Pedal Claw Curvature in Birds, Lizards and Mesozoic Dinosaurs – Complicated Categories and Compensating for Mass-Specific and Phylogenetic Control

Abstract

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.

Aerodynamic performance of the feathered dinosaur Microraptor and the evolution of feathered flight

“…This further highlights the likelihood that asymmetric vanes were a further specialization that evolved in paravian taxa with gliding ancestors; in essence, these allowed a larger wing area for a given skeletal mass and removed the need for feather overlap. The gliding flight of Microraptor, which our experimental results show was remarkably effective over medium distances starting from moderate heights, did not require highly derived lifting surfaces and can be regarded as representing a highly successful experiment in theropod adaptation to aerial behaviour, consistent with at least some evidence for climbing in this taxon 30 . 32 , including Archaeopteryx 8 , possessed feathered legs as well as wings suggests that this generalized, perhaps primitive, form of aerial adaptation was persistent across paravian history and was not a short-lived evolutionary event.…”

Claw morphometrics in monitor lizards: Variable substrate and habitat use correlate to shape diversity within a predator guild

“…It was not surprising that phylogenetic signaling plays a significant role in varanid claw morphology, considering it also strongly influences claw shape in other lizards (Tulli et al., 2009, 2011, 2012) and birds (Birn‐Jeffery et al., 2012; Fowler et al., 2009). We could not develop rigorous phylogenetic conclusions about Australian varanids as a whole, but tentative inferences may be drawn.…”

Morphological and functional diversity in therizinosaur claws and the implications for theropod claw evolution

“…In the past, numerous studies have focused on the morphology and geometry of pedal unguals in theropod dinosaurs [14,15], supplemented with or based on observations in extant birds [16,17] or squamates [18], in an attempt to infer function and behaviour from morphology. The manual unguals of theropod dinosaurs in general, and therizinosaurs in particular, however, have rarely been considered, or have been limited to range-ofmotion studies of the forelimbs [19][20][21].…”