Ratan Kar’s research while affiliated with Birbal Sahni Institute of Palaeobotany and other places

Understanding the recovery of life and its radiation after the Permian–Triassic mass extinction event (PTME) that took place around 252.28 ± 0.08 Ma is a fascinating aspect of Earth science studies. In this backdrop, we have undertaken a study of the floral diversity based on plant macrofossils and megaspores from the late Permian and early Triassic sediments of the Gondwana Supergroup from Peninsular India. The early Triassic in Peninsular India is represented by the Panchet FormationPanchet Formation that overlies the Raniganj FormationRaniganj Formation (late Permian). The outcrops of late Permian (Raniganj Formation) and early Triassic (Panchet FormationPanchet Formation) sediments in the Tatapani-Ramkola Coalfield in Chhattisgarh State are exposed along the major rivers and their tributaries that drain the coalfield. The present work has been carried out on a Permian–Triassic section, exposed at a stream cutting (Iria Nala), in the northern part of Tatapani-Ramkola Coalfield. The macrofloral assemblageMacrofloral assemblage of the Raniganj FormationRaniganj Formation (late Permian) from the base of the outcrop is represented by Schizoneura gondwanensis, Glossopteris sp. and Vertebraria sp., whereas the overlying Panchet FormationPanchet Formation (early Triassic) yielded a moderately preserved macrofloral assemblageMacrofloral assemblage represented by Paracalamites sp., Dicroidium hughesii, D. zuberi, Desmiophyllum sp., Glossopteris angustifolia, G. communis, G. indica and scale leaf of glossopteridsGlossopterids. In addition, a megaspore assemblageMegaspore assemblage hitherto unknown from the early Triassic of Tatapani-Ramkola Coalfield is recorded herein that is represented by nine species belonging to seven genera, out of which one species is new.

The genus Dicroidium Gothan, belonging to Corystospermaceae, is characterised by pinnately compound leaves with proximally forked primary rachis. The genus was earlier included under the genus Thinnfeldia Ettingshausen. Dicroidium is the most consistent macrofloral element in the Triassic strata of Southern Hemisphere. The present reassessment deals with the morphotaxonomy and stratigraphic significance of the species of Dicroidium in India. A critical review of the literature reveals that the specimens of Dicroidium described so far from India require reassessment, because same morphotypes have often been placed under different species names and sometimes dissimilar elements have been assigned to the same species. In view of this, a thorough analysis of Indian Dicroidium was undertaken based on fresh collections along with the species described earlier by previous workers. The present reappraisal reveals that the genus in the Triassic of Peninsular India is represented by eight species. These are D. hughesii (Feistmantel) Lele, D. zuberi (Szajnocha) Archangelsky, Dicroidium sp. cf. D. crassinervis (Geintz) Anderson & Anderson, D. townrovii Retallack, D. nidpurensis Bose & Srivastava, D. gopadensis Bose & Srivastava, D. giarensis Pal and Dicroidium sp. In Indian peninsula, appearance of Dicroidium heralds the onset of Triassic sediments belonging to the early Triassic Panchet Formation (Induan). In the younger sequence of Triassic, i.e. during late Triassic Tiki and Parsora formations (Carnian to Norian–Rhaetian), the diversity and species richness of the genus gradually enhanced and Dicroidium foliages became the most predominant component of Triassic macroflora of India. The genus does not occur in strata younger than the Triassic and thereby the total extinction of Dicroidium signifies the end of the Triassic Period.