A DICYNODONT THERAPSID IN LA PLATA MUSEUM?S COLLECTION: REDISCOVERY OF AN HISTORICAL SPECIMEN FROM THE MIDDLE-LATE TRIASSIC PUESTO VIEJO GROUP (MENDOZA PROVINCE, ARGENTINA)

J.A. ESCOBAR; AGUSTIN GUILLERMO MARTINELLI; FONSECA,P.H.; J.B. DESOJO

Santa Maria, Brasil

Simposio; Reuniao Anual Regional da Sociedade Brasileira de Paleontologia; 2019

universidade Federal de Santa Maria

The Middle-Late Triassic Puesto Viejo Group (San Rafael, Mendoza Province,Argentina) comprises a sequence of volcaniclastic rocks, divided from base to top in theQuebrada de los Fósiles and the Río Seco de la Quebrada formations. Between 1962 and1963, Emilio González Díaz found the first therapsid remains of the Group, including adicynodont skull and elements of cynodonts, figured in 1966 and deposited in the Museode La Plata. Later on, additional specimens were recovered from the same unit by José F.Bonaparte (deposited in the Instituto Miguel Lillo, Tucumán province), and HumbertoLagiglia (housed in the Museo de Historia Natural de San Rafael, Mendoza province).Over the years, several therapsid species were recognized in the Puesto Viejo Group,including the dicynodonts ?Kannemeyeria? argentinensis and Vinceria vieja, and thecynodonts Pascualgnathus polanski, Cynognathus crateronotus, and Diademodontetragonus. However, the fossils collected by González Díaz have been lost of sight andvirtually ignored from most of the literature of Triassic fauna, and the exact composition,procedence and institutional location of them remained unclear. Here, we report theidentification of one of these specimens, during a recent revision of the VertebratePaleontology Collection in La Plata Museum, thanks to the photograph published in 1966.The specimen (previously without collection number) is now catalogued as MLP-Pv 65-VI-18-3, and consists of a partial skull with both mandibular rami and part of the cervicalregion, heavily impregnated with a dark oxide coat. Although it is currently underpreparation, some initial comparisons can be made. As ?Kannemeyeria? argentinensisand Vinceria vieja, MLP-Pv 65-VI-18-3 is a dicynodont with ventrally directedcaniniform process of the maxilla bearing a tusk, and squamosals strongly projectedbackward (beyond the level of the occiput), with a concave dorsal border in occipitalview. Notably, the anterior palatal ridges are exposed in lateral view, as also seen inSangusaurus parringtoni (Middle Triassic Manda Beds, Tanzania) and Ischigualastiajenseni (Late Triassic Ischigualasto Formation, Argentina), but not in Puesto Viejo´sdicynodonts. An exhaustive anatomical description and direct comparisons with theknown dicynodont taxa are needed to test if this specimen represents a new morphotype.[CONICET]