Tyrannosaurus rex was one of the largest land carnivores of all time; the largest complete specimen, measured 12.3 metres (40 ft) long, and was 4 metres (13 ft) tall at the hips. Mass estimates have varied widely over the years, from more than 7.2 metric tons (7.9 short tons), to less than 4.5 metric tons (5.0 short tons), with most modern estimates ranging between 5.4 and 6.8 metric tons (6.0 and 7.5 short tons). Packard et al. (2009) tested dinosaur mass estimation procedures on elephants and concluded that dinosaur estimations are flawed and produce over-estimations; thus, the weight of Tyrannosaurus could be much less than usually estimated. Other estimations have concluded that the largest known Tyrannosaurus specimens had a weight exceeding 9 tonnes.
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The first Dilophosaurus specimens were discovered by Sam Welles in the summer of 1942 in Arizona. The specimen was brought back to Berkeley for cleaning and mounting, where it was given the name Megalosaurus wetherilli in 1954. Returning to the same formation in 1964 to determine from which time period the bones dated, Welles found a new specimen not far from the location of the previous discovery. The specimens were renamed Dilophosaurus in 1970, based on the double crest clearly visible in the new skeleton.
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Yangchuanosaurus is an extinct genus of metriacanthosaurid theropod dinosaur that lived in China during the late Oxfordian (and possibly Kimmeridgian) stage of the Late Jurassic, and was similar in size and appearance to its North American contemporary, Allosaurus. It hails from the Upper Shaximiao Formation and was the largest predator in a landscape which included the sauropods Mamenchisaurus and Omeisaurus as well as the Stegosaurs Chialingosaurus, Tuojiangosaurus and Chungkingosaurus
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