| Pygostylians | |
|---|---|
 | |
| Fossil pygostylian (Confuciusornis sanctus) | |
.jpg) | |
| House sparrow (Passer domesticus) | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Clade: | Avialae |
| Clade: | Avebrevicauda Paul, 2002 |
| Clade: | Pygostylia Paul, 2002 |
| Subgroups[1] | |
Pygostylia is a group ofavialans which includes theConfuciusornithidae and all of the more advanced species, theOrnithothoraces.
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 likeArchaeopteryx lithographica. It was named bySankar Chatterjee in 1997.[2]Luis Chiappe later defined Pygostylia as a node-basedclade, "the common ancestor of theConfuciusornithidae andNeornithes plus all its descendants".[3][4] In 2001,Jacques Gauthier andKevin de Queiroz recommended that Chatterjee's original apomorphy-based clade concept be used instead of Chiappe's node-based definition,[5] but this recommendation has been inconsistently followed. Luis Chiappe and co-authors continue to use Chiappe's definition, often attributing authorship of the name to Chiappe 2001[6] or Chiappe 2002[7] rather than to Chatterjee.
Cladogram following the results of a phylogenetic study by Jingmai O'Connor and colleagues in 2016:[1]
In 2023, Liet al recovered their new taxon,Cratonavis, as the newjinguofortisid that belongs to Pygostylia. The results of theirphylogenetic analyses are shown in thecladogram below:[8]
Pygostylia has been recovered as being within the cladeAvebrevicauda. Avebrevicauda (meaning "birds with short tails") is a group of birds which includes allavialan species with ten or fewer free vertebrae in the tail. The group was named in 2002 byGregory S. Paul to distinguish short-tailed avialans from their ancestors, such asArchaeopteryx, which had long, reptilian tails.[9] 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 ofSapeornis, Avebrevicauda may be a junior synonym of Pygostylia.
Chiappe noted that under his definition, all members of the Pygostylia share fourunique characteristics. The trait that gives the group its name is the presence of apygostyle, or set of fused vertebrae at the end of the tail. Next is the absence of ahyposphene -hypantrum. Next is a reversedpubic bone separated from the main axis of thesacrum by an angle of 45 to 65 degrees. Last is a bulbousmedialcondyle of thetibiotarsus (lower leg bone).[3]
The pygostylians fall into two distinct groups with regard to the pygostyle. The Ornithothoraces have aploughshare-shaped pygostyle, while the more primitive members had longer, rod-shaped pygostyles.
The earliest known member of the group is theenantiornithine speciesProtopteryx fengningensis, from the Sichakou Member of theHuajiying Formation ofChina, which dates to around 131 Ma ago,[10] though at least one other enantiornithine,Noguerornis, may be even older, at up to 145.5 million years ago, though its exact age is uncertain.[11]
.jpg)
