One of the main driving forces behind an animal’s skull morphology is it’s diet and various skull shapes evolved depending on the dietary niche that was being exploited. Excellent examples of this can be seen in many of the previous skulls of the month that I have personally looked at. Gorillas have large molars, much larger than a humans, in order to process rough, fibrous food. The polar bear and dog on the other hand have large canines so they can tear meat from bones. Animals do not only vary in their dental morphology but also the way in which they bite their food. This is turn affects the bite load inflicted on the skull. For example, a one sided bite will produce a different load then that of a bilateral bite. The placement of the bite on the tooth row may also produce a different bite load.
This study by Dumont et al. (2005) attempts to identify whether skull morphology is linked to biting behavior and therefore optimally suited to the feeding type or whether additional constraints play a part in skull shape. In order to do this they compared the craniofacial skeletons of two fruit bats under normal ad atypical loading regimes. By comparing the different bite loads they predicted that the skulls would be the most resist to the bats preferred bite load. Two different species of fruit bats (Artibeus jamaicensis and Cynopterus brachyotis) were used as the authors also wanted to investigate how the two species over came the difficulty of being small animals that eat hard fruits. This was achieved by using finite-element modelling.
The two bat species chosen for study use different biting styles which, when compared, produce very different biting force and loads. When Artibeus uses a unilateral molar bite, as with hard fruit, a very high bite force is produced. Cynopterus, however, uses a bilateral canine bite and this difference may be explained by the tooth morphology of Cynopterus. Their canines are much sharper than their molars and therefore may be more effective and concentrating a force on a small area to produce cracks. Each species has found a way to of getting over the difficultly of being a small animal who eats hard fruits and each produes a very different bite force. Artibeus I showed a greater than expected difference in strength between unilateral molar and bilateral canine biting whilst Cynopterus produced strengths which were similar.
It was also found that Artibeus has a much stronger skull than Cynopterus despite both being similar in size. This strength helps to produce the high force needed to bite through hard foods providing a clear relationship between feeding ecology, behaviour and cranial morphology. This is not so clear in Cynopterus as there was little different between the two loading regimes. These results support the conclusion that an mammals skull is not purely optimized for feeding as both species process strain gradients rather than being designed for uniform loads. Although feeding behaviour may not be the sole driver in skull morphology it plays a large role and if a bite force impacts an animals fitness than a change in skull shape may occur.
Reference for article:
Dumont, E. R., J. Piccirillo, et al. (2005). “Finite-element analysis of biting behavior and bone stress in the facial skeletons of bats.” The Anatomical Record Part A: Discoveries in Molecular, Cellular, and Evolutionary Biology 283A(2): 319-330.