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Re: More reptile stuff



Thomas R. Holtz, Jr. wrote:
> In one sense, yes.  Choosing a particular explicit definition is arbitrary.
> There might be various justifications for it (taxonomic history, species
> diversity, important transformations associated with it), but as with ALL
> taxonomic assignment, the name chosen and the definition chosen is
> ultimately arbitary.  (The group "turtles + (lepidosaurs + archosaurs)"
> could just have easily been called 'Fred', for instance, but for historical
> reasons has been labeled 'Reptilia').

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.
 
> > Does that ancestor have less in common with, say, testudines than 
> > testudines have with archosaurs?
> 
> What do you mean by "in common"?  It would be the same ancestor, the common
> ancestral population of ALL amniotes.
> 
> If you mean "do turtles more closely resemble the most recent common
> ancestor of mammals and reptiles than do archosaurs", the answer might be:
> in some features, probably; in others, no way!!

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?  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?" 
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.
 
> 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
ancestry.
 
> >What is it about these early amniotes that warrants placing them in a
> >taxonomic no man's land instead of placing them with reptilia (which
> >would then necessitate either ditching the term reptilia -- which gets
> >my vote --
> 
> (A parenthetical aside -- Is it REALLY so difficult for people to try and
> adopt a new view of Reptilia?  Didn't everyone once go through the phase
> when you learned that pterosaurs and plesiosaurs and _Dimetrodon_ WEREN'T
> dinosaurs, but you moved on and began to appreciate Dinosauria more?   The
> same goes for learning that spiders aren't insects, or that whales are
> mammals. I *know* that Bakker calls for abandoning "Reptilia" in _Dinosaur
> Heresies_, but is that good enough reason?)

My argument here is that the term doesn't really mean anything anymore. 
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.
 
> I will turn the question around on you: in what positive way would basal
> amniotes be more like turtles + (lepidosaurs + archosaurs) than they would
> like mammals?  Shared primitive traits doesn't cut it: but that reasoning,
> humans are more like turles (in having a full set of fingers and toes) than
> like horses.

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
therein.  I don't think I'd object to the notion of reptilia so much if
the turtles were at least kept out of things.