Angulomastacator (meaning "bend chewer", in reference to both the shape of its upper jaw and to the Big Bend area of the Rio Grande, where the type specimen was found) is a genus of duck-billed dinosaur from the Campanian-age (Late Cretaceous) Aguja Formation of Big Bend National Park, Texas. It is known from a single specimen, TMM 43681–1, a partial left maxilla (the main tooth-bearing bone of the upper jaw). This bone is curved down approximately 45° at its anterior end, with the tooth row bent to fit, unlike any other hadrosaur. The unusual characterisics of the maxilla, which have not been reported from elsewhere, supports the hypothesis that the dinosaurs of the Aguja Formation were endemic forms. It was discovered in the upper shale member of the Aguja Formation, among plant, bone, a