Sunday, November 11, 2007

Mammal origin in India

Many present day plant and animal species might have their origin in India, a new find has suggested.

Scientists have suggested the new theory after the discovery of a 66-million-year old tooth in central India. The newfound tooth was unearthed in a sedimentary rock sandwiched between lava flows from the late part of the Cretaceous period, which spanned from 145.5 to 65.5 million years ago.

According to a new study led by Guntupalli Prasad of the University of Jammu, the tooth may have belonged to one of the condylarths, which were a group of primitive mammals. They included the ancestors of modern hoofed animals such as goats, horses, cows, sheep, and deer.

Because the newfound molar is about three million years older than the earliest known Condylarth specimen, this places it on the Indian subcontinent at a time when the landmass was a drifting island that had just broken away from the super continent called Gondwana. This has fuelled speculation about many mammal species originating in India.

"Many researchers had postulated that mammalian groups may have originated from basal Gondwanan stocks during the northward flight of India and finally dispersed to Asia when India collided with the Asian mainland around 55 million years ago," said Prasad.

Scientists are also supporting this theory because mammal fossils found on the southern continents that date to the time of Gondwana are quite rare.

"With a few minor exceptions, the only other place where there are really good records of mammals at that time is North America," said J David Archibald, an evolutionary biologist at San Diego State University.

But some researchers are puzzled about the primitive tooth's presence in India. "How did this animal get onto India, when the landmass was probably about in the middle of the Indian Ocean on a rapid drift northward?" asks Kenneth Rose, a palaeontologists. "That's one of the really intriguing questions here. If it is an ungulate (hoofed mammal), it provides an interesting scenario that some primitive stock got onto India and later evolved into ungulates," he speculates.

An interesting hypothesis is that good interspecies exchange existed between India and the Asian continent even during the Cretaceous period.

If so, the early ungulates might not have originated in India but somehow moved there from northern locales, where their fossils are more commonly found. "But it's still quite interesting to realize that there is some kind of placental mammal that was on India in the late Cretaceous period," said Rose.
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