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Re: Air sacs in extant non-avian reptiles?
Okay, can you tell me ONE professional ornthologist who belives that birds
are currently reptiles? Not aknowleging the possibility of dinosaur ancestry,
but currently having the same characteristics as lizards, snakes and turtles.
Well, I do not know a single ornithologist who does not accept that birds
are derived from archosaurian reptiles, Being a reptile does NOT mean
"having the same characteristics as lizards, snakes and turtles"; do you
not consider crocodiles to be reptiles?
To quote Frank Gill's standard text "Ornithology" (and I assure you Dr Gill
is an ornithologist!): "Indeed, birds and modern reptiles share many
characteristics. The skulls of both articulate with the first neck
vertebra by means of a single ball-and-socket device - the occipital
condyle; mammals, which evolved from a different line of reptiles, have two
of these. Birds and modern reptiles have a simple middle ear that has only
one ear bone - the stapes; mammals have three middle ear bones. the lower
jaws - or mandibles - of both birds and modern reptiles are composed of
five or six bones on each side; mammals have only one mandibular bone. The
ankles of both birds and modern reptiles are sited in the tarsal bones, not
between the lower leg bone - or tibia - and tarsi as in mammals. The
scales on the legs of birds are similar in structure to the body scales of
modern reptiles. Both birds and modern reptiles lay a yolked, polar egg in
which the embryo develops by shallow divisions of the cytoplasm on the
surface of the egg. Female birds and some female reptiles have the ZW sex
chromosome combination and are referred to as heterogamic; males are the
heterogamic sex among mammals. Birds and reptiles both have nucleated red
blood cells, whereas the red blood cells of mammals lack nuclei."
I could criticize this passage, of course, by pointing out that most of
these character differences refer not to uniting characters of Aves and
Reptilia but to new developments in Mammalia contrasted with primitive
tetrapods, but it is useful to show that ornithologists do not recognize
birds as being as divergent from reptiles (in the broader, paraphyletic
sense Gill uses) as mammals are.
Gill also quotes Charles Marsh, who noted as long ago as 1877 that "The
Classes of Birds and Reptiles, as now living, are separated by a gulf so
profound that a few years since it was cited by the opponents of evolution
as the most important break in the animal series.... Since then... this gap
has been virtually filled by the discovery of bird-like reptiles and
reptilian birds. Compsognathus and Archaeopteryx .... are the stepping
stones by which the evolutionist of today leads the doubting brother across
the shallow remnant of the gulf, once thought impassable."
Also (speaking as someone with a PhD in Ornithology) it is my experience
that at least some ornithologists who think about the matter accept that
maintaining Aves as a class is really a convenience rather than some sort
of law of nature. Most texts simply do not address the matter because they
are concerned about what is going on within Aves only. Certainly the
distinctiveness of birds is pointed out in defining Aves (see, for example,
A. Landsborough Thompson's article "Aves" in "A Dictionary of Birds"
(Campbell and Lack, eds), and I suspect most ornithologists prefer to think
of birds as a class for a number of reasons (of which I still think the
biggest is avoiding having to adjust all the lower ranks within birds).
However, I think Mr Lurio is being uneccessarily excited about this whole
issue. It really doesn't matter, and I am inclined to the idea that naming
heirarchies (at least above the family level) may be outgrowing its
usefulness. Aves is a distinct, monophyletic taxon. What more do you need?
Ronald I. Orenstein Phone: (905) 820-7886
International Wildlife Coalition Fax/Modem: (905) 569-0116
1825 Shady Creek Court
Mississauga, Ontario, Canada L5L 3W2 mailto:email@example.com