TAPHONOMY AND DEPOSITIONAL SETTING OF THE SHRINGASAURUS INDICUS (ARCHOSAUROMORPHA: ALLOKOTOSAURIA) BONEBED FROM THE MIDDLE TRIASSIC DENWA FORMATION, SATPURA GONDWANA BASIN, INDIA

A bonebed of multiple skeletons of the Triassic horned reptile Shringasaurus indicus was discovered in the upper Denwa Formation, Satpura Gondwana Basin, India. The monotaxic bonebed contains multiple individuals of different ontogenic stages indicating herding behavior by Shringasaurus indicus. The herd was a mixed-sex herd. The adult and sub-adult bones in the bonebed exceed the number of juvenile bones. The distribution of the bones was slightly patchy, bones of different individuals were admixed, and several bones were piled up implying mass mortality. The bonebed occurs in a fine-grained mudrock that is hydraulically incompatible with long-distance transport and concentration by currents. Sedimentary facies analysis indicates that the bonebed accumulated and was buried in a crevasse splay deposit between two ENE-WSW trending channel-fill complexes. The northern channel-fill complex was formed by unidirectional flow with lateral channel migration towards the south and with minor contemporaneous tectonic subsidence. Repeated breaching of the levee by this channel flow led to the incremental development of the crevasse splay deposit. The herd of Shringasaurus indicus, which lived near to the perennial channel, was drowned en masse and the carcasses were trapped within the muddy sediments of the crevasse splay deposit. Apart from a partially articulated skeleton, the rest of the bones were disarticulated but remained associated. The bones show little evidence of post-mortem modifications. With a continuous supply of the sediments through the spillover channels, the bones were buried before complete disarticulation and dispersal had taken place.