CONICET | Buscador de Institutos y Recursos Humanos

The Middle Jurassic theropod record is extremely scarce, being based on a fistful of taxa from Europe, China, Australia,and Argentina. Two basal tetanurans are known from the Argentinean Middle Jurassic Cañadón Asfalto Formation:Piatnitzkysaurus Bonaparte and Condorraptor Rauhut. Since the summer of 2008, fieldwork has been undertaken at a newexceptionally rich bone-bed of this formation (Cañadón Bagual). This locality bears several sauropod bones and less numerousturtle and theropod remains, housed at the MPEF collections. Several theropod shed teeth were recovered, showingfour different morphotypes: 1) with chisel-like mesial and distal denticles (frequency: 36%), 2) with chisel-like mesialand squared distal denticles (7%), 3) without mesial denticles (50%), and 4) with chisel-like and large mesial denticlesand convex crown margins (7%). The last three morphotypes differ from Piatnitzkysaurus and Condorraptor, whereasmorphotype 1 matches the dental morphology of these basal tetanurans, as well as an isolated dentary recovered atCañadón Bagual. Nevertheless, this dentary differs from Piatnitzkysaurus in the absence of two lateral rows of foraminaon its anterior end and the presence of a large and deep circular foramen directly ahead the tooth row. Otherwise, thedentary closely resembles Ceratosaurus Marsh in being a proportionally short bone, with a strongly dorsally curved alveolarmargin, and apicobasally enlarged tooth crowns. Furthermore, a large-sized isolated ischium from this bone-bed alsodiffers from Piatnitzkysaurus in the absence of a well-developed distal expansion. Accordingly, these preliminary observationsreveal at least four different theropod taxa in the Bagual-site, widely increasing the South American MiddleJurassic theropod diversity.

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