Biotic response to the India-Asia collision: changing palaeoenvironments and vertebrate faunal relationships

Abstract

The Indian fossil vertebrate record from the Mid-Late Cretaceous to the Early Eocene is now becoming better known and can be used to document the northward drift of the landmass in terms of response of non-marine and near-shore vertebrate faunas. The Nimar Formation (Cenomanian - Turonian) in central peninsular India, has at present yielded no mammals but holds the potential of providing important data on palaeoenvironments in a rift-basin setting, spatially not far removed from Madagascar based on the presence of shallow water marine benthic invertebrates, common presence of large sauropod dinosaurs and mangrove floral elements. The present paper deals mainly with the affinities of mammalian assemblages from the Maastrichtian to the beginning of the Lutetian (Middle Eocene) based on a fairly complete stratigraphic record, associated faunas and floras and inputs from sedimentology. Initial radiations for various elements (vertebrates and floras) are also recorded. Recent data suggest that the Indian landmass may have served as a drifting platform firstly for the dispersal of gondwanic elements into Laurasia, and conversely for the migration of Asiatic forms into India upon collision and lastly, as a center of origin for some mammalian groups (whales) and other vertebrates, an intra-plate evolutionary phenomenon that needs to be better understood. The current data from Cretaceous mammals suggest a close affinity to gondwanathere mammals (the Sudamericidae) known from Madagascar and South America while the affinities of Deccanolestes, Sabnitberium, and ?Otlestidae are either African and/or Laurasiatic. The Palaeocene record has at present yielded only plant remains and provides no significant data. The Lower Eocene mammals of peninsular India have the potential of yielding good evidence for faunal affinities. The mammals comprise anthracobunids from Pakistan, primates, and the oldest record of bats in Asia along with the presence of diverse insectivores. Middle Eocene vertebrate faunas are better known and understood for the last three decades. Several elements such as tapiroids, rhinocerotoids, brontotheres, and chappatymyid rodents migrated into India after collision. The data on endemic biotas are becoming better understood not only in terms of recently recorded extant forms (the anuran family Nasikabatrachidae) but also in the context of fluvio-lacustrine ostracodes which were endemic to a large extent in the latest Cretaceous.