Paleontological record of the Laguna Colorada Formation (El Tranquilo Group) Late Triassic of Patagonia, Argentina

ADRIANA MANCUSO; ROGER SMITH; DIEGO POL; IGNACIO A. CERDA; ALEJANDRO OTERO; CLAUDIA MARSICANO

Buenos Aires

Jornada; XXVI Jornadas Argentinas de Paleontología de Vertebrados? Mayo de 2012,; 2012

Recent fieldwork in the Laguna Colorada Formation resulted in numerous new vertebrate fossils as well as detailed information about their taphonomic history and depositional environments. Previously described specimens from this formation include adults and post-hatchlings (associated with eggs) referred to the basal sauropodomorph Mussaurus patagonicus Bonaparte and Vince and fragmentary remains of a heterodontosaurid ornithischian. We present here an unusual aggregation of at least fourteen juvenile Mussaurus patagonicus that includes partially and fully-articulated, similar-sized individuals. Some of the skeletons retain a life-like crouched position with flexed limbs, whereas others have articulated limbs that penetrate up to 13cm into the underlying strata. This bonebed occurs at the same stratigraphic level and in the same area as the post-hatchlings were found previously. Also, newly collected materials were found under different taphonomic conditions, from articulated to completely disarticulated skeletons, but all remains are contained within the same bed. The Laguna Colorada Formation consists of reddish to brownish siltstones and claystones, fine to medium sandstones and subordinate thin conglomerates deposited by moderate sinuosity fluvial system. All dinosaur remains are preserved in a 2 meter-thick bed of structureless weak-red (10R 4/2) siltstone with scattered small mudrock pebbles which we interpret as a floodplain loess deposits.