A reassessment of Sinornis santensis and Cathayornis yandica (Aves: Enantiornithes). In Proceedings of the VII International Meeting of the Society of Avian Paleontology and Evolution, ed. W.E. Boles and T.H. Worthy
Abstract
The taxonomy of the first two enantiornithine birds named from the Early Cretaceous of China, Cathayornis yandica and Sinornis santensis, has remained controversial despite the relative completeness of both holotype specimens. This is because C. yandica is regarded as a junior synonym of S. santensis by some researchers, and as a distinct taxon by others. This question is revisited in this paper; in order to determine the validity of C. yandica, we conduct a detailed morphological review of both holotype specimens. Despite proposed synonymy we argue that there are clear and distinct anatomical differences between the two taxa; indeed our morphological observations demonstrate that the two birds constitute valid and distinct branches in the diverse enantiornithine evolutionary radiation. Of course, and like many other groups of fossil vertebrates, the diverse Cretaceous bird lineage Enantiornithes requires taxonomic revision yet in the case of C. yandica and S. santensis we attribute much of the confusion to: (1) incomplete specimens being designated as holotypes, and (2) the absence of clear morphological character-based taxon diagnoses founded on rigorous anatomical comparisons.
