A new cynodont from the Upper Triassic Los Colorados Formation (Argentina, South America) and the palaeobiogeography of probainognathian cynodonts

LEANDRO GAETANO; FERNANDO ABDALA; FEDERICO SEOANE; AURELIANO TARTAGLIONE; MICHAEL SCHULZ; ALEJANDRO OTERO; JUAN LEARDI; CECILIA APALDETTI; VERÓNICA KRAPOVICKAS; EUGENIO STEIMBACH

Scientific Reports

Springer

Año: 2022

Probainognathia is a derived group of cynodonts which encompass Mammalia as their crown-group. The profuse record of probainognathians from the Carnian of Argentina contrasts with their Norian representation, with only one named species. Here we describe a new probainognathian, Tessellatia bonapartei gen. et sp. nov., from the Norian Los Colorados Formation of the Ischigualasto-Villa Unión Basin of Argentina. The new taxon, represented by a partial cranium with articulated lower jaw, was analyzed through neutron and X-rays micro-tomography (μCT). The high-resolution neutron μCT data allowed the identification of a unique character state combination, including features inaccessible through traditional techniques such as information regarding dental replacement. We constructed the largest phylogenetic data-matrix of non-mammalian cynodonts. The new species and its sister-taxon, the Brazilian Therioherpeton, are recovered as basal Probainognathia, closely related to Mammaliamorpha. The results of the first quantitative paleobiogeographic analysis of non-mammalian cynodonts indicate that probainognathians originated in South Africa with latter dispersions to Brazil where Mammaliamorpha originated. Finally, China is identified as the ancestral area of Mammaliaformes. The new findings add to the knowledge of probainognathian diversity, evolution, and paleobiogeographic history; in particular, adding to the knowledge of the poorly represented Norian cynodonts in the rich fauna of Los Colorados.