Pygostylia
| Pygostylians Temporal range: Early Cretaceous–Present, 131–0 Ma |
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| Fossil pygostylian (Confuciusornis sanctus) | |
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| House sparrow (Passer domesticus) | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Avebrevicauda |
| Clade: |
Pygostylia Chatterjee, 1997 |
| Subgroups | |
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 long, reptilian tails of more primitive species like Archaeopteryx lithographica. It was named by Sankar Chatterjee in 1997. Louis Chiappe later defined Pygostylia as 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. Louis Chiappe and co-authors continue to use Chiappe's definition, often attributing authorship of the name to Chiappe 2001 or Chiappe 2002 rather than to Chatterjee.
Cladogram following the results of a phylogenetic study by Jinghai O'Connor and colleagues in 2016:
Chiappe noted that under his definition, all members of 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).
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