Saturday, June 5, 2010
Here is an introduction to the Enantiornithes.
"Enantiornithes is an extinct group of primitive birds. They were the most abundant and diverse avialans of the Mesozoic [251 - 65.5 million years ago]. Almost all retained teeth and clawed hands, like other primitive birds. Enantiornithines are thought to have left no living descendants. See protobirds.
A consensus of scientific analyses indicates that Enantiornithes is one of two major sister groups of derived birds. The other group is the Ornithurae, which includes all living birds as a subset. This means that Enantiornithines are a successful branch of bird evolution, but one that diversified entirely separately from the lineage leading to modern birds. This consensus has never been universally accepted and is being challenged by new studies, so that it is possible that enantiornithines may actually represent successive outgroups on the lineage leading to modern birds. See Apsaravis."
Note that there is a growing awareness that the Enantiornithes may actually be on the direct line to modern birds. Here is additional info on that question:
"The 2002 phylogenetic analysis by Clarke and Norell, though, reduced the number of enantiornithine autapomorphies to just four. This raises the possibility that the discovery of new fossils could unite Enantiornithes and the birds closer to living species into one clade. If this proves to be true, then Enantiornithes is a paraphyletic taxon and thus phylogenetically invalid. All enantiornithines would then be united in the next larger clade Ornithothoraces instead, and called "ornithothoracines". (see Apsaravis for more on the possible invalidation of Enantiornithes)".
"In their cladistic analyses, Clarke and Norell (2002) found that Apsaravis had a mixture of primitive and advanced characters (described above in "Sauriurae") that removed most of the supporting characters for the clade Enantiornithes. Twenty-seven characters have been used to support enantiornithine monophyly, but Apsaravis brings the number down to only four. The discovery of further basal ornithurine fossils like Apsaravis could render the Enantiornithes paraphyletic. This would mean that, rather than a radiation of primitive birds separate from the radiation that led to modern birds, "enantiornithines" would actually be steps along the way to becoming modern birds."
THIS IS EXACTLY THE POINT THAT I AM MAKING.
Posted by Dr. Pterosaur at 9:40 AM