Vast Amber Deposit from India: New Trove of Fossils Suggests Global Distribution of Tropical Forest Ecosystems in the Eocene
ScienceDaily (Oct. 26, 2010) — A vast new amber deposit in India has yielded 100 fossil spiders, bees, and flies that date to the Early Eocene, or 52-50 million years ago. These arthropods are not unique -- as would be expected on an island (which India was at that time) -- but have close evolutionary relationships with fossils from the Americas, Europe, and Asia. The amber is also the oldest evidence of a tropical broadleaf rainforest in Asia.
This spider was found in the Cambay amber deposit of western India. (Credit: David Grimaldi/AMNH)
Bees, termites, spiders, and flies entombed in a newly-excavated amber deposit are challenging the assumption that India was an isolated island-continent in the Early Eocene, or 52-50 million years ago. Arthropods found in the Cambay deposit from western India are not unique -- as would be expected on an island -- but rather have close evolutionary relationships with fossils from other continents. The amber is also the oldest evidence of a tropical broadleaf rainforest in Asia.
The discovery is published this week in Proceedings of the National Academy of Sciences.
"We know India was isolated, but when and for precisely how long is unclear," says David Grimaldi, curator in the Division of Invertebrate Zoology at the American Museum of Natural History. "The biological evidence in the amber deposit shows that there was some biotic connection."
"The amber shows, similar to an old photo, what life looked like in India just before the collision with the Asian continent," says Jes Rust, professor of Invertebrate Paleontology at the Universität Bonn in Germany. "The insects trapped in the fossil resin cast a new light on the history of the sub-continent."
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Biogeographic and evolutionary implications of a diverse paleobiota in amber from the early Eocene of India
Jes Rust a,1, Hukam Singh b, Rajendra S. Rana c, Tom McCann a, Lacham Singh c, Ken Anderson d, Nivedita Sarkar e, Paul C. Nascimbene f, Frauke Stebner a, Jennifer C. Thomas g, Monica Solórzano Kraemer a,h, Christopher J. Williams i, Michael S. Engel g, Ashok Sahni e,j, and David Grimaldi f,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.
biogeography, arthropoda, eusociality, tropical forests
Footnotes
1To whom correspondence may be addressed. E-mail: jrust@uni-bonn.de orgrimaldi@amnh.org.
Author contributions: J.R. and D.G. designed research; J.R., H.S., R.S.R., T.M., L.S., K.A., N.S., P.C.N., F.S., J.C.T., M.S.-K., C.J.W., M.S.E., A.S., and D.G. performed research; and J.R. and D.G. wrote the paper.
The authors declare no conflict of interest.
*This Direct Submission article had a prearranged editor.
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