Theropod << THEHR uh pahd >> is the name for a large, diverse group of dinosaurs. The theropod group includes some of the most famous dinosaurs, such as Tyrannosaurus and Velociraptor. The group includes herbivorous (plant-eating), piscivorous (fish-eating), and omnivorous (both plant- and animal-eating) dinosaurs. However, most theropods were carnivorous (meat eating). In fact, all dinosaurs that are known to have been predators (hunters) are classified as theropods.
The name theropod comes from Theropoda, a suborder (a level of scientific classification) that makes up one of two groups of saurischian (lizard-hipped) dinosaurs. The name Theropoda means beast feet.
The first theropods are known from fossils that date to the Triassic Period. Most theropods became extinct when other dinosaurs died out at the end of the Cretaceous Period, about 66 million years ago.
Anatomy.
Theropods show a wide variety of body sizes and adaptations. Extinct theropods ranged in size from about 13 inches (35 centimeters) to around 50 feet (15 meters) in length. The largest theropods may have weighed over 7.7 tons (7 metric tons). The theropod body plan typically included relatively short forelimbs. Nearly all theropods walked on their hind legs. Most had sharp, often serrated (saw-edged) teeth.
Some theropod groups departed from this generalized body plan. These included the oviraptorosaurs, which had short skulls with a parrot-like beak and no teeth. A herbivorous theropod group called therizinosaurs << THAY rih ZY noh sawrz >> had the largest claws of any animal at more than 3 feet (1 meter). Spinosaurids, such as Baryonyx and the enormous Spinosaurus had long, narrow jaws and conelike teeth. Scientists recognize these features as anatomical adaptations for fish eating.
Other evidence from the fossil record shows that many theropods were predators. This evidence includes theropods found locked in combat with their prey and theropod bite marks on fossil bones. Some theropods have been discovered with preserved stomach contents, proving they were carnivorous.
Relation to birds.
A number of small theropods have become pivotal organisms for scientists to better understand of the evolution of birds. Scientists had long noticed similarities between the fossils of Archaeopteryx and theropods like Deinonychus. Today, fossil discoveries of feathered dinosaurs provide a picture of the early evolutionary history of birds and their dinosaur origins.
Fossils of many theropods, including those related to well-known dinosaurs such as Velociraptor, preserve different types of integument (tissue) such as protofeathers (primitive feathers) and branching threadlike filaments. The skeletons of theropods also have a furcula (wishbone), swivel-like wrist joints, and bones with air spaces, which are all features seen in birds. Other theropod fossils have been discovered in a birdlike sleeping pose or sitting on a clutch of eggs.
Today, abundant fossil evidence suggests that feathers originated among theropod dinosaurs, before the appearance of birds. Scientists now also understand that many, if not most, theropod dinosaurs had feathers. Today, most scientists regard birds as living descendants of theropod dinosaurs that survived the dinosaur extinction at the end of the Cretaceous Period.
