|A Tetrapteryx. Photo by Charles J. Sharp, CC-By-SA|
Quick post on a recent taxonomy fail:
I checked my Wikipedia account this morning to discover that several protobirds had been reclassified. Aurornis, Anchiornis, Xiaotingia, and some microraptorians were now displaying the family name "Tetrapterygidae". I was surprised and a little excited. Had a new four-winged dinosaur been found that, when included in a phylogenetic analysis, resulted in the above grouping? Most of these species are scattered among various lineages of the clade Paraves in all other analyses to date, so it would be quite interesting to find that all of these four-winged dinosaurs actually formed a clade. For example, such a result would suggest that the famous "tetrapteryx" hypothesis proposed by William Beebe in 1915 was wrong, and that these "tetrapteryges" were in fact a side branch engaging in an experiment with four-winged gliding flight. Where was this coming from?
Oh. Sankar Chatterjee. Never mind.
Chatterjee apparently named the family Tetrapterygidae in the new 2015 second edition of his book The Rise of Birds, originally published back in 1997. Chatterjee essentially believes that the key character of flight feathers on the hind limbs is enough to unite these handful of paravians into a clade, and he slots them into a cladogram as the sister clade of Avialae without actually performing any kind of analysis. This is old-fashioned typological classification misleadingly disguised as science, and it was enough to trick at least one Wikipedia editor into buying it and changing the pages on these animals accordingly.
I'm not sure if this is supported in Chatterjee's book, but the editor also wrote in the discussion of this family how it is named after and supports Beebe's hypothesis when it in fact does the opposite, as mentioned above. If Beebe is right and birds evolved from four-winged ancestors, we should expect to see four-winged species making up a paraphyletic grade around the base of Avialae... which is exactly what we do see, in the traditional classification where the four-winged dinosaurs do not form a single clade (though it's extremely debatable whether or not the short feathered "trousers" of things like Anchiornis can justifiably be called, or even compared to, "wings").
Not only is this "Tetrapterygidae" bad science, it's bad nomenclature. The ICZN, which governs "family" ranked names, is very clear on it's central "principle of coordination". A family name must be named after an included type genus. That means any family named Tetrapterygidae must include the genus Tetrapteryx (Thunberg, 1818), the type species of which is Tetrapteryx capensis, a junior synonym of Anthropoides paradiseus, the South African Blue crane. According to the ICZN, therefore, Tetrapterygidae is a junior synonym of the family Gruidae and can't be used for four-winged paravians. EDIT: Additionally, as I forgot to mention before, any family-ranked taxon that contains Microraptor should be called Microraptoridae, since Microraptorinae already exists.
Ironically, under the PhyloCode, Tetrapterygidae could be considered a node-based clade that contains the species Chatterjee used. This would make it basically equivalent to Eumaniraptora, which also happens to include cranes. Problem solved!