[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Paravian claw studies
Some comments on claws:
Note: In the supp info for both Fowler et al., (2009: Birds of prey; PLoS) and
(2011: paravians; PLoS) we discuss the various methods, and merits of different
studies. I recommend reading them both for a more complete review of the
Also, as far as I know, one of the most complete claw measurement datasets for
extant birds is used in Csermeley's newest paper:
D. Csermely, O. Rossi & F. Nasi
Comparison of claw geometrical characteristics among birds of prey and
Italian Journal of Zoology (2012)
Although sadly, the data matrix is not included (which would have been VERY
informative). Csermeley's work is very good stuff (mostly concerning
behaviour), and strongly referenced in both Fowler et al 2009 & 2011. You might
also take a look at Peters & Gorgner (1992) and some of the more recent work by
Ward et al. (more about functional considerations for foot proportions than
claws per se; refs in Fowler et al., 2009).
I look forward to seeing Chris Glen's dataset.
From: Jason Brougham <firstname.lastname@example.org>
>There is Feduccia's 1993 method which measures the inner (ventral) curvature,
>following it down to the plantar surface of the fleshy toe pad.. As far as I
>can find, he never published his data set. He divided his samples into three
>behavioral categories: ground, perching, and trunk climbing birds, without
>defining the criteria used to distinguish between them. He did not investigate
>whether claw curvature scales with body mass. He provided no statistical
>evidence for the strength of his signal either. Later authors faulted the use
>of the inner curvature, fit to the best fitting circle, as the inner curvature
>of many birds is not circular.
--Feduccia deliberately excludes predatory birds. See Fowler et al. (2011) supp
info for why this is important: ie. predatory birds plot as mostly trunk
climbers; especially ospreys.
>Fowler et al. 2009 state that they us
that claw curvature scales with body mass. Fowler et al. measured inner AND
outer curvatures. Their data do not seem to draw strong conclusions about
cursorial vs. perching behaviors.
--See Fowler et al (2011); curved claws are hooking devices, but why do you
need a hook?
>Burnham and Martin 2010 followed Feduccia's method, and failed to address Glen
>and Bennet's criticisms of it. They found curvature values for Microraptor
>much greater than Glen and Bnennett did. They also make qualitati
essments of claws - that they have pin like points or "a thicker base". In this
method they cite Yalden. Yet no measurements are taken, and the possibility of
diagenetic lateral compression of the claw shapes is not excluded.
--Yalden's paper (in the pseudo-journal "Archaeopteryx") has a reconstruction
of a Compsognathus claw that is astonishingly dorso-ventrally compressed; this
looks very wrong to me, and unlike pretty much all theropod claws, with the
possible exception of some ornithomimids.. but even they aren't THAT
compressed. I don't think you can use Yalden's paper as justification for
>The literature in this field shows a state of confusion and disagreement. Any
>researcher who attempts to investigate claw curvature correlations would do
>well to begin with a systematic review of methodologies, and then provide a
>very explicit method, and publish their entire data set with the paper, to
>allow the experiment to be reproduced by others.
--Disagreement, yes; but mainly this is disagreement with the Feduccia/Burnham
view. Inner curvature is potentially problematic (as Glen & Bennett say).
Excluding carnivorous taxa doesn't help at all when the taxa you are looking at
(basal paravians) are (probably) carnivorous. Claws alone don't tell you as
much as looking at the complete foot (and preferably, the whole animal). Basal
paravians have a subarctometatarsalian metatarsus; a cursorial adaptation; both
we (Fowler et al, 2011) and Dececchi & Larsson 2011 raise this point.
>There may be a consensus that there is
between increased curvature and tree climbing behaviors,
--Only if you ignore carnivorous taxa.