To begin my DpSU catch-up, I bring you Archaeopteryx Is a Bird. . . Again, from Tuesday.
This is a follow-up to Early Bird Gets the Boot: Researchers Reclassify Archaeopteryx. Basically, some other researchers disagreed with the previous group’s conclusions. They say of it that “this parsimony-based result was acknowledged to be weakly supported.” They ran their own analysis: “Maximum-likelihood and related Bayesian methods applied to the same dataset yield a different and more orthodox result: Archaeopteryx is restored as a basal bird.”
The Archaeopteryx–deinonychosaur clade retrieved by parsimony is supported by more characters (which are on average more homoplasious), whereas the Archaeopteryx–bird clade retrieved by likelihood-based methods is supported by fewer characters (but on average less homoplasious). Both positions for Archaeopteryx remain plausible, highlighting the hazy boundary between birds and advanced theropods. These results also suggest that likelihood-based methods (in addition to parsimony) can be useful in morphological phylogenetics.
If I’m reading the terminology right, if a characteristic is similar, but in a convergent evolution way, then it’s homoplasious. If it’s similar because of shared ancestry, then it’s homologous. What they’re saying is that the characteristics that back up their result are less likely to be the result of convergent evolution, but then I could be wrong.
Where does Mr Thomas come into this? Well, he’s been saying all along that Archaeopteryx is just an extinct bird, so naturally he would be harping on this.
He attacks phylogenetics, something he seems to be rather bad at doing, by my judge of the last time. He accuses cladistics of being based on evolutionary assumptions – which is technically true, but frankly irrelevant. We know that evolution – of birds and other things – happened, this is more about exactly where it goes on the tree. Importantly, the idea that there would be a lot of organisms in the area of Archaeopteryx is practically an evolutionary prediction.
After generations of experts had concurred that it was a bird, why would one group suggest that Archaeopteryx should be reclassified as some kind of a dinosaur? And why would another group, using similar techniques, pull the plug on that assessment so soon afterward? After all, they both have access to the same data.
Because they are using different techniques – see above.
Textbooks and museums still teach that Archaeopteryx is an evolutionary transition from reptiles. But even if its classification waffles again, it is disqualified as an evolutionary ancestor for birds by the fact that scientists found a crow-size bird and extinct four-winged birds in rock layers designated to be below those containing Archaeopteryx.
The crow-like “bird” is Protoavis, which is now generally not considered to be one – creationists have attacked far better preserved fossils in their time. The four-winged “birds” are the ones found by the group that did the reclassification, and weren’t called birds in the first place, so far as I can tell – that’s the point really.
The disagreement – that is, between Mr Thomas and Reality – seems to be with the definition of ‘bird.’ To him, Velociraptor would have been a bird – it had feathers, after all. So to him the point here doesn’t matter. To everyone else it does – but to creationism, it does not.
I covered the original story (not in much detail) here.