Riojasuchus is an extinct genus of ornithosuchid archosaur from the Late Triassic (Norian) of Argentina. Ornithosuchidae was a widespread family of facultatively bipedal pseudosuchians (crocodilian-line archosaurs) with adaptations for scavenging.[1][2] Riojasuchus is notable as one of the youngest and most complete members of the family. The type and only known species, Riojasuchus tenuisceps, was named and described by José Bonaparte in 1967.[3] It was one of the first of many well-preserved Triassic archosaurs to be discovered in Argentina. The holotype specimen, PVL 3827, was found in the Los Colorados Formation of the Ischigualasto-Villa Unión Basin in northwestern Argentina.[4][5]
The holotype specimen is PVL 3827, consisting of a complete skull and mandibles, as well as a nearly complete postcranial skeleton.[4] Three other specimens are known. PVL 3828 is almost as complete as the holotype, including a nearly complete skull. PVL 3826 consists of articulated vertebrae and limb fragments. PVL 3814 only involves a few fragments of vertebrae, limb bones, and osteoderms.[5]
All four specimens were found close together in the upper section of the Los Colorados Formation.[3] The formation's diverse fossil beds have been radiometrically dated to the mid-Norian stage of the Late Triassic.[6] The fossils are stored in the vertebrate paleontology collection (PVL) at Instituto Miguel Lillo in San Miguel de Tucumán.[4][5]
Riojasuchus and its fossils were initially described in papers by José Bonaparte in 1967[3] and 1972. The skull was redescribed by M. Belén von Baczko, Julia B. Desojo, and Denis Ponce in 2016.[4] The postcranial skeleton was redescribed by von Baczko and Desojo in 2019.[5]
The skull of the type specimen is 25 centimetres (9.8 in) long, and has a large, curved snout and short mandibles.
Riojasuchus is a member of Ornithosuchidae, a family of facultatively bipedal carnivores that were geographically widespread during the Late Triassic.[3] Two other genera, Ornithosuchus and Venaticosuchus, are currently known. The group was originally considered to be related to dinosaurs, before many phylogenetical analysises.[1]