[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
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),
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).