CONICET | Buscador de Institutos y Recursos Humanos

We describe tetrapod burrows from the uppermost Middle?lower Upper Triassic (latest Ladinian?early Carnian)Chañares Formation (Ischigualasto-Villa Unión Basin), La Rioja Province, northwestern Argentina. The burrowswere found in different localities of the unit, but restricted to the lowermost 17 m of the formation. They occur atthe same interval as a tetrapod assemblage composed of erpetosuchid and basal paracrocodylomorph pseudosuchians,basal traversodontid and chiniquodontid eucynodontians, and stenaulorhynchine rhynchosaurids. Thisassemblage differs from the typical Chañares fauna that occurs in stratigraphically higher levels. The burrowswere found within the deposits of moderately developed palaeosols formed in volcanically-influenced braidedfluvial facies under semi-arid climate conditions. The burrow systems are cylindrical to sub-cylindrical in crosssection,up to 25 cm in diameter, and characterized by long, multiple branching tunnels, several metres long,that meander horizontally or are slightly inclined (< 30°), forming a complex network that is a result of passivefill of a previously open burrow. In general, these structures have a similar architecture and three-dimensionalorganization to those previously described from the upper parts of the Ischigualasto Formation in the same basin.It is hypothesised that some of these burrows were formed by small eucynodonts (e.g., basal traversodontids,chiniquodontids), and their co-occurrence with diverse, medium to large pseudosuchian predators (e.g.,Luperosuchus, Tarjadia), suggests these non-mammaliaform eucynodonts would excavate burrows to live andavoid climate-stress conditions and/or predation. The new discovery of burrows in the Chañares Formationsheds light on the evolution of the palaeoecology of mammaliaform precursors during the dawn of the archosaurdomain.

enviar mensaje