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Re: Back-evolution of limbs.
Larry Dunn wrote:
>>---Betty Cunningham <email@example.com> wrote:
>>before either reptiles or mammals were terrestrial, their ancestors were
>Does this discussion of traits, and a possible bird-dinosaur nexus,
>have any meaning if we're analogizing to common traits in such such
>broad groups as entire phyla?
Umm... aren't Reptilia, Mammalia and Pisces classes, according to
Also, what is a phylum? My personal definition is "a preferably
paraphyletic assemblage of species designed to neatly package the diversity
of life into quaint disposable pockets while quietly sweeping phylogenetic
relationships under the carpet." Common traits are still common traits, no
matter what typological construct you erect between their possessors.
The concept of phylum is so artificial as to have no place in
phylogenetic discussions. You put our close relatives the echinoderms in one
phylum, the Graptolites et al. in another, the tunicates in a third, and all
of a sudden you have completely lost the fact that some of these fellows are
more closely related to us than others.
I once asked a dear friend of mine, a coral worker, what the
relationships of corals and sponges were. He said "They're separate phyla."
"But," says I, "they are related." "They're separate phyla." "So,
what, they just arose independantly from the primordial ooze?" "Yes."
And we've all seen the primordial ooze, on the inside cover of many
invertebrate paleonbtology texts (I think Boardman has a good one). A big
ring of phyla, each rizing seperately from the protozoan horizon. What kid
of rank B.S. is this?
I recall one of my favorite "phylum frank-ups". Sweet, in his
fabulous book on condodonts, explores the (then even more uncertain than
now) phylogenetic position of the conodonts, and concludes that they are
best left in their own phylum. As if this solves ANYTHING!?!?!?!
>Some dinosaurs, our phylum mates but not much else, were bipedal.
Not much else?!?!? Not much else? We are both amniote tetrapod
vertebrates. I realize that these are just subtaxa in the grand Linnean
schemem, but in the real world of evolution they counts for a whole lot.
>Does that help us at all in determining the geneology of also-bipedal
>Homo sapiens sapiens? Are we "secondarily bipedal" for that reason?
Maybe it does. Code the character and see.
Jonathan R. Wagner, Dept. of Geosciences, TTU, Lubbock, TX 79409-1053
"...To fight legends." - Kosh Naranek