Fossils of bird-like dinosaurs
It is now almost certain that Archaeopteryx was not a direct ancestor to the modern birds, but would have been an offshoot. The fossil of a 4 metre long coelurosaur called Deinonychus showed an anatomy almost identical to Archaeopteryx except that it lacked wings and feathers and was around 50 million years older than Archaeopteryx. Other bird-like dinosaurs include Avimimus, a 1,5 metre bipedal fossil found in Mongolia. This animal had a short deep head, toothless beak, long neck and tail and possibly feathers, which would make it the most ancient of feathered animals. Yet another fossil discovered in North America called Protoavis, may have been a bird or a dinosaur, but certainly pre-dates Archaeopteryx. However, the fossil that has attracted the most amount of interest in relation to the links between birds and dinosaurs is Mononychus, a turkey-sized predator equiped with sharp teeth and a long tail and looked very similar to other theropods. Mononychus does share some anatomical features with birds that are not found in any of the other bird-like dinosaurfossil including Archaeopteryx. For example Archaeopteryx has a fibula (the thin bone in the lower hind limb) that touches the ankle, in birds and Mononychus this does not happen. All birds have a keeled sternum for attachment of wing muscles. Mononychus also has a keeled sternum and some of its wristbones are fused together which is also an adaptation for flight. This evidence suggest that Mononychus evolved from a flying animal, just as ostriches are descended from flying birds. If this is the case Mononychus probably had feathers and the real ancestor of birds goes back still further in the fossil record.
A sitting Deinonychus antirrhopus by paleoartist John Conway. The picture is designed to emphasize the birdlike nature of dromaeosaurs; feathers, feather patterns and thickness are based entirely on educated guesswork, but would be considered plausible by many modern paleontologists.( http://en.wikipedia.org/wiki/Deinonychus