Master's Theses

Document Type

Thesis - campus only access

Date of Award

Fall 2000

Degree Name

Master of Science (MS)

Department

Geosciences

Advisor

Richard Zawerksi

Abstract

Fossilized unassociated teeth and post-cranial elements of three species of tridactyl, grazing equid, Calippus (Calippus) sp., Protohippus gidleyi, and Neohipparion eurystyle, were recovered from the Minium Quarry local biota in Graham County in northwestern Kansas. The quarry is located in sheet flood sediments of the late Miocene Ash Hollow Formation of the Ogallala Group and is eight to nine million years old. A diverse biota, dominated by grasses and large herbivores and indicative of the late Early Hemphilian, was recovered from the quarry. Teeth of Calippus (C.) sp. And P. gidleyi were distinguished from those of N. eurystyle by the connected protocone in the two former taxa and the isolated protocone in the latter. Teeth of C. (C.) sp. were differentiated form those of P. gidleyi by their smaller size and absence of the pli caballing. Average size of the C.(C.) sp. Lower teeth was 19.9 mm anterior-posterior length and 10.0 mm transverse width, whereas the at of P. gidleyi was 23.2 mm anterior-posterior length and 20.8 mm transverse width in the uppers, and 22.3 mm anterior-posterior length and 9.5 mm transverse width in the lowers. Teeth of P. gidleyi, however, have a single pli caballin on the third and fourth premolars and reduced anterostyle on the second premolars. In addition to the isolated protocone, teeth of N. eurystyle were identified based on expanded and constricted styles, a hypoconal groove extending to the base of the crown, more complex plications, and large, elongated metaconids and metastylids. Meapodials and tibiae were found to be diagnostic in each genus. Calippus metapodials and the tibia were distinguished form those of the other two taxa based on small size (metapodials length of 209.0 mm versus 241.0 mm in P. gidleyi and 220.5 mm and 278.0 mm in N. eurystyle, tibia length of 192.0 mm versus 238.0 mm in P. gidleyi and = 240.0-245.0 mm in . eurystyle). Protohippus metapodials exhibit shorter, incomplete scars for the interosseous metapodial ligaments and a shallow posterior gully, whereas Neohipparion metapodials have complete scars for the interosseous metapodial ligaments and a deeper posterior gully. Protohippus tibiae have a deep, well-developed groove for the flexor digitalis longus tendon that has distinct boundaries and extends some way up the shaft, whereas Neohipparion tibiae have a shallow and short groove with indistinguishable borders.

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© 2000 Michelle K. Darnell

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