Abstract

Collecting in the vicinity of El Rosario, B.C., is a continuing project since 1965 supported by the National Geographic Society, Museum of Natural History, Los Angeles County, and the Instituto de Geologia, Mexico. The fauna is small due to difficulties in collecting, scarcity of specimens, and the almost unique sedimentary environmental framework. Dinosaurian archosaurs related to Lambeosaurus of the Canadian Rocky Mountain foothills and Alberta plain are the commonest herbivores. Some were 17 meters long and were aquatic more than terrestrial. A large carnivorous dinosaur has been recognized by isolated teeth as well as cranial material. It was morphologically near Gorgosaurus. Mammals, while exceeding rare, have been found. Mostly specimens consist of isolated teeth but several jaws are in the collection. They are related to forms found in Cretaceous deposits outcropping along the eastern side of the Rocky Mountains. A crocodilian near the ancestry of the lineage leading to modern alligators is present. A very significant avian fossil has been collected. It is the only terrestrial bird to have been recovered from Mesozoic strata other than the famous Archaeopteryx from the Solenhofen Limestone of Germany. Preliminary study indicates that it will serve as a phylogenetic link between the Jurassic Archaeopteryx and modern terrestrial forms.