Fossils of primates and early humans exhibit great diversity in the size and shape of the jaw, teeth, and facial skeleton. Anthro- pologists theorize that these different skull forms were evolutionary adaptations to chewing different types of food. Dr. David S. Strait, anthropologist and assistant professor at the New York College of Osteopathic Medicine of the New York Institute of Technology (NYIT), is testing these theories by simulating the chewing biomechanics of living primates with ALGOR finite element analysis (FEA) software. Dr. Strait’s research may help to explain why there is such diversity among living primates, and could lay the groundwork for future studies of extinct early humans.

Researchers at NYIT used a male monkey skull (left) as the basis for Computer-Aided Modeling and Analysis. CT scan information was used to generate a CAD solid model in SolidWorks (top right). An ALGOR static stress with linear material analysis was performed on the finite element model of the monkey skull to simulate the maximum biting force during chewing (lower right). (Photo courtesy of the Smithsonian Institution’s National Museum of Natural History.)
One challenge facing anthropologists is that much scientific information such as relative muscle forces and material properties of connective tissues is unavailable for extinct species. According to Dr. Strait, with fossils, there is only information about the shape of bones, but the muscles are not preserved. Therefore, there is no direct data about the loads and constraints that should be applied to an FEA model. Another challenge is that one cannot validate a model of an extinct species since none are alive to be observed. The decision was made to simulate living primates.

As a pilot study, Dr. Strait developed an FEA model of the skull of a male Macaque, a type of monkey (Macaca fascicularis) that is widely used in biological and medical research. Computed tomography (CT) scans of a Macaque skull from the Smithsonian Institution’s National Museum of Natural History were digitized and input into SolidWorks CAD solid modeling software to create a 3D solid model of the skull geometry. Dr. Strait then used ALGOR’s InCAD technology for direct CAD/CAE data exchange between SolidWorks and FEA. Next, he used automatic mesh generation capabilities to create a finite element mesh.

Dr. Strait defined custom isotropic material properties to represent the bones of the skull. A variety of nodal and surface forces were used to simulate the muscle groups that act on the skull during chewing. The upper left second molar was fully fixed to represent the point of biting. A static stress with linear material models analysis was performed, which solved for displacements and strains in the model.

Actual bone strain data from previous experiments was obtained. The experimental results were used to validate the FEA model, showing a strong correlation between the data and the FEA results. Dr. Strait plans to model another living primate species, a Capuchin (Cebuss capacinus), a monkey from South America. The intent is to compare and contrast the Macaque and Capuchin models and demonstrate that they can be validated with experimental data.

Dr. Strait wants to build an FEA model of one of the extinct early humans and conduct tests to confirm or reject hypotheses about skeletal traits as chewing adaptations. His research also may have potential health science applications. Modeling skull biomechanics could provide an understanding of stresses and strains in the bones of the face and skull, which could be used to design safer protective gear such as motorcycle helmets or car restraints, or to improve surgical techniques.