In Depth
Yixianornis clearly differs from most other early Cretaceous birds in that the wings are rounded instead of pointed. The tail of Yixianornis is also clearly formed into a pygostyle which allowed for a strong and flexible attachment for tail feathers, which could be fanned out in flight, and then packed tight when resting. Altogether the form of the wings of Yixianornis indicate that this was a bird that was much closer to modern forms than other early Cretaceous birds such as Confuciusornis. The wings also indicate that Yixianornis was flying amongst densely overgrown areas such as forests where space was limited. By having short but broad wings, Yixianornis could avoid unnecessary damage to the wings from brushing against branches and tree trunks. Such wing proportions are still seen in modern birds that frequent forested habitats.
Yixianornis was likely a strong flyer, with the hand bones fused together for greater strength during a flight stroke, while the breast bone has a strong keel allowing for the attachment of larger pectoral muscles, allowing for stronger prolonged flapping flight. Yixianornis still had some primitive feature however, the most obvious of which is the presence of small peg like teeth in the mouth. Most of these teeth seemed to have been packed to the rear of the mouth, particularly in the lower jaw, while the anterior (front) tips of the mouth are lacking any teeth but have pitting. This may indicate that Yixianornis had developed a rudimentary beak that covered the forward portion of the mouth.
Further Reading
- Two new ornithurine birds from the Early Cretaceous of western Liaoning, China. - Chinese Science Bulletin 46(15):1258-1264. - X. Zhou & F. Zhang - 2001. - Insight into the evolution of avian flight from a new clade of Early Cretaceous ornithurines from China and the morphology of Yixianornis grabaui. - Journal of Anatomy, 208(3): 287-308. - J. A. Clarke, Z. Zhou & F. Zhang - 2006.
