How can you work out how hard a predatory mammal bites? Well, one way would be to place an instrumented prey item between the predator's jaws, but this might impose an unacceptable risk to both life and limb of any intrepid investigator. A further problem arises if the animal you wish to investigate is extinct; clearly, any form of behavioural measurement becomes rather difficult. Undaunted by these complications, Stephen Wroe and co-workers sought to determine the scaling relationships of bite force and predator and prey body size in a variety of extant and extinct predatory mammals, in particular a number of marsupial predators. Wroe and his team hypothesised that bite forces should scale with both predator and prey size and that different modes of feeding, such as bone crunching versus only eating flesh, should be reflected in patterns of bite forces.
To determine bite forces of different predators, the team examined the skulls of 39 predatory mammal species (eight of which are extinct). To calculate the maximal theoretical bite force for each species, the authors used a method that models jaws as simple levers. They estimated muscular power to the jaw by measuring the area of the muscular insertions on the jaw. Finally, they determined the distance between the jaw articulations, muscle attachments and the position of the canine and carnassial teeth. By calculating the torque applied to the jaw they derived estimates of the force exerted at the teeth.
Wroe and his colleagues discovered some interesting patterns in the maximal bite forces of the taxa they examined, once they had corrected for body size. Contrary to expectations, the team found that osteophagous (bone crunching) species have relatively lower maximal bite forces than non-osteophagous species. In general, marsupial predators produce higher bite forces than do placental mammals. The authors attribute this to placentals' larger brains, which reduce the available skull surface area for muscle attachment. The implications for hunting performance are that placental predators require a more precise approach to seize their prey than do marsupial predators. The team also observed other differences between taxa; for example, they found a lower mean size-specific bite force in cats than in canids. The authors suggest that possible reasons for this include cats having shorter jaws, more agile forelimbs to immobilize prey, and the possibility that cats recruit their neck muscles to increase bite forces. Perhaps the most interesting insights from this study are those regarding the extinct species, as these may allow researchers to reconstruct the ecological niches of these species. Of particular interest are the inferences that can be made about the predatory behaviour of extinct animals. For instance, the team found that the extinct marsupial lion Thylaceo carnifex appears to have produced very high bite forces, indicating that it was adapted to hunt large prey.
Reconstructing animals' feeding mechanics and behaviour by biomechanical modelling may provide fascinating insights into the life history and ecology of many enigmatic extinct predatory species. In presenting predictions from 39 species representing 7 families, the authors have certainly taken a significant step towards achieving this.
- © The Company of Biologists Limited 2005