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Re: Australodocus a titanosauriform and other new papers



On Tue, Jul 12, 2011 at 12:16 AM, Mickey Mortimer
<mickey_mortimer111@msn.com> wrote:
>
> When we discussed this on your blog, we narrowed our disagreement down to the 
> fact that you don't see genera as clades.  But I can assure you that Taylor, 
> Williams, myself and most others on here DO think of genera as being clades.

Many do, but this is untenable. Ancestral species must belong to a
genus, like any species, but their descendants may be in multiple
genera. In cases like these, there is no option but to assign them a
paraphyletic genus.

We get around this in vertebrate paleontology by noting that we can
never really tell the difference between an ancestor and a close
sister taxon (true so far), and then just pretending that every
ancestor candidate is a sister taxon (likely false). This isn't a very
honest approach, and it's incompatible with other disciplines (in
fact, it gets pretty hard to apply to a lot of Cenozoic fossils).

Fact is, there are many species which must belong to paraphyletic
genera, unless we decide to make all life one genus. (My opinion: it's
highly unfortunate that we seem to be stuck with binomial
nomenclature.)

That said...

> Thus retaining brancai in Brachiosaurus implies it is in a clade with 
> altithorax to the exclusion of Sonorasaurus, Cedarosaurus and every other 
> named genus.  And THAT's the reason we all have a problem with it.  You may 
> view genera as just Linnaean labels, but most of us see them as implying 
> monophyly.

...I don't think you even have to invoke clades here. Your point holds
reasonably well even if you say "taxon" instead of "clade".

-- 
T. Michael Keesey
http://tmkeesey.net/