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Re: Pteromimus and pterosaur origins




On Jan 24, 2009, at 12:47 PM, Michael Habib wrote:

 great at. After thePAUP* tree(s) is(are) created it's time to
 evaluate it(them). MacClade is great at showing exceptions and
 mistakes in coding.

MacClade will map reversals and convergences, but this doesn't make them mistakes in coding. Granted, when you map character state changes you may suddenly realize that you coded something absent that you know actually exists, but major transitions, in and of themselves, need not be errors (more on this below).

Having performed many analyses, and dissected others, I can tell you're talking in philosophical generalities. I'm talking specifics. Here's how it works: If I find through PAUP* a lineage, thereafter it needs to be rechecked in MacClade. For instance: Say all taxa --but one-- have a tiny quadratojugal that ascends the quadrate. Given that, I look again at that exceptional taxon for a loose quadratojugal that may have drifted slightly. Sometimes I find it. Then I reconstruct it back into place. That happened in Huehuecuetzpalli. If I don't find the qj, then indeed it is an apomorphy. and I score it as such.


The other side of the equation is this: If you take 14 taxa you're going to get a tree with 14 leaves. If you take 140 taxa you're going to get 140 leaves with the possibility that some taxa from the small set are going to find new, more parsimonious nesting partners in the 10x larger set. In a large enough taxon set pteros will _invariably_ nest with fenestrasaurs, rather than dinosaurs.

You just have to test and experiment and get the big picture before you can be sure of the validity of the smaller (14 taxa) inclusion set. Virtually all prior attempts, from Gauthier 1986 to the present, have assumed wrongly and, as a consequence, have prolonged the error. It's easily resolved via testing. I say virtually, because Benton 1985 did it right, even with suprageneric taxa, but then he never repeated the experiment. Maybe Hone and Benton in the new Zitteliana volume will show differently.


For instance, note that all of the sister and predecessor taxa of
pterosaurs in Atanassov's phylogeny have a vestigial or absent pedal
digit V. Pterosaurs don't. That's a red flag that should tell any
reasonable person, evolution doesn't work that way and it's time to
look for more parsimonious sister taxa. The same for manual digit IV.

I'd slow down there for a moment - how do we make such judgements about how "evolution works"?

We make such judgments because we know evolution works step by step. Kids, for the most part, look like their parents and great- granparents. One part evolves, blends, lenghthens, shortens, then another then another. Sometimes two or three at a time, but that is within a suite of hundreds to thousands of characters, depending on your skills and patience. Even when one taxon is half the size of the predecessor most of the characters remain similar in proportion. Done well you can produce 100 manual characters rather easily, for instance.


Again, if you have only 14 taxa over a wide gamut, it's going to be harder to see the blend. Make sure those 14 taxa are indeed sisters before you test them. No prior study has yet given us the comprehensive overview of the Amniota using species-based taxa.


If we knew the patterns already, there wouldn't be a need for a cladistic analysis.

Yes, if you did. But we don't. That's why we us CA.

The transitions above indicate is that a given ancestor generated some descendents with a short digit V, and others with a long digit V.

No. The point is you're asking a given ancestor with a short to vestigial to absent pedal digit V to give rise to one with an elongated digit V -- when you know on the next branch, there is a taxon with a long digit V with the same characters -- attached to an torso, skull and extremities with a suite of other pterosaur-ish characters. It's parsimony, pure and simple. Those who refuse to test never know the truth. Testing is all I promote.


Now... if you want a lizard with long fingers to show up in the fossil record, as Wild hoped for, then we can all sit around and wait for that. It's not going to happen. We have published evidence that that was not the morphological prototype.

How far back do you have to go to find a archosaur(omorph) with an elongated manual digit IV and pedal digit V? Try Prolacerta. That's where Bennett 1996 ended up after deleting the hind limbs from the equation. But then, there's no antorbital fenestra, and a long list of other ptero synapomorphies are missing. Let's look somewhere else.

That's hardly shocking, and quite plausible. More to the point, when reversals, mosaics, and other bits of messiness show up in a phylogeny it is not a sign that the answer is wrong - it just reflects the rather stochastic patterns that are biology.

Again, Mike, you're talking philosophical generalities. Get specific, test one against the other, and we'll find answers. the reversals, etc. will reveal themselves.

Look at this way: Based on the methodology you seem to be proposing above, we would end up forbidding apomorphies and reversals in our trees on account of the fact that the tree would be more parsimonious without them - which clearly isn't what we're trying to do with parsimony.

No. If you find an exception you look. What you find is your answer. You may indeed find an error in interpretation. You may also, as you suggest, confirm an apomorphy. Either answer is A-OK.

 And there's a long list that follows. Anyone who claims that
 pterosaurs 'suddenly appeared' in the fossil record with no sister
 taxa demonstrating a gradual acquisition of characters has their
 blinders on. The data is freely available.

There are certainly potential sister taxa, and they show stepwise acquistion of some characters. But there are also all the missing bits and reversals, etc that make the matter rather messy.

If you could be specific please...

More to the point, no matter how confident you are of your sister taxon recovery, there are still a lot of apomorphic features in pterosauria proper.

Such as? Be specific, please, and I will attempt to answer your query with evidence you can confirm elsewhere.


Not the least being the powered flight apparatus, which is what the original reference to "sudden appearance" really alluded to.

By this, do you mean wings? Sternal complex? Pteroids? What? Be specific. Some answers may have to appear OFFLIST if they are the subjects of papers in review. Anything published, I will share ONLIST.


Best, David



Cheers,

--Mike


David Peters davidpeters@att.net