Size Variation Amongst the Non-volant Mammals from the Early Eocene Cambay Shale Deposits of Western India: Paleobiogeographic implications

Abstract

Within the Indian subcontinent, the oldest Cenozoic record of non-volant mammals comprises various groups including perissodactyls, artiodactyls, primates, lagomorphs, tillodonts, proteutherians, rodents and didelphimorphs. These mammals have been reported from the subsurface horizons of the Cambay Shale which are dated at ~54.5 Ma (Early Eocene). A statistical analysis (at the ordinal level) of size variation(s) in the lower dentitions of these taxa from the Cambay Shale allows their size categorization into three broad groups: small, medium and large. Based on the data on (a) phylogenetic relationships of large perissodactyls (e.g., cambaytheres), (b) an Early Eocene age of the fauna, (c) the timing of collision between the Indian plate and Eurasia, and (d) considering that it was unlikely for the large-sized component (perissodactyls) to disperse across oceanic barriers, the potential presence of a short-lived corridor for dispersal between Indian subcontinent and Eurasia prior to ~54.5 Ma cannot be ruled out. Further, the overall data hint at the presence of cambaythere-like mammals during the late Paleocene of the Indian and/or Eurasian continent(s), emphasizing the need for rigorous reconnoitering for Paleocene mammals (presently unknown) within the Indian subcontinent.