Two city-based palaeontologists are studying molluscan fossils from the Miocene Epoch (first geological epoch of the Neogene period and extends from about 23.03 to 5.333 million years ago) found in Kutch, Gujarat.
Vidyadhar Borkar, visiting faculty in the postgraduate section of the department of Geology in Fergusson College, Pune and Kantimati Kulkarni, a senior scientist of Agharkar Research Institute, Pune found fossils of Dosinisca from sedimentary rocks, which were formed 20 million years ago in the Abdasa tehsil of Kutch.
The fossil molluscs occurring in the sedimentary rocks of Sindh and Baluchistan provinces of Pakistan, formed 5.3 million years ago, were studied by Ernest Vredenburg, noted palaeontologist with the Geological Survey of India. He had published the findings of his study 90 years ago. The duo found that certain clams described by Vredenburg under the name of some other genus were in reality species of bivalve Dosinisca.
During early part of Miocene Epoch, vast expanses in Kathiawar, Kutch and Sindh were inundated by marine waters as a result of marine transgression around 20 million years ago.
The two scientists have already established in a research communique published earlier, that certain marine animals of the biota, which flourished in this temporary epicontinental sea (a usually large, shallow sea that usually projects inland into a continent), had migrated up to the northwest of Australia at that time through the East Indies and the Timor island. At about the same time, the last phase of uplifting of the Himalayas was completed.
Thousands of tonnes of sediment that was being deposited at the bottom of oceanic waters which intervened between the Eurasian continent to the north and the Indian peninsula to the south was uplifted and transformed into the loftiest folded mountain range. The habitat of the biota which existed there started shrinking. Very existence of hundreds of genera which merrily thrived there was in jeopardy. Migrating to north was not possible as there was barrier in the form of newly formed Himalayas. To avoid the threat of getting extinct, certain genera managed to migrate towards the East Indies. In the course of time, their descendants slowly migrated to Indopacific region. In the light of this information, it transpires that the genus Dosinisca evolved in the temporary sea which resulted from the marine transgression in early Miocene times in Kutch.
Clams belonging to the genus Dosinisca thrive in the marine waters around New Zealand, Australia and Japan, included in the Indopacific Region. The generic epithet Dosinisca was instituted by William Dall in 1902. In those olden days no information of fossils of this genus was available, and it was taken for granted that this is just a modern genus, and does not have any antiquity. However, Dr Otuka subsequently found fossils of this clam genus in certain rocks of Japan deposited during the Pleistocene epoch (2.5 million years). It was presumed that Dosinisca originated in the Indopacific Region, its antiquity being just 2.5 million years. The research communique describing fossils of Dosiniscafrom Kachchh and discussing their significance was published in the latest issue of a scientific periodical viz.Journal of Earth System Science published by the Indian Science Academy.