Gondwanan dinosaurs of India: affinities and palaeobiogeography

Abstract

The record of Indian dinosaurs is now well known and extends from Late Triassic to the terminal Cretaceous. The Indian dinosaurs are based on fragmentary cranial, skeletal and egg material which is a cause of some uncertainty in the analysis of their taxonomic affinities, age and palaeobiogeography. The Indian dinosaurian record starts with the Triassic Maleri Formation, which yields Alwalkeria maleriensis, a coelurosaur. The overlying Dharmaram Formation contains phytosaurs, aetosaurs, plateosaurids and a sphenosuchid. The early Jurassic Kota Formation has yielded numerous bones (cranial and postcranial) of Barapasaurus tagorei, besides semionotid fishes, coelacanths, pleurosaurs, crocodiles and mammals. The Cretaceous dinosaurian record is from sedimentary sequences associated with the Deccan volcanics and is dominated by skeletal remains of titanosaurid sauropods and theropods, such as Indosuchus raptorius and Indosaurus matleyi. The Kallamedu Bone Bed (Ariyalur Formation) has yielded bones and a tooth of Megalosaurus. The cranial and postcranial skeleton of a stegosaur Dravidosaurus blanfordi is known from the Trichinopoly Group. Khosla & Sahni (1995) have classified Indian dinosaur eggs and eggshell fragments into eight new oospecies (in the oofamilies Megaloolithidae and Subtiliolithidae): Megaloolithus cylindricus, M. jabalpurensis, M. mohabeyi, M. baghensis, M. dholiyaensis, M. walpurensis, M. padiyalensis and Subtiliolithus kachchhensis. Besides these Late Cretaceous eggshells, footprints are known from the Bhuj Formation of Early Cretaceous age (Ghevariya & Srikarni, 1990). Coprolites of dinosaurs and (probable) chelonians are known from the Late Cretaceous of Pisdura, and include four categories of ribbed and non-ribbed forms. The palaeobiogeographic analysis of the Indian dinosaurs implies they are part of a cosmopolitan distribution. However, migrations through an earlier Madagascan connection and through island arcs in the Cretaceous (represented by Dras volcanics) and earlier collision arcs and microplates in Late Permian to Cretaceous (represented by northernmost Gondwana fragments of Tibet, Iran, Iraq and Afghanistan) led to an influx of some taxa. These paths of migration are significant in explaining the cosmopolitan character of the Indian biotas and their similarities to Laurasian faunas during the drift of the Indian Plate.