Cranial Anatomy and Palaeoneurology of the Archosaur Riojasuchus tenuisceps from the Los Colorados Formation, La Rioja, Argentina.

Maria Belen Von Baczko,Julia Brenda Desojo,Andrew A Farke

doi:10.1371/journal.pone.0148575

Maria Belen Von Baczko, Julia Brenda Desojo + Show 1 more

Open Access

https://doi.org/10.1371/journal.pone.0148575

Copy DOI

Abstract

Riojasuchus tenuisceps Bonaparte 1967 is currently known from four specimens, including two complete skulls, collected in the late 1960s from the upper levels of the Los Colorados Formation (Late Triassic), La Rioja, Argentina. Computed tomography (CT) scans of the skulls of the holotype and a referred specimen of Riojasuchus tenuisceps and the repreparation of the latter allows recognition of new features for a detailed analysis of its cranial anatomy and its comparison with a wide variety of other archosauriform taxa. The diagnosis of Riojasuchus tenuisceps is emended and two autapomorphies are identified on the skull: (1) a deep antorbital fossa with its anterior and ventral edges almost coinciding with the same edges of the maxilla itself and (2) a suborbital fenestra equal in size to the palatine-pterygoid fenestra. Also, the first digital 3D reconstruction of the encephalon of Riojasuchus tenuisceps was carried out to study its neuroanatomy, showing a shape and cranial nerve disposition consistent to that of other pseudosuchians.

Highlights

Ornithosuchidae is a clade of pseudosuchian archosaurs known from Upper Triassic continental beds along with aetosaurs, gracilisuchids, “rauisuchians”, and basal crocodylomorphs [1, 2]
On the endocast of Riojasuchus tenuisceps, we identified the exit for the olfactory nerves on the anterior end of the anterior brain, the trigeminal nerve (CN V) exiting laterally through a single foramen, the hypophysis on the ventral region of the anterior brain, and the base of the internal carotids arteries exiting from the ventral edge of the hypophysis (Fig 7;Olf, CN V, Hy, Inc)
A better understanding of the anatomy of Riojasuchus tenuisceps, one of the most completely preserved species of this clade, will shed light on the interrelationships of Ornithosuchidae as well as their phylogenetic relationship within Archosauria. In this contribution we reexamined the skull of the holotype and referred material of Riojasuchus tenuisceps and presented a detailed redescription of its cranial anatomy, which was previously studied by Bonaparte over 40 years ago [6, 17]

Summary

Introduction

Ornithosuchidae is a clade of pseudosuchian archosaurs known from Upper Triassic continental beds along with aetosaurs, gracilisuchids, “rauisuchians”, and basal crocodylomorphs [1, 2]. Ornithosuchids are terrestrial quadrupedal carnivorous archosaurs with sizes ranging from 2 to 4 m. They have distinctive features such as a strongly downturned premaxilla, a two-tooth diastema between the premaxilla and maxilla, the lower jaws shorter than the skull, the presence of a palatine-pterygoid fenestra, and a unique “crocodile-reversed” ankle articulation, only known in this group, which consists of a tarsal articulation with a ventral concavity on the astragalus and a convexity on the calcaneum [3,4,5]. The first two are known from the Ischigualasto-Villa Union Basin, La Rioja, Argentina, and the latter from the Lossiemouth Sandstones Formation (late Carnian–early Norian [9]), Moray, Scotland.

Methods

Results

Conclusion