Revision of Indobune and Cambaytherium from the early Eocene of Vastan (India), and their affinities with anthracobunid and perissodactyl mammals

The early Eocene vertebrates found in the Cambay Shale at the Vastan Lignite Mine represent the oldest Cenozoic Indian vertebrate fauna and their study has yielded major insights for the knowledge of Indian paleodiversity and paleogeography. In 2006, we described the new genus and species Indobune vastanensis based on a small collection of large, bunodont mammal teeth and referred this taxon to the enigmatic tethythere family Anthracobunidae. Nearly simultaneously, another paper described similar specimens as four distinct new species in the new genus Cambaytherium, which was furthermore placed in the new perissodactyl family Cambaytheriidae. Continued fieldwork has yielded additional adult and juvenile skulls, maxillae, dentaries, vertebrae and limb elements of these forms, allowing us here to clarify their evolution and classification. Indobune and Cambaytherium appear to represent a single genus, in which case the latter name takes nomenclatural priority. Many of the characters used to diagnose the different species of Cambaytherium seem to be less distinctive or variable, or seem to be based on misidentification of the dental position of specimens. Most to all of the reported specimens therefore probably belong to a single species. The dental proportions of Cambaytherium are similar to those of Nakusia, an enigmatic, early Eocene anthracobunid, and Cambaytherium resembles younger, better known anthracobunids by the specialized, transversely compressed lower premolars. The specialized premolars of Cambaytherium are markedly different from those of perissodactyls, and Cambaytherium also lacks typical perissodactyl synapomorphies such as distinct transverse lophs on the upper and lower molars or the loss of the astragalar foramen. Some similarities between Cambaytherium and perissodactyls do however remain and may suggest a phylogenetic link between Perissodactyla and Anthracobunidae.

Publication year:2011

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