Fossils: A new mammal belonging to the docodont group has been discovered

Syed Akbar

Hyderabad:  A new mammal belonging to the docodont group has been discovered from the Kota Formation at Paikasigudem village in Adilabad district.

The fossilised mammal is at least 150 million years old and this is the first time that a docodont mammal has been found from the Southern Hemisphere. Docodont mammals are primitive animals found during the Jurassic period along with dinosaurs and they are considered to be the final line of mammalian old-timers.

Scientists the world over thought that docodonts were present only in North America and England as the remains of several species of docodont mammals were excavated only from these parts in the Northern Hemisphere. The latest discovery showed the presence of such animals in Southern Hemisphere too. "It is now quite clear that docodonts were widely spread across the earth," says GVR Prasad, who discovered the animal remains.

The new animal has been named Gondtherium dattai in honour of the local Gond tribal population. The find from Adilabad is of paramount importance as it testifies to the presence of typical docodont mammals in Gondwanan continents.

The Kota Formation, which dates back to late middle Jurassic period (150 million years ago) and lower Cretaceous period (65 million years), had earlier yielded mammal groups like symmetrodontan and eutriconodontan.

Bulk screen-washing of the clays and mud stones found in Kota Formation produced an isolated mammalian upper premolar. A detailed study of the tooth led to the discovery of the new mammal genius Gondtherium.

The premolar tooth has asymmetrical chewing/biting outline, two labial cusps and other features very similar to the upper premolars of docodont mammals. Detailed comparisons with the upper dentition of various known docodont animals showed that the premolar pattern of the new specimen from Adilabad was similar to Haldanodon, an animal found during the Mesozoic period.

The tooth of Gondtherium dattai differed from the upper molars of all known docodont animals in having labial cusps with diverging tips that are separated by a broad notch. The enamel of the tooth was not preserved as also the roots, but from the broken dorsal surface it appeared that there were probably three roots. The pulp chamber was widely open and had a smooth surface and rounded edges as in permanent teeth.

Docodont mammals were earlier known only from the Upper Triassic, Middle and Upper Jurassic, and Lower Cretaceous deposits of North America and Europe, pointing to a typical Euramerican distribution for this group.

"The associated mammalian study helps us in reconstructing a generalised paleobiogeographic scenario. The more recent discovery of Dyskritodon from the Kota Formation first recorded from the Early Cretaceous of Morocco, represents an example of faunal continuity across India and Africa. The occurrence of closely related mammals in the Jurassic of India and Late Triassic and Early Cretaceous of Africa, as well as Middle and Late Jurassic of Europe points to biogeographic connections between these regions," he points out in his study.

This is not surprising because paleogeographic maps show Europe in close proximity of NW Africa and India adjacent to Africa in the Early/Middle Jurassic. The cosmopolitan distribution of the Kota fauna has also been corroborated by the non-mammalian vertebrate groups like ostracods and charophytes.

Barapasaurus and Kotasaurus, sauropod dinosaurs from the Kota Formation, and the Early Jurassic sauropod Vulcanodon of Zimbabwe appear to be closely related to the Late Triassic sauropod Isanosaurus of Thailand.

"In view of this continuity of mammalian as well as non-mammalian animal remains during the Jurassic and Early Cretaceous across Gondwanan continents, it is predicted that early docodonts might have existed on other southern continents as well," says Prasad.

The possible reasons for not finding Docodonts on the southern continents until now are restricted occurrence of Jurassic continental sequences in this part of the globe; low intensity sampling of the known deposits; and taphonomic (decaying) factors.