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Diapsid skull mechanical design tested on Sphenodon

From: Ben Creisler
New in PLoS ONE:
Curtis, N,, Jones, M.E.H., Shi J., O'Higgins, P., Evans, S.E., et al. (2011) 
Functional Relationship between Skull Form and Feeding Mechanics in Sphenodon, 
and Implications for Diapsid Skull Development. 
PLoS ONE 6(12): e29804. 
The vertebrate skull evolved to protect the brain and sense organs, but with 
the appearance of jaws and associated forces there was a remarkable structural 
diversification. This suggests that the evolution of skull form may be linked 
to these forces, but an important area of debate is whether bone in the skull 
is minimised with respect to these forces, or whether skulls are mechanically 
"over-designed" and constrained by phylogeny and development. Mechanical 
analysis of diapsid reptile skulls could shed light on this longstanding 
debate. Compared to those of mammals, the skulls of many extant and extinct 
diapsids comprise an open framework of fenestrae (window-like openings) 
separated by bony struts (e.g., lizards, tuatara, dinosaurs and crocodiles), a 
cranial form thought to be strongly linked to feeding forces. We investigated 
this link by utilising the powerful engineering approach of multibody dynamics 
analysis to predict the physiological forces
 acting on the skull of the diapsid reptile Sphenodon. We then ran a series of 
structural finite element analyses to assess the correlation between bone 
strain and skull form. With comprehensive loading we found that the 
distribution of peak von Mises strains was particularly uniform throughout the 
skull, although specific regions were dominated by tensile strains while others 
were dominated by compressive strains. Our analyses suggest that the frame-like 
skulls of diapsid reptiles are probably optimally formed (mechanically ideal: 
sufficient strength with the minimal amount of bone) with respect to functional 
forces; they are efficient in terms of having minimal bone volume, minimal 
weight, and also minimal energy demands in maintenance.