Scientists already know that birds are the descendants of dinosaurs, although paleontologists cannot yet say exactly how this transformation occurred.. Now researchers have found a complete 120-million-year-old bird skeleton in China that could shed light on the transition, Science Alert reports..

The ancient creature had an archaic, dinosaur-like head combined with a more modern avian body..

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The transition from dinosaur to bird involves dramatic changes in form, function, and environment that eventually led to the avian body.. Some of these changes can still be seen in how modern birds develop..

The discovered creature was named Cratonavis zhui. It was found in 120-million-year-old sedimentary rocks in northern China.. Body prints of feathered dinosaurs and early birds, including Confuciusornis Santus, have been found here..

Scientists studied the remains of a fossil creature using high-resolution computed tomography. Using digital versions of mineralized bones, the team reconstructed the shape and function of the skull as it was when the bird was alive..

This analysis showed that the skull of Cratonavis zhui is almost identical to that of dinosaurs such as Tyrannosaurus rex, not birds..

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Among the avian branches of the dinosaur family tree, Cratonavis zhui sits between the long-tailed Archeopteryx, which looked more like a reptile, and ornitothoracs, which have already developed many features of modern birds..

The scientists also note that the fossil is marked by a surprisingly long scapula and first metatarsal (foot bone)—features that are rare in fossils of other avian ancestor dinosaurs and completely absent in modern birds..

Researchers believe that as the dinosaurs evolved into birds, the first metatarsal went through a process of natural selection that made it shorter.. Once it reached its optimal size, which was less than a quarter of the length of the second metatarsal, it lost its former function..

Previously, scientists discovered in China the remains of a microraptor, a crow-sized dinosaur that lived on Earth about 120 million years ago.. In his stomach they managed to find his last food. To their surprise, it was a mammal.