Specimens of Tyrannosaurus

Tyrannosaurus rex, one of the most popular 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.

Early discoveries
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.

Holotype: CM 9380
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.

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.

AMNH 5027
AMNH 5027 was found in 1907 by Barnum Brown in Montana, and described by Brown the following year. At the time of discovery, a complete cervical (neck vertebrae) series for Tyrannosaurus was not previously known, so it was this specimen that brought the short, stocky tyrannosaur neck to light. Compared to later specimens (BMNH R7994 and FMNH PR2081, for instance) the cervical series of AMNH 5027 is much more gracile, so with later discoveries the distinction between tyrannosaurid necks and the necks of carnosaurs became more obvious. This specimen also provided the first complete skull of Tyrannosaurus rex. In total, Brown found five partial Tyrannosaurus skeletons.

Famous mount
Osborn planned to mount the similarly-sized AMNH 5027 and AMNH 973 together in dynamic poses. Designed by E.S. Christman, the scene was to depict a rearing Tyrannosaurus (AMNH 5027) snapping at another cowering one (AMNH 973), as they fought over the remains of a hadrosaur, described at the time as Trachodon: "It is early morning along the shore of a Cretaceous lake four [we now know to be sixty five] million years ago. A herbivorous dinosaur Trachodon venturing from the water for a breakfast of succulent vegetation has been caught and partly devoured by a giant flesh eating Tyrannosaurus. As this monster crouches over the carcass, busy dismembering it, another Tyrannosaurus is attracted to the scene. Approaching, it rises nearly to its full height to grapple the more fortunate hunter and dispute the prey. The crouching figure reluctantly stops eating and accepts the challenge, partly rising to spring on its adversary. The psychological moment of tense inertia before the combat was chosen to best show positions of the limbs and bodies, as well as to picture an incident in the life history of these giant reptiles." However, technical difficulties prevented the mount from being executed. One obvious problem was that the Cretaceous Dinosaur Hall was too small to accommodate this dramatic display, and AMNH 5027 was already mounted by itself as the central attraction of the hall. The fore-arms of Tyrannosaurus were not well documented and the hands were unknown, so for the sake of the display, the forearms of AMNH 5027 were given three fingers, based on the forelimbs of Allosaurus (the more allosaur-like arms were replaced several years later when better fossils of tyrannosaurid arms were found). The mount retained a rearing pose similar to the initial proposal. By the 1980s it was generally accepted that such a pose would have been anatomically impossible in life, and the skeleton was re-mounted in a more accurate, horizontal pose during a renovation of the museum's dinosaur halls in the early 1990s. The mount can still be seen on display on the fourth floor of the American Museum.

After the war, the holotype of Dynamosaurus imperiosus and a second specimen (AMNH 5881) were also sold and now reside in the collections of the Natural History Museum, London (formerly the British Museum of Natural History), where they are known as BMNH R7994 and BMNH R7995, respectively. The American Museum of Natural History features AMNH 5027 in its famed Dinosaur Hall to this day.

1940s-1990s
Very few other Tyrannosaurus rex skeletons were discovered until the late 1980s. The skull of Nanotyrannus, frequently considered to be a juvenile T. rex, was recovered from Montana in 1942. In 1966, a crew working for the Natural History Museum of Los Angeles County under the direction of Harley Garbani discovered another T. rex (LACM 23844) which included most of the skull of a very large, mature animal. When it was put on display in Los Angeles, LACM 23844 was the largest T. rex skull on exhibit anywhere. Garbani also discovered several other partial skeletons over the next decade (including LACM 23845, the holotype of "Albertosaurus" megagracilis), some of which are maintained in the collections of the University of California Museum of Paleontology in Berkeley, California. Other skulls and partial skeletons were discovered in South Dakota and Alberta, Canada in the early 1980s.

Before 1987, Tyrannosaurus rex was thought to be rare. However, the last two decades have seen the discovery and description of over a dozen additional specimens. The first, nicknamed "Stan" in honor of its discoverer, amateur paleontologist Stan Sacrison, was found in the Hell Creek Formation near Buffalo, South Dakota, in the spring of 1987. After 30,000 hours of digging and preparation by the Black Hills Institute, beginning in 1992, 65% of a skeleton emerged, including a complete skull. Stan (BHI 3033) is currently on display in the Black Hills Museum of Natural History in Hill City, South Dakota following an extensive world tour, and replicas sold by the Black Hills Institute are also found in museum exhibit halls around the world. This specimen exhibits many bone pathologies, including broken and healed ribs, a broken and healed neck and a spectacular hole in the back of its head, about the size of a Tyrannosaurus tooth.

In 1988, local rancher Kathy Wankel discovered another Tyrannosaurus rex in Hell Creek sediments on an island in the Charles M. Russell National Wildlife Refuge of Montana. This specimen was excavated by a team from the Museum of the Rockies led by paleontologist Jack Horner, with assistance from the U.S. Army Corps of Engineers. The specimen, given the number MOR 555 but informally called the "Wankel rex," includes approximately 90% of the skeleton, including the skull, as well as what at the time was the first complete T. rex forelimb. It is now on exhibit at the Museum of the Rockies in Bozeman, Montana.

"Sue": FMNH PR2081
Susan Hendrickson of the Black Hills Institute discovered the best-preserved Tyrannosaurus currently known, in the Hell Creek Formation near Faith, South Dakota, on August 12, 1990. This specimen, named "Sue" in honor of its discoverer, soon became embroiled in a legal battle over its ownership. The land on which the fossil was discovered was found to lie within the Cheyenne River Indian Reservation and is occupied by the family of Maurice Williams, a Native American of the Sioux tribe. In 1992, Williams claimed he still owned the fossil, for which the Black Hills Institute had paid him USD 5,000. The local Cheyenne River Sioux Tribe, of which Williams is a member, also claimed ownership. The fossil, as well as many thousands of pages of field notes and business records, were confiscated by the Federal Bureau of Investigation in 1992 and held throughout the ensuing court proceedings. In 1997, the suit was settled in favor of Maurice Williams because his land is technically held in trust for him by the United States government. Therefore, although the Black Hills Institute had paid Williams for the fossil, it was judged that the fossil could be considered "land" which Williams owned but could not legally sell without government permission. The fossil was returned to Williams' ownership and Pete Larson, vice-president of the Black Hills Institute, was sentenced to two years in federal prison for an unrelated customs violation discovered by the FBI while searching through his business records. Williams quickly offered up "Sue" for auction by Sotheby's in New York, where it was sold to the Field Museum of Natural History in Chicago for USD 8.4 million — the highest price ever paid for a fossil. Preparation of "Sue" (FMNH PR2081) was completed at the Field Museum and her skeleton was placed on exhibit on May 17, 2000. Over 90% of the skeleton was recovered, allowing the first complete description of a Tyrannosaurus rex skeleton. Following the sale of "Sue," another Tyrannosaurus rex skeleton, dubbed "Z-rex", was put up for auction on eBay in 2000 with an asking price of over USD 8 million. It failed to sell online but was purchased for an undisclosed price in 2001 by British millionaire Graham Ferguson Lacey, who renamed the skeleton "Samson" after the Biblical figure of the same name. This specimen, discovered on private land in South Dakota in 1992, includes a complete and undistorted skull, which was prepared by the Carnegie Museum starting in May 2004. After preparation was complete in March 2006, the specimen was returned to its owner, who plans to put it on an educational tour.

"Stan": BHI 3033
BHI 3033 was found near Buffalo, South Dakota by Stan Sacrisen. When Pete Larson and his team at the Black Hills Institute began extracting the fossil, they nicknamed it "Stan", after its discoverer, and from then on, the name stuck.

While examining this fossil, Larson made a number of observations which were consistent with non-fatal injuries sustained during life. These include several broken ribs with signs of bone regrowth; scarring on the ribs; two fused cervical vertebrae, suggesting that "Stan" healed a broken neck; cheeks showing signs of healed injuries; and a hole in the braincase 1 inch in diameter (it is a leap, but a Tyrannosaurus tooth is the right size to inflict such an injury). A thin layer of bone resealed the hole, suggesting this injury fell just short of fatal.

"Jane": BMRP 2002.4.1
In 2001, a small tyrannosaurid specimen nicknamed "Jane" was excavated. Now residing at the Burpee Museum of Natural History as BMRP 2002.4.1, "Jane" is at the center of a debate about whether the small tyrannosaurid genus Nanotyrannus is valid or a juvenile Tyrannosaurus, as "Jane" compares favorably with the original specimen of Nanotyrannus. Although there are dissenters, the majority of paleontologists who have looked at the specimens consider them to be juvenile individuals of Tyrannosaurus rex.

Soft tissue in MOR 1125 (B-rex)
In the March 2005 Science magazine journal, Mary Higby Schweitzer of North Carolina State University and colleagues announced the recovery of soft tissue from the marrow cavity of a fossilized leg bone, from a 68 million-year-old Tyrannosaurus. The bone had been intentionally, though reluctantly, broken for shipping and then not preserved in the normal manner, specifically because Schweitzer was hoping to test it for soft tissue. Designated MOR 1125 (and known informally as B-rex), the dinosaur had been excavated from the Hell Creek Formation. Flexible, bifurcating blood vessels and fibrous but elastic bone matrix tissue were recognized. In addition, microstructures resembling blood cells were found inside the matrix and vessels. The structures bear resemblance to ostrich blood cells and vessels. However, since an unknown process distinct from normal fossilization seems to have preserved the material, the researchers are being careful not to claim that it is original material from the dinosaur. If it is found to be original material, any surviving proteins may be used as a means of indirectly guessing some of the DNA content of the dinosaurs involved, because each protein is typically created by a specific gene. The absence of previous finds may merely be the result of assumptions that soft tissue could not be preserved, so that nobody had looked for it. Since the first, two more tyrannosaurs and a hadrosaur have also been found to have such tissue-like structures.

Paleontologist Thomas Kaye of the University of Washington in Seattle has also hypothesized that the soft-tissue is permineralized biofilm created by bacteria while digesting and breaking down the original specimen. He has discovered this to be true in many specimens from the same area.