A diapsid skull in a new species of the primitive bird Confuciusornis

摘要

Since the description of Confuciusornis (the oldest beaked bird) in 1995, based on three partial specimens, large numbers of complete skeletons have been recovered. Most new material of Confuciusornis can be assigned to a single sexually dimorphic species, C. sanctus. Here we report a new species based on a remarkably well preserved skeleton with feathers and, for the first time in the Mesozoic record, direct evidence of the shape of a horny beak. It has a complete and large preserved postorbital that has a broad contact with the jugal bone. This character is presently only known in Confuciusornis, and may confirm previous suggestions of a postorbital in Archaeopteryx. The squamosal is in tight contact with the postorbital. These two bones form an arch dividing the upper and lower temporal fenestrae, as in other diapsid reptiles. The presence of a typical diapsid cheek region with two openings in Confuciusornis may preclude the presence of prokinesis (upper jaw mobility against the braincase and orbital area), a feeding adaptation found in most modern birds. The presence of a horny beak, characteristic of modern birds, coupled with a primitive temporal region provides new evidence for a mosaic pattern in the early evolution of birds.