New dinosaur fossils from the Late Cretaceous La Colonia Formation, Chubut province, Argentina

HILL, ROBERT; POL, DIEGO; ROUGIER, GUILLERMO W.; MUZZOPAPPA, PAULA; PUERTA, PABLO

Norman, Oklahoma, USA

Congreso; 62nd Annual Meeting, Society of Vertebrate Paleontology; 2002

Sam Noble Oklahoma Museum of Natural History, University of Olkahoma

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; mso-bidi-font-size:10.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:EN-US; mso-fareast-language:EN-US;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> Fieldwork in the marine La Colonia Formation (Late Cretaceous, Maastrichtian) of central Patagonia has resulted in the discovery of numerous lenticular bone beds.  These marine deposits are rich in fossils of dipnoans, actinopterygians, and plesiosaurs, as well as terrestrial mammals, crocodyliforms, anurans, and dinosaurs.  The fauna indicates the presence of a depositional environment under both marine and terrestrial influences, underscoring the importance of these localities as representative of a Maastrichtian marine transgression.  Here we report on dinosaurian remains collected at La Colonia.Sorting of screen-washed concentrate recovered 26 partial teeth referable to Hadrosauridae indet.  Two distinct size classes are present, indicating that some of the material may pertain to juvenile individuals.  A dissociated predentary found at the same locality may also be hadrosaurid.  In addition, five theropod teeth were recovered.  Although surface wear precludes precise taxonomic assignment based on denticle morphology, two distinct tooth morphologies are clearly represented.  The larger, more robust form possesses a straight, vertical distal border, whereas the smaller, more gracile form is more strongly recurved.Although theropods are becoming increasingly well known from Gondwana, ornithischian remains in southern continents are extremely rare.  Abundant hadrosaur remains and a faunal assemblage very similar to that of La Colonia have been found in the underlying Los Alamitos Formation.  The occurrence of hadrosaurs in the Maastrichtian of South America supports the hypothesis of a land bridge connecting the Americas well into the Late Cretaceous.  The high ratio of hadrosaur teeth to theropod teeth might be of paleoecological significance, but further sampling is required to thoroughly test this possibility.  Continued collection in the richly fossiliferous beds of La Colonia, as well as close inspection of concentrate already collected, may yield more diagnostic ornithischian material.