Theropod dinosaurs were mainly carnivorous (meat-eating), although some evolved secondarily to eat plants. Evidence for predatory habits includes grasping hands with sharp claws, and pointed teeth with serrated edges. Most species likely scavenged as well as hunted live prey, like most modern carnivores. Theropods include the largest land carnivores (such as;Tyrannosaurus) as well as species no larger than a sparrow (such as Microraptor), and eventually all modern birds. They first appeared in the fossil record in the Late Triassic (about 230 million years ago). Theropods were bipedal, walking on the main three toes of their hind feet. Their front legs tended to be smaller, used for grabbing and holding prey. They share many features in common with their avian descendants, including air-filled bones, feathers, a unique wrist structure, and other details of the skeleton.

Dinosaurs are land reptiles that include some of the biggest terrestrial life forms ever on Earth. We know dinosaurs from fossilized bones, teeth, footprints, eggs, and occasionally even soft tissues, although complete skeletons are rare. The earliest known dinosaurs are from the late Triassic (about 230 million years ago), when they were still overshadowed by other animals, such as synapsids (related to the ancestors of mammals). By the end of the Triassic, dinosaurs had begun their remarkable diversification, with several major lineages present. The Jurassic and Cretaceous periods saw dinosaurs dominate many land environments, reach enormous sizes, and diversify into thousands of species (including the first birds). Paleontologists have named more than 1200 species of dinosaurs, and that’s probably just a fraction of all the dinosaur species that existed. Most dinosaurs went extinct abruptly 66 million years ago (end of the Cretaceous), along with many other species. A period of severe environmental stress, punctuated by an asteroid impact, was likely responsible for this mass extinction.