The latest Triassic dicynodonts from Gondwana

DOMNANOVICH, NADIA; MARSICANO, CLAUDIA

Cordoba

Congreso; XIX Congeso Argentino de Paleontología y Bioestratigrafía; 2006

The dicynodonts were a very specialized herbivorous synapsids that arose, probably, in the Early Permian. At the end of the Paleozoic, they were the dominant element in the continental tetrapod faunas. Nevertheless, after the Permian-Triassic crisis they were relatively scarce and underwent a modest, second radiation during the Middle-Late Triassic. This radiation was mainly represented by the kannemeyeriiforms, a clade of middle to large size dicynodonts (e.g. King, 1988, 1990). The last representatives of this group are only know from Late Triassic levels of South America (Jachaleria Bonaparte 1971) and North America (Placerias Lucas 1904). Although recently, Thulborn and Turner (2003) mentioned the discovery of remains assigned to a dicynodont from the Early Cretaceous of Australia. Particularly in western Gondwana, the known specimens came from west-central Argentina (Ischigualasto-Villa Unión Basin, La Rioja) and southern Brazil (Paraná Basin, Río Grande do Sul). All know materials was assigned to a single genera, Jachaleria Bonaparte 1971, with two species: J. colorata Bonaparte (1971) from Los Colorados Formation and J. candelariensis Araújo and Gonzaga (1980) from the Caturrita Formation, respectively. The holotype of Jachaleria colorata (PVL 3841) is a poorly preserved specimen but a new nearly complete skull (UNSJ 55) from the same taxon (Martínez et al., 1998), housed in the collections of the Museo de la Universidad Nacional de San Juan, provides new information about J. colorata. When the know diagnoses of J. candelariensis (Araújo and Gonzaga, 1980; Vega-Dias and Schultz, 2004) are evaluated in the light of the new material of J. colorata no differences are found to justify the specific separation of the Brazilian and Argentinean materials. Nevertheless, preliminary analyses comparing the new specimen (UNSJ 55) with the holotype of J. candelariensis suggest the presence of some characters that might be used to differentiate both species as the short preorbital region, the strongly convex snout and the anterior position of the caniniform process of the maxilla in the Argentinean taxon, among others. However, the noticeable resemblance shared between the Argentinean and Brazilian specimens furnishes additional evidence about the close connections between the Ischigualasto-Villa Unión and Paraná basins in Late Triassic times as was previously suggested by other authors (e.g. Langer, 2005a, 2005b)