The discovery breaks the ‘rule’ in the animal kingdom that larger animals are better at chewing large chunks of food. “A Chihuahua, with its relatively small jaws, is less likely to chew a large bone than a German Shepherd,” said lead researcher Rex Mitchell of Flinders University, Australia.
However, the 30 centimeter long Australian dwarf rock kangaroos bite just as hard as their large cousins, the kangaroos, which can grow up to 2 meters long. According to the researchers, there was apparently an evolutionary advantage for extra bite force in being able to chew the same food as their larger counterparts.
Chewing device
The researchers scanned almost 400 skulls of no fewer than 17 species of small rock kangaroos and compared a number of standard features, including a chewing device. The differences in brain and eye size were exactly what you would expect. But the researchers saw something striking in the jaws and teeth. The animals appeared to have developed relatively short, round snouts, with more teeth at the back of the jaw near the jaw muscles: a clear adaptation for more bite force.
The researchers also discovered several types of ‘giant molars’. One species had the largest molars at the back of the mouth, while another had them at the front. The former is useful for grinding tough, gravelly grass and plants close to the ground, the latter is useful for cutting softer leaves and twigs in trees and shrubs.
New choices for life
The findings match what we know about these wallabies. The species that owns the largest molars at the back of the mouth, the nabarlek, is the only known marsupial that grows new molars in its mouth throughout its life. That looks a lot like the perpetually growing gnawing teeth of rabbits and beavers – also animals that have tough, plant material on their diet.
Stephan Spiekman, marsupial expert and affiliated with the Staatliches Museum für Naturkunde in Stuttgart, speaks of an interesting study: “Plants are tough and a huge burden on the teeth, just look at the teeth of a cow or a horse. These little rock kangaroos have to spend their lives chewing this tricky food. That requires strong jaws and big teeth, no matter how big you are.
