7-553: Pygostylia is a group of avialans which includes the Confuciusornithidae and all of the more advanced species, the Ornithothoraces . The group Pygostylia was intended to encompass all avialans with a short, stubby tail, as opposed to the longer, unfused tails of more primitive species like Archaeopteryx lithographica . It was named by Sankar Chatterjee in 1997. Luis Chiappe later defined Pygostylia as
14-443: A node-based clade , "the common ancestor of the Confuciusornithidae and Neornithes plus all its descendants". In 2001, Jacques Gauthier and Kevin de Queiroz recommended that Chatterjee's original apomorphy-based clade concept be used instead of Chiappe's node-based definition, but this recommendation has been inconsistently followed. Luis Chiappe and co-authors continue to use Chiappe's definition, often attributing authorship of
21-436: The cladogram below: † Archaeopteryx † Jeholornis † Sapeornis Jinguofortis Cratonavis Chongmingia † Confuciusornithidae Ornithuromorpha † Enantiornithes Pygostylia has been recovered as being within the clade Avebrevicauda . Avebrevicauda (meaning "birds with short tails") is a group of birds which includes all avialan species with ten or fewer free vertebrae in
28-537: The Pygostylia share four unique characteristics . The trait that gives the group its name is the presence of a pygostyle , or set of fused vertebrae at the end of the tail. Next is the absence of a hyposphene - hypantrum . Next is a reversed pubic bone separated from the main axis of the sacrum by an angle of 45 to 65 degrees. Last is a bulbous medial condyle of the tibiotarsus (lower leg bone). The pygostylians fall into two distinct groups with regard to
35-434: The name to Chiappe 2001 or Chiappe 2002 rather than to Chatterjee. Cladogram following the results of a phylogenetic study by Jingmai O'Connor and colleagues in 2016: † Confuciusornithiformes † Didactylornis † Sapeornis Ornithothoraces In 2023, Li et al recovered their new taxon, Cratonavis , as the new jinguofortisid that belongs to Pygostylia. The results of their phylogenetic analyses are shown in
42-615: The pygostyle. The Ornithothoraces have a ploughshare -shaped pygostyle, while the more primitive members had longer, rod-shaped pygostyles. The earliest known member of the group is the enantiornithine species Protopteryx fengningensis , from the Sichakou Member of the Huajiying Formation of China , which dates to around 131 Ma ago, though at least one other enantiornithine, Noguerornis , may be even older, at up to 145.5 million years ago, though its exact age
49-532: The tail. The group was named in 2002 by Gregory S. Paul to distinguish short-tailed avialans from their ancestors, such as Archaeopteryx , which had long, reptilian tails. Depending on the analysis, Sapeornis may or may not be a member of Pygostylia, but is always within Avebrevicauda. Depending on the true phylogenetic position of Sapeornis , Avebrevicauda may be a junior synonym of Pygostylia. Chiappe noted that under his definition, all members of
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