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Many good points here but I think I will put in quick friendly response before any unfriendly ones appear Jeremy Young >Concerning the debate on classification and extinction I think: >1.- Aves are dinosauria in exactly the same way men are bacteria. Absolutely > Moreover >Aves have a long precedence in definition over dinosauria, thus, even in a >cladistic way, the correct assumption is to say that some previously >considered dinosaurs are in reality aves. A tempting argument but since birds evolved from dinosaurs rather than vice versa then the name dinosaur should be used. [in more cladistic terms the smallest clade which includes all birds would be a subset of the smallest clade which includes all dinosaurs]. >2.- Paraphiletic groups arent real ok. Monophyletic, polyphyletic and >holophyletic (the correct term for what cladists call monophyletic) also >arent real. Only individuals and systems are real, sets, as taxa are, are >mental constructs. Classifications (and cladifications) dont exists >independently from classifiers. I have no idea how/why cladists ended up redefining monophyletic rather than using the word holophyletic, I wish they hadn't. It is, however, indisputable that holophyletic taxa/clades are more rigorous and less subjective than any other type of taxon. However, if cladification is the subdivision of a phylogeny into a limited set of clades, then it will be arbitrary since the potential number of clades will be equal to the number of branching points. It will also be of finite value for practical communication since it is frequently necessary to refer to paraphyletic groups, such as dinosaurs, bacteria, fish, and amphibia. Hence cladification is no substitute for classification. > Sorry for the bad english > E. Bernardez No need to worry/apologize the meaning is not obscured ----------------------------- Dr. Jeremy R. Young Tel: +44 (0)171 938 8996 Palaeontology Dept. Fax: +44 (0)171 938 9277 The Natural History Museum INTERNET: jy@nhm.ac.uk LONDON, SW7 5BD, UK E-Mail Program used: Eudora
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