Strange cladogram from another method, able to leap large evolutionary distances in a single bound, faster than a speeding parsimony analysis... oh, you get the idea.
A supertree is what you get when you add a number of possibly divergent partial phylogenies (evolutionary histories with a root) together to forma single tree. I envisage them as a kind of overlay of various trees, giving you a furry "consensus" and extending phylogenies to form larger phylogenies. How good they are, I can't say.
Anyway, a supertree analysis of most known dinosaurs shows that they did not undergo a sudden evolutionary diversification towards the end of their existence (excluding birds, of course, which are now regarded as theropod dinosaurs), but instead evolved at much the same rate as they always had in their final 50 million years. Since grasses and flowering plants evolved in this period, there was a lot of diversification of insects, mammals and other reptiles.
The tree itself is a cool piece of art, by the way. There's also one for mammals, from a couple of years ago.
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I have to read the paper again, but I think the main point is that while many groups of organisms underwent an explosive diversification in what is termed the Cretaceous Terrestrial Revolution dinosaurs stomped to the beat of a different drummer, diversifying in a different pattern not apparently connected with, say, the explosion of angiosperms. Their diversification was not linked to whatever was driving the KTR, which brings up some interesting questions. (Indeed, I am skeptical of the popular press reporting that dinosaurs as a group "evolved at the same rate.") There is a helluva lot of diversity in the Cretaceous but the question is whether this is an artifact of sampling, particularly in North America, so patterns of dinosaur evolution in the Triassic and Jurassic need to be better understood before the tempo and mode of dinosaur evolution can be teased out.
I also know that not everyone is happy with the supertrees and there may be some upcoming critiques of them. I would definitely recommend checking out Dave Hone's blog, though, since he's one of the authors on the paper and has put up a good summary of it.
Posted by: Laelaps | July 25, 2008 9:43 PM
Thanks Brian. I appreciate the extra info. Hone's post is a good one, although he loses points for misusing "begs the question" (it doesn't beg the question, it raises the question!).
Posted by: John S. Wilkins | July 25, 2008 9:57 PM
If I'm not mistaken there have already been critiques of Supertrees but like all phylogenetic methods they just need to be used appropriately and one needs to be aware of the problems that can arise from them.
Of course I am far more aware of molecular phylogenetics and gene concatenation then I am of building phylogenies from morphological characters but even there I believe there are super matrix approaches that one can use as opposed to supertrees.
Posted by: Daniel Gaston | July 26, 2008 3:26 PM