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Re: Fossil species

Well Steve, this has been a problem for a very, very long time. However, there could someday be computer algorithms (utilizing optimality criteria of information content) which could help eliminate much of the arbitrariness.
Not sure how well they would work for fossils, but they have been tested on a family of extant fishes (Caesonidae). It contains 20 species, and this family's optimal classification was mathematically determined to be 4 genera (two distinctive species were placed in monotypic genera, one genus with 8 species, and another with 10 species). With the added stratigraphic data of fossils, I would guess the computer algorithms might be a little trickier.
Anyway, if you are interested in quantitative methods and optimality criteria, you might find it interesting:

Carpenter, K.E., 1993. "Optimal Cladistic and Quantitative Evolutionary Classifications as Illustrated by Fusilier Fishes".
Syst. Biol. 42(2):142-154.

             ------Cheers,  Ken
Steve  Brusatte wrote:
On Mon, 4 Feb 2002 20:40:10
KiernanCR wrote:
>In a message dated 2/4/02 7:09:11 PM, dinoland@lycos.com writes:
><< >Too bad there is no real scientific method for determining what belongs to a genus.
>Certainly. Every Linnaean rank above species, as mentioned in a previous
>post, is completely arbitrary and based on the observer. >>
>I don't really see *fossil* species as being much, if any, less arbitrary than genera.

Unfortunately, when dealing with fossils, what you allude to is correct. But, the enigmatic concept of a genus applies to everything living and extinct. However, it certainly seems easier to differentiate between say, _Psittacosaurus mongoliensis_ and _P. sinensis_, than to divide the _Psittacosaurus_ species into distinct genera. This was discussed onlist a few months or so ago, with no one able to come up with a distinct set of characters to divide _Psittacosaurus_ into two genera (of course, some may have missed the post...in which case I would be interested in hearing suggestions).

I don't see cladistics as an end to all means, but the idea of a clade is certainly much more stable than something like a "genus."


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