A Systematic, Biostratigraphic, and Paleobiogeographic Reevaluation of the Siwalik Hipparionine Horse Assemblage from the Potwar Plateau, Northern Pakistan

作者：Wolf Dominik^*; Bernor Raymond L; Hussain S Taseer

来源：Palaeontographica Abteilung A-Palaozoologie-Stratigraphie, 2013, 300(1-6): 1-115.

• Hipparion
• Siwalik Hills
• Taxonomy
• Paleodiet
• Phylogeny

The Miocene to Pliocene fossil record of the Siwalik Hills in Pakistan yields abundant material of hipparionine equids. This material has been intensively studied over the last 150 years, but previous reports did not include precise stratigraphic and paleomagnetic data which we have been able to include herein. Our study integrates the Harvard (formerly Yale) Geological Survey of Pakistan (GSP) hipparion material along with specimens from the American Museum of Natural History and other collections to provide a comprehensive evaluation of hipparion species occurrences and evolution in the Siwalik sequence. Results of bivariate and log10 ratio statistical analyses of dental and postcranial measurements suggest that after the initial presence of relatively moderately sized horses similar to North American Cormohipparion, the Siwalik record between ca. 10.7 and at least 9.3 Ma is soon dominated by a more derived taxon with more hypsodont teeth, Sivalhippus nagriensis. There is evidence for another species with massive cheek teeth, Sivalhippus theobaldi, at ca. 9.3 Ma. Some robust postcranial elements of similar age may also belong to this taxon. The later record of Siwalik hipparions especially between ca. 8.5 and 7.8 Ma shows a more derived endemic species with a somewhat reduced preorbital fossa, Sivalhippus perimensis, alongside occasional Sivalhippus theobaldi, co-occurring with an apparent immigrant population of hipparions with small body size, Cremohipparion antelopinum. A new taxon with very high-crowned cheek teeth and robust elongated metapodials appears in the record at ca. 7.3 Ma. Small, Cremohipparion-like horses are also present in the younger beds of the Siwalik sediments, but are rare. Cladistic analysis supports the monophyly of the %26quot;Sivalhippus%26quot; Complex and provides evidence for phylogenetic relationships among the basal members of this lineage that are in accordana with the stratigraphic first appearance of these species. Paleodietary mesowear analysis generally reveals a mixed-feeding signal for Siwalik hipparions, with a steady increase of grazing over time. The Siwalik hipparion evolutionary record has far-reaching consequences for understanding the Old World %26quot;Hipparion%26quot; Datum, and the relationship of Siwalik Hipparions to African and East and West Asian late Miocene Pleistocene hipparion lineages.

• 出版日期2013-9