The Tyrant King Lizards: The Tyrannosauridae
The name says it all. This group of huge carnivores
must have tyrannically ruled the land during the Cretaceous period. 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 U.C.-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 be 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?
Since tyrannosaurs were so huge, you might ask how
they could move well and hunt prey? In the dinosaur
movie Jurassic
Park, T.rex is depicted moving extremely quickly, maybe 50 or 60
mph, isn’t it? Is this
reasonable? For a more in-depth discussion of this, see our dinosaur speeds
site. Recently, scientists studied Jurassic Park to calculate the actual
speed (using the length of the dinosaur's strides) of T. rex in the
movie, and found that it was actually moving at a walking speed of about 10-12
mph (the jeep in the movie was supposed to be moving at about 40mph)! Your eyes
are easily deceived by speeds, especially when movie magic is used to dramatize
them.
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.
Tyrannosaur Fossils
Tyrannosaurs are surprisingly common in many North
American fossil beds, especially their large, serrated teeth (one of which is
shown above), which they shed periodically like most archosaurs.
The teeth of tyrannosaurids are very interesting -- rather than being the flat
knifelike blades as in most other carnivorous dinosaurs, they are, as
Berkeley's Professor Kevin Padian describes them, "like lethal
bananas"; more like giant spikes than razor-edged blades. With a mouthful
of this murderous fruitlike dentition, tyrannosaurs had a whopping bite, which
might have made up for their reduced forelimbs. The bite marks of these teeth
are quite recognizable on some dinosaur bones. Some tyrannosaur fossils show
evidence of bite marks from other tyrannosaurids, suggesting that there might
have been fierce fighting between tyrannosaurs, or even cannibalism. \\
UCMP Special Exhibit: T. rex ExpoNo dinosaur is so famous nor so feared as Tyrannosaurus. UCMP assembled this exhibition in conjunction with the unveiling of its free-standing skeletal mount. |
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