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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.

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
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