[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Synapsids weren't reptiles?



On Mon, Jun 30, 2008 at 8:40 AM, Erik Boehm <erikboehm07@yahoo.com> wrote:
>
> Why should reptile be abandoned? what is wrong with using it synonymously 
> with sauropsid?

Well, for one thing, when used for a clade, it's *not* a synonym of
_Sauropsida_. _Sauropsida_ is branch-based (and specifically a total
group), while _Reptilia_ sensu Gauthier is node-based (and
specifically a crown group). Granted, the known content is pretty much
identical (unless turtles are diapsids, of course!), but that doesn't
make them synonyms.

> is it because some use it paraphyletically by excluding the bird node?

It's because almost everybody has used it paraphyletically since its
inception, and continues to use it that way.

Now, you could say, "But Mike, what about _Dinosauria_?" I think
that's a somewhat different case, because:
1) There were some efforts to include birds even before the advent of
phylogenetic nomenclature (e.g., Bakker).
2) A good number of both researchers and lay public have taken to
using it as a clade, while the cladistic version of _Reptilia_ has
failed to take off. (Possibly, I speculate, because there are living
"classic" reptiles but no living "classic" dinosaurs.)

> Should the term "fish" be abandoned? After all cladistically - we are 
> lobe-finned fish. Unless you define fish paraphyletically, it becomes quite 
> correct to call whales and doplhins "fish". Yet people still know what you 
> are talking about when you say "fish"- so it is still usefull, and thus 
> shouldn't be abandoned.

Sorry, I should have said "abandoned in formal nomenclature". It might
still useful as an informal ecological sort of term. Although, one
problem there is that it has been used as a clade name, so it might be
confusing. "Fish" and "Pisces" do not have that problem (_Vertebrata_
and _Craniata_ being far more suitable terms).

> How else do we talk about studying lobe finned fish today (lungfish, 
> ceolocanths) without considering whales, birds, humans, snakes, etc?

Non-tetrapod sarcopterygians, or primarily aquatic sarcopterygians;
heck, even "sarcopterygian fish" might be all right.

> Synapsids clearly weren't reptiles- they likely had no scales, didn't excrete 
> uric acid, didn't have beta keratin, etc.

Now you're confusing diagnosis with definition. It's not uric acid
that makes the reptile; it's the reptile that makes uric acid (at
least according to your diagnosis--there are other, more traditional
ones that involve traits like sprawling posture, ectothermy, etc.).

> So even though I am fine with paraphyletic groups in some cases, I'm not ok 
> with calling all amniotes, excluding the mammal crown, reptiles.

(Don't forget the bird crown.)

I'm still rather foggy as to your criteria--why pick on this
paraphyletic group and not others?

> So, would a preferable term, in your opinion, for the older more traditional 
> definition of reptiles(which does not include birds), be stem-birds - i.e. 
> the sauropsid stem group minus the crown bird group?

No, that's not a stem group, since it has extant members. A stem group
is a total group minus its *corresponding* crown group. So
"stem-avian" means, "Everything sharing more recent ancestry with
avians than with any other extant organism, except for _Aves_ (i.e.,
the crown group) itself." "Stem-avian" is somewhat similar to the
"classic" usage of "dinosaur", but more inclusive, including
_Lagosuchus_, _Silesaurus_, pterosaurs (probably), etc. on one end and
non-avian avialans on the other end.

-- 
T. Michael Keesey
Director of Technology
Exopolis, Inc.
2894 Rowena Avenue Ste. B
Los Angeles, California 90039
http://exopolis.com/
--
http://3lbmonkeybrain.blogspot.com/
http://dragabok.blogspot.com/