Theropoda (thair-uh-PODE-ah) is the suborder of carnivorous dinosaurs.
Theropods were bipedal; that is, they strode on two legs with their bodies
held close to horizontal and their tails outstretched for balance. They
were equipped with strong jaws and sharp, serrated teeth. As they were
predators, some species of whom hunted in packs (like today's lions), theropods
were very swift creatures. They had to be, because most of their natural
prey were fleet of foot: Hadrosaurs, for example, might have run as fast
as a modern horse.
Theropoda includes the largest carnivore ever to roam the Earth, Tyrannosaurus,
as well as the chicken-sized Compsognathus. Somewhere between the two were
the dromaeosaurids, medium-sized predators that ranged from 10 to 20 feet
(3 - 6 meters) long and were equipped with disproportionately-large sickle-like
claws on their hands and feet. Among the Dromaeosauridae are Utahraptor,
20 feet (6 meters) long with 12-inch toe claws, and Velociraptor, a smaller
version at 11 feet (3.5 meters) long with only slightly smaller claws.
Dromaeosaurids were quick, intelligent, and extremely ferocious.
Interestingly, in Mongolia fossil remains of a Velociraptor, were found
with those of a Protoceratops. It appears that the Velociraptor died in
the act of attacking the Protoceratops with its sickle-toed foot. Perhaps
the Protoceratops was able to deal the predator a death blow with its parrot-like
beak before succumbing itself.
The members of Ornithomimidae closely resembled modern ostriches and emus.
Such ornithomimids as Dromiceiomimus are thought to be among the most intelligent
of the dinosaurs, at least as intelligent as the modern birds they resemble.
The members of Spinosauridae were perhaps the most unusual-looking of theropods.
Running along their backbones were long spines, some of which were as long
as five feet. These spines may have supported a “sail” of skin that might
have helped a Spinosaurus to regulate its body temperature. Another reptile
with such a sail is the Dimetrodon; it is not a dinosaur, however, but
a pelycosaur, extinct before the dawn of dinosaurs.
Archaeopteryx, one of the first creatures we can definitely call a bird,
was a theropod. This small dinosaur has characteristics of other theropods
-- with the addition of feathers. There is however, considerable debate
as to whether Archaeopteryx and Sinornis should be classified as dinosaurs.
Indirect evidence suggests that theropods were endothermic.
One argument for their being endothermic is the two-legged, birdlike stance
of theropods; another is the level of their activity, apparently unlike
that of modern-day reptiles. It is also likely that some theropods were
more intelligent than present-day reptiles. The ratio of their brain capacity
to their size was large in comparison to other dinosaurs; think of the
intelligence of modern pack predators, such as wolves, compared to deer
or elk. The image of a pack of tyrannosaurs or velociraptors stalking its
prey is sobering to contemplate.
That theropods, like other dinosaurs, were extremely successful creatures
is demonstrated by the fact that they existed from the Triassic Period
through the Cretaceous Period, for 160 million years. Theropods, as such,
perished with the rest of the dinosaurs 66 million years ago, but as we
mentioned, their descendants are still among us.
The next time you see a sparrow or a cardinal, remember that the bright-eyed
little creature hopping here and there, head cocked to one side as it regards
you, is distantly related to Tyrannosaurus, the largest predator ever to
stalk the Earth.