Re: questions about the Odontochelys study

[David Marjanovic <david.marjanovic@gmx.at>]

----- Original Message ----- 
From: "Augusto Haro" <augustoharo@gmail.com>
Sent: Tuesday, December 02, 2008 10:09 PM

> seeing an aquatic pleurodire run much faster than a tortoise,

Tortoises are outright graviportal... they have adaptations for 
energy-efficient walking that make running difficult or impossible.

> There are pachyostotic amniotes, as many said above, that were
> correlated with aquatic habitats. However, I have seen cetacean and
> pinniped skulls and they are relatively trabecular and appear to be
> less ossified, instead of more, than those of terrestrial mammals.

Correct. Diving tetrapods that can collapse their lungs are osteoporotic 
rather than osteosclerotic or pachyostotic so they get closer to the density 
of water when their lungs are collapsed.

Incidentally, *Eusthenopteron* has a very, very thin cortex surrounding a 
very large spongiosa. If the cortex were missing altogether, that would be 
the osteoporotic condition.

> almacenating

What does that mean? Storing? (That's a guess. It looks like an Arabic 
import into Spanish that hasn't spread any further.)

> As far as I know, many salamanders are bottom-dwellers in rivers and
> are not pachyostotic, and I do not think all of them are lungless...

While having lungs and not being pachyostotic, they are still 
osteosclerotic: the bones look unspectacular from the outside, but on the 
inside, there is almost no or no spongiosa and almost no or no marrow 
cavity, it's all just massive cortex. This has the same effect as 
pachyostosis, only less extremely so. It is often found in amphibious 
tetrapods.

Figuring out the lifestyle of fossil tetrapods by bone cross-sections and a 
time-calibrated phylogenetic tree is a long-term project of my thesis 
supervisor and several occasional collaborators. There's already a bunch of 
papers out there, and I think one is in press.

----- Original Message ----- 
From: "T. Michael Keesey" <keesey@gmail.com>
Sent: Tuesday, December 02, 2008 11:59 PM

> Out of curiosity, are there any names for a clade that includes
> lepidosaurs and testudines, but not archosaurs?

No, except that Lepidosauromorpha might include the turtles in that case, 
and so might Lepidosauriformes, but I don't know if any definitions that 
make sense currently exist for these names.

And I don't recommend making such a name up just yet :-)