Reappraisal of the genus Dicroidium Gothan from the Triassic sediments of India

Abstract

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.