[D] Austroraptor cabazai [sG] [T]
Novas, Pol, Canale, Porfiri and Calvo 2008
Cretaceous Late Campanian Maastrichtian
Saurischia Theropoda Tetanurae Coelurosauria Maniraptora Unenlagiinae
Allen Formation, Bajo de Santa Rosa, approximately 90 km southwest of Lamarque town, Rio Negro Province, Argentina
5 to 6.5 meters long (16.5 to 21 feet)
Abstract: Fossils of a predatory dinosaur provide novel information about the evolution of unenlagiines, a poorly known group of dromaeosaurid theropods from Gondwana. The new dinosaur is the largest dromaeosaurid yet discovered in the Southern Hemisphere and depicts bizarre cranial and postcranial features. Its long and low snout bears numerous, small-sized conical teeth, a condition resembling spinosaurid theropods. Its short forearms depart from the characteristically long-armed condition of all dromaeosaurids and their close avian relatives. The new discovery amplifies the range of morphological disparity among unenlagiines, demonstrating that by the end of the Cretaceous this clade included large, short-armed forms alongside crow-sized, long-armed, possibly flying representatives. The new dinosaur is the youngest record of dromaeosaurids from Gondwana and represents a previously unrecognized lineage of large predators in Late Cretaceous dinosaur faunas mainly dominated by abelisaurid theropods.
Holotype: Specimen number MML-195 consists of right frontal and postorbital, lacrimals, maxillae and dentaries with teeth, right surangular and prearticular, cervicals 3, 5, 6, 7 and 8, dorsals 2 and 4, isolated ribs and gastralia, right humerus, manual ungual of digit III, left pubic shaft, left femur, and right tibia, astragalus, calcaneum, metatarsal III and pedal phalanges I-2, II-2, III-4 and IV-2.
Etymology: Austroraptor, from austral in reference to southern South America, and raptor, thief; and cabazai, in honour to the late Héctor Cabaza, founder of the Museo Municipal de Lamarque.
Diagnosis: A large dromaeosaurid with the following combination of characters that distinguish it from other members of this group (autapomorphies marked with an asterisk): lacrimal highly pneumatized, with descending process strongly curved rostraly, and caudal process flaring out horizontally above orbit (differing from Laurasian dromaeosaurids, but unknown for other unenlagiines); postorbital lacking dorsomedial process for articulation with the frontal, and with squamosal process extremely reduced (differing from Laurasian dromaeosaurids, but unknown for other unenlagiines); maxillary and dentary teeth small, conical-shaped, devoid of serrations and flutted (as in Buitreraptor); humerus short, representing slightly less than 50 per cent of femur length (a smaller ratio than in other dromaeosaurids and paravians); pedal phalanx II-2 transversely narrow, contrasting with the extremely robust phalanx IV-2 (differing from other dromaeosaurids, including unenlagines, but resembling the condition of advanced troodontids).