Mammals of Assam and the Mammal-Geography of India

Abstract

The northeastern parts of India, comprising Assam, are of exceptional biogeographical interest. It is from this region that the obliteration of the Pre-Tertiary Tethys Sea began, producing in its wake a land connection between the Indian Peninsula and the main Asiatic mass to its north (see Chapters II, III & XX). The Assam region then onwards served as a great faunal gateway, through which the Indo-Chinese elements of the Oriental fauna and also that of Palaearctic could spread to India and colonize the country. In fact, the history of the Post-Tertiary faunal dispersal in India is peculiar, in as much as all the faunal invasions have come through two great faunal gateways, one at the Assam region and the other in the northwest. This was because of the emergence of the rising Himalaya as a great barrier-wall, concomitant with the obliteration of the Tethys Sea, so that except for the montane species, the faunal dispersal had to take place through either of these faunal passes. Of these the importance of the northwest gateway dwindled after the disappearance of the incomparably richer Siwalik fauna in the early Pleistocene and the changes in the physiography of the Indo-Gangetic trough, of which the formation of the Thar or Rajaputana Desert was a major one, constituting barriers to dispersal from the northwest. As a result, we see that most of the faunal dispersal and recolonization in the recent period have taken place through the Assam gateway, so that the Indo-Chinese element constitutes the dominant entity in the mammal fauna of India.