Theropoda

Theropoda is a major clade of saurischian dinosaurs that includes the large majority of traditional carnivorous dinosaurs as well as the lineage that gave rise to birds. First appearing in the Late Triassic, about 230 to 235 million years ago, theropods diversified through the Jurassic and Cretaceous periods, occupying a wide range of ecological roles from small insectivores to apex predators. Birds are the only living members of Theropoda, representing the last surviving lineage from the Mesozoic theropod radiation.

Common features of theropods include a predominantly bipedal stance, elongated hind limbs with three weight-bearing toes, and hollow limb bones. Many theropods also show adaptations for predation such as sharp teeth or beaks and, in several lineages, grasping hands. In many lineages, especially in later theropods, arms are reduced in proportion. Feathers are known from numerous theropod fossils and are now regarded as widespread among the group, with the presence of pennaceous feathers in some theropods predating flight.

The theropod radiation consists of several major clades, including early coelophysoids and ceratosaurs, the more derived tetanuran line that splits into groups such as allosauroids and tyrannosauroids, and the coelurosaur clade that includes dromaeosaurs, troodontids, ornithomimosaurs, and the avian lineage. The non-avian theropods largely became extinct at the end of the Cretaceous, about 66 million years ago, while birds persisted and diversified in the Cenozoic.