CONICET | Buscador de Institutos y Recursos Humanos

Here we report the discovery of a new genus and species of a small theropod dinosaur,represented by cranial remains and several isolated postcranial bones belonging to differentindividuals. The remains come from the Cenomanian Candeleros Formation, cropping out inthe Río Negro Province, NW Patagonia. The yet unnamed taxon is different from other knowntheropods by the following combination of character-states: sacrum with intervertebralforamina bounded posteriorly by a sharp crest, sacral vertebral centra apneumatic, transverseprocesses of anterior caudal vertebrae with pneumatic fossa at their bases, supracetabular crestlarge and thick, and manual unguals acute, curved, and transversely compressed, withproximally bifurcated grooves, as in Troodontidae (Russell, 1969).Preliminar phylogenetic analysis supports the new taxon as closely related toAniksosaurus darwini (Martínez and Novas, 2006) from the Upper Cretaceous of SouthernPatagonia. Both taxa share the presence of strongly upturned transverse processes on proximalcaudal vertebrae, fourth metatarsal and corresponding digit transversely narrow, and brevisshelf of ilium strongly developed and lateroventrally expanded, among other traits.The new theropod from the Candeleros Formation and Aniksosaurus occupy a basalposition within Coelurosauria, showing some plesiomorphic features in the tarsus, such asascending process of astragalus low and narrow, and astragalus with inflated medial condyle.Indeed, the overall anatomy of the ankle and pes of the new theropod closely resemble that ofother basal coelurosaurians (e.g., Coelurus).The discovery of this new Patagonian taxon depicts a previously unknown lineage ofcoelurosaurians, adding evidence of a wide tetanuran diversification in Gondwana, indicatingthat basal coelurosaurs were still present in the Late Cretaceous of Patagonia, whereas theybecame extinct in the rest of the world by Jurassic-Early Cretaceous times.

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