Journal of Mammalian Evolution

, Volume 13, Issue 1, pp 37–61 | Cite as

Scaphohippus, A New Genus of Horse (Mammalia: Equidae) from the Barstow Formation of California

Article

A new genus of hypsodont equid, Scaphohippus, is recognized from the Green Hills Division (Ba1), Second Division (Ba1), and Barstow Faunas (Ba2) of the medial Miocene Barstow Formation, as well as from Ba1 and Ba2 faunas in the Punchbowl Formation of California, the Tesuque Formation of New Mexico, the Pawnee Creek Formation of Colorado, and the Olcott Formation of Nebraska. The genus includes two species, Scaphohippus sumani n. sp. and Scaphohippus intermontanus n. sp. Scaphohippus is a member of the “protohippine” clade, but is differentiated from its more derived sister taxon, Protohippus, by an arc-shaped incisor battery, a shorter I3-P1 diastema, and a more rounded protocone. The upper cheek teeth of S. sumani n. sp. have an unworn crown height of 40 mm. The protocone remains isolated until as much as 60% of wear, and the enamel fossettes are more complex than those of S. intermontanus n. sp. S. intermontanus n. sp. has an unworn crown height of 48–50 mm, the protocone opens by 30% of wear, and the enamel fossettes are simpler than those of S. sumani n. sp. Phyletic analysis shows S. sumani n. sp. to be the more primitive species. Similar facial and dental characteristics reveal a likely common ancestor with Merychippus insignis. The wider geographic and temporal range of S. sumani n. sp. reported here allows for useful phyletic and biogeographic interpretations. S. sumani n. sp. and M. insignis diverged during the late Hemingfordian (He2) of the Great Plains and both taxa dispersed throughout the western United States. S. intermontanus n. sp. is only recognized from the Barstow Formation, where it was likely directly descended from S. sumani n. sp.

KEY WORDS:

Scaphohippus Equidae Hypsodont Barstovian Phylogeny Barstow formation 

Notes

ACKNOWLEDGMENTS

I first recognize and acknowledge the tireless efforts of the late Morris F. Skinner. It was his attention to detail that provided us with the excellent stratigraphic data accompanying the thousands of specimens within the Frick American Mammals collection. I also thank my academic advisor, Mike Woodburne, for his guidance and support throughout this study, as well as for producing the line drawings in Figures 2C and D. I thank Dick Tedford for his invaluable assistance and direction while at the American Museum of Natural History, as well as Jin Meng for additional guidance, and Chris Norris for providing permission to use the Frick drawings in Figures 2E and F. Chris Collins and Denny Dively were also instrumental in helping me access the Frick Collections. Additionally, Bob Evander was of great help in finding numerous specimens throughout the Frick Collections. Thanks to Pat Holroyd for arranging access to the collections at UCMP. Additional thanks go to Ian Browne for his assistance and input. The study was funded in part by a Geological Society of America Student Research Grant, the Theodore Roosevelt Memorial Fund from the American Museum, and an American Museum of Natural History Collection Study Grant.

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Copyright information

© Springer Science+Business Media, Inc. 2006

Authors and Affiliations

  1. 1.Museum of GeologySouth Dakota School of MinesRapid CityUSA

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