Things that are not dinosaurs birds: Archaeopteryx?

Since its discovery 150 years ago, Archaeopteryx has been considered the most basal bird ever discovered.  In fact, current phylogenies show Aves (birds) comprises Archaeopteryx and Pygostylia (every other bird ever), meaning Archaeopteryx comes as close to "not-being-a-bird" as a bird can get.  Its discovery also initially helped support the now firmly established notion that modern birds evolved from within a group of theropod dinosaurs.  In my opinion, Archaeopterxy is as close as you are going to get to finding a "missing link", as it possessed traits found in both non-avian dinosaurs and birds.

The infamous "Berlin Specimen" of Archaeopteryx lithographica (HMN 1880) on display at the Humboldt Museum für Naturkunde. Photograph  by H. Raab, from Wikimedia  Commons.

However, a recent paper published in the journal Nature may have finally proven what some researchers and scientists have been saying for years: Archaeopteryx is a deinonychosaur more closely related to Velociraptor and Troodon than to avialans Gallus and Columba.  The paper describes a new genus of paravian, Xiantingia zheng, and places it in a clade with Anchiornis and Archaeopteryx within Deinonychosauria, not Avialae.

Xiantingia is a remarkable fossil in and of itself.  But it is also very cool because, if its analysis is correct, it has implications for both how we currently understand the evolution of birds, and the evolution of flight in dinosaurs.  It also illustrates beautifully one of the most fundamental principles of science: that our understanding is constantly evolving as well.  When Archaeopteryx was discovered, it was an anomaly.  Half bird, half reptile.  Their was no other animal quite like it.  But the more fossils we unearth, the more we learn that the Mesozoic world was full animals that blur the lines between bird and non-avian dinosaur.  For example, Allosaurus (clearly not a bird) has a furcula, or "wishbone", which was thought to only be found in birds.  And Hesperornis (clearly a bird) had a mouth full of teeth, something thought to not be found in birds.  There are dozens of other examples that show that there were lots of fluffy, fuzzy, feathered critters running around that weren't quite birds, but were closely related cousins.  And Xiantingia is another one of these wonderful creatures.

Artists impression of Xiantingia zheng. Copyright Xing Lida andLiu Yi, from  naturenews. 

As for the new placement of Archaeopteryx outside of the bird clade, I'm sure the story will keep evolving as well.  There is only "tentative statistical support" proving that this new phylogeny is the most accurate one we know of.  And new research may show that it belongs somewhere else on the "Tree of Life", or that it and some of its deinonychosaur kin are actually "birds" after all.  Regardless, as the picture becomes clearer, one thing stays evident, and is worth reiterating: All modern birds are dinosaurs!




For more on Xiantingia and Archaeopteryx, check out the following links:
Nature News press release by Matt Kaplan
Nature News and Views article by Larry Witmer
Nature article by Xu, X., You, H., Du, K., and Han, F.
WitmerLab blog post at Pick & Scalpel
Everything Dinosaur blog post
Theropoda blog post

References


Xu, X., You, H., Du, K., and Han, F. 2011. An Archaeopteryx-like theropod from China and the origin of Avialae. Nature 475: 465-470. doi:10.1038/nature10288