A new early‐diverging probainognathian cynodont and a revision of the occurrence of cf. Aleodon from the Chañares Formation, northwestern Argentina: New clues on the faunistic composition of the latest Middle–?earliest Late Triassic Tarjadia Assemblage Zone

Abstract

The Chañares Formation (Ischigualasto-Villa Union Basin) is worldwideknown by its exquisitely preserved fossil record of latest Middle-to-early LateTriassic tetrapods, including erpetosuchids, “rauisuchians,” proterochampsids,gracilisuchids, dinosauromorphs, pterosauromorphs, kannemeyeriiform dicynodonts,and traversodontid, chiniquodontid and probainognathid cynodonts,coming from the Tarjadia (bottom) and Massetognathus-Chanaresuchus (top)Assemblage Zones of its lower member. Regarding cynodonts, most of its profuseknowledge comes from the traditional layers discovered by Alfred Romer and histeam in the 1960s that are now enclosed in the Massetognathus-ChanaresuchusAssemblage Zone (AZ). In this contribution we focus our study on the probainognathiancynodonts discovered in levels of the Tarjadia Assemblage Zone. Wedescribe a new chiniquodontid cynodont with transversely broad postcanine teeth(Riojanodon nenoi gen. et sp. nov.) which is related to the genus Aleodon. In addition,the specimen CRILAR-Pv 567 previously referred to cf. Aleodon is heredescribed, compared, and included in a phylogenetic analysis. It is considered asan indeterminate Aleodontinae nov., a clade here proposed to included chiniquodontidswith transversely broad upper and lower postcanines, by having a cuspidatedsectorial labial margin and a lingual platform that is twice broader than a lingual cingulum. Cromptodon mamiferoides, from the Cerro de Las Cabras Formation(Cuyo Basin), was also included in the phylogenetic analysis and recoveredas an Aleodontinae. The new cynodont and the record of Aleodontinae indet. reinforcethe faunal differentiation between the Tarjadia and Massetognathus-ChanaresuchusAssemblage Zones, in the lower member of the Chañares Formation, andinform on the diverse chiniquodontid clade with both sectorial and transverselybroad postcanine teeth.