Ancient insects and continental drift
Subbiah Arunachalam
Biogeographic and evolutionary implications of a diverse
paleobiota in amber from the early Eocene of India
- Jes Rusta,1,
- Hukam Singhb,
- Rajendra S. Ranac,
- Tom McCanna,
- Lacham Singhc,
- Ken Andersond,
- Nivedita Sarkare,
- Paul C. Nascimbenef,
- Frauke Stebnera,
- Jennifer C. Thomasg,
- Monica Solórzano Kraemera,h,
- Christopher J. Williamsi,
- Michael S. Engelg,
- Ashok Sahnie,j, and
- David Grimaldif,1
+Author Affiliations
- aSteinmann Institute, University of Bonn, 53115 Bonn, Germany;
- bBirbal Sahni Institute of Palaeobotany, Lucknow 226007, India;
- cDepartment of Geology; Hemwati Nandan Bahuguna Garhwal University, Srinagar 246174, India;
- dDepartment of Earth Sciences, Southern Illinois University, Carbondale, IL 62901;
- eCentre for Advanced Study in Geology, University of Lucknow, Lucknow 226007, India;
- fAmerican Museum of Natural History, New York, NY 10024-5192;
- gDivision of Entomology, Natural History Museum, and Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, KS 66049-2811;
- hSenckenberg Research Institute and Museum, 60325 Frankfurt, Germany;
- iDepartment of Earth and Environment, Franklin and Marshall College, Lancaster, PA 17603; and
- jCentre of Advanced Study in Geology, Panjab University, Chandigarh 160022, India
-
Edited* by David L. Dilcher, University of Florida, Gainesville, FL, and approved August 31, 2010 (received for review June 4, 2010)
Abstract
For nearly 100 million years, the India subcontinent drifted from Gondwana until its collision with Asia some 50 Ma, during which time the landmass presumably evolved a highly endemic biota. Recent excavations of rich outcrops of 50–52-million-year-old amber with diverse inclusions from the Cambay Shale of Gujarat, western India address this issue. Cambay amber occurs in lignitic and muddy sediments concentrated by near-shore chenier systems; its chemistry and the anatomy of associated fossil wood indicates a definitive source of Dipterocarpaceae. The amber is very partially polymerized and readily dissolves in organic solvents, thus allowing extraction of whole insects whose cuticle retains microscopic fidelity. Fourteen orders and more than 55 families and 100 species of arthropod inclusions have been discovered thus far, which have affinities to taxa from the Eocene of northern Europe, to the Recent of Australasia, and the Miocene to Recent of tropical America. Thus, India just prior to or immediately following contact shows little biological insularity. A significant diversity of eusocial insects are fossilized, including corbiculate bees, rhinotermitid termites, and modern subfamilies of ants (Formicidae), groups that apparently radiated during the contemporaneous Early Eocene Climatic Optimum or just prior to it during the Paleocene-Eocene Thermal Maximum. Cambay amber preserves a uniquely diverse and early biota of a modern-type of broad-leaf tropical forest, revealing 50 Ma of stasis and change in biological communities of the dipterocarp primary forests that dominate southeastern Asia today.
Ira Flatow in Science Friday
Friday, October 29th, 2010
Amber Gives a Glimpse of Ancient India
This male spider from the Cambay amber deposit is the oldest or one of the oldest records of the family Pholcidae, a family that exists today. David Grimaldi/AMNH image.
Biological specimens trapped in amber have given scientists a new look at India, millions of years ago. Writing this week in the Proceedings of the National Academy of Sciences, researchers describe their analysis of over 100 ants, bees, spiders, and other organisms dating back over 50 million years to the Early Eocene. The organisms share evolutionary relationships with finds in Europe and Asia, which challenges the idea of early India as being an isolated land mass. The samples from the Cambay amber deposits, they say, are also the oldest evidence of tropical forests in Asia. We'll find out more.
Guests
David Grimaldi
Curator in the Division of Invertebrate Zoology
American Museum of Natural History
New York, New York
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Segment produced by:Annette Heist
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Image: This Psocoptera (Family Lepidopsocidae) from western India is in amber that hardened from Dipterocarpaceae resin (a group of trees that still dominate tropical broadleaf forests).
David Grimaldi/AMNH image.
From BBC
Ancient bugs found in 50-million-year-old Indian amber
By Katia MoskvitchScience reporter, BBC News
Most of the found species are completely new to scienceMore than 700 new species of ancient insect have been discovered in 50-million-year-old amber.
The discoveries come from some 150kg of amber produced by an ancient rainforest in India.
Scientists say in the journal PNAS that many insects are related to species from far-away corners of the world.
This means that, despite millions of years in isolation in the ocean, the region was a lot more biologically diverse than previously believed.
The amber, dubbed Cambay amber, was found in lignite mines in the Cambay Shale of the Indian state of Gujarat.
Jes Rust from the University of Bonn in Germany led an international team of researchers from India, Germany and the US.
According to a predominant theory of continents' formation, at first there were only two so-called supercontinents on Earth. The one in the north was called Laurasia and the other one, located more towards the south, Gondwana.
Drifting awayWhen Gondwana split up into several smaller pieces in the mid-Jurassic, some 160 million years ago, most of its parts stayed in the southern hemisphere, but one started drifting towards the north.
Having shifted for at least 100 million years at a remarkable rate of 15-25cm per year, the plate eventually collided with Asia and became what we know today as the Indian subcontinent. In the process, the Himalayas were formed.
It has long been believed that drifting in complete isolation would have contributed to a potentially unique plant and animal life, found only in the region.
But the mostly tropical climate of India is known to be unfavourable to the preservation of fossils and not much has been found to confirm this hypothesis of what biologists call "endemism". But the present study says the vertebrate fossil record discovered so far reveals little endemism.
Most of the recently discovered bugs also show links to modern insects as well as those that lived millions of years ago in different parts of the world, including Asia, Australia, and even South America.
The lead author Dr Rust told BBC News that this could be explained by land-bridge connections - possibly small islands that formed before the collision with Asia, in the Eocene - between the Indian "ferry" and other landmasses.
"It is possible for plants to drift hundreds of kilometres on open ocean currents, and in the case of insects, some can fly," said Dr Rust.
The researchers found the amber at the Vastan and Tadkeshwar Lignite mines in western India"There are those that are only able to fly during mating, but they can fly at least a few kilometres.
"Not many are able to cross open seaways, but [they can] drift with plant material. Then there are also very tiny insects and they sometimes simply get blown away, up to the jet stream."
Rainforest's ageThe study says the resin that later became Cambay amber originated from an ancient tropical rainforest.
"The Indian amber is from the Lower Eocene and was likely produced by flowering hardwood trees called Dipterocarpaceae, [trees] that predominate in the forests of southeast Asia today," Paul Nascimbene of the American Museum of Natural History in New York, told BBC News.
To determine where the amber came from, the scientists chemically fingerprinted it.
They also analysed the wood anatomy of fossilised branches and trunks on the site.
"Fossil wood samples were also recovered in association with the amber, [and they] showed that these samples preserved details of the wood's microstructure, pointing to dipterocarps as the probable source," added Dr Nascimbene.
The team also said that it was able to determine the age of the modern rainforest.
Up until now, many experts used to suggest that this type of tropical rainforest, found today all over the southeast Asia, first originated in the Miocene some 20 or 25 million years ago.
But the recent discovery challenged that idea.
David Grimaldi from the American Museum of Natural History and another co-author told BBC News that the rainforest is at least 60 million years old.
"What we have here from India is the earliest fossil evidence of a modern type of tropical rainforest [of the Dipterocarpaceae family] in Asia," he said.
"Before, we just had no idea to how ancient the dipterocarp forests that occur in southeast Asia today really are; there really was no indication."
Dr Grimaldi explained that one problem with determining the modern rainforest's age was the lack of information - fossil deposits are simply very uncommon in tropical regions.
Amber looks like yellow-brownish rocks"Most of the fossil outcrops are in drier, very eroded areas of the northern hemisphere or southern parts of southern hemisphere, but not so much in the equatorial belt.
"Most of the fossil evidence from tropical South America indicated that rainforests were no later than Miocene, no more than 25 million years old.
"And secondly, people for a century or more had always thought of the tropics as a place where species are evolving very rapidly.
"And perhaps as a result they thought it was a very recent type of ecosystem.
"But in reality, they're like an ancient cauldron - they're very ancient ecosystems, at least ancient on land, at least twice [the age we previously thought]."
3-D specimensBut besides the rainforest's age and India's biogeography, the most astonishing part of the discovery was the huge number of perfectly preserved specimens of insects, most of which have never been seen before.
Unlike other types of amber found in deposits in the north, the Indian amber is much softer. This unique property allowed the scientists to completely dissolve the amber using solvents - toluene and chloroform - and extract the ancient insects, plants and fungi.
"We have complete, three-dimensionally preserved specimens that are 52 million years old and you can handle them almost like living ones," said Dr Rust.
"Of course they are very fragile, but it is still astonishing.
"We have several examples where it is possible to get a complete specimen out. And of course this opens a new dimension in investigations of this material.
Many insects are related to modern and ancient species found in different parts of the worldThe researcher said that this amber deposit was the first important one found in India.
Though this natural yellow-brownish substance is quite widespread all over the world, the best-known amber deposits are in the Dominican Republic, Mexico and the Baltic region, where some 80% of the world's known amber is found.
"There are tonnes of amber [in this Indian deposit], and what is interesting about it is that it was produced in the tropics, the most highly diverse areas in respect to species diversity," said Dr Rust.
"And the fossil record of the terrestrial tropics is not so good, because usually all the organic material gets rotten very quickly."
With tonnes of amber at their disposal, the researcher said his team hoped to uncover many more secrets of the peculiar world that existed millions of years ago.
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Image: The Cambay amber from western India, dating to 52 - 50 million years ago, has one of the earliest records of diverse ants.
David Grimaldi/AMNH image.