LATE CRETACEOUS GONDWANATHERIAN MAMMALS OF INDIA: DISTRIBUTION, INTERRELATIONSHIPS AND BIOGEOGRAPHIC IMPLICATIONS

摘要

Gondwanatheria is a poorly-known extinct order of the class Mammalia. It represents an enigmatic and distinctive non-tribosphenic radiation of mammals in the Southern Hemisphere with fossils documented from the Late Cretaceous and early Middle Eocene of Argentina, Late Cretaceous of Madagascar and India, ? Cretaceous of Tanzania and ? Middle Eocene of Antarctica. The Indian gondwanatherian mammals are known by two taxa (Bharattherium bonapartei Prasad et al., 2007a and Dakshina jederi Wilson et al., 2007) from the Upper Cretaceous sediments intercalated with the Deccan volcanic flows (= intertrappean beds) of peninsular India. A close examination of the type specimens of both these Indian sudamericids shows that they are morphologically similar, and given that the publication of Bharattherium pre-dates Dakshina, the latter is regarded here as a junior synonym of the former. In addition, recent fieldwork in central India has resulted in the discovery of a new sudamericid tooth in the Upper Cretaceous (Maastrichtian) intertrappean beds of Kisalpuri, District Dindori (Madhya Pradesh). Though in having two independent transverse lophs, distinct shape of the lophs, and in the absence of infundibulum, perikymata, and enamel islet this tooth differs from Bharattherium and other known sudamericid mammals from Madagascar and Argentina, it is tentatively referred to the family Sudamericidae as we are not aware of morphological variation of molariforms in different loci on the dentition of sudamericid mammals. Further, the phylogenetic and palaeobiogeographic relationships of gondwanatherian mammals are reviewed in light of recent fossil discoveries from the Late Cretaceous of India.