Journal of Mammalian Evolution

, Volume 23, Issue 2, pp 191–200 | Cite as

Masticatory Muscle Anatomy and Feeding Efficiency of the American Beaver, Castor canadensis (Rodentia, Castoridae)

  • Philip G. Cox
  • Hester Baverstock
Original Paper


Beavers are well-known for their ability to fell large trees through gnawing. Yet, despite this impressive behavior, little information exists on their masticatory musculature or the biomechanics of their jaw movements. It was hypothesized that beavers would have a highly efficient arrangement of the masticatory apparatus, and that gnawing efficiency would be maintained at large gape. The head of an American beaver, Castor canadensis, was dissected to reveal the masticatory musculature. Muscle origins and insertions were noted, the muscles were weighed and fiber lengths measured. Physiological cross-sectional areas were determined, and along with the muscle vectors, were used to calculate the length of the muscle moment arms, the maximum incisor bite force, and the proportion of the bite force projected along the long axis of the lower incisor, at occlusion and 30° gape. Compared to other sciuromorph rodents, the American beaver was found to have large superficial masseter and temporalis muscles, but a relatively smaller anterior deep masseter. The incisor bite force calculated for the beaver (550–740 N) was much higher than would be predicted from body mass or incisor dimensions. This is not a result of the mechanical advantage of the muscles, which is lower than most other sciuromorphs, but is likely related to the very high percentage (>96 %) of bite force directed along the lower incisor long axis. The morphology of the skull, mandible and jaw-closing muscles enable the beaver to produce a very effective and efficient bite, which has permitted beavers to become highly successful ecosystem engineers.


Beaver Dissection Masticatory muscles Bite force Rodent 



The authors thank Dr Andrew Kitchener of National Museums Scotland for providing the beaver specimen, and Mrs Sue Taft from the Department of Engineering, University of Hull for use of her dermestid beetle colony. Thanks are also due to Gwen Haley and the staff of the X-ray department at The York Hospital for CT scanning the skull and mandible. We are grateful to two anonymous reviewers for their helpful comments.

Supplementary material

10914_2015_9306_MOESM1_ESM.docx (26 kb)
Online Resource 1 Mathematical details of the calculation of the biomechanical metrics. (DOCX 26 kb)


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Copyright information

© Springer Science+Business Media New York 2015

Authors and Affiliations

  1. 1.Department of Archaeology and Hull York Medical SchoolUniversity of YorkYorkUK
  2. 2.Hull York Medical SchoolUniversity of HullHullUK

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