What is the Difference Between Saurischians and Ornithischians?
Saurischians and ornithischians are the two groups of dinosaur, defined in terms of pelvic structure. Saurischians, whose name means “lizard-hipped,” had a pelvic structure more similar to that of modern lizards, while the ornithischians (“bird-hipped”) had a pelvic structure more like modern birds. Confusingly, modern birds actually evolved from a group of lizard-hipped dinosaurs called coelurosaurs, which evolved the bird hip in an example of parallel evolution. All non-avian dinosaurs went extinct 65.5 million years ago in an event called the Cretaceous-Tertiary extinction. Thus, saurischians left no living descendants. Saurischians mostly consisted of theropods, which included all carnivorous dinosaurs including T. rex, and sauropodomorphs, which included the sauropods, by far the largest group of dinosaurs and one of the two great dinosaur herbivore lineages. Ornithischians included a large number of herbivores, some of which traveled in herds, which include ceratopians such as Tr
Saurischia-One of two orders of extinct reptiles popularly known as dinosaurs, the other being the Ornithischia. The two orders are distinguished by a number of anatomical differences, but foremost is the triradiate shape of the saurischian pelvis, in contrast to the tetraradiate pelvis of ornithischians. Both dinosaurian orders originated from thecodont reptiles by Middle Triassic times and are classified together with the order Thecodontia in the infraclass Archosauria. Saurischian bones have been found on all continents except Antarctica, and in rock strata ranging from Middle Triassic to latest Cretaceous in age. ornithischian-Any of the “bird-hipped” dinosaur species (order Ornithischia), herbivores with hip bones arranged like those of modern birds, with the pubis bone pointed backward. Many species had a toothless, horny beak and powerful cheek teeth. Ornithischians flourished from the Late Triassic to the Late Cretaceous Epoch (227 – 65 million years ago). Many species (in the
