Insular India
Insular India was an isolated landmass which became the Indian subcontinent. Across the latter stages of the Cretaceous and most of the Paleocene, following the breakup of Gondwana, the Indian subcontinent remained an isolated landmass as the Indian Plate drifted across the Tethys Ocean, forming the Indian Ocean. The process of India's separation from Madagascar first began 88 million years ago, but complete isolation only occurred towards the end of the Maastrichtian, a process that has been suggested to be the creation of the Deccan Traps. Soon after, the land mass moved northward rather quickly, until contact with Asia was established 55 million years ago. Even then, both landmasses did not become fully united until around 35 million years ago,[1][2] and periods of isolation occurred as recently as 24 million years ago.[3]
For other uses, see Insular South Asia and List of islands of India.
Thus, for a period of 53 million years India retained a degree of isolation, 11 of which it was a complete island continent. This allowed its local biota to follow the typical patterns seen in islands and diversify in unique ways, much as in modern Madagascar, its sister landmass. Faunal interchanges with other landmasses, like Africa and Europe (then an archipelago of islands across the Tethys) occurred during this period, and a considerable Asian influence can already been seen long before contact was made. This rendered India rather peculiar as not just an isolated continent but also a "stepping stone" in the dispersal of many animal and plant clades across Africa, Europe, Madagascar, Asia and possibly even Oceania. Still, several "archaic" clades managed to survive. The vast majority of India's terrestrial vertebrate life was wiped out in the Cretaceous-Paleogene extinction event; only 3 extant tetrapod lineages can trace their ancestry to Cretaceous India. Most of India's few other surviving Gondwanan lineages were outcompeted during the Paleogene by newly-arriving lineages. However, plants and invertebrate fauna were less affected.[4][5]
During the Paleogene, dispersing tetrapod lineages from Asia repopulated India, with some, such as lagomorphs, evolving on the continent.[6] By the time full contact was established, a large percentage of India's old and new indigenous fauna had been outcompeted by Eurasian species. However, several groups like lagomorphs[6] have become widespread across the world, as have floral groups such as dipterocarps, which went on to become dominant tree species throughout much of tropical Asia.[5] A significant portion of Asian mantises also originated on Insular India.[7] The islands of the Seychelles still retain an indigenous herpetofauna, presumably an echo of the amphibian and reptile species seen in India as an island.
Geology[edit]
The Burma Terrane or West Burma block, an isolated island arc that was present in the Tethys Sea during the Cretaceous, collided with Insular India during the Paleocene and was pushed northwards, eventually colliding with mainland Asia independent of Insular India's own collision. Much of western Myanmar consists of the former Burma Terrane.[8]
Flora[edit]
The Dipterocarpoideae, the largest subfamily of the Dipterocarpaceae, is thought to originate from ancestors that dispersed from Africa to India during the Late Cretaceous. Surviving the K-Pg extinction event, the Dipterocarpoideae were isolated on Insular India (aside from some representatives in the Seychelles) until India's collision with Asia, after which they migrated out of the continent and diversified. The Dipterocarpaceae are now among the most widespread and dominant tree groups in tropical Asia. Fossil evidence indicates that the other subfamily of Dipterocarpaceae, the Monotoideae (presently found in Africa, Madagasar, and South America), also colonized India and was present until the Eocene, but ultimately went extinct in India and thus did not disperse to other parts of Asia.[5]