Discovery of an ornithurine bird and its implication for Early Cretaceous avian radiation

Abstract

An ornithurine bird, Hongshanornis longicresta gen. et sp. nov., represented by a nearly complete and articulated skeleton in full plumage, has been recovered from the lacustrine deposits of the Lower Cretaceous Jehol Group in Inner Mongolia, northeast China. The bird had completely reduced teeth and possessed a beak in both the upper and lower jaws, representing the earliest known beaked ornithurine. The preservation of a predentary bone confirms that this structure is not unique to ornithischian dinosaurs but was common in early ornithurine birds. This small bird had a strong flying capability with a low aspect ratio wing. It was probably a wader, feeding in shallow water or marshes. This find confirms that the aquatic environment had played a key role in the origin and early radiation of ornithurines, one branch of which eventually gave rise to extant birds near the Cretaceous/Tertiary boundary. This discovery provides important information not only for studying the origin and early evolution of ornithurines but also for understanding the differentiation in morphology, body size, and diet of the Early Cretaceous birds.

Fig. 1.

Holotype of ornithurine bird Hongshanornis longicresta gen. et sp. nov. from the Lower Cretaceous of Inner Mongolia, China (IVPP V14533). (Left) Part. (Right) Counterpart. AL, alula; BF, body feathers; C, coracoid; CE, cervical vertebrae; FE, femur; FU, furcula; H, humerus; IL, ilium; IS, ischium; MA, manus; PD, pedal digits; PM, primaries; PU, pubis; PY, pygostyle; R, radius; S; scapula; SC, secondaries; SK, skull; T, tibiotarsus; TF, tail feathers; TR, thoracic rib; U, ulna; TM, tarsometatarsus.

Fig. 2.

Skull of the holotype of Hongshanornis longicresta gen. et sp. nov. (IVPP V14533). D, dentary; HY; hyoid bones; MA, maxilla; NA; nasal; NO, nostril; PD, predentary; PR, premaxilla.

Fig. 3.

Reconstruction of the hyoid bones of the holotype of Hongshanornis longicresta gen. et sp. nov. (IVPP V14533). BB, basibranchial; CB, ceratobranchial, EG, entoglossal; UH, Urohyal.

Fig. 4.

Reconstruction of the sternum, coracoids, and furcula in dorsal view. CO, coracoid; FU, furcula; ST, sternum.

Fig. 5.

Line drawing of the left wing (A) and left foot (B) of Hongshanornis longicresta gen. et sp. nov. (IVPP V14533). AD, alular digit; CM, carpometacarpus; MD, major digit; MID, minor digit; MT1, metatarsal I.