[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Pterosaur structure, good job JC
re: adductors on the prepubes, well, without modern analogs, there's
just no telling, is there? I would suggest as a hypothesis that since
bones serve as anchors for muscles -- and we first see prepubes on
Sharovipteryx, a creature with hyper-elongated legs and without all
the presacral mass exhibited by pterosaurs -- that prepubes probably
developed to assist that sprawl-legged biped to maintain its
You missed my point, which was mechanical and had nothing to do with
analogies. If you let a leg adductor originate on the prepubis, it will pull
the leg and the prepubis together -- and the prepubis has nothing to resist
this force! Fine, it's probably anchored to its counterpart by ligaments or
whatnot, but that merely means that each adductor will pull both bones
sideways. Now, if the legs touch the ground, the result won't be that the
legs move, it will be that the prepubic bones move from side to side.
Now, I provisionally accept the recent idea that the prepubic bones are
weirdly enlarged gastralia and had a respiratory function. That means we
should expect ligamentary connections to other bones: to the other
gastralia, and to the ischia. But these connections are all longitudinal.
Leg adductors would still pull the prepubic bones sideways; the longitudinal
ligaments would only spread this motion over more pairs of gastralia, but
they couldn't prevent it.
That's because it is not a new bone, but a former centralia.
_A_ central_e_. :-)
The migration to the anterior surface can be traced beginning with
Macrocnemus, which, like Cosesaurus, has a poorly ossified carpus
(for whatever reason). The predecessor of Macrocnemus,
Why do you call it a predecessor when it's 100 million years younger?
likewise has a poorly ossified carpus,
Because it's obviously immature, with sutures between neural arches and
centra and at most open sutures between epi- and diaphyses on all
endochondral bones including the suproccipital. No wonder that the text says
it's immature, too. I have read the description and looked hard at the
illustrations because I coded the little beastie for a phylogenetic analysis
so it's phylogenetic situation over a series of taxa.
"Logic -- you're doing it wrong."