Many families of large dinosaurs, including apathosaurs, stegosaurs, and
allosaurs (Fig. 154) became extinct at the end of the Jurassic.The allosaur was
a carnivorous dinosaur with a thick skull to withstand a high-impact attack on
prey. The dinosaur would ambush its victim, slam into it at high speed with
jaws wide open, and drive its sharp teeth into the flesh.
Following the large dinosaur extinction, the population of small animals
exploded, as species occupied niches vacated by the large dinosaurs. Most of
the surviving species were aquatic, confined to freshwater lakes and marshes,
and also small,land-dwelling animals.Many of the small, nondinosaur species
were the same types that survived the dinosaur extinction at the end of the
Cretaceous, probably due to their large populations and ability to find refuge
during climatic disturbances.
THE BREAKUP OF PANGAEA
Throughout Earth’s history, continents appear to have undergone cycles of
collision and rifting.Smaller continental blocks collided and merged into
Figure 154Allosaurs
were among several
dinosaur genera that went
extinct at the end of the
Jurassic.
(Photo courtesy National
Museums of Canada)JURASSIC BIRDS