The hadrosaurian dinosaurs (ornithiscia: hadrosauria) of Big Bend National Park, Brewster County, Texas, with implications for late Cretaceous paleozoogeography
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.