Problematic Worms and Priapulid-like Fossils from the Nagaur Group, the Marwar Supergroup, Western Rajasthan, India

Abstract

Worm-like problematic megafossils, comparable with priapulids, are reported from the Lower Cambrian Nagaur Formation of the Marwar Supergroup, Western Rajasthan, India. These fossils occur as positive epireliefs on the top surface of siliciclastic sandstone beds in the Dulmera area of Bikaner district, western Rajasthan. Occurrence of these structures is significant, as the fossil bearing strata also exhibit the preservation of trilobite traces and Treptichnus pedum (three-dimensional subhorizontal burrows). The latter is a Precambrian-Cambrian boundary marker fossil, which has a worldwide distribution. Recently, it has been experimentally demonstrated that priapulids (ecdysozoa) or similar organisms are responsible for the construction of treptichnid burrows. Co-occurrence of these body fossils and treptichnid burrows in the same stratigraphic horizon indicate their close relationship and supports the inferences that these organisms are responsible for the formation of T. pedum. It also projects strong evidence demarcating the Precambrian/Cambrian boundary in the Nagaur Group. These faunal remains are considered to be a significant tool in comparative studies of the evolution from invertebrate to vertebrate animals. Detailed study may certainly shed light on different aspects of macroevolution and radiation among animal clades, and the palaeoecology prevailing at the time of the Nagaur Sandstone deposition.