[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: the tonight show (my final post on this)
> A simple Interstate analogy for cladograms might make this clearer.
> Cladograms are usually constructed in such a way that the highest
> evolutionary rates generally occur on the main line (Interstate), but once
> group branchs off (forming an off-ramp or exit) their evolutionary speeds
> usually decline in comparison. They find their niche and often don't need
> to evolve as fast any more. Groups that have been going down their
> particular offramps extremely slowly for a very long time, we often call
> them living fossils (coelacanths, horseshoe crabs, etc.).
Nope. When people draw cladograms, they put that clade at the right that is
of most _interest_ to them.
> Once the dromaeosaurs branched off the Interstate (in the
> they might not have slowed much (but all roads connected to that offramp
> eventually came to deadends---many marked with a K-T Extinction Sign).
> next major offramp is probably Archaeopterygiformes (very short, probably
> never even got beyond end of Jurassic). Some people think the
> Alvarezsaurids are the next exit (while others think they branched off
> before the dromaeosaur offramp), but pretty much everyone agrees that the
> Enantiornithine offramp comes next (and their roads all dead-end by K-T as
> well). Then comes the Hesperonithiformes exit, and then the
> Ichthyornithiformes exit (both deadends by K-T). If the end-Cretaceous
> extinction had not occurred, many of these offramps would have eventually
> formed highways in their own right (as Tom noted in his own way), but it
> occur and those groups dead-ended for good. That's life.
> Then comes the exit for Palaeognatha Road--- they find their niches
> and slow down evolutionarily, and some were lucky enough that they haven't
> reached deadends yet (tinamous and the more derived ratites). After that
> last exit, some call it the Neognatha Interstate, the biggest part of the
> overall Aves Interstate System.
Good analogy though. Are Palaeognatha and Neognatha examples of your
standardisation of higher taxon names or just typos? (The ending -a is
standardly used for domains: Bacteria, Archaea, Eucarya.)
> Traditionally the Aves System has been
> regarded as a separate system in its own right, but phylogeneticists
> it as part of the increasing larger Dinosauria and Reptilia Systems. They
> usually name a new subsidiary system at each exit----which creates a lot
> names----but they claim this is less arbitrary (and supposedly useful).
As is regularly discussed on this list ad nauseam, cladists have abandoned
ranks -- "subsidiary systems" -- at all.
> Anyway, the Neognatha System hasn't been mapped in detail yet, and
> only thing most agree upon is that the first big exit is to the
> Galliformes-Anseriformes clade. The ordering of the rest of the exits
> not been mapped out enough to form a definite consensus. The Interstate
> probably splits into various major highways, each with their own offramps.
> Which highway to call the Interstate then become rather arbitrary, but
> Passeriformes is the biggest and gets the most attention.
> The major point is that the highest evolutionary rates (driving
> speeds) are usually on the Interstate, and things tend to slow down on
> offramps (not always though). Therefore in evolutionary distance, most of
> the present neognath groups are a lot farther away from the dromaeosaur
> than the present paleognaths are. The paleognaths slowed down a long time
> ago, while the neognath evolutionary radiation continued to race ahead.
> By comparison, the crows and jays (in a long line of evolutionary
> speedsters) are much, much further down the Interstate System. Just how
> depends on which part of the genome you look at, so there is no single
> answer to that question. But the overall evolutionary distance from
> dromaeosaur exit to any present paleognath is probably shorter than to any
> present neognath (although some primitive galliformes might not be much
Just things become easier when one doesn't use "evolutionary distance" for