Stenonychosaurus (North American Dinosaurs)

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That’s when everything fell together and we were able to confirm that there were in fact two different species — named Latenivenatrix mcmasterae and Stenonychosaurus inequalis— in the Dinosaur Park Formation, instead of just one,” van der Reest said. Varricchio et al. (1997) described the exact structure of the nests. They were built from sediments, they were dish shaped, about 100cm (39in) in internal diameter, and with a pronounced raised rim encircling the eggs. The more complete nests had between 16 (minimum number in MOR 246) and 24 (MOR 963) eggs. The eggs are shaped like elongated teardrops, with the more tapered ends pointed downwards and embedded about halfway in the sediment. The eggs are pitched at an angle so that, on average, the upper half is closer to the center of the nest. There is no evidence that plant matter was present in the nest. However, Russell's thought experiment has been met with criticism from other paleontologists since the 1980s, many of whom point out that his Dinosauroid is overly anthropomorphic. Gregory S. Paul (1988) and Thomas R. Holtz, Jr., consider it "suspiciously human" and Darren Naish has argued that a large-brained, highly intelligent troodontid would retain a more standard theropod body plan, with a horizontal posture and long tail, and would probably manipulate objects with the snout and feet in the manner of a bird, rather than with human-like "hands". [15] Paleobiology [ ] Currie, P. (1987). "Theropods of the Judith River Formation". Occasional Paper of the Tyrrell Museum of Palaeontology. 3: 52–60. Polyodontosaurus, represented by the holotype CMN 8540, was found in the Steveville area in the Dinosaur Park Formation. It was found about 37m (121ft) below the highest layer of the formation, and comes from the MAZ (Megaherbivore assemblage zone)-2 portion of the fauna, which existed after MAZ-1. This exact stratigraphic location cannot be verified. MAZ-2 spans from 75.9 to 75.3 million years ago, CMN 8540 is from slightly above (younger) than the middle of the formation. [3]

This genus can be distinguished from other troodontids (particularly its close relative Latenivenatrix) due to the following features:With an estimated skull length of 45 centimetres (18in) and a full body length of 3–3.5 metres (9.8–11.5ft), Latenivenatrix is the largest troodontid known. It was described as distinguishable from other troodontids thanks to the following diagnostic (autapomorphic) traits residing in the pelvis: the pubis is retroverted forming a 17° angle; the pubic shaft is anteriorly curved; a large muscle scar on the lateral surface of the pubic shaft is present, slightly proximal to the pubic boot (this is seen also in dromaeosaurid Hesperonychus). [2] Eberth, David A. (1997). "Judith River Wedge". In Currie, Philip J.; Padian, Kevin (eds.). Encyclopedia of Dinosaurs. San Diego: Academic Press. pp. 199–204. ISBN 978-0-12-226810-6. According to van der Reest and his co-author, University of Alberta Professor Philip Currie, Latenivenatrix mcmasterae and Stenonychosaurus inequalis roamed the Earth around 72 million years ago during the Campanian, the fifth of six ages of the Upper Cretaceous epoch. My research and writing (including the material that appears here) is supported by the contributions I receive via patreon. If you value what I do, please consider supporting it here. Xu X, Tan Q, Sullivan C, Han F, Xiao D (2011) A Short-Armed Troodontid Dinosaur from the Upper Cretaceous of Inner Mongolia and Its Implications for Troodontid Evolution. PLoS ONE 6(9): e22916. doi:10.1371/journal.pone.0022916

The first specimens currently assigned to Troodon that were not teeth were both found by Sternberg in 1928, in the Dinosaur Park Formation of Alberta. The first was named Stenonychosaurus inequalis by Sternberg in 1932, based on a foot, fragments of a hand, and some tail vertebrae. A remarkable feature of these remains was the enlarged claw on the second toe, which is now recognized as characteristic of early paravians. Sternberg initially classified Stenonychosaurus as a member of the family Coeluridae. The second, a partial lower jaw bone, was described by Gilmore (1932) as a new species of lizard which he named Polyodontosaurus grandis. Later, in 1951, Sternberg recognized P. grandis as a possible synonym of Troodon, and speculated that since Stenonychosaurus had a "very peculiar pes" and Troodon "equally unusual teeth", they may be closely related. No comparable specimens were available at that time to test the idea. However, the concept that all Late Cretaceous North American troodontids belong to one species began to be questioned soon after Currie's 1987 paper was published, including by Currie himself. Currie and colleagues (1990) noted that, while they believed the Judith River troodontids were all T. formosus, troodontid fossils from other formations, such as the Hell Creek Formation and Lance Formation, might belong to different species. In 1991, George Olshevsky assigned the Lance formation fossils, which had first been named Pectinodon bakkeri but later synonymized with Troodon formosus to the species Troodon bakkeri, and several other researchers (including Currie) reverted to keeping the Dinosaur Park Formation fossils separate as Troodon inequalis. [11]

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Stenonychosaurus inequalis is known from the Dinosaur Park Formation of southern Alberta, Canada, which at the time was a warm coastal floodplain covered by temperate forests. Apex predators included tyrannosaurids such as Daspletosaurus and Gorgosaurus. Herbivores included hadrosaurids such as Lambeosaurus, Corythosaurus, and Prosaurolophus; ceratopsids such as Styracosaurus, Centrosaurus, and Chasmosaurus; ankylosaurs such as Scolosaurus, Euoplocephalus, and Edmontonia; and pachycephalosaurs such as Stegoceras and Foraminacephale. CONVERGENCE: Professor Russell says dinosaurs could have developed along similar lines to us (Image: Canadian Museum of Nature) The name was originally spelled Troödon (with a diaeresis) by Joseph Leidy in 1856, which was officially amended to its current status by Sauvage in 1876. [2] The type specimen of Troodon has caused problems with classification, as the entire genus is based only on one single tooth from the Judith River Formation. Troodon has historically been a highly unstable classification and has been the subject of numerous conflicting synonymies with similar theropod specimens. [3]