Understanding Locomotion in Primates

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

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

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

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

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!