Smithsonian Contributions to Paleobiology 93: 113–147.

T. Downs. 1953. A mandible of the seal Allodesmus kernensis from the Kern River Miocene of California. Bulletin of the Southern California Academy of Sciences 52:93-102.

T. Downs. 1955. A fossil sea lion from the Miocene of the San Joaquin Hills, Orange County, California. Bulletin of the Southern California Academy of Sciences 54:49-56.

T. Downs. 1956. A new pinniped from the Miocene of southern California: With remarks on the Otariidae. Journal of Paleontology 30(1):115-131.

R. Kellogg. 1922. Pinnipeds from Miocene and Pleistocene deposits of California. University of California Publications in Geological Sciences 13(4):23-132.

M. Kimura, K. Hirota and C. Kiyono. 1998. Fossil pinniped mandible from the Middle Miocene of Haboro-Cho, Hokkaido. The Bulletin of the Hobetsu Museum 13:1-7.

N. Kohno. 1996. Miocene pinniped Allodesmus (Mammalia: Carnivora); with special reference to the "Mito seal" from Ibaraki Prefecture, Central Japan. Transactions and Proceedings of the Palaeontological Society of Japan, New Series 181:388-404.

E. D. Mitchell. 1966. The Miocene pinniped Allodesmus. University of California Publications in Geological Sciences 61:1-105.

Update to research trends, 1960-2014

First of all, it's been over a month since I've posted anything, and I feel that apologies are in order. I have been devilishly busy with dissertation writing, and feel like I am finally at about the halfway point. Things have relaxed somewhat, and I've got a few ideas for quicker posts and some longer ones. Relatively soon I'll be tackling an issue I've always wanted to talk about but have never had the time to read all the relevant papers in depth - controversies surrounding the highly derived, extinct pinniped Allodesmus from the Miocene of California, Mexico, Washington, and Japan.

Before I do any of that, it's been about six months since I posted the review of publishing trends for marine vertebrates from the eastern North Pacific. In the meantime, eleven (11!) new articles have been published (that I know of). The newest addition to the list is a new kentriodontid dolphin from the middle Miocene Rosarito Beach Formation - I had updated the list over the weekend, but thanks to this new paper (in Spanish with English abstract - pdf freely available online here) I had to update it again this evening.

Here's the updated chart:

There are two things you should notice. 1) 2013 has the largest number of publications on record dealing with marine vertebrates from our corner of the globe. There are five papers on fossil birds, mostly by colleague N. Adam Smith at NESCENT. 2) We're only four months into 2014, and at this rate we're already looking to beat the record of 2013 (although it is very possible that things may slow down). Regardless, 8 publications is fairly high for any year - only a handful reach 8 or higher.

Unlike the last time I posted this in October, I've now placed my excel file up on the web - so, you are free to download it, and if you so desire, notify me of glaring errors or omissions. Click here to download the excel file. At the moment, it's set up very simply: just four columns, with the aforementioned subjects (Taphonomy, Sirenia, Osteichthyes, Odontoceti, Mysticeti, Elasmobranchii, Desmostylia, Chelonia, Aves, Assemblages, and Aquatic Carnivora).

A publication need not be alphataxonomic in scope to merit inclusion - those certainly count, but minimum requirements for inclusion in this list include any of the following: 1) extensive discussion of the morphology, functional anatomy, age, or biogeography of marine vertebrates from Cenozoic rocks in the eastern North Pacific (e.g. Smith and Clarke, 2013, who used bones of the flightless auk Mancalla for histologic study); 2) published figures of said marine vertebrates, even if focusing on fossils from elsewhere (e.g. Velez-Juarbe and Pyenson 2012, in their paper on Bohaskaia - an Atlantic odontocete - figure the holotype skull of Denebola brachycephala); 3) extensive sampling of ENP marine vertebrates for any sort of quantitative study (e.g., Ando and Fordyce 2014, who used data on fossil occurrences from many ENP vertebrates for a large part of their analysis). If you are confused by a particular inclusion or omission, at least you can make some sense out of my strategy.

Future efforts: it would be nice to include a proper citation for each publication, but boy there are a lot of them, and it would take me a lot of time that I don't have. If there is a paper you see but were unaware of, shoot me an email - I've either got a pdf of it, or a paper copy in a box back in California (in which case you should use interlibrary loan, since it's going to be another 12 months until I'm home again).

Other future tweaks I might investigate and post in the future: the ratio of marine mammal to non-mammal publications, and the ratio of regular articles to book chapters/edited volumes. I believe that 90% of the big 1994-1995 spike is because of the 1994 Frank Whitmore marine mammal paleontology volume and the 1995 Island Arc volume (also heavily marine mammal-themed).

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.

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 18^th 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!

References

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.

 

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:

Ancient Sea Mammals - Radio Live

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.

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