CONICET | Buscador de Institutos y Recursos Humanos

The Cretaceous witnessed the greatest diversity of crocodyliforms, among them, the notosuchians. The Gondwanan notosuchian crocodyliforms displayed high levels of diversity and a notable array of specialized forms that developed in different ecological niches. This diversified notosuchian fossil record is the highest in South America, where the Argentinean (Patagonia) and Brazilian specimens are the best known. Here we report the first crocodyliform from the Cretaceous exposures of the Los Llanos Formation in La Rioja Province, northwestern Argentina, which represents a new species of a small-bodied Notosuchia. The specimen (CRILAR-Pv 502) includes fragments of the left and right maxilla (supporting the left palatal lamina) with teeth, fragments of the left jugal, left pterygoid and ectopterygoid, right dentary with teeth, fragment of left dentary and angular. Based on these remains, we estimate the skull to be 10 cm long. In addition, CRILAR-Pv 502 shares several derived features with Notosuchus terrestris (e.g., maxilo-palatal characteristics, similar dentition and arrangement of tooth row, mandibular symphysis, sculpturing patterns, and pterygoid/ectopterygoid morphology). CRILAR-Pv 502 was found in an immature sandy paleosol section formed in a semi-arid environment with active eolian sedimentation. The presence of a new small-bodied mammal-like crocodyliform in the Cretaceous of western Gondwana halfway between the known South American species (Brazil, Argentina and Bolivia), has interesting biogeographic implications. Furthermore, the striking similarities with Notosuchus among notosuchians, and the association with derived titanosaurs and abelisaurids, support a Late Cretaceous age for Los Llanos Formation, with huge implications in the regional tectonic models for La Rioja Province

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