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Re: going offlist on Protista, bacteria




Ken Kinman wrote:


Probably best to go offlist to continue these somewhat offtopic discussions.

Perhaps a little off-topic, but since it relates to the last 4 billion years of evolution, of which dinosaurs played an important part for 150 million years, I?ll beg the indulgence of Dinolist Central. Also, your comments concern some fundamental aspects of taxonomy and phylogeny, one of which is central to dinosaur classification.


However, I think it is grossly unfair (and inaccurate) to >characterize dinosaurs (and all the rest of the metazoans) as occupying a tiny twig >on the tree of life. Such exaggeration will only confuse and >intimidate students and everyone else.

Or enlighten them as to the wondrous diversity of unicellular, microbial life. This isn?t taking anything away from the success of us multicellular life-forms, just putting our success into perpective. We are just one corner of the huge domain of Eucarya. And the Eucarya is just one of three domains of life on Earth.


The number of Metazoan phyla has also gotten out of hand (I >recognized 24, and even that is too many).

?Phyla schmyla?, as I once saw written on a T-shirt. A lot of your irritation over what constitutes a phylum is resolved if you just abandon them altogether. A taxon?s position on the tree is all that really counts.


Order Tullimonstrida (Tully monsters) is probably just an aberrant group of sipunculans or molluscs.

Then it?s probably just an aberrant group within the Sipuncula or Mollusca. Why agonize over whether the Tullimonstrida should be ranked as a phylum or class or order. The same problem surrounds whether the black-smoker-loving Vestimentifera are just unusual pogonophorans, or whether the parasitic Pentastomida (tongue-worms) are just highly specialized crustaceans. Should they be granted their own phylum? Who cares? It?s their phylogenetic position that?s important, so why bother weighing up whether these bizarre groups are ?different enough? from their ancestors to qualify as a new phylum. (I?m reminded of Tom?s example of the wayward daughter who comes home one day sporting pink hair. ?She?ll never be part of our family again? rants the father. ?No,? says the mother. ?No matter what she looks like, as our daughter she?ll always be part of our family.?)


Again, you seem to be your own worst enemy Ken. Your concern over the delineation of the Class Aves from the rest of the dinosaurs is rooted in the same preoccupation over whether certain groups deserve to be promoted to higher ranks - whether it be Class, Phylum or Kingdom.

I?m sorry to harp on this, but it concerns a very fundamental aspect of evolution. One thing I?ve come across when discussing evolution with other people is the misguided notion that the past 3-4 billion years of evolution can be interpreted as a march of progress. Vertebrates are not superior to flatworms, any more than flatworms are superior to sponges, or any metazoan life form is superior to any bacterium. Each branch on the Tree of Life just does things differently.

Ken, I?m not accusing you of you of subscribing to this view of evolution, but your ?Kinmanian? classification perpetuates this myth ? like the Linnaean hierarchial system which it draws upon. Birds are not superior to dinosaurs, so why give them a ?Class? of their own. Go way back to the base of the Aves, and the differences between birds and dinosaurs resolves into one or two evolutionary innovations. There?s nothing so different between _Archaeopteryx_ and (say) _Sinornithosaurus_ that one deserves to be raised into a ?higher? class than the other.

And finally, ether-linked lipids are not restricted to the so-called "Archaea" (also called Metabacteria, which is an older and more appropriate
name).

I disagree. Completely. The Archaea are fundamentally different to Bacteria in their genetic machinery and more similar in this respect to eukaryotes (animals, plants, fungi, ?protists?).


Tim


------------------------------------------------------------

Timothy J. Williams

USDA/ARS Researcher
Agronomy Hall
Iowa State University
Ames IA 50014

Phone: 515 294 9233
Fax:   515 294 3163

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