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.