Camposaurus

Camposaurus (/ˌkæmpoʊˈsɔːrəs, -pə-/ KAMP-o-SOR-əs) is a coelophysoid dinosaur genus from the Norian stage of the Late Triassic period of North America. The pertinent fossil remains date back to the early to middle Norian stage, and is widely regarded as the oldest known neotheropod. Camposaurus is a small, carnivorous, theropod dinosaur. Its approximate length and weight cannot be reliably estimated because of the sparse material that is known from this genus. Camposaurus is known from partial lower leg bones, holotype UCMP 34498 (which includes distal tibiae, distal fibulae, and astragalocalcanea), and other fragmentary material. Like other coelophysids, it has fused tibio-tarsals and fibulo-tarsals. Unlike its relatives, the area of the tibia that fits with the fibula has a distinct ridge at the back. Another unique feature is the lack of a large medial condyle on the astragalus. The type species, C. arizonensis, was formally named and described by Adrian Hunt, Spencer G. Lucas, Andrew B. Heckert, Robert M. Sullivan and Martin Lockley in 1998. As the species name suggests, it was found in Arizona, in the United States. The holotype specimen UCMP 34498 was discovered in the Placerias quarry of the Bluewater Creek Formation of Arizona, from the Norian stage of the Late Triassic period. Camposaurus is considered to be the oldest known neotheropod dinosaur. Camposaurus was originally placed in the clade Ceratosauria based on the analysis of Long and Murray (1995). It is morphologically similar to, and was incorrectly considered for some time to be a species of, Coelophysis. In 2000, Downs examined Camposaurus and concluded that it is a junior synonym of Coelophysis, because of its similarity to some of the Coelophysis Ghost Ranch specimens. The review by Nesbitt et al. in 2007, revealed that a specific feature of the ankle (the ventral astragalar margin) was found to be straight, and is indistinguishable from that of Coelophysis bauri. Based on this Nesbitt et al. (2007) concluded that the two genera were synonymous. In 2011, it was entered into a phylogenetic analysis and found to be a close relative of Coelophysis rhodesiensis. The lack of material has led many paleontologists to reject it as a nomen dubium. A reassessment of the holotype UCMP 34498 of Camposaurus arizoniensis by Ezcurra and Brusatte revealed two autapomorphies, thereby firmly establishing this material as a valid genus and species. This analysis also demonstrated that Camposaurus is definitely a neotheropod, and based on phylogenetic analysis its closest known relative is Coelophysis rhodesiensis, because they share similarities in the tibia, and ankle. Spielman et al. (2007) assigned Camposaurus to the family Coelophysidae.