Tuesday, December 4, 2012

US Research trip part 5: fossil pinniped bonanza at the USNM

One of my alternative goals for research at the USNM was to photograph as many fossil pinnipeds (seals, sea lions, and walruses) as I could. The USNM has an unparalleled collection of fossil pinnipeds - primarily due to the efforts of my hero Douglas Emlong. In fact, most of the fossil pinnipeds in this post were collected in the 1960's and 1970's by Emlong. Emlong's collection has been very important for understanding the early evolution of pinnipeds, and has been utilized in many publications of new species and genera, functional analyses, and phylogenetic analyses.

A partial skull referred to Pinnarctidion rayi by Annalisa Berta (1994). Pinnarctidion was a tiny pinniped - although this specimen is a bit larger than the type, which I've shown below. 

A cast of the holotype humerus of the walrus Valenictus imperialensis from the Pliocene Imperial Group of southern California. This species of Valenictus is known only from the humerus, but another species from the coeval San Diego Formation (Valenictus chulavistensis) is known from multiple partial skeletons and skulls, which show that it lacked all teeth aside from the canines.

A cast of the holotype skull of Homiphoca capensis from the Pliocene of Langebaanweg in South Africa. At the time of my visit I had not anticipated seeing casts of foreign specimens like this, as I did not know about them beforehand - but finding them was certainly a welcome surprise. I had not yet seen a cast of Homiphoca; Homiphoca is a fossil monachine seal that has something to do with the evolution of leopard, ross, crabeater, weddell, and elephant seals.

A skull from the Emlong collection from the latest Oligocene/earliest Miocene of Oregon, referred to Enaliarctos mitchelli by Annalisa Berta (1991). The species was previously reported by Larry Barnes (1979) from the earliest Miocene Jewett Sand at Pyramid Hill in Kern County, California, based on a rostrum (holotype) and a palate (paratype).

A skull of the early pinniped Pteronarctos goedertae, referred by Annalisa Berta (1994). Berta synonymized two species with P. goedertae - Pteronarctos piersoni, and Pacificotaria hadromma, all from the Astoria Formation near Newport, Oregon. Pteronarctos was a late surviving enaliarctine and would have probably looked like a small sea lion.

While not explicitly a pinniped and may seem a bit out of place in the theme of this post, the "beach bear" or "oyster bear" Kolponomos newportensis is another marine carnivore, also collected by Doug Emlong. This specimen was found near what is now the Wal-Mart in Newport, Oregon. I believe that Kolponomos has something to do with early pinniped evolution; as I've pointed out in an earlier post, if the otter-like early Miocene Puijila darwini has anything to do with pinnipeds, then so does Kolponomos, because all of the cranial features linking Puijila to pinnipeds are also present in Kolponomos.

The tiny holotype skull of Pinnarctidion rayi, described by Annalisa Berta (1994) from the early Miocene Nye Mudstone of Newport, Oregon. This specimen was collected near the Kolponomos specimen above. Pinnarctidion is another enaliarctine pinniped, which in some phylogenetic analyses has cropped up near or as the most basal member of the Phocoidea (desmatophocid seals and modern earless seals). Pinnarctidion was originally described from the early Miocene Jewett Sand of Pyramid Hill, along with Enaliarctos mitchelli and Enaliarctos mealsi.

The large and beautiful holotype skull of Proterozetes ulysses, from the early Pleistocene Port Orford Formation of Oregon - also collected by Doug Emlong. The genus Proterozetes may or may not be a junior synonym of Eumetopias, the steller's sea lion - and it was originally mentioned as a new species of Eumetopias in the 1970's.

My labmate Yoshi Tanaka with the beautiful skeleton of Enaliarctos mealsi - also from Pyramid Hill, and also collected by Emlong - described by Berta et al. (1989). This fossil appeared in two counterpart slabs of a concretion, which were glued together with a ton of epoxy, and prepared out from both right and left sides and mounted on this slab. Although Yoshi is currently studying archaic fossil dolphins from New Zealand for his Ph.D., he studied primitive walruses from Japan for his master's thesis with Naoki Kohno and also has a research interest in fossil pinnipeds.

Finally, another pinniped that was not collected by Emlong: a cast of a skeleton of Acrophoca longirostris from the latest Miocene/earliest Pliocene Pisco Formation of Peru. A mount of the whole skeleton is shown right above the in-situ display; I'll include photographs of the mounted skeleton in a subsequent post.

An adorably sized partial left maxilla of the Pliocene walrus Ontocetus emmonsi (formerly Alachtherium) from the Yorktown Formation in North Carolina (Lee Creek Mine), described by Kohno and Ray (2008). This specimen shows that even derived walruses possessed enamel caps on their teeth, just at a very young age - in contrast to previous studies that have indicated the loss of enamel in odobenine walruses such as Odobenus, Valenictus, Ontocetus, and Protodobenus.

Another view of the referred skeleton of Enaliarctos mealsi.

Further Reading:

L. G. Barnes. 1979. Fossil enaliarctine pinnpeds (Mammalia: Otariidae) from Pyramid Hill, Kern County, California). Contributions in Science of the Natural History Museum of Los Angeles County 318:1-41

L. G. Barnes, C. E. Ray, and I. Koretsky. 2006. A new Pliocene sea lion, Proterozetes ulysses (Mammalia: Otariidae) from Oregon, U.S.A. Mesozoic and Cenozoic Vertebrates and Paleoenvironments 57-77

Berta, A. 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. A new species of phocoid pinniped Pinnarctidion from the early Miocene of Oregon. Journal of Vertebrate Paleontology 14:405-413

Berta, A., and Ray, C. E. 1990. Skeletal morphology and locomotor capabilities of the archaic pinniped Enaliarctos mealsi. Journal of Vertebrate Paleontology 10:141–157.

Berta, A., C.E. Ray and A.R. Wyss. 1989. Skeleton of the oldest known pinniped, Enaliarctos mealsi. Science 244:60-62.

Kohno, N. 2006. A new Miocene odobenid (Mammalia: Carnivora) from Hokkaido, Japan, and its implications for odobenid phylogeny.  Journal of Vertebrate Paleontology 26:411–421.

N. Kohno and C. E. Ray. 2008. Pliocene walruses from the Yorktown Formation of Virginia and North Carolina, and a systematic revision of the North Atlantic Pliocene walruses. Virginia Museum of Natural History Special Publication 14:39-80

E. D. Mitchell. 1961. A new walrus from the imperial Pliocene of Southern California: with notes on odobenid and otariid humeri. Los Angeles County Museum Contributions in Science 44:1-28

R. H. Tedford, L. G. Barnes, and C. E. Ray. 1994. The early Miocene littoral ursoid carnivoran Kolponomos: Systematics and mode of life. Proceedings of the San Diego Society of Natural History 29:11-32

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