Avian features of Archaeopteryx feeding apparatus reflect elevated demands of flight

Powered flight, as the most physically demanding form of vertebrate locomotion, involves elevated energetic demands. The appearance of dinosaurian flight should therefore be associated with novel features related to increased feeding or digestive efficiency. Neornithines have several unique rostral features that facilitate complex oral tasks, increasing feeding efficiency; these include a mechanoreceptive bill-tip organ, highly mobile tongue, and oral papillae. Here, we provide the first evidence for the presence of these features in Archaeopteryx, the oldest known avian dinosaur. Large neurovascular openings at the tip of both the upper and lower jaw indicate the neurovasculature contained within the sensitive rostrum of non-avian theropods exited the tip of the snout. This suggests the presence of a mechanoreceptive soft tissue structure that was apparently widespread in early-diverging toothed birds, adding to the recognized structural diversity of the avian bill-tip organ. The co-occurrence of soft tissue oral papillae and an ossified basihyal indicative of increased tongue mobility is consistent with the interdependence of these structures in extant birds. The appearance of these three features close to the origin of feather-driven flight suggests that they evolved through pressures imposed by the increased caloric demands associated with the transition from terrestrial predator to volant bird.