A cloacal opening in a non-avian dinosaur.

The Frankfurt specimen of Psittacosaurus sp. (SMF R 4970) from the Early Cretaceous Jehol deposits of Liaoning (Figure S1) exhibits exceptional preservation of scale-clad integument1. Preservation of colour patterns and countershading allowed a detailed reconstruction of this individual's physical appearance. It was previously noted that the cloacal region was preserved2, but its detailed anatomy was incorrectly reconstructed. We show here that the fine anatomy of the vent is remarkably well preserved and can be retrodeformed to illustrate its three-dimensional nature. The vent's scale anatomy and pigmentation are distinct from adjacent body regions, and although its anatomy does not reveal much information about the ecology, or sex, of this dinosaur, it suggests possible roles for visual and olfactory signalling.