NEW DINOSAUR DISCOVERIES IN THE LA COLONIA FORMATION: INSIGHTS INTO THE LATE CRETACEOUS FAUNA OF PATAGONIA BEFORE THE K-PG EXTINCTION EVENT

POL, DIEGO; BECERRA, MARCOS G.; CARBALLIDO, JOSE LUIS; KRAUSE, MARCELO; BAIANO, MATTIA; PITTMAN, MICHAEL

Cincinnati

Congreso; Society of Vertebrate Paleontology - 83rd Annual Meeting Cincinnati 2023; 2023

Society of Vertebrate Paleontology

The La Colonia Formation contains the most important record of latest Cretaceous vertebrates from Central Patagonia and recent geochronological work has constrained this unit to be deposited between 69 and 64 Ma. So far, it is the only unit in South America that preserves an abundant terrestrial fauna and is dated precisely to record the biodiversitydynamics before the K-Pg mass extinction event. Collecting efforts over the last two decades yielded a diverse vertebrate fauna including dipnoans, anurans, mammals, ophidians, turtles, dinosaurs, and plesiosaurs. Recent exploration that yielded four new dinosaur species for this unit. First, a new abelisaurid theropod represented by an articulated partial skeleton with cranial remains reveals a second member of this clade for the unit, in addition to Carnotaurus. Skull features indicate this taxon lacked horns, bear nasal ridges and associated foramina, and had a small parietal crest, suggesting an array of cranial plesiomorphies. Second, a virtually complete postcranial skeleton of an ankylosaurid with an associated skull roof and lower jaw indicates the presence of a small bodied and slender limbed new taxon. Postcranial features reveal the presence of synapomorphies of the recently recognized Gondwanan clade Parankylosauria, including a caudal shield of osteoderms. The skull, sacrum, and pelvis reveal numerous differences with Stegouros, indicating large morphological disparity within this poorly known clade. Third, an articulated skeleton of a hadrosaur with a complete skull represents the most complete hadrosaur from South America. It shares with other South American kritosaurini the presence of cranial synapomorphic features but represents a new taxon due to numerous cranial features (e.g., absence of a V-shaped nasofrontal suture; dorsoventrally high maxilla with short palatal process; narial fossa restricted to the posterodorsal portion of the  premaxilla; lack of a prominent nasal crest). Fourth, a dissarticulated titanosaurian specimen with vertebral, pelvic, and appendicular elements represent a new small titanosaurian taxon.The humerus and femur with robusticity indices, femur with dorsomedially directed head, and strongly compressed shaft suggest affinities with Saltasaurinae. These new taxa, coupled with vertebrates and the recently established age of the formation, demonstrate the persistence until the end of the Cretaceous of a distinct fauna recorded since the Campanian of Patagonia.