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Sphenodon & diversity




Jerry,
One should indeed use a combination of taxon diversity (including fossil taxa!) and morphological diversity, plus non-diversity factors as well/
Sphenodon is so distinctive morphologically that I follow the tradition of recognizing a separate Order Sphenodontiformes, and as of 1994, I coded it as sister group to Order Squamatiformes (which is species rich). I assume they are still regarded as sister taxa, but haven't looked at it recently. In mammals, Tubulidentiformes only has the aardvark, while Rodentiformes is species rich.
Many different factors come into play in producing a balanced Linnean classification which recognizes various kinds of diversity, the fossil record, whether to follow tradition or not, and balancing the views from cladistic and eclectic perspectives. Doing all these things is difficult, but not impossible.
-----Ken
*******************************************************
From: "Jerry D. Harris" <dinogami@hotmail.com>
Reply-To: dinogami@hotmail.com
To: dinosaur@usc.edu
Subject: Re: warm-bloodedness
Date: Wed, 21 Jun 2000 21:36:15 MDT


Ken Kinman wrote:

    The crocs and turtles and rest of the "reptiles" didn't diversify
anywhere near the extent that birds and mammals did, so they have never
been
seen as candidates for elevation to class status.

This is surely a fallacious argument! We know of far more crocodylomorph
taxa in the Mesozoic than we do birds. Am I correct in perceiving that your
assessment of "diversity" is based on the _modern_ number of bird taxa?
Also, what is the "magic number" at which diversity becomes sufficient to
stand up and be recognized? Why not use morphological distinctiveness? For
example, the modern _Sphenodon_ is very distinctive compared to other taxa
-- does it get its own group for this reason? It's certainly not very
diverse!


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Jerry D. Harris

AS OF JULY 1, 2000:

Dept of Earth & Environmental Science
University of Pennsylvania
240 S 33rd St
Philadelphia PA  19104-6316

Phone: (215) 898-5630
Fax: (215) 898-0964

E-mail: jdharris@sas.upenn.edu
and     dinogami@hotmail.com

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