Yanornis

Yanornis is an extinct genus of Early Cretaceous bird, thought to be closely related to the common ancestor of all modern birds. One species, Yanornis martini, has been described from fossils found in the Jiufotang Formation at Chaoyang, Western Liaoning province, PRC, and as of 2004, five specimens were known. The age of the Jiufotang Formation is somewhat unclear, but most estimates point towards an early Aptian origin, about 125-120 million years ago.

It was the size of a large pigeon, had a long skull with about 10 teeth in the upper and 20 teeth in the lower jaw, and was both able to fly and walk well, having a well-developed U-shaped furcula (wishbone). It ate fish, and in the associated adaptations shows remarkable convergent evolution to the unrelated enantiornithine Longipteryx. Furcula and teeth, on the other hand, are more like in the enantiornithine Aberratiodontus.

The absence of the prefrontal bone and the non-diapsid skull place Yanornis into the Ornithurae which also includes the common ancestor of living birds. Similarly, its scapula and coracoid had evolved the basic shape and layout as in modern birds; enable Yanornis to lift its wings far above its back for an efficient upstroke. It thus was a more efficient flyer compared to Enantiornithes (which have the modern condition in a less well developed form), let alone Confuciusornis which like Archaeopteryx was only marginally able to perform an upstroke. To allow for the necessarily large flight muscles, its sternum was longer than wide, again representing an essentially modern condition, as did many features of its arm skeleton.

Taxonomy and systematics
Yanornis gained notoriety when the front half of a fossil bird was combined with the tail of a Microraptor to make the paleontological forgery "Archaeoraptor". Upon discovering this, the bird half was described as Archaeovolans repatriatus, which was later found to be a junior synonym of Yanornis. See Archaeoraptor.

In a 2006 study of early bird relationships, it was found that Yanornis, Yixianornis, and Songlingornis formed a monophyletic group; since Songlingornis was the first of these birds to be described, the family containing this group is Songlingornithidae. The order Yanornithiformes has been erected to mark their distinctness from other early Ornithurae such as Gansus, but might be called Songlingornithiformes; especially if the present taxon is indeed a junior synonym of Songlingornis as sometimes proposed. On the other hand, other analyses seem to suggest that these two genera were well distinct.