
The roles of joint tissues and jaw muscles in palatal biomechanics of the Savannah monitor (Varanus exanthematicus) and their significance for cranial kinesis
Author(s) -
Alec T. Wilken,
Kevin M. Middleton,
Kaleb Sellers,
Ian N. Cost,
Casey Holliday
Publication year - 2019
Publication title -
journal of experimental biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.367
H-Index - 185
eISSN - 1477-9145
pISSN - 0022-0949
DOI - 10.1242/jeb.201459
Subject(s) - protractor , anatomy , skull , biomechanics , bite force quotient , joint (building) , biology , orthodontics , medicine , geometry , mathematics , architectural engineering , engineering
Many vertebrates exhibit cranial kinesis, or movement between bones of the skull and mandible other than at the jaw joint. Many kinetic species possess a particular suite of features to accomplish this movement, including flexible cranial joints and protractor musculature. Whereas the musculoskeletal anatomy of these kinetic systems is well understood, how these joints are biomechanically loaded, how different soft tissues affect joint loading and kinetic capacity, and how the protractor musculature loads the skull remain poorly understood. Here we present a Finite Element Model of the savannah monitor, Varanus exanthematicus, a modestly kinetic lizard, to better elucidate the roles of soft tissue in mobile joints and protractor musculature on cranial loading. We describe the 3D resultants of jaw muscles and the histology of palatobasal, otic and jaw joints. We tested the effects of joint tissue types, bite point, and muscle loads to evaluate the biomechanical role of muscles on the palate and braincase. We found the jaw muscles have significant mediolateral components that can impart stability across palatocranial joints. We found articular tissues affect the magnitude of strains experienced around the palatobasal and otic joints. We found that without protractor muscle loading, the palate, quadrate and braincase experience higher strains suggesting this muscle helps insulate the braincase and palatoquadrate from high loads. Finally, we found the cross-sectional properties of the bones of Varanus exanthematicus are well suited for performing under torsional loads. These findings suggest that torsional loading regimes may have played a more important role in the evolution of cranial kinesis in lepidosaurs than previously appreciated.