Re: "Morosaurus" agilis

[Jonathon Woolf <jwoolf@erinet.com>]

Thomas R. Holtz, Jr. wrote:

> Under current taxonomies, Coelurosauria refers to birds and all theropods
> sharing a more recent common ancestor with birds than with Carnosauria
> (Gauthier, 1986), and Carnosauria refers to Allosaurus and all theropods
> sharing a more recent common ancestor with Allosaurus than with
> Coelurosauria (Padian et al., in review; see also Holtz & Padian 1995
> (abstract for SVP)).  Many theropods, however, are neither coelurosaurs nor
> carnosaurs.

Question: Does this scheme seem a bit circular to anyone else?  I mean,
you have two groups of theropods each of which is at least partly
defined in terms of the other.  There's no firm anchor point.  That's a
no-no in mathematics; is it acceptable in taxonomy?  

Suppose instead you were to say "Coelurosauria is birds and all
theropods sharing a more recent common ancestor with birds than with
_Allosaurus_, and Carnosauria is _Allosaurus_ and all theropods sharing
a more recent common ancestor with _Allosaurus_ than with birds."  I
think that says basically the same thing, but all the taxa referred to
are firmly anchored by independent definitions and even the hint of
circularity is gone.

-- JSW