CYNODONTIA Owen 1861

Oliveira, Téo Veiga De, Soares, Marina Bento & Schultz, Cesar Leandro, 2010, 2382, Zootaxa 2382, pp. 1-71 : 6-7

CYNODONTIA Owen 1861

EUCYNODONTIA Kemp 1982

TRUCIDOCYNODON gen. nov.

Type species. Trucidocynodon riograndensis sp. nov.

Etymology. From the Latin, “ trucido ” meaning “to kill cruelly”, regarding to its conspicuous specializations to carnivory; “cynodon” refers to the clade Cynodontia .

Distribution and Age. Sequence Santa Maria 2 (upper half of Santa Maria Formation), from Rhynchosaur Cenozone (sensu Schultz et al. 2000), in a stratigraphic level with great abundance of the traversodontid Exaeretodon riograndensis . Carnian in age (by the presence of hyperodapedontid rhynchosaurs); the fossiliferous outcrop is named “Sítio Janner” (coordinates 29°40’45”S / 53°17’34”W), Agudo Municipality (approximately 200 km east from Porto Alegre), Rio Grande do Sul State, Brazil ( Fig. 2).

Generic diagnosis. As for the species, by the monotipy of the genus.

Trucidocynodon riograndensis sp. nov.

Etymology. The specific word “ riograndensis ” refers to Rio Grande do Sul State, where the fossil was found.

Holotype. UFRGS PV-1051 - T; an almost complete specimen in which are preserved the skull, the mandible, thirty two pre-sacral vertebrae (probably the whole series), five sacral vertebrae, some caudal vertebrae and several haemapophyses (associated to the corresponding vertebrae or disarticulated), complete pectoral girdle, almost complete right forelimb (lacking only some metacarpals and phalanges), left humerus, ulna, and fragment of the radius, complete pelvic girdle, the almost complete right hind limb (lacking some metatarsals and phalanges), left femur, three fragments probably from left tibia and fibula, fourteen disarticulated metapodials and phalanges (probably from the left foot), and several ribs (some associated with the corresponding vertebrae and others disarticulated and fragmented).

Paratypes. UFRGS PV-1053 -T, right scapula, humerus, radius and ulna; UFRGS PV-1069 -T, two posterior trunk vertebrae, an?anterior/?middle trunk vertebra, a vertebra of uncertain position and some ribs fragments; UFRGS PV-1070 -T, a right tibia lacking its distal end; UFRGS PV-1071 -T, a partial right ulna probably from a young individual due to its shorter length and its less ossified nature in olecraneal region.

Specific diagnosis. Eucynodont with the combination of the following characteristics: four upper and three lower incisors, all bearing serrations in their distal margin; very long upper and lower serrated canines; serrated sectorial postcanines with posteriorly directed cusps mesiodistally aligned; preorbital and postorbital portions of the skull subequal in length; short secondary osseous palate (reaching only the half-length of the postcanine tooth row); absence of foramina for internal carotids in parabasisphenoid; paracanine fossae dorsally open; extensively ossified orbitosphenoid; prootic partially flooring the cavum epiptericum; postorbital covering dorsally the jugal in the ventral margin of orbit; posterior opening of the post-temporal foramen between tabular and squamosal; open pterygoparoccipital foramen; jugular foramen and fenestra rotunda confluent; hypoglossal foramina near to the jugular foramen inside a jugular fossa; large dentary, almost reaching the articular region; reduced post-dentary bones; thirty-two pre-sacral vertebrae; axis with a very long and slender neural spine; posterior presacrals with “lumbar-like” anatomy; middle and distal caudals progressively reduced; ribs without costal plates; short coracoidal plate (relative to the scapula length); long acromion; anteroposteriorly short interclavicle, as long as wide; slender humerus, with not greatly expanded extremities; long olecranon process; preacetabular portion of the iliac blade well developed; postacetabular portion of the iliac blade not very reduced; very large obturator foramen; overall morphology of the astragalocalcaneum resembling that of the cynodont Diademodon and the therocephalian Bauria . From these features the only that seems autapomorphic for T. riograndensis is the postorbital overlapping the jugal in the orbital margin, whereas the remaining characters are distributed also in several other cynodonts.