Thar Desert was once tropical forest, new fossil discovery reveals

Dr Ravi Mishra Vasco-Da-Gama | Updated on April 26, 2018 Published on April 26, 2018

Trace fossils in section at Barmer, western Rajasthan

Western Rajasthan in the present age is well known for the Thar Desert. But this was not the case in the past. Indian researchers have discovered a set of rare wood boring trace fossils in the Barmer region, which reveal that this area was a tropical forest and even had a vast river network 55 million years ago.

A team of researchers from Jai Narain Vyas University, Jodhpur, have found mayfly insect fossils. The rare almond-shaped ‘trace fossils’ of Asthenopodichnium lignorum and J-shaped fossils of Asthenopodichnium lithuanicum have been discovered for the first time in India in the Barmer sandstone formations.

Fossils are preserved remains, impressions or traces of any past living organisms. These are records of evolutionary process. Trace fossils are non-body remains, which indicate the activity or behaviours of organisms such as tracks, trail, impressions, burrows, borings for resting, locomotion and respirations. Mayflies are relatively primitive insects having delicate transparent wings and two or three long filaments on the tail. Mayflies live close to water, where their aquatic larvae develop, whose presence is an indicator of a clean and unpolluted environment.

“These trace fossils are indicators of a fluvial freshwater environment and tropical climate, and clearly endorse that a large part of western Rajasthan was under tropical forest 55 million years ago,” Dr V S Parihar, a member of the research team, told India Science Wire. The results of the study have been published in journal Current Science.

The length of the trace fossils found in the western Rajasthan region range from a few millimetres to three centimetres, and are loosely to tightly packed traces. These were shelter houses of mayfly nymphs or larvae living in a colony in wood logs or wood stems. The trace fossils are well preserved in 10-20-cm thick and about 0.3-1.2-metre long wood logs in fine-grained sandstone of 50 metre thick section.

According to the researchers, these trace fossils and structures are found in clusters of millions of iron rinds preserved in Barmer sandstone formation. This sandstone formation is about 66 to 59.2 million years old (Palaeocene age) – a period just after the extinction of dinosaurs - in western Rajasthan at Gehun hills near Barmer.

Dr S.C. Mathur, senior researcher and team leader explained: "The tropical region around the world has the highest diversity of life, but we know very little about tropical biodiversity in the past. Barmer Basin was a mega bio-diversity region of the world in the Palaeocene time. Our team has discovered many fossils of dinosaurs, fishes, turtles, crocodiles, gastropods and many trace fossils in the last one decade from various sandstone formations of the Cretaceous-Paleocene age from western Rajasthan. These findings tell us that the tropics were full of life and diversity even millions of years ago”.

These trace fossils are significant to ascertain how life started and evolved after the mass extinction of species, including dinosaurs, at the end of the cretaceous period around 65 million years ago. This research also illustrates the evidence of a fluvial freshwater palaeo-environment and tropical palaeo-climate, indicating the presence of a tropical forest and a huge network of rivers.

Scientists say the wood boring trace fossils of mayfly are rare and intact. These findings could help to unfold the past climate changes and track how the mayfly physiologically modified. It will also facilitate understanding how this particular tropical region converted into the present Thar Desert region over time.

The research team included S. C. Mathur, N. S. Shekhawat, S. L. Nama, C. P. Khichi, A. Soni, Saurabh Mathur and V. S. Parihar.

(India Science Wire)

Twitter handle: @Ravimishra1970

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Published on April 26, 2018
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