Archaeopteryxis the oldest known and the most primitive bird yet found. It is very theropod like with a hyperextended "slashing" second toe as in dromaeosaurs. Recent work with the fossil melanosomes suggests that it was a black raven-colored animal. The first complete Archaeopteryx skeleton with feathers was found in 1861, and since then at least 6 other skeletons have been recovered.
Updated 121016
The key features that distinguish Archaeopteryx are a long bony tail,
teeth, with three claws on the wing, hyper-extensible second toes, and
a partially reversed first toe. Most recently, a fossil shows leg
feathers like those on Microraptor.