They first showed up during the Triassic period, 231.4 million years ago, and were the leading terrestrial vertebrates for 135 million years, from the start of the Jurassic (about 201 million years ago) till the end of the Cretaceous (66 million years ago), when the Cretaceous-- Paleogene termination occasion led to the extinction of most dinosaur groups at the close of the Mesozoic Era. The fossil record shows that birds evolved from theropod dinosaurs during the Jurassic Period and, as a result, they are taken into consideration a subgroup of dinosaurs by numerous paleontologists.
While dinosaurs were ancestrally bipedal, several extinct groups included quadrupedal species, and some were able to shift between these positions. Specify display frameworks such as horns or crests are common to all dinosaur teams, and some vanished teams created skeletal alterations such as bony shield and spines. While modern dinosaurs (birds) are usually tiny due to the restrictions of flight, numerous prehistoric dinosaurs were large-bodied-- the largest sauropod dinosaurs may have accomplished lengths of 58 meters (190 feet) and elevations of 9.25 meters (30 feet 4 inches).
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