Prestosuchus nyassicus (von Huene, 1939) Desojo & Baczko & Rauhut, 2020

Desojo, Julia Brenda, Baczko, María Belén von & Rauhut, Oliver W. M., 2020, Anatomy, taxonomy and phylogenetic relationships of Prestosuchus chiniquensis (Archosauria: Pseudosuchia) from the original collection of von Huene, Middle-Late Triassic of southern Brazil, Palaeontologia Electronica (a 04) 23 (1), pp. 1-55 : 7-8

Prestosuchus nyassicus (von Huene, 1939) , comb. nov.

Lectotype. GPIT /RE/3831/1–21, right articular and fragmentary postcranial skeleton, including vertebrae from all parts of the vertebral column, partial pectoral girdle, partial pelvic girdle, partial fibula.

Paralectotype. GPIT /RE/3832/1–15, probable jugal, sacral and caudal vertebrae, humerus, largely complete pelvic girdle, proximal tibiae .

Horizon and age. Uppermost level of the upper bonebed of the Manda Beds, Anisian, Middle Triassic.

Type locality. Njalila locality, northwestern slope of the Lihandje Mountains, east of Lake Malawi (Lake Nyasa), southwestern Tanzania.

Diagnosis

Prestosuchus nyassicus differs from Prestosuchus chiniquensis in the following derived characters (modified from Lautenschlager and Desojo, 2011): eighth cervical vertebra with additional infrapre- and infrapostzygapophyseal laminae; postacetabular process of the ilium with a pronounced, boss-like lateral protuberance; dorsolateral crest of the ischium short; round protuberances on the midline of the ventral ischial contact.

Remarks

In 1939, von Huene described two fragmentary skeletons from the uppermost part of the Manda Beds of the Ruhuhu basin of Tanzania as a new taxon of “thecodont”, Stagonosuchus nyassicus . First thought to be a stagonolepid (aetosaur), the taxon was later referred to the Rauisuchidae (von Huene, 1956) , but received surprisingly little attention until recently. However, Gebauer (2004) presented a revision of Stagonosuchus nyassicus , redescribing all of the material and presenting several new interpretations of the elements described by von Huene (1939). Recently, Lautenschlager and Desojo (2011) offered additional observations and comments, including a revised diagnosis that included autapomorphic characters of the taxon (see diagnosis).

On the basis of these new data, we evaluated the phylogenetic position of Stagonosuchus nyassicus and found it to be most closely related to the type series of Prestosuchus chiniquensis (see below). As both taxa share numerous, largely apomorphic characters on generic level (see diagnosis of genus), we propose to refer both species to the same genus, Prestosuchus . However, as Prestosuchus nyassicus shows a number of apomorphic characters not seen in Prestosuchus chiniquensis , we retain both taxa as separate species.

A single skull element found with the material was interpreted as a postfrontal by von Huene (1939), but the triradiate shape of this element is unlike any postfrontal found in other archosauromophs (see Nesbitt, 2011). Gebauer (2004) suggested that this element might be a postorbital, which would be more consistent with the triradiate shape. However, there are significant differences with other pseudosuchian postorbitals, in which especially the ventral ramus is usually considerably longer than the other processes, and the ventral ramus and the orbital rim are thickened. Thus, we here tentatively suggest that the element in question might be a partial jugal, but more detailed comparisons would be necessary to clarify its identity.