Excerpted from Colbert, M. W. 2005. The facial skeleton of the early Oligocene Colodon (Perissodactyla, Tapiroidea). Paleontologia Electronica 8:12A:27p

ABSTRACT

Two skulls of the early Oligocene Colodon from the White River Group in South Dakota are much more derived than previously reported. In particular, morphologies of the facial skeleton and narial region are surprisingly modern, including a deeply retracted nasoincisive incisure, and other indicators of prehensile proboscis development. High resolution X-ray computed tomography (HRXCT) is used to explore the internal anatomy of these tapiroids, and reveals frontal sinuses, and an internal facial skeletal anatomy approaching that of modern tapirs. This not only records an earlier origin for these anatomical conditions than than previously indicated, but in a phylogenetic context indicates that Colodon is more closely related to Tapirus than is Protapirus.

This specimen was collected from Shannon Co., South Dakota; northeast of the Indian Stronghold on the divide between west Big Corral Draw and Cottonwood Creek. It was found in a lower Protoceras channel, which would be in the upper Oreodon beds or lower Poleslide Member of the Brule Formation of Jim Bump (Whitneyan, Oligocene). The specimen was made available to The University of Texas High-Resolution X-ray CT Facility for scanning by Matthew Colbert of the Department of Geological Sciences, The University of Texas at Austin courtesy of the American Museum of Natural History.

Dorsal view	Left-lateral view	Ventral view

This specimen was scanned by Matthew Colbert on 9 February 2002 along the coronal axis for a total of 556 slices. Each slice is 0.4 mm thick, with an interslice spacing of 0.4 mm and a field of reconstruction of 125 mm.

Colbert, M. W. 1999. Patterns of evolution and variation in the Tapiroidea (Mammalia: Perissodactyla). Ph.D. dissertation, The University of Texas at Austin, Austin, Texas, 464 pp.

Colbert, M. W., and R. M. Schoch. 1998. Tapiroidea and other moropomorphs; pp. 569–582 in C. M. Janis, K. M. Scott, and L. L. Jacobs (eds.), Evolution of Tertiary Mammals of North America. Cambridge University Press, Cambridge, United Kingdom.

Dashzeveg, D., and J. J. Hooker. 1997. New ceratomorph perissodactyls (Mammalia) from the Middle and Late Eocene of Mongolia: their implications for phylogeny and dating. Zoological Journal of the Linnean Society, 120:105–138.

Holbrook, L. T. 1999. The phylogeny and classification of tapiromorph perissodactyls (Mammalia). Cladistics, 15:331–250.

Radinsky, L. B. 1963. Origin and early evolution of North American Tapiroidea. Bulletin of the Peabody Museum of Natural History, 17:1–115.

Radinsky, L. B. 1965a. Evolution of the tapiroid skeleton from Heptodon to Tapirus. Bulletin of the Museum of Comparative Zoology, 134:69–103.

Radinsky, L. B. 1965b. Early Tertiary Tapiroidea of Asia. Bulletin of the American Museum of Natural History, 129:183–263.

Scott, W. B. 1941. The mammalian fauna of the White River Oligocene. Part V. Perissodactyla. Transactions of the American Philosophical Society, 28:747–775.

Schoch, R. M. 1989. A review of the tapiroids; pp. 298–320 in D. R. Prothero and R. M. Schoch (eds.), The Evolution of the Perissodactyls. Oxford University Press, New York.

Witmer, L. M., S. D. Sampson, and N. Solounias. 1999. The proboscis of tapirs (Mammalia: Perissodactyla): a case study in novel narial anatomy. Journal of Zoology, 249:249–267.

Colbert, M. W. 2005. The facial skeleton of the early Oligocene Colodon (Perissodactyla, Tapiroidea). Paleontologia Electronica 8:12A:27p

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