David Grimaldi: Clues to India’s geologic past in ancient insects in amber

Insects encased in 50 million-year-old amber deposits suggest that India’s geological history may have to be revised, according to an October 2010 report. We spoke with David Grimaldi, a paleontologist at the American Museum of Natural History, and a co-author of the study.

David Grimaldi: The deposits are very large, chock full of amber, and the amber contains a wealth of insect and plant and fungal remains. We’ve found at least 1,000 pieces containing insects, well over 100 species.

Amber is formed from tree resin from ancient forests. The sticky resin can trap debris like seeds, leaves – and insects. Over millions of years, the resin gets fossilized into amber – and any trapped insects are preserved inside. Grimaldi said that the insects they found in these Indian amber deposits were similar to species found in Europe, Australia, and South America.

David Grimaldi: The point being, what’s preserved in this India amber was widespread.

Grimaldi said that the discovery of these insects reveals something surprising about where the landmass of India was at the time. It changes geologists’ estimates of when India became a part of Asia, he said. It’s known that India spent about 100 million years drifting across the Earth on a continental plate until it crashed into Asia, forming the Himalayas. Scientists thought that 50 million years ago, India was still surrounded by ocean, but the insects in the amber show otherwise, he said.

David Grimaldi: It either docked earlier than geologists think, or there was some way that India was connected to Asia.

He said that another significant part of the finding was discovering the age of tropical forests.

David Grimaldi: We’ve been able to show this is one of the oldest remains of a tropical forest from Southeast Asia. And that’s significant, because the age of tropical forests has been a controversy for quite some time – mostly because there’s very little data.

In other words, scientists don’t know when modern-day tropical forests started to appear on the planet.

David Grimaldi: The reason it’s a controversy is because people wonder, why do tropics have so many species in them? I mean, this is where the great proportion of the world’s species are, in tropical forests. Why? Is it because they are such ancient ecosystems? Is it because of the high rainfall and warm temperatures that fosters growth and development of life forms? There are all these questions. At least now we can say that one of these is true – that tropical forests are ancient ecosystems.

Grimaldi said that means that species have been accruing in tropical forests for at least 50 million years – and that’s at least part of the reason why tropical forests are such hotbeds for biodiversity.

March 28, 2011

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