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Eukaryota : Metazoa : Bilateria : Deuterostomia : Vertebrata : Tetrapoda : Diapsida : Archosauria : Dinosauria : Theropoda : Coelurosauria
The name says it all. This group of huge carnivores must have tyrannically ruled the land during the last part of the Cretaceous, 85 to 65 million years ago. Short but deep jaws with banana-sized sharp teeth, long hind limbs, small beady eyes, and tiny forelimbs (arms) typify a tyrannosaur. The Tyrannosauridae included such similar animals (in rough order of increasing size) as Albertosaurus, Gorgosaurus, Daspletosaurus, Tarbosaurus, and of course Tyrannosaurus rex. A tremendous skeleton of Tyrannosaurus now stands guard in the Valley Life Sciences Building, which houses the UCMP and the Department of Integrative Biology at UC Berkeley. Tyrannosaurs belong to the Saurischia, or "reptile-hipped" dinosaurs. Within the Saurischia, tyrannosaurids belong to the group of carnivorous dinosaurs known as theropods. Traditionally, the tyrannosaurs have been included within the Carnosauria. In this classification scheme, carnosaurs represent the largest carnivorous animals to ever walk the land. However, recent work has shown that tyrannosaurs are in fact a highly derived group of coelurosaurs, which is mostly composed of smaller animals (including the smallest of all non-avian dinosaurs, the crow-sized Compsognathus, and also the birds).
How did tyrannosaurs move?
Many scientists familiar with the principles of biomechanics (physics applied to living organisms) think that tyrannosaurs could move fairly fast, maybe 10-20 mph, but not as fast as the smaller theropod dinosaurs. Smaller tyrannosaurs like Albertosaurus or young individuals may have moved faster than the bigger ones like T. rex. Yet we still lack any clear evidence that tyrannosaurs could even run; some think that their body size limited them to only a fast walk, like an elephant. Trackways that unambiguously were made by tyrannosaurs would clarify the matter, but so far these are not known, apart from one probable footprint.
Just about two dozen good specimens of these animals have been found and these finds are from highly restricted areas in western North America. Henry Fairfield Osborn, of the American Museum of Natural History in New York City, first described Tyrannosaurus rex in 1905. This first specimen of Tyrannosaurus is now on display at the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania. The skeleton on display at UCMP is a cast of a skeleton (excavated in 1990) now in the Museum of the Rockies in Bozeman, Montana. Berkeley's mount is 90% complete, one of the best specimens found to date. Some 1520 other specimens around the country range from about 10% to 80% complete; missing ribs and tail bones are common.
T. rex: scavenger or predator?
Paleontologist Jack Horner of the Museum of the Rockies (Bozeman, MT) has proposed that T.rex could not have been a predator. His arguments against predation include its small eyes (needed to see prey), small arms (needed to hold prey), huge legs (meaning slow speed) and that there is no evidence for predation bones have been found with tyrannosaur teeth embedded in them or scratched by them, but so far no study has shown that tyrannosaurs killed other dinosaurs for food (a bone showing tyrannosaur tooth marks that had healed would be strong evidence for predation).
His evidence supporting scavenging include its large olfactory lobes (part of the brain used for smell), and that its legs were built for walking long distances (the thigh was about the size of the calf, as in humans). Vultures have large olfactory lobes and are good at soaring to cover long distances.
There are arguments against scavenging. Most large living predators (such as lions and hyenas) do scavenge meat happily when it is available, but most do prefer fresh meat. Horner argues that its arms were too weak to grab prey, but sharks, wolves, snakes, lizards and even many birds are successful predators without using their forelimbs (if any). Whether T.rex was a slow animal is tough to tell, as our dinosaur speeds page will tell you.
What is the public to think of all this? It is suggested that you make up your own mind; the fact is that reconstructing the behavior of extinct animals is difficult, especially when there are no close modern relatives with which to compare them. Tyrannosaurs may have been scavengers, predators or both; Horner is merely presenting an opposing argument that shows that we are not yet 100% sure what ecological niche the great tyrannosaurs filled.
Tarbosaurus: is it or isn't it a tyrannosaur?
Some paleontologists feel that Tarbosaurus was so closely related to Tyrannosaurus that the two should be placed in the same genus. If this proposal is adopted, then Tarbosaurus will be renamed Tyrannosaurus bataar.
See how our T. rex was assembled back in 1995.
Original page created by John Hutchinson 11/1995; modifications since 2005 by David Smith. Both T. rex photos by Dave Smith, © UCMP. Tarbosaurus photo by Ben Waggoner(?), © UCMP.
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