Re: Air sacs in extant non-avian reptiles?

[Ronald Orenstein <ornstn@home.com>]

> 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.
>
> eric l.

> 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:ornstn@home.com