Reassessment of the Middle Triassic rauisuchian archosaurs Ticinosuchus ferox and Stagonosuchus nyassicus

Abstract

The Middle Triassic (Anisian) rauisuchian archosaurs Ticinosuchus ferox and Stagonosuchus nyassicus are two of the earliest representatives of this group and therefore of special importance for our understanding of the evolution and early diversification of Rauisuchia. Both taxa are well preserved and, in the case of the holotype of Ticinosuchus ferox, nearly complete and articulated. However, the original descriptions and recent revisions of the material do not sufficiently cover all aspects of their osteology. We identify new skull elements previously unknown for Ticinosuchus ferox and present new reconstructions of the pectoral and pelvic girdle elements. Vertebral laminae and fossae are described for the first time in both Ticinosuchus ferox and Stagonosuchus nyassicus. Newly recognised character states of Stagonosuchus nyassicus include the presence of additional infraprezygapophyseal and infrapostzygapophyseal laminae in the cervical vertebrae, a hyposphene-hypantrum articulation in the dorsal vertebrae and a fibula with a posteromedial depression. Furthermore, we provide a revised and emended diagnosis for both taxa, including several autapomorphies for Stagonosuchus nyassicus (e.g. a boss-like protuberance on the postacetabular process of the iliac blade and a marked short dorsolateral crest on the proximal ischium). We review the taxonomic status of a further specimen of Ticinosuchus ferox, as well as material related to Stagonosuchus nyassicus from the Manda Beds of Tanzania. Additionally, we discuss the distribution and possible function of rauisuchian characters, such as accessory neural spines in the caudal vertebrae, in these and other rauisuchian taxa.Kurzfassung Aufgrund ihres stratigraphischen Alters sind die beiden Rauisuchier Ticinosuchus ferox und Stagonosuchus nyassicus aus der Mittleren Trias (Anisium) für das Verständnis der Evolution und frühen Diversifikation der Rauisuchier von besonderer Bedeutung. Obwohl beide Taxa gut erhalten sind, und der Holotyp von Ticinosuchus ferox fast vollständig und artikuliert ist, weisen sowohl die Erstbeschreibungen, als auch neuere Bearbeitungen, Lücken auf. Wir beschreiben bisher unbekannte Schädelelemente von Ticinosuchus ferox und präsentieren neue Rekonstruktionen des Schulter-und Beckengürtels. Erstmals beschreiben wir detailliert die Lamina und Fossa der Hals-und Rückenwirbel beider Taxa, sowie neu identifizierte Merkmalen von Stagonosuchus nyassicus. Dazu zählen: Zusätzliche infraprezygapophyseale und infrapostzygapophyseale Lamina in den Halswirbeln, Hyposphen-Hypantrum-Gelenkungen in den Rückenwirbeln und eine charakteristische posteromediale Vertiefung in der Fibula. Desweiteren präsentieren wir eine erweiterte und

New Specimen Sheds Light on the Anatomy and Taxonomy of the Early Late Triassic Dinosauriforms from the Chañares Formation, NW Argentina

“…V: dg) that it is delimited by a medial ridge (Fig. M, V: dmr), resembling the condition in dinosauriforms and poposauroids (Nesbitt, ) and some other loricatans (e.g., Stagonosuchus nyassicus : Lautenschlager and Desojo, ; Prestosuchus chiniquensis : UFRGS‐PV‐0152‐T). The origin of the M .…”

The Sail-Backed Reptile Ctenosauriscus from the Latest Early Triassic of Germany and the Timing and Biogeography of the Early Archosaur Radiation

“…The abundant and diverse archosaur assemblage from the Lifua Member of the Manda Beds of Tanzania [12], [13], [22], [23], [25] has been correlated to Subzone C of the Cynognathus Assemblage Zone of South Africa of late Anisian age [23], [134].…”

The Early Evolution of Rhynchosaurs

“…Subsequently, Huene (1939) considered the holotype of Stenaulorhynchus major [SAM-PK-10653(a)] indistinguishable from the humerus of the suchian archosaur Stagonosuchus nyassicus from the same locality and horizon, and he referred the former bone to the latter species. More recently, Lautenschlager and Desojo (2011) reinterpreted the maxillae and vertebrae of the original referred material of S. stockleyi as belonging to an archosaur rather than a rhynchosaur. The reinterpretation of the maxilla [SAM-PK-10651(d)] as belonging to an archosaur is supported here, but in the case of the vertebrae (SAM-PK-10652), we could not find features that are inconsistent with those present in rhynchosaurs.…”