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RE: the tonight show
>From Ken Kinman (January 09, 2001 10:21 AM):
> However, palaeognaths are indeed one of the
>many cladistic "halfway-houses" between the Neognaths
>and primitive forms (like Archaeopteryx and
>dromaeosaurs). Other halfway-houses are the extinct
>Ichthyornithiformes, and further back the
> Paleognaths are admittedly the closest of the
>halfway-houses to the Neognaths as a whole, but I
>think it is unnecessary quibbling to say that
>they are not an evolutionary halfway-house.
>And from Ronald Orenstein:
>Calling a cassowary a "dino-bird" will imply to a
>general audience not that it is marginally more
>like a Velociraptor than a sparrow is (and I am
>not sure I buy this either), but that it is some sort
>of halfway-house between birds and (other) dinosaurs.
The latter point reopens that can of worms that seems to be inherent in
phylogenetic taxonomy, and really comes home to roost in the birds as
dinosaurs scenario. What would the public envision when the term
"dino-bird" comes up? Probably some big marauding monster that growls
rather then chirps, peeps, or quacks. So, does it really help communication
by labeling any birds this way?
Then, what does it mean in PT to say that paleognaths are more like
dinosaurs than neognaths (and thus might be called "dino-birds" or a
"half-way house"), when the distance between them is phylogenetic (number of
evolutionary novelties) rather than morphological? Might it be true that
the most derived members of a lineage that split off early might, in fact,
have developed as many, if not more, novelties on the way to being derived
forms in their own lineage than the most derived members of the original
branch (now a separate lineage) which we might characterize as more
advanced? In other words, aren't some paleognaths as advanced (i.e., as
distant from dinosaurs) as some neognaths, even while retaining some
primitive feature which allows us to identify them as paleognaths? Surely
Ron is correct in saying "It is a perfectly good modern bird, though a
And the poor ichthyorniths had the misfortune of becoming extinct. But if
they had survived, they would also be just as distant from dinosaurs, and
perfectly good, modern birds. Therefore, I am not sure what significance
there is in referring to such "half-way houses."
>From Ken Kinman:
>P.S. I would certainly not say a koala is "more like"
>a crossopterygian than an elephant, but Metatheria is
>one of the many cladistic halfway-houses between the
>sarcopterygian Order Coelacanthiformes and the mammalian
Again, I can't see what a "half-way" house is. The point at which
metatherian grade was reached is indeed closer to fish than elephants are,
but koalas and other metatheres are not the same animals that were at this
point millions of years ago, just like the placentals aren't. Metatheres
have had their own independent evolutionary role for maybe 100 million
years, and so have as much of a post-split history as placentals even though
it did not involve developing a placenta. Thus, they do not represent any
kind of "half-way house," even though the grade at which the split occurred
was indeed between fish and elephants.
Maybe it's the word "house" that has me hung up. Am I quibbling? I'm
struggling with cladistics as it is. I don't need to be confused even more!