The Murine Cradle

The unique geological, geophysical, and tectonic setting of the Indian Subcontinent created a theater of evolution that provided a relatively insulated refuge for origination and early diversification of many Mesozoic and early Cenozoic age vertebrate groups. This phenomenon continued into the Miocene Epoch in association with developing physical barriers: mountains, major river systems, and oceanic borders. The terrestrial barriers were semi-permeable filters that allowed differential passage of select organisms, and endemic evolution of certain clades. Muroid rodents of modern grade are a group that evolved by the earliest Miocene, in part endemically after they appeared on the subcontinent. One endemic muroid lineage led to the Murinae, extant mice and rats, and the semi-isolated physical setting of India and Pakistan promoted local evolution of murines during the middle Miocene, prior to their dispersion throughout Eurasia and beyond around ten million years ago. Here we note dental morphological features that appeared early in the evolution of Murinae to document the divergence of two major clades leading to extant murines. Their earliest presumed members are morphologically similar in older samples before clear taxonomic separation of molar phenotypes.