A New Lagerpetid Dinosauromorph from the Late Triassic of Argentina

Martínez, R. N., Apaldetti, C., Correa, G. A., and D. Abelín. 2015. A Norian lagerpetid dinosauromorph from the Quebrada del Barro Formation, northwestern Argentina. Ameghiniana (future issue) doi:10.5710/AMGH.21.06.2015.2894

Abstract: The early evolution of Ornithodira, the clade that includes pterosaurs and dinosaurs, is poorly known. Until a decade ago, the basal radiation of Dinosauromorpha, the clade including dinosaurs and birds, was poorly understood because of a scarce of fossil record, which was restricted to specimens known of the Ladinian Chañares Formation from Argentina. In the last years the discovery of several non-dinosaurian dinosauromorphs dramatically expanded this record and also demonstrated that this group—previously restricted to the Middle Triassic—persisted at least well into the Norian. Although Norian non-dinosaurian dinosauromorphs have been reported from several places around the world, the only known Norian non-dinosauriform dinosauromorphs—Dromomeron romeri and Dromomeron gregorii—come from North America. We report here the first record from the Southern Hemisphere of a non-dinosauriform dinosauromorph, Dromomeron gigas sp. nov., from the Norian Quebrada del Barro Formation, northwestern Argentina. A phylogenetic analysis recovers Dromomeron gigas nested into the monophyletic group Lagerpetidae, and as the sister taxon to Dromomeron romeri. The inclusion of D. gigas within Lagerpetidae suggests that body size increased in this lineage over time, as was previously demonstrated for Dinosauriformes as a whole, and that lagerpetids reached a larger size than previously thought. Finally, the new finding provides novel information on the basal radiation of Dinosauromorpha constituting the first record of a Norian association of dinosaurs with non-dinosauriform dinosauromorphs outside North America.