Dubbed by Rolling Stones as one of the greatest songs of all time, “the locomotion” has been making people dance for decades, but it takes on an entirely different meaning in the world of primatology. We use the term locomotion to describe the way a primate usually travels or moves about in its habitat.  All animals spend the most time traveling by what feels comfortable to them. You wouldn’t want to go for a three mile hike on hands and knees, and neither would a dog follow beside you the entire time upright on two legs. The body postures that we take during travel are dictated by our bone structures and musculature. Human leg muscles work most efficiently when we are using them to walk upright, thanks to our hip, knee, and toe alignments. Other nonhuman primates tend to move in a somewhat upright posture as well, especially compared to most other mammals. However, there is quite a bit of variability among primate groups, which allows for us all to show off some real locomoting style!

Bipedalism: what humans are most familiar with since this is how we get around. The word is taken from the Latin words bi meaning “two” and -ped meaning “feet.”  Bipedal primates have certain features in common including:

• S-shaped backbones
• Short and wide pelvises
• Short arms and long legs
• Short fingers and toes
• Big toe projects forward and cannot bend to touch all our other toes (non-opposable)
• Foramen magnum (opening at the base of the skull where the spinal cord joins the brain) is centrally located on the skull

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Quadrupedalism: form of locomotion used by many primates that tend to travel long distances on the ground or across tree branches. The word comes from quad meaning “four” and –ped meaning “feet.”  Examples include patas monkeys, baboons, and macaques. Quadrupedal primates have the following physical features in common:

• Curved backbones
• Long and narrow pelvises
• Arms and legs about equal length
• Big toe can bend and grasp, much like your thumb does
• Short fingers and toes
• Foramen magnum located towards the back of the skull

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Quadrumanous climbing/Knuckle Walking: form of locomotion seen in larger primates that spend much of their time in trees but also move about on the ground. Quadrumanous comes from quad meaning “four” and –man meaning “hand.” This term describes primates that use all four limbs as hands, such as the heavy bodied orangutans which use the muscles of both hands and feet to slowly climb through trees. Knuckle-walking describes the way gorillas, chimpanzees, and bonobos walk on the ground, placing much of their body weight onto their middle finger bones, or knuckles. (FYI: Orangutans make their hands into fists when walking on the ground!) Traits of living large-bodied apes include:

• Curved backbones
• Long and narrow pelvises
• Long arms and short legs
• Big toe that functions for grasping
• Long fingers and toes
• Modifications to the bones of the wrist, hands, and fingers that enable a locking mechanism that can support knuckle walking
• Foramen magnum located towards the back of the skull

Photo By: Jochen Ackermann*

Vertical clinging and leaping: locomotion used by many lemurs and small-bodied primates such as tarsiers that frequently jump from branch to branch. Traits of clingers and leapers include:

• Curved backbones
• Long and narrow pelvises
• Short arms, long legs
• Opposable big toes
• Long fingers and toes
• Sometimes with modified nails that resemble claws for clinging onto trees
• Foramen magnum located towards the back of the skull

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Brachiation: style of moving used by primates such as gibbons, siamangs, and spider monkeys. These guys are true aerial acrobats and capable of flying through trees hand-over-hand at break-neck speed. (Watch the video below for brachiators in action!) Physical features of primate brachiators include:

• Curved backbones
• Long and narrow pelvises
• Long arms, short legs
• Opposable big toes
• Long curved fingers, reduced thumbs
• Foramen magnum located towards the back of the skull

So, although primates may be capable of performing all of these styles of movement, there’s only one type that is used the most, and that’s the one that you use to do the locomotion with me!

As a spanking new grad student, I showed up for my first class, “Primate Ecology” uber-excited and ready to learn all I could about the fascinating world of primates. Pen in hand, I was armed and ready to furiously copy down pages of notes as I had done before in my undergrad courses. But then, without so much as a greeting to the class, my adviser waltzed into the room, dumped a box of jaw fragments on the table, and said “You have the remainder of the class to detail all you can about these primates. You may leave your papers on the podium, and I will see you tomorrow.” Several of my peers quickly jumped up, eager for the challenge, while I seriously considered high-tailing it out the door. I had never studied human anatomy, let alone primate dentition! What was I doing here, and how in the world was I to come up with anything to write?

I decided to stay and muddle my way through that first day. I wrote about variables such as how large or small I thought the primate was, and whether any of the teeth were obviously missing. Little did I know that so much more can be learned from primate jaw fragments or that the next two years of primate classes would generally involve some form of huddling over a dissecting microscope, carefully analyzing details of tiny little primate teeth. And if I was taught anything during my time volunteering as a primate dentist’s apprentice, I definitely learned how to tell what kind of “oogivore” you are.

• Frugivore: predominantly eats fruit: back teeth tend to be broad with round cusps, two incisors in the front are wide and somewhat spoon-shaped
• Folivore: munches on leaves and vegetables: back teeth tend to be large with high cusps to shred tough leaf material, two front teeth are narrow
• Graminivore: likes seeds/nuts and grains: back teeth are tall and strong, incisors are variable
• Gummivore: scrapes up gums, saps, and other tree fluids: all teeth are small and somewhat pointy, front teeth stick out straight for scraping bark
• Carnivore: devours meat: back teeth are adapted for shredding meat (not grinding), canines and incisors are long and sharp
• Insectivore: chomps insects: all teeth are small and very sharp for crushing exoskeletons of insects
• Omnivore: sophisticated palate and likes to eat a little bit of everything: teeth are variable in size and appearance

And what good are these little parcels of dentary knowledge? Put quite simply, animal teeth reflect the type of foods that predominates the diet. In turn, the type of diet tells us a lot about where the individual might have been living and even how his social system may have been set up.

Though the dietary descriptions based on tooth shape make sense, perhaps even seeming self-explanatory, it has taken extensive research to construct these types of generalizations. And just why are the teeth of primates and other animals so well-studied? The answer is rooted (no pun intended) in paleontology, more specifically in fossil preservation. Some of the most consistently well-preserved mammal fossils are the lower jawbones (mandibles), which are very hard bones.

Have you ever read the Biblical story of how Samson puts the mandible of a donkey to use? Judges 15:16 reads, “Then Samson said, “With the jawbone of a donkey, I’ve piled them in heaps! With the jawbone of a donkey, I’ve killed a thousand men!”

Mandibles are thick, strong bones, and they are often all that remains of a fossilized organism after the more delicate bones of the body are destroyed over time. Thousands of scientists have spent countless hours studying the intricacies of teeth and jaw bones, using the teeth of living specimens to make predictions about fossilized organisms. In addition to dietary type, other variables, such as species identification, age, health, and body size, can be garnered from looking at dentition. Just a couple of teeth embedded in a mandible are enough to tell a scientist that she is looking at the remains of a juvenile spider monkey approximately five pounds in weight that liked to feed predominantly on fruit. Not too shabby!

So, get out a mirror and check out your chompers. What type of oogivore are you?