Non-marine invertebrate fossils, though rare, are very valuable in geological record as they are susceptible to environmental changes in the terrestrial part of a continent. Important palaeoenvironmental interpretations are made from studies on such fossils which are also helpful for palaeobiogeographic interpretations. Conchostraca, broadly known as ‘estheriids,’ is a paraphyletic term of the order Spinicaudata within Phylum Arthropoda, and is an important terrestrial crustacea (extant ones are known as ‘clam-shrimps’). The Indian fossil conchostraca have been collected from all the major coal basins of India, and the present collection is made from twenty one (21) different localities within the ambit of Indian Gondwana basins. The Indian fauna described herein belongs to five Superfamilies which include fifty seven (57) species, of which fifty two (52) are new. The fauna is, thus, varied and of wide geographic distribution throughout the early Palaeozoic to middle Mesozoic periods in the subcontinent. Several time restricted and environment-indicative taxa found in the Indian collection help in establishing ten biostratigraphic horizons or Estheriid-biozones within the Indian Gondwana sequence. Scanning Electron Microscopy (SEM) is of considerable importance in studies related to ontogenetic changes in chitinous valve taxometry and carapace ornamentation. Field studies on basin analysis (includes 7000 palaeocurrent data) of Raniganj coalfield, the easternmost Gondwana basin, as a test case in the present study, along with tectonic set up of the basin, have enabled unfolding the geological history of the basin development and changes in palaeoslope during the Permo – Triassic (P/T) periods. REE and trace element profiles have been carried out across the undisturbed lithological boundary between Raniganj and Panchet formations as encountered in bore holes drilled in the eastern part of Raniganj coalfield. Samples collected from the borehole cores were fresh and least affected by surface contamination yielded better geochemical results under Neutron Activation Analyses. Biostratigraphic correlation, on the basis of the estheriid biozones established from surface and sub-surface data, enables us to carry out intra- and inter- basinal correlation within the subcontinent. Correlation of these biozones with those of other countries, along with Bivariant Taxometric comparison, suggests proximity of the Indian block with the European plate during P/T transition zone. Height and length of fossil carapaces of Indian and faunae of other countries indicates a striking similarity among some taxa suggesting a circum-Tethyan land and/ or near-shore migratory route for these taxa between the northern and the southern continents of Pangea. All these new data throw fresh light towards palaeogeographic reconstruction of ‘Gondwanaland’. Chances of preservation of such terrestrial deposits of limited lateral extent are always very less compared to continuous marine beds and thus, even in Indian subcontinent, however, their fossil records are scanty and widely separated and more so because of very thick surface weathering zone often as deep as thirty (30m) meter. There are however, some excellent index fossils which help to distinguish the Late Permian and early Triassic faunal assemblages which in turn help to demarcate the Permo-Triassic (P/T) boundary.
Moreover, majority of taxa in this group of fossils appear to be resilient to changes in environment like salinity, temperature, water current and nature of the mud substrate, which in turn caused endemic fossils to appear in the assemblage. The present research shows that India, being palaeo-geographically in a nodal position during the Permo-Triassic period, aided in migration of certain taxa from China, Russia and Germany in the north to Australia and Antarctica in the south, from the northern to the southern halves of Pangaea.
