Re: Fwd: Are dinosaurs really reptiles? (2)

["T. Michael Keesey" <keesey@gmail.com>]

On Sun, Apr 27, 2008 at 9:44 PM, David Peters <davidpeters@att.net> wrote:
>
>   |--Diadectomorpha
>       I'm seeing a pattern here: Small, flat-headed and short-toed gives rise 
> to big,
>       and short-toed. There's some logic to it. The intertemporal is gone. So 
> this must be an
>       amniote.Or is it? A fat, slow, plant-eater is the father of us all?

It's a stem-amniote, not an amniote (i.e., it's not part of the crown
group). As to whether it's an "apo-amniote" or not (i.e., as to
whether embryos had an amniotic sac), I'm not sure that we know.

Why would you say "father" when it's probably more like "uncle" or "cousin"?

>   `--+--Caseidae
>         The pattern of giant, weird, plant-eaters continues. So it must be 
> true.
>         No doubt this is an amniote [representing the Synapsida?].

No doubt.

>   `--+--+--Mesosauridae
>        Suddenly we're aquatic! With a decidely long premaxilla! And long 
> teeth!
>        And a long tail. And a long neck. And long toes! So derived! So early!
>        This one seems misplaced.

It's a side-branch, not an ancestor. (Repeat this for everything in the list.)

>   `--+--+--Protorothyris
>        Another close cousin. Say, isn't this fanged taxon getting 
> uncomfortably close to
>        the Synapsida? But didn't we leave those guys way back yonder with 
> Casea?

I'm a little outside my area of knowledge here, but since when is
_Protorothyris_ a synapsid relative? I've never seen it as anything
but a sauropsid.

>   `--+--Petrolacosaurus
>      Suddenly, after all these 'anapsids' a diapsid! Two holes at once! Isn't 
> it interesting that he
>      went straight for two, rather than dawdling about with one or the other 
> for awhile?

What prevents the final common ancestor of _Cephalerpeton_ and
(crown-)_Diapsida_ from having existed a good while before the final
common ancestor of _Petrolacosaueus_ and (crown-)_Diapsida_? (On
another note, how long does it take to evolve cranial fenestrae,
anyway? Do we even know?)

> And
>      that's not all. Long toes. Long limbs. Long neck. Long tail. Sharp 
> teeth. The only taxon on this l
>      list, other than Araeoscelis [and Anthracodromeus] who remotely 
> resembled this one is
>      Mesosaurus...way... back ...yonder. [shudder]

Presumably other characters outnumbered those five (all of which are
pretty damn homoplastic).

>    `--Araeoscelis
>      yes. A good sister
>  line: Credit is given where credit is due, but this seems to be very 
> scattered famiy tree. I don't have any problem with big lumbering plant 
> eaters giving rise to gracile little insect-eaters or visa versa... but the 
> change ought to be gradual. Evolutionary. Not like this see-saw.

The plant eaters are most likely derived sister taxa, not ancestors.

>  Next question: What were the five to ten sister genera leading up to 
> Herrerrasaurus? No suprageneric taxa please. And please include at least one 
> pterosaur.

What is a "sister genus"? You mean "sister clade"?

-- 
T. Michael Keesey
Director of Technology
Exopolis, Inc.
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