Yanornis

Yanornis (simplified Chinese: 燕鸟; traditional Chinese: 燕鳥; pinyin: Yān niǎo; lit. 'Yan bird') is an extinct genus of fish-eating Early Cretaceous birds. Two species have been described, both from Liaoning province, China: Yanornis martini, based on several fossils found in the 120-million-year-old Jiufotang Formation at Chaoyang, and Yanornis guozhangi, from the 124-million-year-old Yixian Formation.

Description

Y. martini was the size of a chicken, had a long skull with about 10 teeth in the upper jaw and 20 teeth in the lower jaw, and was both able to fly and walk well, having a well-developed U-shaped furcula (wishbone).

The absence of the prefrontal bone and the non-diapsid skull allows Yanornis to be classified as an ornithuromorph, a member of a group of stem-birds 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, enabling Yanornis to lift its wings far above its back for an efficient upstroke. It was probably a more efficient flyer compared to Enantiornithes (which have the modern condition in a less well-developed form), and especially compared to Confuciusornis and Archaeopteryx, which were only marginally able to perform upstrokes. To allow for the necessarily large flight muscles, the sternum of Yanornis was longer than it was wide, again representing an essentially modern condition.

The feet of yanornis had long toes, with elongated phalanges and relatively strait unguals. The toe pads (soft fleshy sturctures present on the toes of tetrapods) on the 3rd toe are mesarthral (the separation between each pad corresponds to an articulation point) and are most similar to those of ground birds like chickens.