Riojasuchus tenuisceps Bonaparte, 1967

Nesbitt, Sterling J., 2011, The Early Evolution Of Archosaurs: Relationships And The Origin Of Major Clades, Bulletin of the American Museum of Natural History 2011 (352), pp. 1-292 : 22

Riojasuchus tenuisceps Bonaparte, 1967

( fig. 8A–B)

AGE: Norian-?Rhaetian, Late Triassic ( Arcucci et al., 2004).

OCCURRENCE: Los Colorados Formation, El Salto, Argentina ( Arcucci et al., 2004).

HOLOTYPE: PVL 3827, complete skull, cervical, dorsal, sacral and caudal vertebrae, scapula, coracoid, humerus, distal portion of the radius and ulna, partial manus, ilium, pubis, femur, tibia, fibula, nearly complete pes.

REFERRED MATERIAL: PVL 3828, nearly complete skull, cervical, dorsal, sacral and caudal vertebrae, scapula, coracoid, humerus, ulna, radius, pubis, ischium, ilium, femur, tibia, fibula, calcaneum; PVL 2826 cervical, dorsal, sacral and caudal vertebrae, coracoids, scapula fragments, humerus, ulna, radius, ilium, femur, and tibia; PVL 3814 vertebrae, humerus, and tibia.

REMARKS: Riojasuchus is represented by nearly all portions of the skeleton. The wellpreserved complete skull was well described by Bonaparte (1971), followed by Sereno (1991a). It is clearly the youngest member of the Ornithosuchidae and apparently represents a late surviving member of the clade.

Sereno (1991a) provided a list of autapomorphies that all differentiate Riojasuchus from Ornithosuchus . However, autapomorphies I, K, and L have a wider distribution. For example, aetosaurs (e.g., Aetosaurus, SMNS 5770) possess a sloping occiput much like that of Riojasuchus .

KEY REFERENCES: Bonaparte, 1967; 1971; Sereno, 1991a.