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The rise of India: the complex biological history of a subcontinent

If you try and draw family trees for animals and plants in India, you will discover something that will take your breath away. Relatives do not occur in the same area; in extreme cases, they can be in other continents. And atop the tallest mountains in the Himalayas, you will find marine fossils.

The relative position of the Indian subcontinent changed dramatically over the last 200 million years, and the signatures of India’s adventures across the seas can be seen in the flora and fauna of the subcontinent. The purple frog (Nasikabatrachus sahyadrensis) is an extreme example illustrating this complex history. A large, bloated looking burrowing frog, the species spends most of the year underground, and emerges for two weeks during the monsoon to mate. It was during the monsoon season in 2000 that a team of researchers at a cardamom plantation in the southern Indian state of Kerala stumbled across this species for the first time. But its most remarkable aspect emerged after careful taxonomic analysis – genetic and morphological analysis showed that the frog belonged to a family thought to be restricted to the Seychelles islands in the Indian Ocean.

A small rust and red colored butterfly from the high altitudes of the Western Ghats in southern India was thought to be a kind of bushbrown (of the genus Mycalesis), closely related to other Mycalesis species found at the lower elevations. However, in 2010 a molecular study discovered that the butterfly’s closest relative was not from India at all, but from Madagascar.

The purple frog (<i></img>Nasikabatrachus sahyadrensis</i>).  Photo by Karthickbala.” ><br></br><i>The purple frog (Nasikabatrachus sahyadrensis).  Photo by Karthickbala.</i><br></br>
<p>These are just two examples showing the strange affinities of Indian flora and fauna. Looking at where India is on the world map, it is easy to make the connection that species found in Northeast India have sisters in Southeast Asia; similarly, Northwestern Indian species will have relatives from Central Asia. But how did this strange cross-oceanic relationship between southern Indian mountains and Seychelles and Madagascar come about?<br></br>
<p><b>A giant jigsaw puzzle</b><br></br>
Keep looking at the world map, and with a little imagination you can see that the eastern coast of South America can fit snugly into the Western coast of Africa. Move Madagascar a bit closer to the African mainland. Keep putting the pieces together, and you will finally arrive at how these landmasses looked during the earth’s infancy.</p>
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<img src= width=360 alt=“A map of Pangea.  Courtesy of Adrignola.”></img><br></br>A map of Pangea.  Courtesy of Adrignola.
<p>In the beginning of the twentieth century, the German scientist Alfred Lothar Wegener started toying with the idea that all present day continents were part of one huge landmass, a supercontinent, millions of years ago. Wegener called this landmass Pangaea, derived from the Greek words “Pan” meaning entire, and “Gaia” meaning earth.<br></br>
The earth’s crust can be visualized as plates floating around on a liquid core. These plates move slowly, and sometimes crash against each other, in a process called continental drift. The crust follows what is called a “supercontinent cycle”, meaning periods of continental collision, like the forming of Pangaea, and continental rifting. So after Pangaea formed, it was soon (meaning a few million years down the line) time for it to break up.<br></br>
It started rifting about 175 million years ago (mya), forming two supercontinents – Laurasia, which was comprised of the continents that occupy today’s Northern Hemisphere, and Gondwana, which included continents from today’s southern hemisphere, i.e. Antarctica, the Australian continent, Africa, South America, Madagascar, and the Indian subcontinent. Between the two supercontinents was a huge water body, the Tethys Sea.<br></br>
<b>A “biotic raft”</b><br></br>
Gondwana then began to break up, with a lot of fanfare (as it were). Accompanied by massive eruptions of basaltic lava, East Gondwana – Antarctica, Madagascar, Indian subcontinent (henceforth India) and Australia – began to separate from Africa 160 million years ago. The same kind of granulite, a kind of rock that forms under high temperature and pressure, is found in parts of peninsular India (called the Deccan), and in Madagascar. This would have formed the eastern part of Gondwanaland.<br></br>
Leaving its partners behind one by one, India floated across the Tethys Sea toward Eurasia. Antarctica first broke away, and moved toward the South Pole; then India and Seychelles together left Madagascar behind. As India and Seychelles together continued their journey toward Eurasia, they moved over the Reunion hotspot, an active “plume”: a place where hot rock swells up from deep within the earth and breaks the surface. Sixty five million years ago, the hotspot covered today’s western India (near Mumbai) with 2,000 feet of lava over 30,000 years.<br></br>
Other stratigraphic studies identified a meteorite impact site called the Shiva crater, close to the Reunion hotspot. Studies concluded that a meteorite 40 kilometers in diameter had crashed onto western India. A combination of Reunion hotspot erupting, and the meteorite crashing, forced India to make an abrupt counter-clockwise turn, separate from Seychelles, and then cover the rest of the distance to Eurasia. (For the dinosaur fans out there, yes this is when they made their exit). Much like a ship docking into a harbor, India landed on the banks of Tethys Sea in southern Eurasia. Difference being – it was such a huge “ship”, the Tethys Sea ceased to exist.<br></br>
Imagine a sheet of cardboard pressing against a wall. The area in contact with the wall will fold up, and rise above the rest of the sheet. India is the piece of cardboard, and Eurasia is the wall. When India “docked”, an event that would influence every aspect of the subcontinent took place. From the depths of the erstwhile Tethys Sea rose the majestic Himalayas; the marine fossils from atop the Himalayas is proof that the area was a former seabed. India is still pushing against Eurasia, which explains the seismically active areas in north India, and why the Himalayas are still slowly increasing in height.<br></br>
With the Himalayas in place, rainfall patterns over the Indian subcontinent changed, and there was a period of transition that finally resulted in the flora and fauna that can be seen today.<br></br>
<B>Evidence of the jigsaw</B><br></br>
<p>An extinct fern called Glossopteris (meaning tongue shaped leaves) was a Gondwana inhabitant, and its fossils have been discovered in all southern continents. Fossils of a family of dinosaurs, called Abelisauridae, has been found in Africa, South America, India and Madagascar. Molecular studies on the DNA of some Indian flora and fauna also show that India acted as a biotic raft. Some species, like the purple frog and a few other amphibians, are related to species from Africa, Madagascar and Seychelles.<br></br>
Within India, they have remained in the peninsular region without moving around too much; they are not related to other amphibians from India. Other species have moved on to Eurasia from the Indian subcontinent, dispersing “Out of India” in the process – like frogs from the family Rhacophoridae, cichlid fishes, agamid lizards and Dipterocarp trees.<br></br>
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The dispersion of Glossopteris fossils (green) on the continents in their locations as sections of Pangaea. Legend: 1 South America, 2 Africa, 3 Madagascar, 4 Indian subcontinent, 5 Antarctica, 6 Australia. Courtesy of Petter Bøckman.

In effect, India acted as a biotic raft, a Noah’s ark, carrying a variety of plants and animals from Africa to Asia; whichever species found the right conditions to survive, did. Going back to where we started, the butterfly got onto India before India split away from Madagascar. The purple frog and its relatives in Seychelles would have evolved when India and Seychelles were still together, after which, only Nasikabatrachus sahyadrensis got on with life as usual in southern India, and we see it today.
Ultimately, the Indian subcontinent is an amalgam of species from Africa, which it passed on to Eurasia; species from South and Southeast Asia; and species from Central Asia, making it unique, and perhaps worthy of the title, subcontinent.

Red-disc Bushbrown (<i></img>Heteropsis oculus</i>).  Photo by Balakrishnan Valappil.” ><br></br><i>Red-disc Bushbrown (<i>Heteropsis oculus</i>).  Photo by Balakrishnan Valappil.</i><br></br>
Biju, S.D. and Bossyut, F. (2003) New frog family from India reveals an ancient biogeographical link with the Seychelles. Nature, 425, 711-714.<BR><br></br>
Briggs, J.C. (2003) The biogeographic and tectonic history of India. Journal of Biogeography, 30, 381–388.<BR><br></br>
Datta-Roy, A. (2009) The Out-of-India hypothesis: What do molecules suggest? Journal of Biosciences.<BR><br></br>
Karanth, P. (2006) Out-of-India Gondwanan origin of some tropical Asian biota. Current Science, 90(6), 789-792.<BR><br></br>
Kodandaramaiah, U., Lees, D.C., Müller, C.J., Torres, E., Karanth, K.P. & Wahlberg, N. (2010) Phylogenetics and biogeography of a spectacular Old World radiation of butterflies: the subtribe Mycalesina (Lepidoptera: Nymphalidae: Satyrini). BMC Evolutionary Biology, 10, 172.</p>
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