same family of dinosaurs as the brontosaurs. Others, such as Tyrannosaurus rex,
perhaps the fiercest land carnivore of all time, maintained a permanent two-
legged stance with powerful hind legs, a muscular tail for counterbalance, and
arms shortened to almost useless appendages.
Tyrannosaurus rexwas at a distinct disadvantage as a galloping predator,
however. It was bipedaled with very strong legs, but its weak forelimbs were
unable to break a fall. If a 7-ton T. rexcharging prey at a top speed of 25 miles
per hour were to trip and fall, the crash could be fatal. More likely, the
dinosaurs traveled in hunting packs that surrounded their prey. This would
have required much less speed, thereby resulting in fewer crashes. About 90
million years ago, when the continents became isolated and evolved separate
faunas,Tyrannosaurus rexbegan to roam the American West.
Oviraptor was a fleet-footed predator, whose name, which literally means
“egg hunter,” was a misnomer because it was originally thought to have raided
nests of other dinosaurs. A fossil oviraptor was found sitting on a nest filled with
as many as two dozen eggs neatly laid out in a circle, with the thinner ends point-
ing to the outside.The dinosaur resembled a wingless version of an ostrich with
a shortened neck and a long tail. It sat with its pelvis in the middle of the nest
and had its long arms wrapped around the nest the way birds do.
The oviraptor was perhaps protecting the eggs against a gigantic sand-
storm that apparently engulfed and fossilized it along with its clutch 70 to 80
million years ago. The oviraptor was in the exact position a chicken would
take sitting on a nest. Whether the dinosaur was keeping the eggs warm as
birds do, shading them from the hot sun, or protecting them is unknown.TheFigure 149Dinosaurs
such as apathosaur
reached their maximum
size during the Jurassic
period.
Historical Geology