rising@utzoo.uucp (Jim Rising) (11/27/89)
It is probably correct to say that the closest relatives of birds are dinosaurs, but the alligators are also close relatives of dinosaurs--and they do grow continuously. Basically, birds, dinosaurs, and crocodiles are in the subclass Archosauria. The crocs. are in the Order Crocodilia, and the birds are apparently derived from animals that would have been classified in the Order Saurischia, Suborder Theropoda--the bipedal, carnivorous dinosaurs, like Tyrannosaurus rex (actually more like Compsognathus, for those of you who know it). Thus, if the Reptilia were a "monophyletic" group in the sense of Hennig the birds would be included--and probably the mammals as well. Contrary to what is apparently a popular belief, the above arrangement is NOT a new one, based on fancy new molecular data (although they support the relatively close arrangement of crocodiles and birds--havn't figured out a way to look at dinosaurs in this way yet), or on insights from cladistics, but rather was proposed in the 19th Century by T.H. Huxley--and has been widely accepted by comparative anatomists since. Concerning hair on pterosaurs, that is apparently possibly an artefact of preservation. In any event, it probably would not be homologous to hair on mammals, and feather of birds are indeed very like scutes (not scales) on "reptiles"--more like scutes than hair is. Lots of animals have hair- like structures that are not mammalian hair. This is not intended as a criticism of the suggestion that dinosaurs may have shown definitive growth. I suspect this isn't known, and may be unknowable--but certainly isn't something that I can comment on. --Jim Rising -- Name: Jim Rising Mail: Dept. Zoology, Univ. Toronto, Toronto, Ontario, Canada M5S 1A1 UUCP: uunet!attcan!utzoo!rising BITNET: rising@utzoo.utoronto.bitnet