Fri, November 15, 2019

Gorilla Anatomy

Fact 1

Gorillas basically have 4 thumbs!

Like most primates, gorillas have opposable thumbs on their hands. But did you know that they also have semi-opposable feet? Their big toe is longer and placed lower on the foot than human big toes are. Gorilla big toes are also very flexible, which helps with the grasping and climbing behaviors that are so integral to daily gorilla life (Tocheri et. al., 2011). Humans, on the other hand, have shorter, forward facing big toes which provide pushing power for walking, rather than grasping ability (Rolian et. al., 2009).

Fact 2

Gorilla (and other great ape) bones are much denser than their human counterparts.

This contributes to their average weight (300 – 450 lbs) being much higher than average human weight. The greater weight is due to non-human great apes having a high density of spongy bone, while humans do not (Chirchir et. al., 2015). With less spongy bone, this increases our chances of breaks and fractures. However, the more weight makes non-human great apes less buoyant, leaving them unable to swim.

Fact 3

Like other great ape species (except modern humans), gorillas have a significant “brow ridge” above their eyes.

Like other great ape species (except modern humans), gorillas have a significant “brow ridge” above their eyes. While humans have a curved, unpronounced brow ridge, gorilla brow ridges are continuous and straight, and stick out over their eyes. It is theorized that a large, sturdy ridge helps to support weaker bones in the skull, and reduces strain on the skull when chewing particularly hard food items, like nuts. Between the eye ridge and the sagittal crest (discussed in our Halloween episode), gorillas have enough skull strength to bite through a coconut!

Fun Fact! While “brow ridge” is its common name, the actual name of this part of the skull is “supraorbital ridge”, which literally means “ridge above the eye”. (Endo, B. 1965)

Fact 4

Gorillas have a longer arm length to height ratio than humans.

While gorillas usually move quadrupedally, or with 4 limbs on the ground, when they stand bipedally they are about 6 feet tall! Their arm span averages about 8 feet, giving them a longer arm length to height ratio. Humans have an equal arm to height ratio, meaning your height is usually equal to the length of your arm span. The gorilla’s arm to height ratio helps them with climbing and is better adapted for quadrupedal movement than human skeletons are.

Fact 5

Gorillas have a larger head than humans, but a smaller brain.

While gorillas have larger skulls than humans, humans have a lot more room in their skulls to fit their brains. On average, humans have a “cranial capacity”,  the amount of space for a brain, of about 1325 cubic centimeters. Gorillas, on the other hand, only have about 500 cc’s. The reduced space in the gorilla’s cranial capacity is due to the differences in the shape of the skull(diagram of differences). The actual brain of gorillas are averaged at one-third the size of human brains. (Herculano-Houzel & Kaas, 2011)

Bonus!

Gorillas don’t have chins!

If you compare a human and a gorilla skull, you might notice that the area underneath the mouth of the human sticks out and away from the skull, while the area under the gorilla mouth actually slopes back towards the skull. This slope may look strange to you, but it’s far more common than you think! In fact, humans are the only animals that we know of that have the bony protrusion beneath their mouths known as a chin. Researchers are still trying to understand why that is! (Pampush & Daegling, 2016).

References


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