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Yet more reptile stuff (long)



At 12:00 AM 12/18/98 -0600, Chris Campbell wrote:
>> But there are a lot of derived features unique to turtles PLUS lepidosaurs
>> PLUS archosaurs.
>
>Beyond skeletal features?  Like what?

Uricotely: the ability to eliminate wastes as uric acid (saving water)
rather than as urea.
Four or more type of color receptors in the eye, giving greater potential
for color acuity.
A unique system of striated ciliary muscles in the eye that inserts on the
lens in an equatorial ring for rapid focusing.
A fully developed and highly mobile nictating membrane.
Specialized keratinized scales (using different keratins than fish and so
forth).
Great reduction in the number of glands in their skin.
Among others: people more familiar with modern reptilian physiology can add
these.

Several authors have pointed out that this points to greater diurnal ability
in Reptilia than in other vertebrates (which, by and larger, are crepuscular
or noctural).

>Are there any significant features which don't deal with skeletal
>characteristics?  

See above.  Me, I mostly deal with bones, so I am most familiar with them.

>> Yes, BUT they *do* have their own category.  They have Testudines, and they
>> have their larger group Anapsida.
>
>That wasn't quite what I meant.  Of course they have their own category;
>everything does, at some point.  I meant their own category as distinct
>from other so-called reptiles.

See again my sentence: they have two groups (actually more, intercalated in
between those two) which separate them from diapsids.

If you are talking about "rank" concepts (subclasses, superorders, etc.),
that is a whole other issue.  And, quite frankly, a dead issue for most
practicing systemacists.

>Of course there is, I know that.  I suffered through CVA just like the
>rest of you.  That doesn't change the fact that "reptile" has lots of
>different meanings, creates confusion in folks who aren't taxonomists,
>and carries with it heavy implications in terms of biology and
>behavior.

Okay, I DO agree that "Reptilia" comes with a lot of non-scientific baggage,
and all in all I would have liked to see a different name used.  However,
that was the term that was used, with an explicit definition, and by the
principles I work under that is necessary and sufficient to use it.

And anyway, folks who aren't taxonomists tend to think "animals" just means
"mammals" anyway.  That doesn't mean that we should stop using Animalia.

>It's not the same as, say, "diapsida" since diapsid refers to
>one thing and one thing only -- holes in the skull.

No, it doesn't refer to one thing and one thing only.  It refers to a
pattern of common ancestry, and in fact has always done so.  In fact, since
that's terms inception, it has been recognized that the VAST majority of
species in Diapsida lack a typical diapsid skull condition.  Squamates
(lizards and snakes) and birds have long been a part of Diapsida, but both
have lost one of the two openings.  Textbooks refer to this as a "modified
diapsid condition" (yes, so modified that it isn't justified calling it
"di-"...).  The concept of common ancestry has been in play since the
beginning: squamates and birds were considered diapsids, even if they had
lost the eponymous condition.

>Now, I know you don't include these things in
>your definition, and that's fine, but that's what the definition means
>to a lot of people.  You're redefining the word, which is fine for
>cladists, but who's gonna catch up the rest of the world?

That's what education, including a forum like this, is about.

>> What is it you want it tell us?  No, really, I am intrigued by this
>> question.  You (and you are not the only one this list: the same questions
>> rise up every six to nine months, it seems) seem to be expecting something
>> from taxonomy other than labelling particular branches of the tree of life.
>
>I want it to tell us something readily observable about the animals in
>question.  Mammal tells me an animal bears and nurses live young and
>that it has hair of some sort.

Please don't leave the monotremes out in the cold: they are nursed, but they
aren't "born live" as the phrase goes.  (The writer of Science Made Stupid
points out that animals whose young are born dead aren't going to leave a
lot of descendants...).

>Reptile, particularly the cladistic
>definition, tells me nothing whatsoever about the animal in question. 
>It doesn't tell me what it looks like, how it acts,

And "fish" does?  Please check up on fish diversity some time.

>how it's covered,

No, that it does, even down to the protiens used.

>how it reproduces,

Sure it does: egg-laying, except for some weird lepidosaurs and euryapsids
with vivparity.

>how it moves,

This is different from "Mammalia" how?  Mammals have quadrupedal walkers,
bounders, and runners; fliers and gliders; arbors and fossors; bipedal
stripers and jumpers; and swimmers of all sorts.  Reptilia has quadurpedal
walkers, bounders, and runners; fliers and gliders; arbors and fossors;
bipedal striders and jumpers; swimmers of all sorts; and legless slitherers
to boot.  With the exception of the addition of the snake body plan, how is
this different?

>how good it is with circulation or
>temperature regulation, or anything beyond skeletal characteristics.

Except for the various physiological things mentioned above.  Please check
into things once and awhile.  I did mention some possible sources for you to
examine.

>I
>don't expect a definition to tell me all of the above, but I expect
>*something* to go on, particularly if it's a definition in common use
>not only in the biological sciences but in the world at large.

Again, there is a vast world of difference between the common use of the
term "animal" and the scientific use of the word "animal".

>What I suggested forces a focus on groups sharing readily observable
>common characteristics.  Turtles have that big ol' shell, birds have
>feathers and kick-ass homeothermy, crocs have dermal armor and a divided
>circulatory system, and lepidosaurs have that cool motion that scoffs at
>so-called better ways of getting about (among other things, of course). 
>"Reptilia" lets a reader stop right there without considering just how
>different these groups are.

Only if they chose to go no deeper.  But if they do, there are all these
other details within.  The same applies for almost any taxonomic group: you
could stop at Actinopterygia, and miss all the wonderful diversity within
this clade of fish.

>> Amniota is the "main" (or at least most inclusive) group.  Synapsida and
>> Sauropsida are the two main divisions within it.  Within Sauropsida we have
>> Mesosauria and Reptilia; within Reptilia with have Anapsida and Diapsida;
>> within Diapsida we have Lepidosauromorpha and Archosauromorpha and
>> Euryapsida (which might belong in one or the other, who can tell).
>
>Which is great for cladists.  The rest of us aren't in the same boat.

Then time to play catch up.  Sorry about this, but if you want to get into
scientific disucssions, you have to learn how the terms are used, even if
they might be the same as commonly used words.  After all, the physicists
use of the common words momentum, mass, weight, inertia, chaos,
acceleration, and so forth are often very different from the use us ordinary
folks use.

>> As a loyal Terrapin, I find your comments bigoted and outragous.  Turtle
>> Power!! :-)
>
>I'm *trying* to empower them, but you just wanna demote them to the rank
>of common reptile!

*BING*!!!  I thought that might be at the heart of this.  "Rank".  Ugh.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:tholtz@geol.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661