Lehman T.M.,Texas Tech University |
Barnes K.,HC 65
Journal of Paleontology | Year: 2010
A specimen of the aquatic reptile Champsosaurus sp. from the Paleocene Black Peaks Formation in southwestern Texas is the southernmost yet known. The fragmentary specimen exhibits some unusual features, such as a great anterior extent of the quadratojugal on the lower temporal arch, and cannot be attributed with confidence to any of the named species. Champsosaurus appears to have been tolerant of temperate climates and had a northern latitudinal range exceeding that of crocodylians. It seems likely that the brief southward extension in range of Champsosaurus during early Paleocene time resulted from a decrease in mean annual temperature, comparable to over 10° of paleolatitude. © 2010 The Paleontological Society.
Longrich N.R.,Yale University |
Barnes K.,110 CR 322 |
Clark S.,424 Riverside Blvd. |
Millar L.,HC 65
Bulletin of the Peabody Museum of Natural History | Year: 2013
Caenagnathid theropods are a relatively common part of the theropod fauna in the Late Cretaceous of Asia and North America, but have not previously been described from the southernmost United States. Here, we describe caenagnathid fossils from the late Campanian Aguja Formation of West Texas, and revise the systematics of caenagnathids from the Campanian of North America. Caenagnathids from the late Campanian of Canada represent three species in three genera: Caenagnathus collinsi, Chirostenotes pergracilis and Leptorhynchos elegans gen. nov. Leptorhynchos is diagnosed by its small size, its short, deep mandible, and the upturned tip of the beak. A single caenagnathid is known from the late Campanian of Utah, Hagryphus giganteus. Two caenagnathid species occur in the Aguja Formation, ?Chirostenotes sp. and Leptorhynchos gaddisi sp. nov. L. gaddisi differs from L. elegans in that the tip of the beak is narrower and less upturned. Phylogenetic analysis recovers Caenagnathidae and Oviraptoridae as monophyletic sister taxa. Within Caenagnathidae, the North American species seem to form a monophyletic assemblage, the Caenagnathinae, within which Chirostenotes and Caenagnathus form a clade to the exclusion of Leptorhynchos. The discovery of Chirostenotes gaddisi provides more evidence for the existence of a distinct dinosaurian fauna in southern North America during the Campanian. Furthermore, the Aguja fossils show that caenagnathids were widespread and highly diverse in the Late Cretaceous of North America. This diversity was maintained in two ways. First, variation in body size and beak shape suggests that diversity within formations is maintained by niche partitioning, in a way analogous to Darwin's finches. Second, diversity is maintained by high degree of endemism, with different species of caenagnathids occurring in different habitats. © 2013 Peabody Museum of Natural History, Yale University. All rights reserved.