Postcranial anatomy and osteoderm histology of Riojasuchus tenuisceps and a phylogenetic update on Ornithosuchidae (Archosauria, Pseudosuchia)

VON BACZKO, M. BELÉN; DESOJO, JULIA B; PONCE, DENIS

JOURNAL OF VERTEBRATE PALEONTOLOGY

SOC VERTEBRATE PALEONTOLOGY

Lugar: Lawrence; Año: 2019

0272-4634

Ornithosuchidae is a group of terrestrial quadrupedal pseudosuchianarchosaurs from the Late Triassic of South America and Europe. Riojasuchus tenuisceps is arguably one of the best representative species of this clade because it comprises very well preserved three-dimensional specimens with almost complete skeletons. However, R. tenuisceps was originally described 50 years ago, only in comparison with Ornithosuchus woodwardi and their affinities were strongly discussed. Here we provide a detailed description of the postcranial skeleton of R. tenuisceps, which showed several remarkable features within pseudosuchians. When a wide spectrum of pseudosuchian archosaurs is considered, the alleged character that linked ornithosuchids with dinosaurs resulted in convergencies and some were also registered in other pseudosuchian groups as well. R. tenuisceps also provided crucial information about the ?crocodile-reversed? tarsus, which is a unique feature of ornithosuchids but was not completely preserved in O. woodwardi and unknown in Venaticosuchus rusconii. In addition, the first histological analysis of its cervical and dorsal osteoderms was carried out as well, in order to test the utility of these structures as skeletochronological tools. Finally, the phylogenetic context of Ornithosuchidae is discussed based on the latest phylogenetic studies developed, which showed their close affinity with Erpetosuchidae.