FW: Paravian claw studies

[Jason Brougham <jaseb@amnh.org>]

Sorry, a few words of text were cut out the first time I hope not this time too.
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From: Jason Brougham
Sent: Monday, May 28, 2012 10:49 AM
To: tijawi@gmail.com; dinosaur@usc.edu
Subject: Paravian claw studies

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 
e 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 circle. Therefore, anyone 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.


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