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Re: More reptile stuff
Thomas R. Holtz, Jr. wrote:
> At 03:05 PM 12/17/98 -0600, Chris Campbell wrote:
> >And since it's arbitrary, why not choose groupings which have some
> >significance beyond mere convenience? Turtles are so distinct from
> >lepidosaurs or archosaurs that lumping them together makes little sense
> >to me.
> But there are a lot of derived features unique to turtles PLUS lepidosaurs
> PLUS archosaurs.
Beyond skeletal features? Like what?
> >No, what I mean is "do turtles have more in common with archosaurs than
> >they do with the ancestors of reptilia, thus justifying the use of such
> >a broad taxonomic category?
Are there any significant features which don't deal with skeletal
> > Do they have enough features in common with
> >this group we're calling reptiles that they ought to be lumped in with
> >it, rather than being given their own category a la mammals?"
> 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.
> >Testudines seem to have diverged from the lepidosaur and archosaur lines
> >so early on that grouping them with these lines seems a bit pointless to
> >me. You can, using their common ancestor as a point of reference, but
> >then you could do the same thing with these groups and mammals.
> And we do.
> As per my biannual statement, just because some systematic grouping seems
> pointless "to you" doesn't mean it is pointless (or more to the point,
> useless) to people interested in, or even actively researching, basal
> amniote relationships. These groupings DO become useful to such individuals.
Of course, but said individuals are using a term with lots of baggage in
a very specific and precise sense. "Reptile" has a lot of connontations
attached to it, and most of them don't really apply to most of the
animals you're including in the group.
> >> As Gauthier has said, there are no animals alive which closely resemble a
> >> Paleozoic amniote. All living amniotes (mammals, turtles, tuataras,
> >> squamates, crocodilians, and birds) have highly specialized anatomies. The
> >> idea that Permian or earlier amniotes were somehow "lizard-like" or
> >> "turtle-like" comes from peoples unfamiliarity with how sophisticated the
> >> anatomies of lizards or turtles actually are.
> >Which is why it seems odd to me to even retain the notion of Reptilia at
> >all. There don't seem to be a whole lot of things uniting the groups
> >other than a general tendency toward egg-laying and some common
> And a whole lot of shared detailed skeletal features. There is a lot more
> to vertebrate anatomy than 100-level college courses (or their textbooks) go
> into. (This isn't a put-down: I helped write a 100-level college course
> textbook chapter on dinosaur osteology).
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. It's not the same as, say, "diapsida" since diapsid refers to
one thing and one thing only -- holes in the skull. "Reptile" refers to
poor thermoregulation, sluggish behavior, scales, egg-laying, particular
forms of locomotion, goofy reproductive patterns (by mammalian
standards, of course, which don't count for much), and a half-assed
(though admittedly effective) circulatory system. Perhaps two of these
apply to birds; at least one does not apply to turtles, and another
doesn't apply to crocs. 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?
> >My argument here is that the term doesn't really mean anything anymore.
> On the contrary, it has a very specific and precise meaning, if by "meaning"
> we mean "definition". If by "meaning" you are talking about something more
> metaphysical, then ask a philosopher, not me.
What it means depends on who you ask. The cladists have one version,
while the rest of the world has another, and they don't quite gel.
> >We basically lump all extant vertebrates who aren't fish or mammals into
> >one group, even though they don't really have much in common beyond
> >common ancestry. Yes, lumping lepidosaurs and archosaurs and testudines
> >together is a valid clade, but what's the point? I'm just not very
> >clear on what this really tells us about the groups involved.
> 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. Fish tells me an animal is an aquatic
vertebrate with a two-chambered heart and gills. Bird tells me an
animal is covered with feathers, has forelimbs modified into wings, lays
eggs, and has exceptional respiratory and circulatory systems. Arachnid
tells me an animal has eight limbs and a body divided into a
cephalothorax and an abdomen. 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, how it's covered,
how it reproduces, how it moves, how good it is with circulation or
temperature regulation, or anything beyond skeletal characteristics. 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. If
you're talking sauropsids or pelycosaurs fine, go to town with skeletal
characteristics. I really think, though, that we should have more to go
on with a term which sees as much use as "reptilia".
> What is the "point" of labelling siliciclastic sedimentary rocks with less
> than 10% mud matrix and more than 90% of the sand-sized particles a quartz
> arenite? Not much point beyond a reference term. Giving such rocks a name
> allows us to talk about such things in comparison to lithic arenites, or
> felspathic arenites, or quartz wackes, or what have you.
Which is a term that isn't used outside of geological and
paleontological circles. It's not quite the same thing.
> >The thing is, I'm not arguing that basal amniotes should be included in
> >turtles + lepidosaurs + archosaurs; I'm just arguing for more of a
> >lumper mentality, wherein amniota is the main group and pelycosaurs and
> >other synapsids, testudines, arcosaurs, and lepidosaurs are branches
> Yes. And this differs from what I was discussing how?
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.
> 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.
> You might not care if turtles are closer to diapsids than to synapsids, but
> I do. It is useful to me to have labels to refer to this group.
Truth be told, it's not the labelling of the group that really bugs me.
It's the labelling of such a group as "reptile" that really weirds me
> >I don't think I'd object to the notion of reptilia so much if
> >the turtles were at least kept out of things.
> 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! Turtles of the world unite! Come forth and be
recognized for the cool critters you are!
> (For those who don't know, the U Maryland mascot is Testudo the Terrapin,
> and so I would object to those who object to keeping turtles out of things).
I prefer to think of it as elevating them above the common people. :-)
> More importantly, there is a group which excludes turtles (probably: unless
> the "turtles as really derived lepidosauromorphs" hypothesis turns out to be
> true!): Diapsida. A name well loved in paleontological circles.
It certianly is. I just wish it wouldn't try to suck up those glorious
testudines with a mere label change . . .