Re: warm-bloodedness

["Timothy Williams" <twilliams_alpha@hotmail.com>]

Ken Kinman wrote:

> Aves is a little trickier, being mired in all
> this controversy, but warm-bloodedness certainly is not a candidate as a 
> diagnostic characteristic.

Nevertheless, it is why you separate Aves from the archosaurs, and the 
Mammalia from the other synapsids.

>     The crocs and turtles and rest of the "reptiles" didn't diversify
> anywhere near the extent that birds and mammals did, so they have never 
> been
> seen as candidates for elevation to class status.

So we're talking Linnaean hierarchies, yes?  One nice thing about cladistics 
is that you can dispense with these ranks.  "Mammals, the grades are just 
in, and you achieved an A+ in Morphological Diversity, so you get to have 
your own Class.  Congrats!  Crocs - oh, bad news I'm afraid.  Unfortunately 
that spurt of evolution in the Triassic wasn't quite enough.  You get a D 
for Diversity - I'm afraid you'll have to stay in the Reptilia.  Better luck 
next time!"

Apologies for the facetiousness, but do you get my point?

> If birds had died out at
> the K/T extinction, I would classify them as another order of reptiles, but
> that didn't happen.

Here's something else that didn't happen: Birds didn't switch ancestors the 
moment they became successful.  They began as theropod dinosaurs, and 
they'll continue to be theropod dinosaurs until Armageddon.

>     And like it or not, these early thecodonts are going to problematic 
> for
> a long, long time, so I'm not abandoning Thecodontiformes any time soon.
> And as for Sphenosuchidae, I show it as sister group to Order
> Crocodyliformes.

> Is the phenetic gap between Sphenosuchidae and
> Poposauridae all that much bigger than the phenetic gap between
> Sphenosuchidae and Protosuchidae?  If so, I'll consider making
> Sphenosuchidae the basal clade of Crocodyliformes.

"Phenetic gaps"?  What be "phenetic gaps"?  You see the hole you're digging 
yourself into Ken?  You have to attach some kind of quantitative value to 
morphological difference.

Say (for example) the Troodontidae, Dromaeosauridae, and Archaeopterygidae 
represent three consecutive outgroups to the Aves (i.e. a paraphyletic group 
of three families relative to the Aves (birds)).  You want to find out 
whether archeopterygids belong in the Saurischia or the Aves.  So, you have 
to determine if the morphological differences between _Archaeopteryx_ and 
birds is greater or lesser than that between dromaesaurids and 
_Archaeopteryx_?  How do you *measure* this?  Do you have a formula?  Write 
a list?  What if you do determine that _Archaeopteryx_ belongs in the Aves.  
If you happen to discover a fossil intermediate between dromaeosaurids and 
_Archaeopteryx_, you have to go thru the whole damn process again.

With cladistics, _Archaeopteryx_ is a member of the Aves - as well as a 
member of the Saurischia, AND a member of the Dinosauria.  There is no 
reason for these categories to be mutually exclusive.



Tim
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