Cretaceous Dinosaurs And The World They Lived In: A New Species Of Ornithischian Dinosaur From The Early Cretaceous (Aptian) Of Texas, Reconstruction Of The Brain Endocast And Inner Ear Of Malawisaurus Dixeyi, And Reconstruction Of The Paleoclimate And Paleoenvironment of Cretaceous Terrestrial Formations In Texas And Oklahoma Using Pedogenic Minerals

Material from over thirty individuals of a new ornithopod was recovered from the Proctor Lake locality in the Twin Mountains Formation (Aptian) of north-central Texas. This material includes various ontogenetic stages, providing insight into the growth patterns of this species. The new ornithopod is recovered basal to Iguanodontia, but more derived than Hypsilophodon foxii. The presence and morphology of 4 premaxillary teeth along with a combination of both basal and derived characters distinguish this taxon from all other ornithopods. A braincase of the Cretaceous titanosaurian sauropod Malawisaurus dixeyi was CT scanned and a 3D rendering of the endocast and inner ear was generated. The arrangement of the cranial nerves and relative proportions of the semicircular canals of the vestibular labyrinth are congruent with the interpretation of Malawisaurus as a basal titanosaurian. Physiological aspects of M. dixeyi including habitual head posture, body mass, and vestibular sensitivity are calculated using the data recovered from this analysis. The clay mineralogy, chemistry, and stable oxygen and hydrogen-isotope compositions were measured from 11 phyllosilicate samples representing Cretaceous paleosol profiles which span the Early to Late Cretaceous boundary in north-central Texas and southern Oklahoma. Chemical data is used to estimate paleoprecipitation for each locality using the CALMAG weathering index. Paleotemperature is then estimated by measuring the hydrogen and oxygen-isotope compositions for each sample and applying calculated fractionation factors. The results show cooler temperatures correspond to periods with markedly higher precipitation estimates which also correlate with the presence of extensive shallow seas upon the Texas craton