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Re: Synapsids weren't reptiles?



On Mon, Jun 30, 2008 at 3:31 PM, Erik Boehm <erikboehm07@yahoo.com> wrote:
>
> I am unsure as to the distinction between branch vs node based. Can you 
> elaborate?

A branch-based definition is of the form: "The first ancestor of X
which is not also ancestral to Y, and all descendants of that
ancestor."

A node-based definition is of the form: "The last common ancestor of X
and Y, and all descendants of that ancestor."

A crown group is a special type of node-based clade, and a total group
is a special type of branch-based clade. For crown and total groups,
the specifiers (e.g., "X" and "Y") are extant.

More here: http://www.ohiou.edu/phylocode/art9.html#art9.4

>> It's because almost everybody has used it
>> paraphyletically since its
>> inception, and continues to use it that way.
>>
> I guess thats valid, its common usage in the past was pretty vague and not 
> well defined - I seem to recal some early tetrapods (including 
> temnospondyli?) were called reptiles, obviously the synapsids, all the while 
> leaving out birds.

And neontologists/herpetologists tend to use it for "crown sauropsids
minus avians" (or something like that).

> So if it were to take off, and birds were considered reptiles in common 
> usage(birds, take off - theres a pun there, I just know it), would you still 
> object as much?

Not at all, or even if most researchers started using "reptile"
cladistically (as they have for "dinosaur").

> So Pisces and fish weren't ever considered "clades", or the equivilant before 
> emphasis on clades?

Can't think of anyone who considered them such, but I could be missing
something. If they ever were considered clades, it must have been a
long while ago.

> Are you fine with using the group reptilia, as long as the group is not 
> considered a clade?

Not formally.

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

And all informal.

> Would you be ok with relegating Reptilia to the same status as the group 
> Non-tetrapod sarcoptygians/ sarcopterygian fish?

I'd prefer to refer to that general group by the relevant criterion:
"ectothermic amniotes", "sprawling amniotes", "crown sauropsids",
"ectothermic sauropsids", "sprawling sauropsids", etc. In less
technical literature, maybe it could be used informally.

(We do really need a better term for "crown sauropsids", though --
that is one argument for using "Reptilia" as a clade. But there has to
be a better name!)

>> 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.).
>
> Its not a reptile, because its ancestral to mammals, not lizards.

Okay, now you're confusing Reptilia with _Sauropsida_. "Reptilia" has
never been used for a branch-based clade.

> My point is that before grouping via evolutionary relationships, they grouped 
> on morphological features, and the synapsids fail to group with reptiles 
> under either system.

All of those characters you mentioned are only known for extant forms,
though. We don't really know whether they were present in stem-mammals
or not (although we can make inferences).

> And I know- some mammals excrete uric acid too, like kangaroo rats?

I think all do, actually, but not in a concentrated form like crown
sauropsids. Actually, I'm not really clear on this, so someone more
knowledgeable should feel free to step in. And don't turtles differ
somehow from other crown sauropsids in this respect?

>> > 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 consider birds to be reptiles,

Right, which is why you would be "not ok" with that.

> and last I knew, it was being taught this way in school

Really? Interesting.

> I'm not sure they got rid of the idea of "mammal-like reptiles" or mammals 
> evolving from reptiles.

Yes, I've seen many people who should know better continue to use that
phrase. Come on, "stem-mammals" -- it's shorter *and* accurate!
Win-win!

>> I'm still rather foggy as to your criteria--why pick on
>> this paraphyletic group and not others?
>
> huh? I'm defending the sort-of paraphyletic group reptilia - and bringing up 
> other more paraphyletic groups no one seems to have a problem with (fish). 
> Which group do you view me as picking on?

Reptilia. You're arguing that it shouldn't be used paraphyletically,
but you say you're okay with having other paraphyletic taxa.

(Also, at least "fish" is singly paraphyletic, unlike "classic"
Reptilia. The original "Reptilia" was actually polyphyletic[!],
although we can safely ignore that.)

Actually, I'm okay with paraphyletic taxa, in theory. I just think
they should be clearly distinguished from clades, so I don't support
using capitalized uninomials to refer to them. Also, I think they
should have more meaningful definitions than just "Clade X
(arbitrarily selected) minus Clade Y (arbitrarily selected)". Stem
groups are an example of useful paraphyletic groups. Their names can't
be confused with the names of clades (since they are informal and
start with "stem-" or are of the formula "the x-an stem group"), and
they reflect useful information (vis-a-vis phylogenetic inference).
-- 
T. Michael Keesey
Director of Technology
Exopolis, Inc.
2894 Rowena Avenue Ste. B
Los Angeles, California 90039
http://exopolis.com/
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