Cretaceous mammals of India–Stratigraphic distribution, diversity and intercontinental affinities

Abstract

Extensive research carried out on the Cretaceous deposits of Laurasia has revealed an overwhelming presence of eutherian, metatherian and multituberculate groups of mammals in the Cretaceous ecosystems of Northern Hemisphere continents. In contrast, the relatively poorly documented fossil record of Cretaceous mammals from Gondwanan continents is represented by gondwanatherians, dryolestoids, and a few multituberculates and haramiyidans. Until now, no undoubted eutherian mammals have been reported from the Cretaceous strata of the southern continents except for India. In this context, Indian Cretaceous mammals assume great significance for understanding the origin and evolution of these mammals in Gondwana. Currently, the Cretaceous mammals of India include three groups, viz., eutherians, gondwanatherians, and haramiyidans. These three mammalian groups were recovered primarily from the Upper Cretaceous Deccan infra–and inter–trappean beds of peninsular India exposed near Bacharam, Naskal and Rangapur (Telengana), Upparhatti (Karnataka) and Kisalpuri (Madhya Pradesh) villages. Eutheria is by far the most diverse clade comprising three named genera (Deccanolestes, Sahnitherium, Kharmerungulatum) and one unnamed taxon (Eutheria incertae sedis). The gondwanatherians are known by Bharattherium bonapartei and Sudamericidae gen. et sp. indet. The third mammalian group, a possible haramiyidan, is represented by a solitary species Avashishta bacharamensis. Overall, the Cretaceous mammal fauna of India presents a complex biogeographic history with eutherians of Laurasian affinity, pan–Gondwanan gondwanatherians and a possible late surviving haramiyidan. Numerically abundant and speciose Deccanolestes, identified as an adapisoriculid, has been interpreted to have had originated in northward drifting Indian Plate in the Late Cretaceous and dispersed out of India into Africa and Europe over island arc systems (Oman–Kohistan–Dras) and the Ladakh magmatic arc at or near the Cretaceous–Paleogene boundary. A similar dispersal mode has also been visualized for Kharmerungulatum and Eutheria incertae sedis of Laurasian affinities. The close similarity of dental morphology between Madagascan and Indian gondwanatherians attests to the fact that these taxa derived from a common endemic Gondwanan stock had evolved in isolation following the separation of Indo–Madagascar from other Gondwanan continents. Avashishta represents a late Gondwana survivor of a group that had a Pangaean distribution until the Early Cretaceous.