Browsing by Subject "Paleontology -- Cretaceous"
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Item A vertebrate bone-bed in the Aguja formation (Upper Cretaceous), Big Bend National Park, Texas(Texas Tech University, 2001-05) Anglen, John JeffreyAll known specimens of the giant crocodilian Deinosuchus riograndensis have been recovered from a limited stratigraphic interval within the Terlingua Creek Sandstone and upper shale members of the Upper Cretaceous Aguja Formation in Big Bend National Park. The habitat and behavior of this giant crocodile have long been the subject of speculation. A vertebrate bone-bed near Grapevine Hills that includes remains of D. riograndensis as well as a variety of dinosaurs, turtles, and a mesosuchian crocodile provides an opportunity to study the geology, paleontology, and taphonomy of this stratigraphic interval. The Terlingua Creek Sandstone and upper shale members, as observed in the study area, were divided into 3 related sedimentary facies. Deltaic distributary channel deposits are composed of multi-storied, lenticular bodies of trough cross-bedded sandstone with adjacent, inclined heterolithic strata indicative of channel migration. These channel deposits grade into thin, laterally extensive, coarsening-upward sheet sandstones interpreted as crevasse splay deposits. Crevasse splay deposits contain transported logs and resulted from paleocurrents flowing over a 60-degree arc perpendicular to the distributary channel. The sheet sandstones are separated vertically by layers of bioturbated, carbonaceous mudstone interpreted as interdistributary bay and marsh deposits. An extensive bone-bed within one interdistributary deposit contains a single D. riograndensis individual that died in an interdistributary bay or marsh setting. Overbank flooding scattered and aligned some of the remains and winnowed others away. The same interdistributary bay deposit contains remains of hadrosaur. ceratopsian, and ankylosaurian dinosaurs, as well as turtles and mesosuchian crocodiles in transported and attritional assemblages. Fossil wood containing Teredolites borings indicative of brackish-water conditions is intimately mixed with the bones. Thicknesses of sets of trough cross-beds provide minimum water depths of 1.2 to 2.4 meters for the interdistributary bays. The preferred habitat of Z). riograndensis appears to have been these shallow, brackish-water interdistributary bays. All of the other vertebrates in this environment could have been potential prey for D. riograndensis. Although there is no conclusive evidence, such as abundant bite marks on bones, to conclude that D. riograndensis was responsible for the attritional assemblage of vertebrate remains here, this possibility is as likely as others.Item The hadrosaurian dinosaurs (ornithiscia: hadrosauria) of Big Bend National Park, Brewster County, Texas, with implications for late Cretaceous paleozoogeography(Texas Tech University, 2001-05) Wagner, Jonathan R.Hadrosaur (Dinosauria: Omithischia) fossils are the most abundant large terrestrial vertebrate fossils in Big Bend National Park. They are most commonly recovered from the Campanian Aguja Formation; predominantly in the upper shale member, rarely in the lower shale member. Hadrosaur fossils are rare in the overlying Late Maastrichtian Javelina Formation, and have also been recovered from the neighboring San Carlos and El Picacho formations of Trans-Pecos Texas. Systematically useful hadrosaur material is commonly found in transported or stream-winnowed tidalcreek deposits, as well as overbank microvertebrate lag deposits. Recovered material most commonly consists of maxillae and postcrania. Examination of new and previously described material from the region allows a greater degree of taxonomic resolution than was previously possible for the hadrosaurs of Big Bend National Park. The Early Campanian lower shale member of the Aguja Formation has produced a partial skull and skeleton, the most complete hadrosaur to date from the Park. The specimen represents a new species of Kritosaurus. This new animal is characterized by an unusual conformation of the rostral mandible, possibly an indication of trophic specialization. Previous reports of Kritosaurus cf. K. navajovius and an indeterminate lambeosaurine are confirmed by new cranial material. The former species is currently not distinguishable from Kritosaurus navajovius from the San Juan Basin, while the latter is distinct from all other known hadrosaurs. Contrary to previous reports of cf. Edmontosaurus from the Javelina Formation, the only diagnostic material from the Javelina clearly pertains to Kritosaurus cf. K navajovius.