Saurischia



Saurischia is one of the two major dinosar groups, the other being Ornithischia. The name Saurischia means "lizard-hipped" and the term was first coined by Harry Seeley in 1888 when he classified dinosaurs into two major group sbased on hip structure.

Saurischia is further split into the clades Sauropodomorpha, containing prosauropods (Prosauropoda) and sauropods (Sauropoda), and Theropoda. Saurischia is the only surviving group of dinosaurs as they include Aves, or modern birds.

Fossil Record
The fossil record of saurischians is very extensive, owing in part to the extreme diversity of saurischians. In general theropods are better represented in the fossil record than sauropods, owing partly to the smaller size of theropods and also their greater numbers.

Nests of saurischian dinosaurs have been uncovered, ranging from the thousands of sauropod eggs discovered in South America to the discoveries in Asia of oviraptorosaurs having fossilized while brooding their nests. Coelurosaur eggs appear to have usually been thin and tapering in shape, especially those of oviraptorosaurs, while known sauropod eggs are usually almost completely round.

Extensive skin impressions have also been found of saurischians, especially of coelurosaurs. The discovery of feather impressions on a Sinosauropteryx specimen in 1996 was the final proof of the fact that birds are indeed coelurosaurian theropods, while it has been discovered that some titanosaurian sauropods have some sort form of thin armor on their backs.

Classification
When Seeley first coined the names Saurischia and Ornithischia in 1888, he believed that Dinosauria was a polyphyletic group - that is, the common ancestor of all dinosaurs was not a dinosaur but something else. Before this the prevailing theory of dinosaur classification was one proposed by Othniel Marsh a decade before, in which he had classified dinosaurs into Sauropoda, Theropoda, Ornithopoda and Stegosauria. Though Seeley's theory that dinosaurs were a polyphyletic grouping was disproved, his theory on the two different major groups has withstood analysis and is still used today.

Within Saurischia, however, classification is less clear, especially with sauropodomorphs. The dinosaur Saturnalia, thecodontosaurids, prosauropods and sauropods are thought to form the group sauropodomorpha, though some also include the basal bipedal dinosaur Eoraptor within this group, as is supported by many modern studies.

Theropoda, meanwhile, includes the major groupings Ceratosauria, Tetanurae and Herrerasauria, which in turn are divided into a large number of smaller groups.

Saurischian classification according to The Dinosauria (2nd edition)

Saurischia

Eoraptor?

      Saturnalia

      Thecodontosauridae

Prosauropoda

Sauropoda

Theropoda

Herrerasauria

Ceratosauria [including Coelophysoidae]

Tetanurae