Шувозавр: ежелгі кескіштер эволюциясы мен жіктемесі

Genus of beaked reptile

Shuvosaurus (meaning "Shuvo [Chatterjee]'s lizard") Although precise dating is lacking for much of the Dockum Group, including the Post Quarry, it has been correlated to the Adamanian teilzone, a local biostratigraphic unit in the southwestern United States—that has elsewhere been dated to the early to middle Norian stage of the Late Triassic, between 224–215 million years old. The fossils of Shuvosaurus were preserved in a bonebed containing the remains of at least nine partially articulated and associated skeletons alongside the skeleton of a Postosuchus, with a minimum of 14 total individuals indicated by the number of right partial femurs collected. Following Long and Murry (1995), opinions were divided on the identity of Shuvosaurus and its proposed synonymy with Chatterjeea. Notable among them, Oliver Rauhut (1997, 2000, 2003) argued that Shuvosaurus was indeed a theropod and distinct from Chatterjeea, but that it was instead a specialised basal member convergent with ornithomimosaurs. In the early 2000s, Sterling Nesbitt and Mark Norell prepared previously unopened jackets of an unknown archosaur from the Whitaker Quarry at Ghost Ranch combining a Shuvosaurus like skull with Chatterjeea like postcrania, which they named Effigia in 2006. This discovery showed that Shuvosaurus is more closely related to crocodilians and other pseudosuchians, and that similarities between it and ornithomimids are result of convergent evolution, while also demonstrating that the bodies of Chatterjeea almost certainly belong to Shuvosaurus and that the two are synonymous. Indeed, the two are so similar that in 2007 Spencer Lucas and colleagues proposed that the two genera were synonymous, tentatively referring Effigia to Shuvosaurus as S. okeeffeae, a proposal that has not been followed in subsequent research. Shuvosaurus itself would not be thoroughly redescribed for many years until late 2023 and early 2024 when two separate redescriptions were published. The skull was first redescribed by Lehane (2023), following on from the work of his previously unpublished 2005 master's thesis, and was then followed shortly after by a complete skeletal osteology from Nesbitt and Chatterjee (2024). Although both were published closely together, the work in each was conducted independently and published in parallel. Notably, Nesbitt and Chatterjee (2024) provide differing and novel interpretations of some of the cranial material compared to previous interpretations, including that of Lehane (2023).

Shuvosaurus was at first tentatively classified as a member of the otherwise Cretaceous coelurosaurian theropod group Ornithomimosauria by Chatterjee, based on the superficial resemblance shared by their skulls. In an early report at the annual Society of Vertebrate Paleontology meeting in 1991, Chatterjee even explicitly referred Shuvosaurus to the family Ornithomimidae. However, in its formal description in 1993 he instead more cautiously referred it to the broader group Ornithomimosauria and therein erected the monotypic family Shuvosauridae. Notably, despite its age and classifying it individually from other ornithimosaurs, Chatterjee regarded Shuvosaurus as very derived and especially similar to Dromiceiomimus. Chatterjee nonetheless offerred an alternate possibility that it represented a basal theropod extensively convergent with ornithomimosaurs, but considered this less likely. and was taken even further by Hunt et al. (1998) and Heckert & Lucas (1998) who argued that Chatterjee (1993) did not demonstrate that the skull even had any diagnostic traits of dinosaurs. Theropod affinities for Shuvosaurus were nonetheless still supported by some researchers in the late 1990s and early 2000s, most notably by Oliver Rauhut. In 1997, Rauhut rejected Long and Murry's proposal Shuvosaurus was synonymous with Chatterjeea (and therefore a pseudosuchian) on the basis of theropod like features of its skull absent in any known pseudosuchians at the time, but did not identify it as an ornithomimosaur. Instead, he believed Shuvosaurus to be an early diverging theropod but could not confidently determine its relationships further due to its derivity. Lehane later revised this classification when formally publishing his description of the skull in 2023, subsequent to the discovery of Effigia. However, this claim was never followed up on in literature, and in the 2024 redescription Chatterjee accepted Shuvosaurus was a poposauroid pseudosuchian related to Effigia.