Triassic flora of India-a transition

Abstract

Extensive floral modifications occurred from Late Palaeozoic to Triassic (Early Mesozoic) Period. Differentiation of Permian and Triassic strata in the Indian subcontinent has been done mostly on lithological, palaeontological and palaeobotanical grounds, but recent investigations on Triassic succession in the Damodar Basin (Panchet Formation), South Rewa Basin (Tiki and Parsora formations), Satpura Basin (Mahadeva Formation) and Pranhita-Godavari Basin (Maleri Formation) have demonstrated gradual changes in palaeofloristics from Early Triassic to Late Triassic. The concept that there was a sudden change in the composition of megaflora from the Late Palaeozoic to Early Triassic reflecting a floral break is modified in the light of palaeofloral data accumulated from various Triassic formations.

In Peninsular India, the megaflora of Late Permian Period is usually dominated by glossopterids and their representative taxon Glossopteris continued further in Permo-Triassic contact associated with some newly emerged forms like the genus Dicroidium, which dominated the vegetation and thrived for nearly 30 million years. In the early part of Triassic, Dicroidium appeared in a very low frequency in association of Lepidopteris but towards the

mid-part of Triassic it exhibited overwhelming dominance and superseded the Glossopteris flora. As a result the seed-bearing plants possessing pinnate leaves appeared on the floristic scene and lasted throughout the Triassic time. They started declining in the Late Triassic giving way to the cycadean and coniferous forms which later constituted a considerable part of plant community during Jurassic-Cretaceous period. Dicroidium, its associates, and the seed taxon Savitrispermum, which were prolifically represented in the Gondwana continents during Triassic, vanished out. Pterophyllum, Pagiophyllum and Elatocladus were represented in abundance during Late Triassic, whereas the pteridospermous forms registered a decline. The presence of zamoid seed cones and archegoniate seeds became most distinguishing feature for the Late Triassic floral deposits. Gymnosperms were the main components of the flora associated with some lower plant groups. Seed plant groups attained potential value in defining the floral regions of this period. Thus, the Early Mesozoic flora contained new taxa, as well as those continuing from the Palaeozoic times. Systematic analysis has now shown that the transition from Permian-Early Triassic-Late Triassic was a gradual one.