Sapeornis

Sapeornis is a genus of primitive bird which lived during the Early Cretaceous (late Aptian to early Albian, roughly 120-110 mya). The genus contains only the species Sapeornis chaoyangensis which is known from fossils found in Jiufotang Formation rocks near Chaoyang, PRC. Several nearly complete skeletons have been found (Zhou & Zhang 2003).

This animal was about 30-33 cm long in life, excluding the tail feathers (which are unknown). From its general morphology and some peculiar similarities with oviraptorosaurs such as Caudipteryx, it is usually considered to be fairly close to Omnivoropteryx (Czerkas & Ji 2002).

The hand of Sapeornis was far more advanced than that of Archaeopteryx. It had 3 fingers, the outer ones with 2 and the middle one with 3 phalanges, and a well-fused carpometacarpus. Its arms were about half again as long as the legs, suggesting a large wing area. On the other hand, its shoulder girdle was apparently ill-adapted to flapping flight and its furcula was unusual, with the hypocleidum of more advanced birds but a general conformation even more primitive than in Archaeopteryx (Senter 2006). The humerus was large and bore holes, apparently to save weight, as in the Confuciusornithidae.

The skull has a handful of teeth in the upper jawtip only. It was altogether similar to Archaeopteryx, but even more so to small oviraptorosaurs and Omnivoropteryx. Sapeornis had gastralia but no (or unossified) uncinate processes. A sternum was either not present or small and easily lost. The pygostyle was rod-like as in Confuciusornis and Nomingia, but like in the former there was no long bony tail anymore. While the tarsometatarsi were more fused than in Archaeopteryx, the fibula was long and reached the distal point of the tarsal joint, not reduced as in more modern birds (and some non-avian theropods like Avimimus). The first toe pointed backwards. In specimen IVPP V12375, the stomach contained numerous small gastroliths.

In conclusion, regarding the absolute numbers of modern bird features, S. chaoyangensis is about as more advanced than Archaeopteryx as was Confuciusornis. However, the apomorphies were largely different from Confuciusornis, and a character analysis demonstrates that these two were not closely related (Zhou & Zhang 2006). As its plumage is not known yet, the airfoil shape of Sapeornis is unknown. As indicated by the slender pygostyle, its tail plumage was (unlike in the reconstruction above) probably short as in the Enantiornithes or even vestigial as in Confuciusornis. The reduced fingers suggest that it might have had an alula. Not being well-adapted to flapping flight, Sapeornis probably was a glider and/or soarer that preferred more open country compared to the Enantiornithes and other predominantly woodland birds, although it was able to perch on branches. The small gastroliths, overall large size, and the inferred habitat indicate that Sapeornis was most likely a herbivore, possibly eating plant seeds and fruits.(Zhou & Zhang 2003)