Some of the oldest known birds are from China's Liaoning province and are between 120 and 145 million years old.

These Liaoning birds lacked the long bony tail of their ancestors and had larger, keeled breastbones and true flight feathers, suggesting that they could fly for some distance. As in modern birds, the large wing feathers were asymmetric, meaning that the barbs were not the same length on each side of the shaft. This gave the wing feathers an 'air foil' shape in cross-section that created the lift necessary to fly.

Some of the Liaoning birds still had grasping fingers and some retained teeth, but others had toothless beaks like modern birds.

Archaeopteryx lithographica
Artist: James Reece