Paravian claw studies

[Jason Brougham <jaseb@amnh.org>]

Claw studies are frought with peril. Please, please, whatever we do, let's be 
aware that claw curvature studies must fully respond to the literature. And 
let's reconsider using photographs as the only evidence in any claw curvature 
study.

In 2010 Martin and Burnham published a paper finding that Microraptor had third 
toe claw curvature of 138 degrees, and Archaeopteryx had 137. They ruled this 
to be arboreal. They did not even acknowledge Glen and Bennett 2007, or Hopson 
2001.

Burnham and Martin used Feduccia's method with minor adjustments. He ruled 
Archaeopteryx to be arboreal. Feduccia, of course, never published his data set 
for his original 1993 Science paper.

In 2007 Glen and Bennett developed a more detailed and explicit system for 
measuring toe claw curvature, both with the ungual core and preserved sheaths. 
They got a range of results from different specimens, from about  90 degrees in 
Microraptor to about 70 in Archaeopteryx. their methodology also recognized 
that bahevioral categories are a continuous spectrum, rather than discrete 
cohorts of ground vs. tree birds. They found both animals to lie near the 
overlap between strict ground birds and predominantly ground birds. I'm not 
sure they ever published their data set either.

Larsson and DeCecchi in 2011 did a multivariate analysis and again found basal 
paravians to cluster within the range for ground birds. Their methods were a 
bit harder to interpret, as they used indices that grouped many measurements 
together and expressed most measurements as ratios.

So, to be of clear value, any new study on this subject must respond explicitly 
to all these previous studies and account fully for all methodological choices 
and for any differences with the measurements in past studies.

Lastly, let me mention that holding a camera at anything other than absolute 
perpendicular in both free dimensions to an absolutely flat bedding plane can 
distort the apparent curvature in the photograph. When we draw a teacup resting 
on a table the top is an ellipse, not a cir
 who proposes to use a method of measuring curvature from a  photograph should 
calibrate their photographic procedures first against subjects of known 
curvature. I don't think that using published photos without an explicit 
photographic method will really be valid at all.

Therefore it may be premature to claim that all other work on claw curvature in 
basal paravians is obsolete. Even after publication of such work problems with 
or limitations of the methodology may be discovered.


________________________________________
From: owner-DINOSAUR@usc.edu [owner-DINOSAUR@usc.edu] on behalf of Tim Williams 
[tijawi@gmail.com]
Sent: Sunday, May 27, 2012 11:00 PM
To: dinosaur@usc.edu
Subject: Re: Microraptor hanqingi, new species from China.

GSPaul <GSP1954@aol.com> wrote:

> I have measured central toe claw curvature in a large number of specimens
> with complete keratin sheaths via high res images and they are strongly
> curved and in the arboreal range. No bird that has such hook toe claws spends
> much time on the ground. This will effectively close the case on this, and 
> past
> publications on this are errant becaus they did not have access to quality
> images of a lot of specimens. Can't discuss this openly because some
> journals won't then consider the paper.


Thanks for the info.  I look forward to the publication and to the
mooted data.  As a way of making the manuscript as strong as possible,
and just in case you haven't adopted this approach already: when
discussing claw curvature it's a good idea to differentiate
"trunk-climbing" and "perching" in the context of arboreality.  Also
helps to differentiate claw curvature in predatory birds (many of
which don't spend much time on the ground).  I'm sure these are things
that have occurred to you already, but I guess it can't hurt to
mention them.



Anthony Docimo <keenir@hotmail.com> wrote:

>  Given that those modern bird you name, are all *groups* of birds, I 
> completely expect that they'd be a bad comparison with *A. lithographica*. (If
> you were to use that
, you're comparing apples with citruses (or apples with fruits))
>
> So perhaps the question should be, of those pigeons, which are in the same 
> morphospace as *A. lithographica*? (and the same for the birds of
> prey, trogons, galliforms)


No, I don't think it makes a difference.  The differences in
locomotory styles (hip-based vs knee-based) means that using hindlimb
proportions to compare _Archaeopteryx_ to *any* modern avian has
profound limitations.








Cheers

Tim