LATE CRETACEOUS DINOSAURS, EGGS, BABIES, DROUGHTS, AND FIRES IN BIG BEND NATIONAL PARK, TEXAS

Late Cretaceous dinosaurs from Big Bend National Park, Texas are some of the southernmost in North America. In contrast to northern areas such as Alberta, slower sedimentation rates resulted in fewer fossils in Big Bend and considerably less is known about Big Bend's dinosaurs and other vertebrates. Big Bend was warmer and more arid than northern areas; evidence for periodic droughts comes from abundant horizons of conglomeratic lags with paleo-caliche nodules and evidence for fires is from burned wood. New sites have been collected (surface collected and screened) during the past five years from the inland floodplain deposits of the upper Aguja Formation (Campanian to early Maastrichtian) at Rattlesnake Mountain, increasing the vertebrate record for Big Bend. The best horizon is a silty mudstone to fine sandstone with abundant plant fragments, burned wood, clay balls, coprolites, burrows, snails, dinosaur eggshell fragments, and bones and/or teeth from fish, salamander, lizard, turtle, crocodylian, and dinosaur (hadrosaur, ankylosaur, tyrannosaurid, Saurornitholestes, and other small theropods). Numerous dinosaur eggshell fragments and small teeth from hatchlings or juveniles of hadrosaurs and theropods (tyrannosaurid and Saurornitholestes) demonstrate that dinosaurs nested in Big Bend. However, no nests have been found yet. The Big Bend dinosaur fauna was less diverse compared to northern areas as a result of the warmer and drier climate. Similar results are expected from other Late Cretaceous southern faunas such as those from Mexico.