clutch was probably a communal nest similar to that used by ostriches, into
which hens deposit their eggs and take turns incubating them.
The giant herbivores might have traveled in great herds, with the largest
adults in the lead and the juveniles placed in the center for protection. Duck-
billed hadrasaurs (Fig. 150), among the most successful of all dinosaur groups,
were up to 15 feet tall and lived in the Arctic regions.There they had to adapt
to the cold and dark or else migrate in large herds over long distances to
warmer climates.Triceratops, whose vast herds roamed the entire globe toward
the end of the Cretaceous and were among the last to go during the dinosaur
extinction, might have contributed to the decline of other species of dinosaurs
possibly due to extensive habitat destruction or the spread of diseases.
Fossils of western North American triceratops have been found in
sediments deposited between 73 and 65 million years ago, when the region
was covered by a warm, shallow sea. Parallel sets of footprints and bone
beds with large numbers of remains suggest that triceratops congregated in
large herds that might have migrated over long distances. Rather than walk-
ing with a sprawling, crocodilelike gait as originally thought, the animal
walked erect similar to a rhino. It could probably run as fast as one. It could
also lock its knees like cows and horses do when they sleep standing up.
The dinosaur was one of the dominant herbivores long before grasses
evolved. It had an enormous head, weighing nearly half a ton and used its
turtlelike beak and bladelike teeth to graze on flowering shrubs, palm
fronds,and small trees.
Figure 150Hadrasaurs
lived in the Arctic regions
during the Cretaceous.JURASSIC BIRDS