A taxonomical revision of the Confuciusornithiformes (Aves: Pygostylia).
The Confuciusornithiformes is a basal clade of Early Cretaceous birds that includes the oldest and most basal birds with a toothless beak and an abbreviated bony tail. Over the last two decades, thousands of specimens have been collected, more than for any other group of Mesozoic birds or non-avian dinosaurs. Ten species separated into four genera have been erected with limited taxonomic phylogenetic scrutiny. Here, we perform a comparative study of these ten species, and demonstrate that most of these taxa were originally diagnosed by characters that prove to be either preservational artifacts, intraspecific variations, subject to ontogenetic variation, or widely distributed among the Confuciusornithiformes or a more phylogenetically inclusive group. Our results suggest that 'Confuciusornis suniae', 'C. feducciai', 'Jinzhouornis yixianensis', 'J. zhangjiyingia', and 'C. jianchangensis' are all junior synonyms of C. sanctus. 'C. chuonzhous' lacks autapomorphies of C. sanctus and is referred to Confuciusornithiformes incertae sedis. Our taxonomic reappraisal of published materials indicates that the Confuciusornithiformes consists of one family, three genera, and four species: C. sanctus, C. dui, Changchengornis hengdaoziensis, and Eoconfuciusornis zhengi, for which we provide revised diagnoses.Â