So far, China has provided us with a trove of dinosaur discoveries, including their evolutionary offshoot, the birds. Those fossils explain a lot of the evolution of the first birds. An impressively preserved new Chinese fossil bird fills a gap in this evolution.

Eoconfuciusornis ("early Confuciusornis"), described in the Science in China journal, represents a missing link between Archaeopteryx, the oldest found bird, and more evolved birds encountered in the Yixian geological formation (China).

This site has provided a trove of bird and small dinosaur fossils that have significantly boosted our knowledge of bird evolution, but the remains have come all from 125 to 120 Ma ago, which is a too narrow period to explain bird lineage. The Archaeopteryx lived about 150 Ma ago, thus a 25 Ma gap existed between it and Yixina birds. Eoconfuciusornis, found in the Dabeigou formation, fills in this gap, as it lived 131 Ma ago.

Its name shows its kinship to Confuciusornis ("Confucius bird"), the most frequently met bird in Yixian. The two types of fossil have many common bone traits, toothless horny bills and specific long paired tail feathers.

"The new discovery gives us a span of 11 million years of history for the Confuciusornis family, long enough to show patterns of evolution. Archaeopteryx was an efficient powered flapping flyer, but lacked many of the adaptations of the skeleton seen in modern birds - especially fusions of bones that support flight muscle and reduce length of the tail," Mike Benton of the University of Bristol, UK, co-author of a description of Eoconfuciusornis with paleontologists from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) in Beijing, told NewScientist.

Confuciusornis was already well adapted to flight, with flight muscles attached on the wing via a large bone ridge called the deltopectoral crest, and on the body by a well developed fused sternum.

Eoconfuciusornis had a pair of distinct sternal plates and smaller deltopectoral crest, mixing Confuciusornis traits with more archaic ones like the ones found in Archaeopteryx, a fact that revealed it as the earliest known member of the Confuciusornis family, Confuciusornithidae.

Confuciusornithidae were the first birds lacking teeth, but they still retained many primitive traits and were a dead evolutionary branch, leaving no descendants. Later toothed birds had more advanced traits resembling modern birds, thus modern birds lost their teeth independently.