Re: Nest-depth phylogenetic bracket?

["John R. Hutchinson" <jrhutch@socrates.berkeley.edu>]

John Bois wrote:

><<I'm looking at a cladogram on the inside cover of _Encyclopedia of
>Dinosaurs_.  I notice that the only species of non-avian dinosaurs whose
>depth is known (Oviraptor and Troodon both lay on the surface) are on
>separate branches.  Can a phylogenetic bracketting argument be put
>forward about the nesting habits of other species above and below them
>on thosebranches (including _T. rex_)?>>

Just a side note, not a criticism of this statement: I'm starting to see a
lot of people referring to Witmer's (1995, and other references)
formulation of the extant phylogenetic bracket (EPB).  I think people are
starting to misuse/misunderstand it.  As Witmer originally formulated it in
his 1995 paper, it was for the formulation and testing of hypotheses about
unpreserved features of fossil taxa, especially but not only soft tissues.

The features should have an osteological correlate (implying a causal
relationship between unpreserved structure and osteological feature) for
the hypothesis to be testable for congruence with the entire phylogenetic
bracket.

For example, aside from the fact that Oviraptor and Troodon are extinct and
not extant, using nesting evidence from Oviraptor+Troodon to infer similar
habits in their most recent common ancestor is not the extant phylogenetic
bracket.  It is merely character optimization.  The nesting evidence does
not rely on osteological correlates per se (you are just optimizing "eggs
laid on surface" from two taxa to their closest node).  There is a
difference between Maddison et al.-style outgroup optimization and the EPB;
read Witmer (1995) to find out what it is.

Not that you can't use the term "phylogenetic bracket" to refer to outgroup
optimization, as John did, which is just fine.

Just wanted to make sure folks were clear on that; see the paper for more
details.

REF:
Witmer, L.M. 1995. The extant phylogenetic bracket and the importance of
reconstructing soft tissues in fossils. pp. 19-33 in Thomason, J.J. (ed.)
_Functional Morphology in Vertebrate Paleontology_, Cambridge Univ. Press.

                        John R. Hutchinson
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