Theropoda is arguably the best known and most studied of all dinosaur clades. A combination of body and trace fossil evidence for theropods speaks of their long and rich history, which started at the beginning of the dinosaurian reign in the Late Triassic and continues today through birds, their probable descendants. Eoraptor of the Late Triassic of Argentina may have been both the earliest known dinosaur and theropod, although not all paleontologists accept this designation. Among the first possible theropods were the herrerasaurids (e.g., Herrerasaurus and Stauriko-saurus), which were affiliated with Theropoda but may represent a separate saurischian clade. By the end of the Triassic, ceratosaurs (e.g., Coelophysis and Syntarsus) showed that non-avian theropods had arrived to stay in terrestrial ecosystems for the next 150 million years or so. This was ably demonstrated by other ceratosaurs of the Jurassic (Ceratosaurus) and Cretaceous (abelisaurids, such as Carnotaurus), but most prominently by tetanurans beginning in the Middle Jurassic. Tetanurae is the most diverse of theropod clades and included some of the most famous dinosaurs, such as Allosaurus, Deinonychus, Giganotosaurus, Tyrannosaurus, and Velociraptor. Tetanurans also had one of their lineages contribute to the evolution of birds by the Late Jurassic, and numerous examples of feathered tetanurans have been recently found in Cretaceous strata of China. Theropods occupied the entire geologic range for dinosaurs, and their fossils occur on every continent.
Despite their widespread distribution through time and space, theropods are relatively uncommon as body fossils in comparison to most dinosaurs. Fortunately, their tracks are exceedingly abundant in places, more so than those of other dinosaur clades, and other theropod trace fossils are becoming more recognized. Theropod evolution is reflected by characteristics that show:
1 pneumatization and consequent lightening of the skeleton, especially the skull;
2 increased endocranial volume with proportion to total body volume;
3 changes in hind limb and pelvic girdle anatomy that further enhanced bipedalism and mobility; and
4 fore limb alterations that allowed for better grasping, especially with digits I through to III.
These and other characteristics show apparent tendencies toward specialization in their respective environments, and theropods were among the most diverse dinosaurs known.
Theropods are normally generalized as the meat-eating dinosaurs and are often synonymized with dinosaur predation. They were mostly carnivorous, but a few, such as some ornithomimosaurs and oviraptorsaurs,
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