The nature of cladistics (one more attempt)
kinman2 at YAHOO.COM
Fri Nov 19 23:25:36 CST 2004
Okay, I'll spend the time on one more attempt to explain my position. That's it!! Have you really spent much time exploring reptile phylogeny in depth? I would first point out that the majority of herpetologists (especially dinosaurologists) now believe that turtles are cladistically diapsids (as are dinosaurs), and are closest to either lizards or crocodyliforms, or even perhaps something cladistically in between (maybe close to ichthyosaurs?). But even IF turtles split off further out (pre-diapsid), the most "manifest and abundant" differences would still be between Velociraptor and the synapsids (including cynodonts), so let's look at those.
If you want to play a numbers game, the differences MAY be more abundant (quantitatively), but they certainly are not more manifest or of greater importance. Most of the synapomorphies separating clades between ancestral synapsids and the tyrannosauroids are a series of minor changes in bone shapes (often in the skull) or gradual shifts in their topological arrangements relative to one another. Even the significance of these minor differences are often controversial. Of what I would consider major changes, there are only: (1) the shift to bipedality (which occurred in several different reptile clades independently), (2) thecodont teeth (which apparently arose at least twice independently and with intermediate types in between), and only one I that I would consider really major and happening only once---evolution of the diapsid skull.
But just how significant is a second hole in your skull (especially if turtles lost both of them and became secondarily anapsid). Other diapsids apparently lost just one of these holes (euryapsids). Anyway, it seems pretty piddly compared to something like the development of flight feathers, which completely transformed the ecology and evolution of an entire clade (birds). Birds also presently exceed all reptiles in numbers of species (balanced classifications are more useful than those which are severely asymmetric, but strict cladists seem to generally care less about balance and stability).
And as for diversity of form and ecology, a hummingbird is a far cry from either an elephant bird or a penguin. On the other hand, the major differences between a primitive synapsid and a tyrannosaur is an extra hole in the head and bipedality (oh, and also a different number of fingers, reduced to three in primitive tyrannosauroids, two in tyrannosaurs proper). Bipedality means tyrannosaurs could run somewhat faster, but this hardly compares to the ecological niches that flight opened up to birds. And remember, birds survived the end-Cretaceous extinction, while all the sauropodomorphs, ornithischians, and non-avian theropods went extinct. Even at the end of the Cretaceous, the birds had developed enough diversity to outlast all those taxa, and their diversity continued to expand after that.
But I fear that I could keep arguing with you indefinitely like the energizer bunny, and you still would continue to object to this or that. If so, I give up. If you want to stick with strict cladism, that's your choice. Just don't complain when the repercussions of strict cladism come back to roost, and the real costs of strict cladism become sadly apparent. That's when your students start asking, "what were you thinking?", the pendulum finally shifts back, and a new synthesis emerges.
P.S. I think I have addressed many of your points, but when one point is answered new ones keep emerging. Not that this is unusual, since I get that from other strict cladists as well. You guys are just wearing me down, and frankly, I'd much rather spend my time classifying a lot more taxa. From now on, I'd rather spend more time exploring new phylogenies and revised classifications, rather than keep on debating the methodologies. You strict cladists can go your own way if you choose, but don't ever say you weren't warned about the repercussions.
Curtis Clark wrote:
But you've not addressed my point at all. We have to look carefully to find the differences between Tyrannosaurus and Velociraptor, but the differences between either, or even their common ancestor, and a turtle or cynodont are manifest and abundant.
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