Coelurosauria is a group of theropod dinosaurs that includes the subgroups Tyrannosauridae, Ornithomimidae, and Maniraptora.
Coelurosaur characteristics include an extended sacrum, a distally stiffened tail and a bowed ulna. The tibia is also characteristically longer than the femur in coelurosaurs. Recent fossil evidence shows that some coelurosaurs were feathered, and it is conceivable (and indeed the most parsimonious hypothesis) that feathers may have been a feature of the entire group.
Most coelurosaurs are bipedal predators, and the group houses some of the largest (Tyrannosaurus rex) and smallest (Microraptor gui) carnivorous dinosaurs discovered thus far. Modern birds are classified by most palaeontologists as an extant group of coelurosaurs (in the subgroup Maniraptora).