Finite Element Analysis of Ungulate Jaws:
Can mode of digestive physiology be determined?

Thomas M. Fletcher, Christine M. Janis, and Emily J. Rayfield

ABSTRACT

In order to efficiently deal with cellulose-rich vegetation, different ungulate (hoofed) mammals utilize either foregut (e.g., ruminant artiodactyls) or hindgut fermentation (e.g., perissodactyls, proboscideans and hyraxes). Hindgut fermenters are known to have a greater food intake than ruminants (of similar size and diet), and horses may chew their food more thoroughly on initial ingestion. These facts have led to the prediction that jaws of hindgut fermenters should be more 'robust' than those of ruminants, and on this basis extinct hindgut or foregut fermenters may be identified in the fossil record. This hypothesis was tested by creating 2D finite element (FE) models of the mandible of six pairings of extant foregut and hindgut fermenters matched for body mass. All models were scaled to the same size, constrained at the jaw condyle and first molar, and loaded with 100 N of muscle force, divided between the temporalis and masseter muscles in proportion to the size of their relative insertion areas. Mean Von Mises stress through the mandible at a mid-point transect of the tooth row was recorded and the two groups compared with a paired t-test. The mandibles of extant hindgut and foregut fermenters differed significantly in robustness (p = 0.023) with very little overlap in mean stress values.

Thomas M. Fletcher. Department of Earth Sciences, Wills Memorial Building, University of Bristol, Bristol, BS8 1RJ, United Kingdom.
Christine M. Janis. Department of Ecology and Evolutionary Biology, Brown University, Providence, Rhode Island 02912.
Emily J. Rayfield. Department of Earth Sciences, Wills Memorial Building, University of Bristol, Bristol, BS8 1RJ, United Kingdom.

Key words: Digestive physiology; finite element analysis; functional morphology; herbivory; ungulate