Theropods ("beast foot") are a group of bipedal, primarily carnivorous dinosaurs, belonging to the saurischian ("lizard-hip") family. They flourished from the Late Triassic (about 220 million years ago) until the close of the Cretaceous (65 million years ago), yet are today represented by the 8600 living species of birds.
Some theropod species are: tyrannosaurs, including the famous Tyrannosaurus rex, the dromaeosaurs, including Velociraptor and Deinonychus, the herbivorous ornithomimids and omnivorous oviraptorosaurs, and the birds. A number of features link them to birds, including a three-toed foot, a wishbone, air-filled bones, and (in some cases) feathers and brooding of the eggs.
Theropod classification is an area of research in a state of flux, but broadly speaking, there are three main groups recognised. The Ceratosauria are a diverse group which includes animals with odd cranial morphology. Examples include the twin-crested Dilophosaurus of Jurassic Park fame and Ceratosaurus which had bony nodules on its nose and over each eye. The other two groups are more closely related and are referred to as the Tetanurae. This clade includes many of the most famous theropods and is subdivided into Spinosauroidea and Avetheropoda . The Avetheropoda is again divided into the Carnosauria (including Allosaurus) and the Coelurosauria, which includes animals as well known and diverse as Velociraptor and Tyrannosaurus rex. It is from this last sub-group that birds are descended.
Known theropod species include: