First record of vertebrates (Actinopterygii, Pseudobeaconiidae) from the Mollar Formation (lower Middle Triassic) of the Cuyana rift basin, Argentina

Abstract

We present a new record of Actinopterygii from continental Triassic rocks from southern South America, Argentina. The material provenance is the Mollar Formation, Santa Clara subbasin, Cuyana rift basin. We studied three specimens preserved in black finely laminated mudstones with different grades of preservation, most of them incomplete but articulated or in casts. These Actinopterygii specimens have been identified as members of the Pseudobeaconiidae family based on their unique combination of diagnostic characters. Pseudobeaconiidae is endemic to southwestern Gondwanan lacustrine settings and in Argentina is restricted to the Ischigualasto-Villa Unión and Cuyana rift basins, being the fishes reported here the first vertebrate remains from the Mollar Formation. Considering Anisian age previously obtained for the overlying Santa Clara Abajo Formation, the fish remains reported here could represent early Anisian or older times, extending the biochron of Pseudobeaconiidae some Myr back. In this context, we revised fish remains from the Middle-to-Upper Triassic Estratos El Bordo unit, in northern Chile, previously assigned to Pseudobeaconiidae, and reassign them as cf. Pseudobeaconiidae because the morphological characters observed hinder the confirmation of most of the diagnostic characters of the family. Further exhaustive preparation of the Mollar Formation material will allow more accurate taxonomic assignments, for example, if these specimens represent a new species of the family Pseudobeaconiidae.