ETYM Greek dinos terrible + sauros lizard.
Any of a group of extinct reptiles living between 215 million and 65 million years ago. Their closest living relations are crocodiles and birds, the latter perhaps descended from the dinosaurs. Many species of dinosaur evolved over the millions of years during which they were the dominant large land animals. Most were large (up to 90 ft/27 m), but some were as small as birds and lizards, into which some evolved. There were carnivorous as well as herbivorous types. Early forms were bipedal, and some later forms remained so, although many herbivorous forms walked on four legs. Most became extinct 65 million years ago for reasons not fully understood, although many paleontological, astronomical, and ecological theories exist.
They never coexisted with the human species, which began to evolve only some 6 million years ago.
Dinosaurs are divisible into two unrelated stocks, the orders Saurischia and Ornithischia. Members of the former group possess a reptilelike pelvis and are mostly bipedal and carnivorous, although some are giant amphibious quadrupedal herbivores. Members of the latter group have a birdlike pelvis, are mainly quadrupedal, and entirely herbivorous.
The Saurischia are divided into: Theropods, including all the bipedal carnivorous forms with long hindlimbs and short forelimbs (Tyrannosaurus, Megalosaurus); and Sauropods, including the large quadrupedal herbivorous and amphibious types with massive limbs, long tails and necks, and tiny skulls (Diplodocus, Brontosaurus).
The Ornithischia include a number of varied groups: Ornithopods, Jurassic and Cretaceous bipedal forms (Iguanodon) and Cretaceous hadrosaurs with duckbills; Stegosaurs, Jurassic quadrupedal dinosaurs with a double row of triangular plates along the back and spikes on the tail (Stegosaurus); Ankylosaurs, Cretaceous quadrupedal forms, heavily armored with bony plates (Nodosaurus); and Ceratopsians, Upper Cretaceous quadrupedal horned dinosaurs with very large skulls bearing a neck frill and large horns (Triceratops).
Species variation.
Brachiosaurus, a long-necked plant-eater of the sauropod group, was about 12.6 m/40 ft to the top of its head, and weighed 80 metric tons. Compsognathus, a meat-eater, was only the size of a chicken, and ran on its hind legs. Stegosaurus, an armored plant-eater 6 m/20 ft long, had a brain only about 3 cm/1.25 in long. Not all dinosaurs had small brains. At the other extreme, the hunting dinosaur Stenonychosaurus, 2 m/6 ft long, had a brain size comparable to that of a mammal or bird of today, stereoscopic vision, and grasping hands. Many dinosaurs appear to have been equipped for a high level of activity.
An almost complete fossil of a dinosaur skeleton was found in 1969 in the Andean foothills, South America; it had been a two-legged carnivore 6 ft/2 m tall and weighing more than 220lb/100 kg. More than 230 million years old, it is the oldest known dinosaur. Eggs are known of some species. In 1982 a number of nests and eggs were found in “colonies” in Montana, suggesting that some bred together like modern seabirds. In 1987 finds were made in China that may add much to the traditional knowledge of dinosaurs, chiefly gleaned from North American specimens. In 1989 and 1990 an articulated Tyrannosaurus rex was unearthed by a paleontological team in Montana, with a full skull, one of only six known. Tyrannosaurs were huge theropod dinosaurs of the Upper Cretaceous in North America and Asia.
Any of numerous extinct terrestrial reptiles of the Mesozoic era. + prikaži više