The Historic Biogeography of India: Isolation or Contact?

Abstract

Geophysical maps depicting continental movement have consistently shown India, as it moved northward, to be located far out in the Tethys Sea. India split off from the African east coast about 148 m.y.a. From that time onward, according to almost all geophysical accounts, India was isolated from all of other continents until the early Miocene when it made contact with Eurasia. But the biological data, both fossil and Recent, indicate that this concept cannot be correct. If India had really existed as an isolated, oceanic continent for about 100 m.y., it should have developed a peculiar biota with many endemic genera and families in its terrestrial and shallow marine habitats. But there are virtually no remains of organisms indicating that India was isolated for any substantial time (millions of years). Instead, we find that almost all Indian taxa were possessed in common with other continents. As time went on, the northern relationships became stronger and the southern ones weaker. Most of the recent geophysical accounts show India not making contact with Eurasia until the early Miocene, but fossil materials show that this event must have taken place by the early Eocene. It has been postulated that, as India moved northward, it created a biogeographic barrier that separated marine fish populations and resulted in the east-west provinces that are now apparent in the Indian Ocean. At the same time, the barrier effect was supposed to have resulted in the formation of sister species that are now located far apart. Information currently available indicates that most living, tropical marine species are probably not over 3 m.y. old. Consequently, the northward movement of India, which took place primarily between 148 and 50 m.y.a., could have no bearing on the relationships of modern species.

The Earth expansion theory and its transition from scientific hypothesis to pseudoscientific belief

“…Removing the Tethys Ocean in a smaller planet should also solve uncertainties about the size and position of India during the Mesozoic and explain evidence of faunal connections between continents divided by the Tethys (Patterson and Owen, 1991;McCarthy, 2005a, b). These biogeographical problems have been addressed using various traditional approaches (Hallam, 1986;Stanley, 1994;Holloway and Hall, 1998;Briggs, 1989;Sanmartín and Ronquist, 2004;Sanmartín et al, 2006;Ali and Aitchison, 2008;Noonan and Sites, 2010;Goswami et al, 2011;van Hinsbergen et al, 2012), and the expansionist claims have been already refuted in various papers (Thewissen and McKenna, 1992;Briggs, 2004Briggs, , 2006Ali, 2006;Ali and Aitchison, 2008). However, this case probably merits some further consideration because, as expansionists like to remember, although biogeographic correlations were probably the clearest evidence supporting ancient continental connections (Wegener, 1924), contemporary geologists and paleontologists still persisted in denying mobilism.…”

Endemic ranid (Amphibia: Anura) genera in southern mountain ranges of the Indian subcontinent represent ancient frog lineages: evidence from molecular data

“…Its long northward drift across the Tethys sea, with disconnection from Madagascar at $88 Ma (Storey et al, 1995) and the Seychelles at $65 Ma (Courtillot et al, 1988), ended only in the Palaeogene (Najman et al, 2001), after accretion to the Eurasian block. The first contact between both landmasses momentarily enabled Eurasian animal and plant groups to invade the subcontinent (Briggs, 1989;Prasad and Sahni, 1988), and lineages of Gondwanan origin, if they persisted on the drifting subcontinent, to disperse to Eurasia (Bossuyt and Milinkovitch, 2001;Conti et al, 2002;Gower et al, 2002;Wilkinson et al, 2002a). Second, the Cenozoic subsidence of the Indian plate under the Eurasian plate caused the rapid rise of the Himalayan mountain range, creating a barrier to dispersal along the northern limits of the subcontinent.…”

Distributional patterns and possible origin of leafhoppers (Homoptera, Cicadellidae)

“…Evidence from fossil records suggest that the terrestrial biota were once broadly distributed over the entire Pangaean supercontinent (BRIGGS 1989). It is probable that leafhoppers (and all other insects as well) were similarly distributed .…”

“…The dearth of endemism here may be related to intermittant periods ofisolation ofthe northem land mass, the effects of glaciation and discontinuous access of fauna from the southem land mass by the periodical opening and closing of the Isthmus of Panama. The Australian (Australia only) fauna is also particularly paucious, indicating that continental isolation was the limiting factor for dispersai and radiation ofbiota (BRIGGS 1989).…”

“…Only a brief account of the historical biogeography is given here, much of it following BROWN & GIBSON (1983) and BRIGGS (1989). Details, as they apply to the distribution of the various leafhopper taxa, are discussed below under their respective subfamilies.…”