Jinguofortis
Jinguofortis is a genus of primitive avialan belonging to the clade Pygostylia that lived during the Valanginian stage of the Early Cretaceous. It was found in the Dabeigou Formation in northeastern China, and isotope dating from the samples overlying the bird-bearing horizon is 127 million years ago.
Description
Jinguofortis is notable for having a combination of primitive and advanced traits. Some of these are typical of stemward avialans while others occur in crownward avialans. The scapula and coracoid bones of the shoulder girdle are fused into a single bone, the scapulocoracoid. A fused scapulocoracoid is a plesiomorphic feature which is not present in modern birds. This plesiomorphic state is found in pterosaurs and non-avian dinosaurs, including coelurosaurian theropods ancestral to birds.However, these bones become unfused in the famed early avialan Archaeopteryx, and in more crownward avian clades. Outside of Jinguofortis and its closest relatives, the presence of a fused scapulocoracoid is found only in confuciusornithids among other avialans. This is an apparent example of convergent evolution, suggesting that these early avialans likely acquired a high rate of osteogenesis similar to other theropods. Later, separation of the coracoid and scapula becomes evolutionarily “fixed” across more advanced birds in the clade Ornithothoraces. By this time, the pectoral girdle developed further modifications, including an ossified sternal keel and formation of the triosseal canal. The strong tendency for convergent evolution in early avialans points to high developmental plasticity for anatomical systems in the shoulder region.
Other traits are more advanced, such as the highly reduced digits of the hand. Jinguofortis is morphologically similar to Chongmingia, another early avialan which preserved a fused scapulocoracoid. The two genera were placed in a new family, Jinguofortisidae. However, Jinguofortis could still differentiated from Chongmingia in several ways. Its furcula was less robust, with a smaller angle of 70° between the clavicular branches. Pedal digit I was approximately 70% of the length of digit II, which itself was shorter than digit IV. In addition, these two taxa are separated in time by approximately seven million years.
Etymology
The name Jinguofortis is a combination of jinguo, from Mandarin, referring to female warrior, and fortis, Latin for brave.Classification
Wang et al. recovered Jinguofortis as a basal pygostylian more derived than Confuciusornithiformes, but more primitive than Sapeornithiformes, and as sister to the previously problematic genus Chongmingia.Cladogram of Mesozoic birds