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Re: Ancestors... (was Re: Stratigraphy, biogeography & cladograms)

On Wed, 20 Jan 1999, Thomas R. Holtz, Jr. wrote:

> Jack Horner has a lot to say about ancestors these days, some of which is
> discussed in "Dinosaur Lives".  He may have even convinced me to drop my
> (hitherto still morphologically- and specific mate recognition system-based)
> species concept altogether and like him recognize that a lot of taxonomy is
> bass-ackwards: that lineages are the real thing, and species are the human
> constructs.

I had an idea once; goes a little like this:

When a clade (e.g., Marginocephalia) is defined, the definition uses
certain anchor taxa, preferrably genera (in this case, _Triceratops_ and
_Pachycephalosaurus_). It is generally understood that this really means
that the type species of the genera are the true anchors (_T. horridus_
and _P. wyomingensis_). But why not go further and say that the true
anchors are the individual organisms which the type material of these type
species (YPM 1820 and USNM 12031, I believe) comes from? Thus
Marginocephalia is really the most recent common ancestor of the
individuals represented by YPM 1820 and USNM 12031, plus all of its

The species definition should similarly rest on the type individual -- the
most inclusive breeding population that includes that individual. Or, to
be more explicit, any organism whose parents could, at least
hypothetically, interbreed with the parents of the type individual (just
to allow for cases of infertility). (Strict application would cause some
lumping of modern-day species, like _Canis lupus_ into _C. familiaris_,
and even _Bison bison_ into _Bos taurus_. Also, by this definition
species could be paraphyletic and could overlap. Not sure how this
applies to asexual organisms ... But who cares about them? :) 

This would create two separate systems, one for species, one for lineages,
but they would work together since they both use the same type
individuals. Additionally, both systems would be based on something real. 

Of course, it would be impossible to apply the species system to fossil
organisms (and still hard to apply it to modern forms), but it *does* give
an absolute, Platonic ideal to shoot for.

I have no idea how "Genus" should be defined ...


--T. Mike Keesey                                   <tkeese1@gl.umbc.edu>
THE DINOSAURICON                http://www.gl.umbc.edu/~tkeese1/dinosaur