The Jurassic Period (200 million to 145 million years ago): During the Jurassic Period the Earth continued to divide into northern and southern super-continents. The land became drier in many areas and climates became more varied. Places that are land now were underwater then. (Seashells found from this time in what is now the Jura Mountains of France gave this period its name.) This is basic information about dinosaurs?
The northeastern part of North America was underwater for much of the Jurassic Period and the Cretaceous Period that followed. But in other regions, like the American West, forests spread and shallow lakes formed. Evergreen plants, including conifer trees, grew in deep forests.
Dinosaurs grew to many new shapes and sizes during this period, while many other reptiles disappeared fro the land. Dinosaurs became the dominant land animals in the Jurassic Period. The new bird hipped groups included armored and plated dinosaurs, as large as the truck size Stegosaurus, Giant, four legged, plant eating sauropods evolved from the prosauropods, including the six-story-high sauropods Branchiosaurus. Many other giant plant-eaters also appeared at this time. The longest of all dinosaurs were the whip-tailed diplodocids, including Seismosaurus, the 150-foot-long (45 m) earth-shaker.
In the following pictures you can judge the actual size of dinosaur, if they are in present era.
Meanwhile, meat-eaters grew as large as the 35-foot-long (11 m) Allosaurus, and as small as the beagle size Compsognathus. The biggest meat-eaters were powerful hunters with strong jaws and arms. The small hunters were the fastest dinosaurs of the Late Jurassic. Small meat eating dinosaurs much resembled the first birds, which appeared at this time. Giant sea reptiles and huge flying reptiles evolved in the Jurassic, too.