New Mexico Geological Society Annual Spring Meeting — Abstracts

In 1924, a paleontological expedition from Amherst College in Massachusetts led by Dr. Frederic Brewster Loomis explored the Upper Cretaceous deposits in the San Juan Basin in northwestern New Mexico. This expedition has been overlooked by various workers on San Juan Basin paleontology, and, indeed, none of the fossils Loomis collected have been described in print. From 1917 to 1937, Loomis was a professor of biology and geology at Amherst College. He led many successful paleontological expeditions around the country and collected numerous important vertebrate fossils, which today are a part of the collections of Amherst College and the Springfield Science Museum, Massachusetts. The 1924 expedition to the San Juan Basin collected several partial but exceptionally well-preserved isolated bones and partial skeletons of dinosaurs and other vertebrates, including two species of turtles, Adocus bossi and Denazinemys nodosa. The dinosaur specimens include Ankylosauridae, Ceratopsidae, Hadrosauridae, Titanosauridae, and Tyrannosauridae. The ceratopsian skeletal materials are identified only to the family level, because their fragmentary preservation, whereas bones of other dinosaurs are identified to the genus and species level and include Glyptodontopelta mimus, the hadrosaurid Kritosaurus navajovius, and the titanosaurid sauropod Alamosaurus sanjuanensis. The tyrannosaurid skeletal material consists of an isolated, diagnostic right dentary, which may represent a new taxon. No field notes of this important expedition can be located, and only a brief report exists that does not specify the exact locality of the dinosaur bones and in what formation they were collected, beyond the designation "Ojo Alamo Formation." However, based on their preservation, the ceratopsian, hadrosaurid, and tyrannosaurid were probably collected from the De-na-zin Member of the Kirtland Formation, whereas a large, nearly complete left humerus of Alamosaurus and a cluster of osteoderms of Glyptodontopelta were collected from the Naashoibito Member of the Ojo Alamo Formation. The discovery of these specimens has historical and paleontological significance, because the Amherst College expedition and the specimens were largely forgotten and never described in the literature. The left humerus of Alamosaurus is the first and the most complete humerus of this giant sauropod recovered from the Upper Cretaceous deposits of New Mexico and provides new and important anatomical information. The identification of a possibly new tyrannosaurid adds to the growing record and diversity of tyrant reptiles in North America.