Fig. 1

The skeletons of the nonavian maniraptoran Velociraptor, the Jurassic bird Archaeopteryx, the Early Cretaceous short-tailed bird Sapeornis and enantiornithine Longipteryx, the Late Cretaceous Ichthyornis, and the living Gallus (chicken). In recent years, a wealth of bird-like nonavian maniraptorans and primitive (“dinosaur”-like) birds have been unearthed from Mesozoic rocks worldwide—these discoveries have consolidated the notion that birds evolved from maniraptoran theropod dinosaurs. Drawings not to scale