King Tyrant-Lizard

Tyrannosaurus rex
(Osborn, 1905)

       The Tyrannosaurs evolved from small ornithomime-like dinosaurs in the late Jurassic.  Using their mouths rather than their hands to catch food, the proto-tyrannosaur's bodies grew larger while their arms atrophied.  While theropod predators continued to dominate the southern continents, the tyrannosaurs superseded the theropods everywhere else.

    By the time of the Cretaceous, the world is divided between two groups of large predators.  In Africa and South America, allosaurs like Carcharodontosaurus and Giganotosaurus are the dominent predators.  In the Northern Continent,  Asiamerica, Tyrannosaurus and its relatives occupy this niche (see T. Mike Keesey's maps of this time).  The largest of these tyrannosaurs is the clade's namesake, Tyrannosaurus. Most species of this genus live in the eastern half of Asiamerica, leaving the west to such tyrannosaurs as Albertosaurus, Gorgosaurus, Daspletosaurus and Dinotyrannus.  However, one species of Tyrannosaurus , Tyrannosaurus rex has migrated to North America and displaced the other predators there (see Jeff Poling's Catalog of Tyrannosaurus rex material ).

     Tyrannosaurus rex is the dominant predator of the deep woods (see Christopher Srnka's illustration of this lifestyle), its favorite prey being Triceratops horridus (see Brian Franczak's beautiful sketch of this)(see also Luis Ray's "The Chase" )(see also John Bindon's painting "No Escape" ).  Armed with three large horns and a sharp beak, these elephant-sized herbivores are quite capable of killing a large tyrannosaur. To hunt these dangerous animals successfully, the T. rex have evolved a barrage of weapons designed to maim the prey before it can maim the predator. Unlike the varied teeth of a mammalian predator, most of the teeth of a predatory dinosaur are all similar in shape. The size of bananas, these teeth are serrated on the front and back and are intended to slice through flesh, rather than hold it.  This arrangement is almost universal with predatory dinosaurs, but  T. rex's jaws are of a slightly different construction.  Scoop-shaped fangs are arranged in an arc at the front of the mouth.  These teeth function rather like a cookie cutter, allowing a T. rex to scoop out large chunks of flesh from the belly or flank of a triceratops . Driven by roughly 3,000 pounds of force, a tyrannosaur's jaw severs muscles and crushes bone.  The sudden depletion of blood, bone and muscle effectively cripples a T. horridus, allowed the tyrannosaur to eat at it leisure, with little or no threat to itself. This bleed-your-prey-to-death method is so efficient that it is the most commonly used form attack for almost all predatory dinosaurs.  This has also arisen independently among several kinds of mammals, reptiles and fish. (see Gregory S. Paul's book, Predatory Dinosaurs of the World)(see also Jeff Poling's Tyrannosaur hunting techniques )  Also, rather than chewing up-and-down like a mammal, a T. rex can slide its jaws forward and back, shearing its teeth across the meat.  This action, unlike any other method of mastication, pulverizes the bone and gristle and renders the meat easily digestible.  For a hunter that uses it's mouth and not its hands to hunt, construction of the skull is crucial to survival.  T. rex proves this point with it's powerful, wonderfully designed  jaws (see Peter Buchholz's T.rex skull )(see also Peter Buchholz's other T.rex skull )(see also Frank DeNota 's skull restorations of Gorgosaurus libratus and Tyrannosaurus rex)(see also Patrick O'Brien's reconstructed head of T. rex)(see also Shiraishi Mineo's reconstructed T. rex head )(see also Truett Garner's reconstructed T. rex head )(see also Mikko Haaramo's reconstructed T.rex head )(see also Christopher Srnka's reconstructed T.rex head ).

    The mating and child rearing rituals of T. rex are, by necessity, much like those of any other large dinosaur.  During the mating season, large, female tyrannosaurs are courted by smaller males.  Releasing pheromones and flashing bright colors, the males construct large, crater-shaped nests.  If the female excepts the nest, the male mates with her and leaves, his job done.  The female, upon laying the eggs in the nest, buries them beneath a pile of vegetable matter.  Besides, insolating the eggs and protection them with protection from the elements, the vegetable matter that makes up the nest ferments and creates the heat necessary for incubation.  While the eggs are in their nest, the mother is never far away from the nest.  Every few minutes, she buries her snout in the mound to test its temperature.  If it is too cold, she will build the pile up; if it is too warm, she will remove part of it or dump water on it so the evaporation will cool it.

At the time when the large animals (like T. rex ) are incubating eggs, all small, carnivores become egg-eaters.  These creatures will endlessly torment mother dinosaurs into exhaustion, then steal her eggs (see Jeff Poling's Scavenging and Sexual Dimorphism in T. Rex ).

        For a little while after the eggs have hatched, the mother T. rex will continue to look after her young, feeding them and guarding them from predators.  Once they have learned to hunt for themselves, however, the female T. rex pushes them out of the nest and walks away to hunt for herself.  The babies look entirely different from their adult form, more closely resembling their gracile, ornithomime ancestors than they do their own parents.  Because of this dimorphism, the babies and the adults fill entirely separate ecological niches.  Because of a combination of growth rate and a set time of birth for T. rex, the time at which there are no babies to fill their niche is small (see Tinker the kid rex ).

        Although T. rex have no real enemies, they are a fiercely territorial and non-gregarious species. T. rex adults are not above killing and eating members of their species.  In fact, at times it seems almost as if the T. rex is the main predator of itself.  This form of cannibalism does have a purpose, however.  When the year has been bad and there is not enough food to support a large number of tyrannosaurs, the adults will begin to eat the next generation (although never their own children) out of hunger.  As a result, next year's the population of adult T. rex will be smaller than the previous year's.  Without so many predators, the population of prey will boom, making it possible for the predator population to grow as well (see Jeff Poling's Tyrannosaurus the cannibal ).
 
 

Thanks to Jordan Mallon , for supplying the first illustration, and Ray Stanford, of course.
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© Daniel Bensen 2000
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