Jinguofortis

Jinguofortis is notable for a mosaic of primitive and advanced characters, including a fused scapulocoracoid and highly reduced manual digits. A fused scapulocoracoid is a plesiomorphical feature that evolved before the origin of limb digits.[2] These two bones become separate and form a suture contact among some reptiles (e.g., lizards, crocodilian), but become fused independently in a few lineages, including non-avian dinosaurs and pterosaurs.[3] The tendency for fusion between the coracoid and scapula stems from their developmental origins as a unified homogenous condensation.[4] However, that coalescence becomes detached during chondrogenesis because the osteogenic pattern and/or the differentiation of the preskeletogenic cells is delayed,[2] resulting a sutural contact between the elements.

The fusion between the coracoid and scapula is present predominantly in non-avian theropods.[3] However, these two elements are separated in Archaeopteryx,[5] and in more crownward avian clades,[6][7] but fused in stemward pygostylians confuciusornithids and jinguornithids. The convergently evolved scapulocoracoid in jinguornithids and confuciusornithiforms suggests these basal clades likely reacquired a similar level of osteogenesis present in their non-avian theropod ancestors that is responsible for the co-ossification of the pectoral girdle.[1] Then separation of the coracoid and scapula becomes evolutionarily “fixed” (with a few exceptions in the crown groups) across Ornithothoraces, and underwent further modifications including an ossified sternal keel and formation of the triosseal canal. These developmental changes to the skeleton likely correspond to intense selective pressure to improve flight capability that eventually lead to the musculoskeletal system present among volant crown birds, suggesting developmental plasticity[8][9]

Jinguofortis is morphologically similar to the another stemward avialan Chongmingia (also preserved a fused scapulocoracoid). Differences from Chongmingia include: furcula less robust with a smaller interclavicular angle of 70°; pedal digit I approximately 70% of the length of digit II; and pedal digit II shorter than IV; and these two taxa are separated by approximately seven million years.[1]

The name Jinguofortis is a combination of jinguo, from Mandarin (巾帼), referring to female warrior, and fortis, Latin for brave.[1]

Wang et al. (2018) recovered Jinguofortis as a basal pygostylian more derived than Confuciusornithiformes, but more primitive than Sapeornithiformes, and as sister to the previously problematic genus Chongmingia.[1] Cladogram of Mesozoic birds[1]