The feathered dinosaur also had bird-like arms similar to wings.
Scientists used high-powered lasers to reveal invisible details of what the creature looked like.
The research could give insights into the origins of flight, which is thought to have evolved more than 150 million years ago.
Michael Pittman of the University of Hong Kong said the study was a landmark in our understanding of the origins of birds.
"In this study, what we've done is we've used high-powered lasers to reveal unseen soft tissues preserved alongside the bones of a feathered dinosaur called Anchiornis," he said.