Jeholornis prima

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Based on the morphological study of this specimen, we provide the following revised diagnosis for J. prima. A large stem bird with the following combination of features: premaxilla edentulous with short maxillary process; two teeth with blunt crowns in maxilla and three relatively smaller teeth in dentary (new); paired, sheet-like preorbital ossifications present near the nasals (new, autapomorphy); C-shaped lacrimal with short rostrodorsal ramus and lacrimal foramen (new); unreduced postorbital forming a complete postorbital bar with jugal (new); pterygoid rami of vomer much longer than the fused rostral portion, expanded in the middle and lacking the caudodorsal process (new); palatine with broad pterygoid wing and jugal process (new); narrow and restricted mandibular fenestra between prearticular and surangular (new); 27 caudal vertebrae in total, with the transition point occurring after the fifth vertebra; lateral trabecula of sternum absent; caudalmost pair of sternal ribs expanded; first phalanx of the third manual digit twice as long as the second phalanx; ratio of forelimb (humerus plus ulna plus carpometacarpus) to hindlimb (femur plus tibiotarsus plus tarsometatarsus) of ~ 1.2: 1; dorsal margin of the ilium nearly straight and craniodorsal – caudoventrally oriented (modified from Zhou & Zhang, 2002; O’Connor et al., 2012; Zheng et al., 2020).