Pongo pygmaeus, what big jaws you have…
Central Kalimantan
The better to eat tough foods like cambium!
Bornean orangutans eat a large variety of foods ranging from soft leaves to hard fruits. However, one of the most fascinating foods they consume, is bark material from several different species of trees. Compared to other orangutans, Bornean orangutans consume large amounts of fallback foods, (foods which tend to be lower quality, and abundant, important for when preferred foods are not available). Bark is an important fallback food for Bornean orangutans and with such tough foods, a tough masticatory system is needed (see their massive jaws below). The unique mandibular features of the Bornean orangutan, like their deep thick mandible and large central incisors support this unique diet including the consumption of inner bark, or "cambium".
To get access to the cambium inside the bark requires the orangutan to use their large teeth to break off the bark and then scrape off the cambium from within. Here is my favorite orangutan Gismo, and the marks he left behind after snacking on some cambium.
A little more about Orangutans…
Orangutans are large bodied, semi-territorial, and semi-solitary great apes living in the rainforests of Borneo and Sumatra in Southeast Asia. They are closely related to humans, less so than chimpanzees, bonobos, and gorillas. A unique feature in orangutans, not common in other primates, are the two “types” of sexually mature male orangutans; flanged and unflanged males. The flanged males have these distinctive cheek pads which can be seen in the image of Gismo above. Currently, there are three recognized species in the genus Pongo (Pongo pygmaeus (Bornean), Pongo abelii (Sumatran), and Pongo tapanuliensis.
Pongo pygmaeus wurumbii are the orangutans of focus in my current research, residing in Central Kalimantan, Borneo, Indonesia.
Further Readings
Arnason, U., Gullberg, A., & Janke, A. (1998). Molecular timing of primate divergences as estimated by two nonprimate calibration points. Journal of Molecular Evolution, 47, 718-727.
Brandon-Jones, D., Eudey, A. A., Geissmann, T., Groves, C. P., Melnick, D. J., Morales, J. C., ... & Stewart, C. B. (2004). Asian primate classification. International journal of primatology, 25, 97-164.
Delgado Jr, R. A., & Van Schaik, C. P. (2000). The behavioral ecology and conservation of the orangutan (Pongo pygmaeus): A tale of two islands. Evolutionary Anthropology: Issues, News, and Reviews: Issues, News, and Reviews, 9(5), 201-218.
Knott, C., Beaudrot, L., Snaith, T., White, S., Tschauner, H., & Planansky, G. (2008). Female-female competition in Bornean orangutans. International Journal of Primatology, 29, 975-997.
Marshall, A. J., Lacy, R., Ancrenaz, M., Byers, O., Husson, S. J., Leighton, M., ... & Wich, S. A. (2009). Orangutan population biology, life history, and conservation. Orangutans: Geographic variation in behavioral ecology and conservation, 311-326.
Van Schaik, C. P. (1999). The socioecology of fission-fusion sociality in orangutans. Primates, 40, 69-86.
Vogel, E. R., Alavi, S. E., Utami‐Atmoko, S. S., van Noordwijk, M. A., Bransford, T. D., Erb, W. M., ... & Rothman, J. M. (2017). Nutritional ecology of wild Bornean orangutans (Pongo pygmaeus wurmbii) in a peat swamp habitat: Effects of age, sex, and season. American journal of primatology, 79(4), 1-20.
