A New Late Cretaceous Abelisaurid Species from La Rioja Province, Northwestern Argentina

Abstract

Abelisauridae is a group of ceratosaurian theropods that thrived mainly in Gondwana during the Cretaceous. Their fossil record is currently represented by more than 25 species, and their most complete and abundant records are from the Argentinean Patagonia. Outside Patagonia, the record of named Argentinean ceratosaurians has been limited to the Cretaceous of the Salta Province, with the noasaurid Noasaurus–represented by a fragmentary skeleton–and the brachyrostran abelisaurid Guemesia–represented by a nearly complete braincase and partial skull roof–. Here, we report a new abelisaurid theropod specimen (CRILAR-Pv 506) from the Late Cretaceous of La Rioja Province, northwestern Argentina. It was found at the Tama locality, in outcrops of the Campanian Los Llanos Formation, and associated with titanosaurian sauropod remains. The new abelisaurid specimen is represented by a first dorsal centrum, a second dorsal vertebra, a partial sacrum, left ilium, pubis and ischium, and other indeterminate elements. A unique combination of character states led us to propose the new genus and species Vitosaura colozacani. Phylogenetic analyses found Vitosaura either as a non-brachyrostran abelisaurid, closely related to Indo-Malagasy species in some trees, or a non-carnotaurinin furileusaurian. However, the interrelationships among abelisaurids are poorly supported. Our comparisons confirm the presence of abelisaurids in the Los Llanos Formation and this is the first named theropod taxon in the Cretaceous of La Rioja Province.