New Mexico Geological Society Annual Spring Meeting — Abstracts

This is the first description of infant dinosaur remains from the Cretaceous of New Mexico. In 1983, a quarry situated at the edge of a stream channel deposit and containing hadrosaur remains, excavated by James Baldwin of Silver City and Mary Ann Pattison of Carrizozo, unexpectedly yielded a partial, infant dinosaur lower jaw. The jaw occurred immediately below adult (hadrosaur) ribs and near a partial adult hadrosaur jaw. Subsequent work in an extension of the same channel has yielded adult hadrosaur pelvic and limb bones. The infant remains consist of most of a dentary with a hadrosaur tooth battery and an edentulous predentary. The teeth are virtually pristine and indicate that the individual was very young and recently hatched at the time of death. It seems most likely that the infant represents Edmontosaurus ("Kritosaurus") or Parasaurolophus. The quarry site is situated between the fourth and fifth forest levels, most likely above the Campanian-Maastrichtian palynological boundary in the study area. It is approximately at the same level that has yielded dinosaur egg shell fragments and structures interpreted to be abandoned dinosaur nest. The fossil Forest was situated very near sea level; indeed it is likely that the area was periodically inundated as shown by mineralogical data, the presence of marine bivalve shells, a weathered ammonite, and other data. Turtles and crocodiles were very adundant as were amiids, gar and various selachians. The infant inhabited an area of sandy flats near the mouth of a broad, slow moving river, possibly emptying into a lagoon. The area was in the midst of a palm groves with interspersed stands of cypress bordering rivers and tributaries, and broad leaved deciduous tress probably occupying better drained. Study of inclusions in associated resins indicates that the atmosphere contained an oxygen level of about 30%; the biotic effects of this are uncertain. Previous interpretations from nesting sites elsewhere in North America hold that dinosaurs preferred upland habitats away from the sea for nesting. The Montana nesting areas excavated by Horner were situated upland near a lake. It is likely that the Fossil Forest data requires modification of this view; nesting occurred at or very near sea level. It may well be that eggs, nests and infants are preserved because of the proximity of fluctuating water levels at sea level or upland habitats.