[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: New gliding reptile: Mecistotrachelos
Just so as not to give a false impression: as usual, I agree with everything
I don't comment.
Fraser also notes that closely related forms (Icarosaurus, Kuehneosaurus,
and Kuehneosuchus) DO have exceptionally elongate thoracolumbar ribs AND
markedly elongate transverse processes. (Emphasis mine)
(Obvious because you didn't put any quotation marks anywhere.)
The only problem is, (phylogenetically) elongate transverse processes
are no where else to be found in ANY sister taxa near or semi-far.
They had to evolve at _some_ point. They have to be an autapomorphy of
_some_ clade. In other words, _some_ clade that has the feature will have a
sister-group that lacks it.
What that means is, the 'markedly elongate transverse processes ARE the
ribs, straightened and fused to the vertebrae for (one could readily
assume) strength and stability as they anchor the 'wings'.
No, it doesn't mean any such thing. Compare *Draco*, which has elongate
transverse processes that articulate with lengthened ribs. Also note that
*Coelurosauravus* has a lot more neomorphic rods than ribs, which is how the
fact that they aren't ribs was discovered in the first place.
And that means the 'wings' are, as in Coelurosauravus, still supported by
folding neomorphic ossifications. As a matter of fact, in Icarosaurus at
the transitional dorsal vertebrae -- the ones not supporting neomorph
ossifications between the scapulae -- this fusion is visible because it
is incomplete. Heck, these lines are even drawn on the 1970 Colbert
restoration that Fraser's group includes!!!!
OK, I'll try to dig up that paper tomorrow.
1) a pointed snout (in ventral view).
2) not having a good understanding of the fossil itself (a Photoshop
tracing and a reconstruction in various views should always be attempted
because it opens your eyes to new possibilities, especially in
low-contrast situations such as this)
Rather, you should take the _fossil_ and try various methods of _lighting_:
different angles, different strengths, perhaps UV...
3) not having a good understanding of the phylogeny of the Reptilia
(Mecistotrachelos is NOT an archosauromorph, BUT a lepidosauromorph).
We'll maybe believe that when your paper to this effect will have passed
peer-review. I'm not saying the current view is set in stone, I'm saying I
have yet to see evidence that it's wrong.
Coelurosauravus (Permian) has 23 ossified rods. The first 11 are bundled
proximally and emerge from the second and third dorsal rib. The
remainder, 12-23, are each associated with a rib tip
How precise is that association? -- I'll try to look it up.
Icarosaurus (Triassic) has 13 ossified rods, all of which are
associated with rib tips that look like transverse processes.
And articulate with the "rib tips" in the same way that ribs articulate with
Mecistotrachelos has 9 ossified rods, all of which are associated
with rib tips that look like transverse processes. The first ossified
rod is very short, no longer than one dorsal vertebra.
That sounds like a cervical rib to me.
Is this a valid genus? Yes. IMHO. Based on ossified rod element
numbers and cervical length principally.
Genera are a feel-good affair. You could always declare it a subgenus or
even just a species of *Icarosaurus*. Nobody can stop you. :-)