Wednesday, October 27, 2010

Fossils In Amber From Eocene Cambay Basin India

This story is being covered by a number of science news outlets. Science Daily covers it here. The link to the paper in PNAS is here.

Cambay basin in which these fossils were found is a cratonic rift basin that formed beginning mid-late Cretaceous as India broke away from Africa and then Madagascar and finally from Seychelles. The fossils have been found in near shore deposits rich in lignite and shale which contains fossil wood as well. The graphic below shows the configuration of continents in early Cretaceous.

 The Cambay basin formed along the eastern continental margin of the evolving Indian continent, its orientation following ancient Precambrian mobile belt trends, ancient weak zones of the crust along which fragments of Gondwanaland broke. The figure below shows the position of the Cambay basin among other Indian sedimentary basins.

Source: Geotimes

 After its breakup from Gondwanaland the Indian subcontinent drifted northeastwards as a seemingly isolated block for tens of millions of years  until it slammed into Asia, initial contact beginning perhaps around 50 million years or so.

The preserved insect fossils date from a time just before or at the beginning of contact between India and Asia when there would have been island chains or perhaps the first land bridges between the two continents. They don't show similarities with fauna of Madagascar or Africa the two fragments of Gondwana that India most recently broke away from.  Instead they show similarities with fauna from the Eocene in N. Europe, Asia, to recent Australiaasia  and the Miocene to recent of Americas suggesting faunal exchange between these continents by early Cenozoic times.

Perhaps oceanic currents were favorable in bringing flotsam and jetsam to Indian shores from these continents and along with it an exchange of insect passengers. The faunal similarities from this time period between India and other continents though might be restricted to small animals like insects which could perhaps survive long journeys on rafts. Interesting to speculate whether larger animals groups like reptiles and early mammals from India show some degree of Cretaceous and Early Cenozoic endemism.

The amber in which these fossils insects are entombed has been shown to be chemically similar to Dipterocarpaceae, a family of hardwood trees, implying that these types of broad leaf forests were present during the early Eocene and evolved perhaps even earlier.

The Early Cenozoic was a period of global warm climate and the evolutionary radiation of several groups of social insects took place during this time. The variety of insect fossils preserved in the Cambay shale reflects this diversification.

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