Tyrannosaurus rex

Paul, G. S., 1988, Predatory Dinosaurs of the World, Predatory Dinosaurs of the World, New York: Touchstone Books, pp. 323-349 : 343-346

TYRANNOSAURUS (TYRANNOSAURUS) REX Osborn, 1905

synonym— Dynamosaurus imperiosus

type— CM 9380

best specimens— type , AMNH 5027 , TMP 81.6.1

SPECIMENS on display at—AMNH, CM, LACM (skull), SDSM (skull), ANSP (cast), TMP

time—late Maastrichtian of the latest Late Cretaceous

horizon and distribution—Lance, Hell Creek, Scollard, Willow Creek, Frenchman, and upper Kirtland? Formations of western North America

main anatomical studies— Osborn, 1906 , 1912 , 1916

	AMNH 5027/ type	UCMP 118742
SKULL LENGTH—	1355 mm	~1750
TOTAL LENGTH—	10.6 m	~13.6
FEMUR LENGTH—	1300 mm	-~675
HIP HEIGHT—	3.4 m	~4.4
TONNAGE—	5.7	~ 12

This is the theropod. Indeed, excepting perhaps Brontosaurus, this is the public’s favorite dinosaur, having fought King Kong for the forced favor of Fay Wray and smashed Tokyo (with inferior special effects) in the guise of Godzilla. Even the formations it is found in have fantastic names like Hell Creek and Lance. Its place as the greatest of known land predators remains secure—no other giant consists of such complete skeletons, is bigger, or as powerful. Everything said about tyrannosaur strength goes furthest with this species, and no other theropod has such a large, thickly built, powerfully muscled skull, and such large teeth for its bulk. Only Dilophosaurus and juvenile A. libratus have teeth that are nearly as large in relative measure. Sickle-clawed Velociraptor antirrhopus may be as formidably armed for its weight, but it is a small animal. And along with its power, T. rex is the fastest known animal for its size!

A number of new finds are coming onto line, including the first combination of a skull with a fairly complete skeleton, at the TMP. The skeletal restoration is after the composite New York mount. Made from the first two known skeletons, these are identical in size. 5027 provides the skull, vertebral column, rib cage, and hips; 9380 the fore and hind limbs. The 5027 skull is crushed a little, giving it a falsely dished dorsal profile and little more breadth at its back end than it really had. Since this is the most complete and best known skull, these crushed features have misled many. On the other hand, Ralph Molnar has made the back of the skull too narrow and triangular.21 The new skulls prove that this animal really was a very broad-cheeked animal. The roguse posterior orbital horn is larger than the reduced preorbital one, much as in T. bataar . The lower arm and hand are not known, but since the humerus is smaller than in other Tyrannosaurus species, it is likely that the arm as a whole was also. It was not until 1970 that Newman noted that the partial tail was restored with too many vertebrae. With a proper tyrannosaur tail count of thirty-seven to thirty-nine vertebrae, 5027 is thirty-four feet long, not forty-five as once claimed. Kenneth Carpenter has recently mounted a cast of this skeleton in a modern, accurate, and dynamic pose in Philadelphia. Estimates that 5027 massed close to 7 tonnes22 are reasonable if they are presumed to include fat reserves, but these estimates are not really useful because they were based on unreliable museum models, and a commercial toy made by the BMNH. Substantial growth is possible even after the skull bones start to fuse together as in 5027 . I note this because this and the other big T. rex specimens may or may not be subadults. This is possible because the biggest specimen is a toothbearing UCMP maxilla from the upper jaw that is 29 percent longer than 5027 . It indicates a 12-tonne individual that could rear its head some twenty-three feet high, and could slide something the size of a whole human body down its gullet as if it were a raw oyster.23 It is possible that this titan, known as it is from only one bone, represents a different species. If not, then 15- tonne individuals were probably fairly common, 20-tonne “record holders” were possible—though so rare that they may never be found. For comparison, most bull African elephants are 5- tonners and a fair number reach 7.5 tonnes; extremely rare are 10-tonners.

Suggestions that T. rex is really two species, or even two genera, have been circulating lately. Two genera is completely out of the question; at most it is a-lion-versus-a-tiger kind of species separation. But the type of Dynamosaurus imperiosus (a wonderful name) is a front lower jaw that is hardly distinguishable from the T. rex type. The somewhat distorted AMNH 5027 skull may be adding to the confusion because the upper jaw’s left maxilla is too low. The right side is not so crushed and looks like other T. rex specimens. The hind limbs of some specimens do seem to be longer and more slender than those of the type, and they vary somewhat in the teeth. On the other hand, all the skulls are quite consistent in the preorbital horns and other skull details, more so than in A. libratus . So one species is most likely, perhaps one that came in “robust” and “gracile” versions, but the verdict is not in.24

Of course, T. rex is the most illustrated of theropods, and the most famous rendition is Charles Knight’s FMNH painting of a confrontation with Triceratops.25 The horizontal body pose is ahead of its time; on the debit side are such anatomical mistakes as the overly shallow back of the head and a small chest. Another well-known Knight T. rex effort26 is much less satisfying, especially since the head is too small and lizard-like. Burian’s oftenreproduced T. rex 27 has a badly dwarfed head and lipless teeth —it is not at all good. Neither is Rudolph Zallinger’s bloated and simplistic version in the YPM mural.28 The rather uninspired commercial model put out by the BMNH is too small in the head and chest, too long-tailed, and has inappropriate plated skin.

The reason for the bulk and firepower of T. rex is apparent when one considers its main prey, Triceratops. Prior tyrannosaurs were going after rhino-sized duckbills and ceratopsids, but by the late Maastrichtian, elephant-sized Triceratops was far and away the most numerous herbivore. Triceratops was horrendously big, fast, and agile, and it was well-armed with beak and horns. Hunging it required an equally gigantic, faster, and even more formidably armed predator. Just how formidable only became clear to me as I did the illustration of T. rex biting Triceratops in Figure 2-6 (page 35). I had to measure things out, and was appalled to find that the tyrannosaur could bite out a wound a yard long, and well over a foot deep and wide. This would have wrecked the entire upper thigh of Triceratops, and cut down to the femur. Some “scavenger”! It is hard to conceive of such titanic battles, with elephant-sized predators sprinting alongside a thundering herd of horned dinosaurs.

Some remains indicate that T. rex lived in New Mexico’s Kirtland Shale; if so, it hunted the brontosaurs there, while Triceratops was absent. As for competition, the smaller, more gracile and rare Albertosaurus megagracilis was about all, and it preferred the duckbills. A. lancensis was too small to be much more than its occasional prey, except when the albertosaur dared pick off a juvenile T. rex from under its parents’ noses!

The culmination of tyrannosaur evolution, T. rex was one of the very last North American dinosaurs. Nothing else combined its size, speed, and power. Since its demise we have had to make do with lions and tigers and bears, and other “little” mammalian carnivores.