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Bird, dinosaur, and lizard claw curvature

From: Ben Creisler

New in PLoS ONE:

Aleksandra V. Birn-Jeffery, Charlotte E. Miller, Darren Naish, Emily
J. Rayfield & David W. E. Hone (2012)
Pedal Claw Curvature in Birds, Lizards and Mesozoic Dinosaurs –
Complicated Categories and Compensating for Mass-Specific and
Phylogenetic Control.
PLoS ONE 7(12): e50555.

Pedal claw geometry can be used to predict behaviour in extant
tetrapods and has frequently been used as an indicator of lifestyle
and ecology in Mesozoic birds and other fossil reptiles, sometimes
without acknowledgement of the caveat that data from other aspects of
morphology and proportions also need to be considered. Variation in
styles of measurement (both inner and outer claw curvature angles) has
made it difficult to compare results across studies, as have
over-simplified ecological categories. We sought to increase sample
size in a new analysis devised to test claw geometry against
ecological niche. We found that taxa from different behavioural
categories overlapped extensively in claw geometry. Whilst most taxa
plotted as predicted, some fossil taxa were recovered in unexpected
positions. Inner and outer claw curvatures were statistically
correlated, and both correlated with relative claw robusticity
(mid-point claw height). We corrected for mass and phylogeny, as both
likely influence claw morphology. We conclude that there is no strong
mass-specific effect on claw curvature; furthermore, correlations
between claw geometry and behaviour are consistent across disparate
clades. By using independent contrasts to correct for phylogeny, we
found little significant relationship between claw geometry and
behaviour. ‘Ground-dweller’ claws are less curved and relatively
dorsoventrally deep relative to those of other behavioural categories;
beyond this it is difficult to assign an explicit category to a claw
based purely on geometry.