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Re: was: Wukongopterus and Darwinopterus now: cladistics.



On Nov 30, 2009, at 6:02 PM, David Marjanovic wrote:

Many recent phylogenies place turtles somewhere within Diapsida
(deBraga & Rieppel, 1996, 1997; Rieppel & Reisz, 1999; Hedges &
Poling, 1999; Mannen & Li, 1999).  In such trees, the lack of
fenestra in turtles is recovered as a reversal.

It is rather useless to cite any molecular phylogeny that dates from before 2001, because they all consist mostly of long-branch attraction... though all more recent molecular analyses, except for Frost et al. (2006) which has other problems, have so far found the turtles next to or inside Archosauria. I'll look at this, and at the morphological analyses that find turtles and lepidosaurs close together, during... it's going to be a postdoc, most likely. I'm supposed to finish my thesis in June -- theses are limited to 3 years in France. :-| So far I think that turtles and procolophonoids look like close relatives (at least more so than turtles and dwarf pareiasaurs), and note that even *Odontochelys* shows no sign of having ever had temporal fenestrae.

Point well taken - I was not necessarily arguing that turtles must be archosaurs (or diapsids, more generally), but merely that they *could* be, and that there was no reason to suppose that they must fall outside of such groups out of a supposition that a fenestra cannot reverse. The molecular analyses largely indicate that they have in turtles, and even if this proves weakly supported later, there are still plenty of other cases of a closed fenestra (which you wonderfully supplied). Good note on the long-branch attraction problem; it was a quick off-the-cuff list; I don't work on turtle phylogeny myself and couldn't remember what the more recent papers were. Was just making a point.


But anyway, fenestrae can definitely disappear. The dorsal temporal fenestra closes during the late ontogeny of extant *Crocodylus*, the ontogeny of *Pachycephalosaurus*, and so on; it's also closed in several squamates (don't know about the ontogeny of those). In thalattosaurs and *Vancleavea*, the dorsal temporal bar approaches the skull roof to make the dorsal temporal fenestra slit-shaped in some thalattosaurs and absent in the other thalattosaurs and *Vancleavea*. The lateral temporal fenestra is closed, and most likely secondarily so based on the shapes of the bones in that region, in *Araeoscelis*, and an analogous (and partly or entirely primarily homologous) fenestra closes during the ontogeny of *Milleretta*. The antorbital fenestra shows a trend to closure in ornithischians and crocodiles. The orbit is closed in scolecomorphid caecilians... the nares are closed in some waterbirds such as pelicans... the pineal foramen (a fenestra in all but size!) has closed again and again, once in our ancestors... the posttemporal fenestra is closed in anthracosaurs yadda yadda yadda... you name it, it can close.

Better examples than the turtles; happy you pitched in again.


I don't understand the point behind this, though. That point was something about ordering. For logical reasons, a character with only two states cannot be ordered in a meaningful sense (all the programs let you do it, but it doesn't change anything), and you were proposing such binary characters (given fenestra absent/present), right?

Surely you didn't believe that "ordered" means "irreversible"?

No, I don't believe that in the slightest: David P. suggested that fenestrae might be irreversible during the character ordering discussion. I simply indicated that I thought this assumption of irreversibility was weak. I certainly did not mean to imply that ordered characters are irreversible (you can force them to be, but it's not a good idea in any situations I can think of - but maybe there's something I have overlooked).

Cheers,

--Mike H.