Functional Relationship between Skull Form and Feeding Mechanics in Sphenodon, and Implications for Diapsid Skull Development

Abstract

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.

The Tendinous Framework in the Temporal Skull Region of Turtles and Considerations About Its Morphological Implications in Amniotes: A Review

“…Recently, Jones et al (2012) mentioned that "the ligamentum quadratomaxillare […] may represent a passive tension cord [Sverdlova and Witzel, 2010] for resisting tensile strains that might arise along the ventrolateral edge of the dome-like cranium during biting. This hypothesis may be tested using finite element modeling similar to that used in Curtis et al [2011]." Poglayen-Neuwall (1953) hypothesized that the ligament serves to protect the rictal plate from tearing and in this context he mentioned that it is medially connected to the rictal plate by connective tissue.…”

Coupling finite element analysis and multibody system dynamics for biological research

“…It is important to differentiate the FMSD, which couples the equations of the MSD and the FEA during the simulation from the other excellent approaches that can be found in the literature. Firstly, in Curtis et al (2009Curtis et al ( , 2010a, Bates and Falkingham (2012) and Snively et al (2013) only the MSD equations are used to determine the forces that are acting in the model without any interaction with FEA and secondly, in Moazen et al (2008a) and Curtis et al (2011) there is a combination between MSD and FEA but they are not coupled during the simulation. Uncoupled analysis does not account for strains being a result of dynamics response of a flexible object.…”

“…Uncoupled analysis of MDA and FEA have been used before to estimate forces acting on a skull and then applied to a Finite Element Model of this same skull to obtain patterns of strain and stress across it (Moazen et al, 2008a(Moazen et al, , 2008b(Moazen et al, , 2009a(Moazen et al, , 2009bCurtis et al 2008Curtis et al , 2010aCurtis et al , 2010bCurtis et al , 2011. Those results have been combined with knowledge of evolutionary paths to develop hypotheses regarding the genetic and epigenetic factors that shape the skeleton or the feeding mechanism in vertebrate structures.…”

“…The technique has been applied to studies of craniofacial form to simulate musculoskeletal function and facilitates in-depth exploration of the relationships between musculoskeletal geometry, muscle parameters, forces and motion in vertebrate structures (Curtis et al, 2009;Bates and Falkingham, 2012;Gröning et al, 2013;Snively et al, 2013). In spite of it, the research utilizing both the musculoskeletal modeling and deformable body modeling together has rarely been seen in publications (Moazen et al, 2008a(Moazen et al, , 2008bCurtis, 2011;Curtis et al, 2010aCurtis et al, , 2010bCurtis et al, , 2011. The current research utilizes the flexible multibody dynamics, which is mostly employed in the field of machine dynamics.…”

A Sensitivity Analysis to the Role of the Fronto‐Parietal Suture in Lacerta Bilineata: A Preliminary Finite Element Study

“…It could potentially shed light on the evolution of cranial kinesis (Metzger, 2002) and the upper temporal fenestra (Carrol, 1982;Evans, 2003;Curtis et al, 2011). In Squamata (lizards, snakes, and amphisbaenians), there is a large diversity in the structure of this region.…”