Dinosaurs

Dinosaurs. . The animals portrayed by these models are two of the most familiar and well known of all dinosaurs. However, these two animais did not live at the same time. The brontosaur died out over 40 million years before the tyrannosaur appeared. Nor were either of these responsible for the Dinosaur Valley footprints. The park's tracks were made by Pleurocoelus, a smaller, later relative of the brontosaur, and by Acrocanthosaurus, a smaller, earlier relative of the tyrannosaur. , Dinosaurs first appeared about 210 million years ago. They shared all basic reptilian adaptations for life out of water, including a dry, scaly, water-tight skin and eggs suited for development on land with membranes and shells to protect the embryo. The group of reptiles which gave rise to dinosaurs had two holes or windows in their cheek bones. This allowed muscles of the jaw to bulge outward when flexing the jaw shut for better biting and chewing. , The most unique features of dinosaurs were their hip bones and their tails. The hip was modified allowing many dinosaurs to become the first animals able to stand on two legs, using the tail as a counterbalance, and to move the legs faster and more efficiently. , With these modifications, dinosaurs increased in size, numbers and diversity of forms. They dominated the earth for 140 million years. Then, 65 million years ago, they disappeared for reasons still uncertain. Their only legacies are petrified bones, fossil footprints, and a new type of animal known as birds. , Acrocanthosaurus , maximum length: 40 ft (12 m) , maximum weight: 7 US tons (6.4 metric tons) , time period: Early Cretaceous, 140 to 100 million years ago , place: Oklahoma and Texas , classification: spinosaurid family of carnosaurs, Pleurocoelus , maximum length: 50 ft (15 m) , maximum weight: 27 US tons (24 metric tons) , time period: Early Cretaceous, 140 to 100 million years ago , place: Maryland to Montana and Texas , classification: brachiosaurid family of sauropods , Tyrannosaurus , maximum length: 50.ft (15 m) , maximum weight: 8 US tons (7.3 metric tons) , time period: Late Cretaceous, 100 to 65 million years ago , place: Montana to Texas , classification: tyrannosaurid family of carnosaurs , Apatosaurus , maximum length: 75 ft (23 m) , maximum weight: 33 US tons (30 metric tons) , time period: Late Jurassic, 160 to 140 million years ago , place: Montana to Oklahoma to Baja California , classification: diplodocid family of sauropods