Specimens of Tyrannosaurus

Tyrannosaurus rex, one of the most iconic dinosaurs, is known from numerous specimens, some of which have acquired a degree of notability in their own right because of their scientific importance and coverage by the media. See Tyrannosaurus for more information on the genus itself.

The holotype of Tyrannosaurus rex, a partial skull and skeleton originally called AMNH 973 (AMNH stands for American Museum of Natural History), was discovered in the U.S. state of Montana in 1902 and excavated over the next three years. Another specimen (AMNH 5866), found in Wyoming in 1900, was described in the same paper under the name Dynamosaurus imperiosus. At the time of their initial description and naming, these specimens had not been fully prepared and the type specimen of T. rex had not even been fully recovered. In 1906, after further preparation and examination, Henry Fairfield Osborn recognized both skeletons as belonging to the same species. Because the name Tyrannosaurus rex had appeared just one page earlier than Dynamosaurus in Osborn's 1905 work, it was considered the older name and has been used since. Had it not been for page order, Dynamosaurus would have become the official name.

The first named fossil specimen which can be attributed to Tyrannosaurus rex consists of two partial vertebrae (one of which has been lost) found by Edward Drinker Cope in 1892. Cope believed that they belonged to an "agathaumid" (ceratopsid) dinosaur, and named them Manospondylus gigas, meaning "giant porous vertebra" in reference to the numerous openings for blood vessels he found in the bone. The M. gigas remains were later identified as those of a theropod rather than a ceratopsid, and H.F. Osborn recognized the similarity between M. gigas and Tyrannosaurus rex as early as 1917. However, due to the fragmentary nature of the Manospondylus vertebrae, Osborn did not synonymize the two genera.

CM 9380 is the type specimen used to describe Tyrannosaurus rex. Fragments of (then) AMNH 973 were first found in 1902 by Barnum Brown, assistant curator of the American Museum of Natural History and a famous paleontologist in his own right. He forwarded news of it to Osborn; it would be three years before they found the rest of it. It has been reconstructed in recent years, it measured an estimated 11.9 meters in length and an estimated weight of 7.4-14.6 metric tonnes, 9.1 metric tonnes being the average estimate in that study, although most earlier studies have suggested lower weight figures. In 1905 when the type was described by Osborn, previous knowledge of dinosaur predators at the time were based on Jurassic carnosaurs, so the short fore-arms of the Tyrannosaurus were treated with extreme caution, with suspicion that bones of a smaller theropod had become jumbled with the remains of the bigger fossil. Following the 1941 entry of the United States into World War II, the holotype was sold to the Carnegie Museum of Natural History in Pittsburgh for protection against possible bombing raids. The specimen, now labeled CM 9380, is still mounted in Pittsburgh, at first with the tail acting as a tripod in the old fashioned kangaroo pose. It has since received a modernization of its posture and can now be found balancing with tail outstretched.

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