Micro‐ <scp>CT</scp> informed cranial anatomy of the early rhynchosaur <i>Howesia browni</i> , with implications for rhynchosaur skull evolution

Abstract

Abstract Rhynchosaurs are unusual archosauromorph reptiles that lived between the Induan and early Norian (Early to early Late Triassic). They are characterized by their stocky build and broad skull with a beak‐like premaxilla. This rather charismatic configuration is most clearly expressed in Late Triassic hyperodapedontine rhynchosaurids. However, the exact sequence in which morphological traits were acquired early in their evolution, leading to this body plan, remains incompletely resolved. Here, we present two new skulls of the early rhynchosaur Howesia browni , one of which is virtually completely preserved and analysed using high‐resolution micro‐computed tomography. The specimens derive from the Trirachodon ‐ Kannemeyeria Subzone of the Cynognathus Assemblage Zone in South Africa (early Olenekian to early Anisian, Early to earliest Middle Triassic), which was previously considered to harbour three distinct early rhynchosaur taxa. On comparison two of the species are conspecific, with Eohyosaurus wolvaardti Butler et al . 2015 representing a junior synonym of Howesia browni Broom 1905. The new cranial information for Howesia browni corroborates that its skull morphology shows a distinctly intermediate condition between that of the non‐rhynchosaurid rhynchosaur Mesosuchus browni and rhynchosaurids, sharing with the latter among other characteristics a beak‐like premaxilla, marginal tooth plates, and an ‘anguli ori crest’. These findings provide the impetus for a refined review of the cranial evolution of Rhynchosauria. In contrast to other early archosauromorphs, rhynchosaurs exhibit a clear trend in their cranial evolution. This is likely to be related to their unique feeding strategy, which drove the evolution of an increasingly shortened and widened skull.