Gorilla diets are characterized by large amounts of fruits and plants. Hard-object feeding is not generally associated with these great apes as the high crests on their molar teeth would be at risk of damage from the mechanically challenging woody shell. Now, an international team of researchers from Germany and the United States has observed a population of western lowland gorillas (Gorilla gorilla gorilla) in Loango National Park, Gabon, using their teeth to crack open the woody shells of African walnuts (Coula edulis).
“I was amazed when we first observed the nut eating by the gorillas,” said study senior author Dr. Martha Robbins, a researcher in the Department of Primatology at the Max Planck Institute for Evolutionary Anthropology, Germany.
“We can not only see it, but also hear it, as the shell gives way to the incredible strength of their bite. Gorillas obviously have large, powerful jaws, but we did not expect to see this because their teeth are not well-suited to such behavior.”
African walnuts are encased in a hard, woody shell that takes around 271 kg of force to crack.
Yet for the three months (January, February, and December) the nuts are available, the gorillas of Loango National Park concentrate their feeding on the energy rich kernels, spending up to three hours a day chomping through nuts.
This is surprising as animals that eat very hard food items tend to have strong, rounded molars that act like a pestle and mortar and are very efficient at cracking brittle foods.
Like other foliage eaters, gorilla teeth have higher crests providing extra cutting edges for slicing tough material.
Under the monumental bite force required to crack nuts, teeth with sharp edges are prone to break meaning they may be worn away quickly.
“We were surprised to learn that the gorillas at Loango are regularly gambling with their teeth and taxing them close to their predicted mechanical limits,” the scientists said.
“While some primates, like chimps, protect their teeth by using tools to crack open nuts, it appears that the gorillas at Loango National Park reply on brute strength to break through the woody shells of African walnuts.”
“The fact they do this year after year indicates that gorilla teeth may be stronger than previously thought.”
The research also implies that western lowland gorillas have much greater dietary breadth than previously believed.
“The fact that this nut eating is observed in Loango but not in other forests in central Africa where the nut occurs stresses the importance of studying and conserving gorillas throughout the habitat where they are found,” Dr. Robbins said.
The findings were published in the American Journal of Physical Anthropology.
Adam van Casteren et al. Unexpected hard-object feeding in Western lowland gorillas. American Journal of Physical Anthropology, published online August 2, 2019; doi: 10.1002/ajpa.23911