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Re: Synapsids are NOT reptiles!
> No, no, no, no, no!! For about ten years now, the movement has been on to
> use cladistic definitions of amniote (& other!) taxa. Under the new
> definitions, Reptilia is defined as the most recent ancestor of turtles,
> lepidosaurs, and archosaurs, and all of that ancestor's descendants. This
> EXCLUDES the Synapsida from Reptilia, and raises some important points. For
> example, uricoteley, enhanced color acuity, "reptilian" scales, and so forth
> were probably never present in Dimetrodon and it's ilk.
I'm a little bit hazey about the way cladistics assigns terminology. I
was under the impression that not saying mammalian
ancestors were reptiles was simply a matter of terminology, but that if
you went back afr enough you could find what probably be called a reptile
except that it was a mammal ancestor, so "technically" you couldn't CALL
it that. However, here you seem to be saying that the line that led to
mammals came straight from amphibians (oops, excuse me. I meant basal
tetrapods), independant of "reptiles", and that all the synapsid
modifications for dry land, such as a skin that wouldn't dry out
(presumably with SOME kind of scales) developed independantly from
"reptiles" starting with those first sem-aquatic critters.
What does cladistics have to say about, say, oue WAY earliest
ancestors, the Monera (or whatever they are these days). Are we
considered a part of this group because we are descended from Monerans?
How about fish? I would think that unless those marine and freshwater
critters that led to tetrapods was an example of amazing covergant
evolution starting with those basal vertebrates, you would have to say
we are descended from fish.
Getting on to what this means for dinosaurs, I've heared people say
that birds HAVE to be considered dinosaurs because they are descended
from them (or something like that), as though no matter how innovative
and unique you got, you would still be considered the same type of
critter as your ancestors. However, it has always sounded to me
that the whole labelling business (birds ARE dinosars, humans not from
reptiles and fish) was more of a case of toMAEto toMAHto than something with
real implications toward restoration of these extinct forms. The only way I
that we couldn't be called reptiles or fish or bacteria if if those
ancesters of ours were developed those reptilian or fishlike traits TOTALLY
INDEPENDANT of true reptiles and fish and bacteria, and that resemblance
to thise forms was simply an amazing example of covergent evolution
(or independant development of life, in the case of bacteria).
I am admittadly ignorant of cladistic terminology, so please clear
this up for me.