Confuciusornis, the "Confucius Bird," is a well-documented genus of animals from the Yixian and Jiufotang Formations in China. With a length of fifty centimeters and a wingspan of seventy centimeters, the Confuciusornis was not very different from modern birds. It was one of the earliest birds known to have a toothless beak, despite not being closely related to modern birds. The beak therefore developed through convergent evolution, which is the evolution of similar features in unrelated animals. Fossils of its wings include many melanosomes (cells that contain pigment), allowing us to learn that it was colored grey, red/brown, and black. The wings were probably white, with the long tail feathers being dark along their entire length. Confuciusornis was a piscivore, catching and feeding upon small Cretaceous fish with its beak. This diet is demonstrated in a fossil specimen preserved with its last meal in its belly, similar to the famous Compsognathus fossils. As a whole, Confuciusornis fossils are intriguing because some have the long tail feathers but others do not, and some are much larger than others. The best explanation for this variability is sexual dimorphism: the leading hypothesis states that the larger ones are the females, and both sexes lost the feathers during molting season.