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AW: FW: Paravian claw studies
A few thoughts:
First, it must be demonstrated that the curvature of the sheath follows the
curvature of the ungual closely enough to make measurements of the latter in
absence of the former actually worthwhile.
The taxon set would be Archosauria. Especially as many fossil paravians with
the sheath preserved (as trace if no other way) as possible.
Second, the more important curvature is the inner, i.e. the contact surface.
But this cannot be considered in isolation; rather, the ungual angle and/or toe
pad development must be considered too; these also affect the extent of the
contact surface. Probably two (curvature and angle) measures, or even three
(curvature, angle of ungual, plantad expansion of toe pad) are necessary. Three
measurements are unlikely to be available for most fossil taxa. Even two may be
difficult; you need highly conserved articulated skeletons.
Third, feeding (or generally: non-locomotive) behavior must be taken into
account. I.e., raptorial birds must be tested regarding whether they are not
confused with scansorial etc birds by the analysis. This can be done with crown
Aves, indeed all the necessary taxa are found among "higher landbirds"
(woodpeckers, wrynecks, owls, barn owls, falcons, eagles, parrots and
passeriforms would be a good taxon set for example) which has the additional
advantage of allowing for good phylogenetic coverage in the taxon set used
(i.e. you actually come close to getting a proper measure of evolutionary
plasticity). Here, the outer curvature might be most significant, because its
role in foraging is larger than in locomotion.
Fourth, allometry needs to be taken into account.
Fifth, it cannot generally harm to do a dense taxonomic sampling for
ecomorphologically diverse parts of the tree, to get as good a measure of
evolutionary plasticity as possible (i.e. to see what is *dys*functional).
Especially fairly close relatives (say, a dozen years of evolution betwen them
or so) that differ markedly ecologically are interesting, since they will show
how plastic claw development actually *can* be in real life, and whether
certain parts of the parameter space are genetically inaccessible or whether
claw evolution is essentially free-form within the constraints of the ecosystem.