A new horned and long-necked herbivorous stem-archosaur from the Middle Triassic of India

Saswati Bandyopadhyay,Saradee Sengupta,Martín D. Ezcurra

doi:10.1038/s41598-017-08658-8

Abstract

The early evolution of archosauromorphs (bird- and crocodile-line archosaurs and stem-archosaurs) represents an important case of adaptive radiation that occurred in the aftermath of the Permo-Triassic mass extinction. Here we enrich the early archosauromorph record with the description of a moderately large (3–4 m in total length), herbivorous new allokotosaurian, Shringasaurus indicus, from the early Middle Triassic of India. The most striking feature of Shringasaurus indicus is the presence of a pair of large supraorbital horns that resemble those of some ceratopsid dinosaurs. The presence of horns in the new species is dimorphic and, as occurs in horned extant bovid mammals, these structures were probably sexually selected and used as weapons in intraspecific combats. The relatively large size and unusual anatomy of Shringasaurus indicus broadens the morphological diversity of Early–Middle Triassic tetrapods and complements the understanding of the evolutionary mechanisms involved in the early archosauromorph diversification.

Highlights

The evolutionary radiation of archosauromorphs in the aftermath of the catastrophic Permo-Triassic mass extinction (~252 Ma) contributed to reshape Mesozoic terrestrial ecosystems and lead to the dominance of dinosaurs[1, 2]
The holotype and referred specimens of Shringasaurus indicus have been collected from the Denwa Formation of the Satpura Gondwana Basin[9] (Fig. 1)
The most striking feature of Shringasaurus indicus is its pair of large supraorbital horns (Figs 2 and 3)

Summary

Introduction

The evolutionary radiation of archosauromorphs (archosaurs – crocodylians and dinosaurs – and several extinct stem-clades) in the aftermath of the catastrophic Permo-Triassic mass extinction (~252 Ma) contributed to reshape Mesozoic terrestrial ecosystems and lead to the dominance of dinosaurs[1, 2]. As part of the outstanding diversification of dinosaurs, multiple theropods and ornithischians (e.g. ceratosaurians, oviraptorosaurians, hadrosaurids, ceratopsids) developed elaborate cranial structures, including bony weapons and ornaments[3,4,5,6,7]. The presence of horns in Shringasaurus indicus is dimorphic and as in horned extant mammals, these structures were probably used as weapons in intrasexual combats driven by sexual selection[8]. Shringasaurus indicus expands the ecomorphotypes recorded during the early diversification of archosauromorphs and shows that morphologies driven by sexual selection were involved in this macroevolutionary process

Methods

Results

Conclusion