Large herbivorous Sauropods and equally large carnivorous Carnosaurs lived during the Jurassic period, as well as smaller, quicker animals. Additionally, the first birds evolved from dinosaurs with simple feathers during the Jurassic period.
The largest animals to live during the Jurassic period were Sauropods. These large herbivores, such as Brachiosaurus and Apatosaurus, were some of the largest land animals in geologic history, sometimes weighing in at over 80 tons. Despite their proportionally small heads and brains, Sauropods were very successful and Sauropod remains occupy every modern continent, except Antarctica. The immense size of the Sauropods was an excellent defense against the large carnivores of the time, such as Allosaurus. Like modern predators that hunt prey larger than themselves, Allosaurus most likely hunted very young or injured animals.
The plated Stegosaurus was another Jurassic-era herbivore equipped to defend itself against predators. Interestingly, the dinosaur associated most famously with the Jurassic period due to modern entertainment, Tyrannosaurus rex, did not evolve until after the Jurassic period. This giant creature lived during the Cretaceous period.
Small, fast dinosaurs, such as coelurosaurs, were also common in the Jurassic era. Many of these smaller dinosaurs had simple feathers. The late Jurassic era saw the evolution of feathered Theropods into the first birds, such as Archaeopteryx.