SAURISCHIAN

any member of an order (Saurischia) of dinosaurs with hip bones arranged like those of modern reptiles, hence their name (lizard-hipped). The saurischians were one of the two major orders of dinosaurs, the other being the ornithischians. Their chief distinguishing feature was a hip girdle in which the pubis bone pointed forward and down. The saurischians are thought to have evolved from small, primitive, bipedal dinosaurs called thecodonts. They evolved somewhat earlier than did the ornithischians and first appeared in the Late Triassic Epoch (230 to 208 million years ago). Of the three known suborders of saurischians, the two main ones were the theropods and the sauropodomorphs. The theropods were two-legged flesh-eaters divided into two infraorders: ceratosaurs and tetanurans. While the ceratosaurs were primitive theropods, the tetanurans included the more advanced members of the suborder, notably the coelurosaurs and the carnosaurs. The coelurosaurs were small, slender-limbed, lightly built, fast-running reptiles that preyed upon their smaller reptile contemporaries. The carnosaurs were larger and more heavily built animals who preyed upon the larger plant-eating dinosaurs; Tyrannosaurus is the best known of the group. The coelurosaurs and carnosaurs had the same basic body plan, with highly developed hind legs for support and locomotion, small forelimbs, pointed teeth that were present along the entire length of the jaws, relatively large heads, and hollowed-out skulls and long bones. The other main suborder, Sauropodomorpha, consisted entirely of four-legged dinosaurs, most of whom were plant-eaters. Its earlier and more primitive infraorder was that of the prosauropods, or plateosaurs; these heavy, clumsy creatures died out in the Early Jurassic Epoch (208 to 187 million years ago) but gave rise to the larger and more advanced sauropods, which remained one of the dominant dinosaur groups until the end of the Cretaceous Period (66.4 million years ago). The sauropods included the largest of all dinosaur species, among them Apatosaurus (formerly Brontosaurus), Diplodocus, and Brachiosaurus. In general, the sauropods were distinguished by their huge size, long necks and tails, small heads, columnar legs, and heavy, solid limb bones. Another saurischian suborder, Staurikosauria, is known only from the incomplete remains of a few species but seems to have consisted of medium-sized flesh-eaters similar to some theropods. The coelurosaurs, carnosaurs, and sauropods persisted into the Cretaceous, though in fewer numbers than the ornithischians.