The tetrapod assemblage for the earliest Cretaceous of the Neuquina Basin

GALLINA, PABLO ARIEL; CANALE JUAN IGNACIO; APESTEGUÍA, SEBASTIÁN; CARBALLIDO, JOSE LUIS; GARDERES, JUAN PABLO; RIGUETTI, FACUNDO

Mendoza

Jornada; 34 Jornadas Argentinas de Paleontología de Vertebrados; 2021

In 2004, H. Leanza and colleagues identified six tetrapod assemblages for the Cretaceous of the Neuquina Basin, being the earliest the Amargan assemblage (Barremian–Early Aptian), considered as representing late Pangean fauna. At that time, no fossil vertebrates were yet found from the earlier Bajada Colorada and Mulichinco formations. Along the last decade both units have been enriching our knowledge on the earliest Cretaceous dinosaurian fauna. Then we consider it is time to propose a new tetrapod assemblage, the Bajadan assemblage, mainly represented by the combination of both formations. This assemblage groups tetrapods recovered from units deposited by Berriasian–Early Hauterivian times, as part of thelower and middle Mendoza Group, underneath the Coihuequical unconformity. So far, its content is understood as characterized by the co-occurrence of globally distributed clades of dinosaurs as originated previous to the Pangean spread in Laurasia and Gondwana by Late Jurassic times (i.e., neosauropods, basal neotetanurans and neoceratosaurian theropods, eurypodan and basal iguanodontian ornithischians), devoid of suprageneric Gondwanan endemisms. The Bajadan assem- blage thus includes flagellicaudatan (Diplodocidae, Dicraeosauridae) and basal titanosaurian sauropods; abelisauroid cer- atosaurian, megalosauroid, and carcharodontosaurid tetanuran theropods; and thyreophoran (either a eurypodan form or a new lineage), as well as basal iguanodontian ornithischians. Although still solely represented by dinosaurian components, the potential of preservation of the Bajada Colorada Formation, with well-preserved remains of two meters-long theropods, allows the possibility of finding other small tetrapod components in the future. The Bajadan fauna shows strong similari- ties with the Late Jurassic-earliest Cretaceous African fauna.