An Early Cretaceous theropod dinosaur from Brazil sheds light on the cranial evolution of the Abelisauridae

Hussam ZAHER,Diego POL,Rafael DELCOURT,Alberto B. CARVALHO,Bruno A. NAVARRO

doi:10.5852/cr-palevol2020v19a6

Abstract

Abelisaurid theropods dominated the predator role across Gondwana during the Late Cretaceous. They are characterized by highly reduced forelimbs and one of the most specialized cranial morphologies among carnivorous dinosaurs, exemplified by a broad skull, short rostrum, high occipital region, and highly kinetic intramandibular joint, suggestive of a specialized feeding strategy. Late Cretaceous abelisaurids are known from some remarkably complete taxa with well-preserved skulls. However, little is known about the pattern of character transformation that led to their highly modified condition because there are no well-preserved abelisaurids before the Late Cretaceous. Here we report a basal abelisaurid from the Early Cretaceous of Brazil that preserves a complete skull and reveals an early stage in the cranial evolution of the group. It lacks the specialized temporal and mandibular features characteristic of derived abelisaurids, including the kinetic intramandibular joint and knob-like dorsal projection of the parietals.

Highlights

The Early Cretaceous is an interval of over 40 million years that is critical for understanding the latter phases in the evolutionary history of dinosaurs
The scarcity of Early Cretaceous theropods is marked in Gondwanan landmasses, where a diverse assemblage is mainly known from the Late Cretaceous of South America (Novas 1997; Weishampel et al 2004; Novas et al 2013)
Abelisauridae was a dominant clade of ceratosaurian theropods in Gondwana during this period, they were present in Europe (Accarie et al 1995; Ősi & Buffetaut 2011; Tortosa et al 2014)

Summary

INTRODUCTION

The Early Cretaceous is an interval of over 40 million years that is critical for understanding the latter phases in the evolutionary history of dinosaurs. We report a basal abelisaurid from the Early Cretaceous (Barremian-Aptian) of Brazil that represents the first definitive abelisaurid from this critical interval with a complete and wellpreserved skull, mandible, and informative postcranial skeleton.

MATERIAL AND METHODS

Findings

DISCUSSION AND CONCLUSIONS