Чиндезавр: Исчезнувший род динозавров позднего триаса

Extinct genus of dinosaurs
Chindesaurus (,/tʃ//ɪ//n//d//ɪ/'/s//ɔːr//ə//s/ CHINdissORəs) is an extinct genus of basal saurischian dinosaur from the Late Triassic (213 210 million years ago) of the southwestern United States. It is known from a single species, C. bryansmalli, based on a partial skeleton recovered from Petrified Forest National Park in Arizona. The original specimen was nicknamed "Gertie", and generated much publicity for the park upon its discovery in 1984 and airlift out of the park in 1985. Other fragmentary referred specimens have been found in Late Triassic sediments throughout Arizona, New Mexico, and Texas, but these may not belong to the genus. Chindesaurus's classification is debated, and various papers have had different conclusions on its affinities. Its fossils were originally believed to belong to "prosauropods" (basal sauropodomorphs), but its original description and numerous subsequent papers argued that it was a herrerasaurid A 2019 redescription of its holotype considered Chindesaurus to be a theropod closely related to Tawa, a slightly smaller dinosaur known from the Hayden Quarry of Ghost Ranch, New Mexico.

Although many specimens have been referred to Chindesaurus, only one specimen has enough material to remain within the genus with certainty. Holtz (2012) estimated that Chindesaurus had a length of about 2 meters (6.6) feet and a weight equivalent to that of a wolf (23–45 kg, or about 50 100 pounds). Nesbitt et al. (2007) and Irmis et al. (2007) argued that Chindesaurus was a probable basal saurischian dinosaur, and noted that it shares a wide range of characteristics with several lineages of basal saurischians, making any classification problematic. Rauhut (2003) noted that the medially expanded brevis shelf of Chindesaurus resembles that of "crurotarsans" (pseudosuchians), unlike that of most dinosaurs, which is usually laterally expanded. A partial ilium originally assigned to Chindesaurus, from the Tecovas Formation of Texas, was later placed in its own genus and species, Caseosaurus crosbyensis, by Hunt et al. (1998). Nesbitt et al. (2007) corroborated this, stating that the differences between Caseosaurus and Chindesaurus cited by Hunt et al. (1998) were probably a result of size related variation. However, Nesbitt et al. refrained from formally synonymizing the two taxa due to the fragmentary nature of Chindesaurus's ilium.

A phylogenetic analysis by Cabreira et al. (2016) found an unusual result, where Chindesaurus was placed as the sister taxon of Tawa hallae, a carnivorous dinosaur from the Hayden Quarry of Ghost Ranch in New Mexico. A Chindesaurus + Tawa clade was also found in a revision to Baron et al. (2017)'s controversial Ornithoscelida hypothesis. The hypothesis of close relations to Tawa was elaborated upon in 2019, when the holotype specimen of Chindesaurus was redescribed by Adam D. Marsh, William G. Parker, Max C. Langer, and Sterling J. Nesbitt. They included a phylogenetic analysis which placed the Chindesaurus + Tawa clade in the base of Theropoda, a similar position to that first described for Tawa. Their sister taxon relationship was supported by one apomorphy, or unique derived trait: a posterior margin of the proximal end of the tibia which is divided by two notches. It was also supported by the absence of an oblique ligament sulcus on the rear of the femoral head, a low cnemial crest and prominent posterolateral process of the tibia, and a low astragalus with a prominent anterior groove. The authors noted that two right tibiae from the Cooper Canyon Formation may be referable to this clade based on their possession of two notches on posterior margin of the proximal tibia. Guaibasaurus may also belong to the clade based on its tapering posterolateral process of the distal end of the tibia. The following cladogram represents the phylogenetic analysis of Marsh et al. (2019), recovering a Chindesaurus + Tawa clade in basal Theropoda:

The Upper Petrified Forest National Park member of the Chinle Formation was an ancient floodplain where phytosaurs, rauisuchids, archosaurs, pseudosuchians, and other tetrapods lived and competed with the dinosaur Chindesaurus and its relative Coelophysis for resources. This paleoenvironment also had abundant lungfish and clams.