Gorillas, like all great apes, do not possess an external tail. Gorillas belong to the family Hominidae, which includes chimpanzees, orangutans, and humans. All members of this family share this tailless characteristic.
The Anatomical Truth About Gorilla Tails
While gorillas lack a visible tail, their anatomy includes a remnant structure known as the coccyx, or tailbone. This internal structure is located at the base of the spine, a vestigial echo of the long tail found in their distant ancestors. The coccyx is composed of three to five small, fused vertebrae, which are reduced compared to the many vertebrae that would form a functional tail.
This small, curved bone serves as an anchor point for several structures. The coccyx provides an insertion site for muscles, including the gluteus maximus and the levator ani, a muscle of the pelvic floor. It also helps to support and stabilize the gorilla’s body weight when it is sitting upright.
The Key Difference Between Apes and Monkeys
The presence or absence of a tail is one of the most immediate visual cues used to classify primates into apes or monkeys. Gorillas are classified as apes, and a defining feature of all apes is their lack of a tail. This group includes the smaller apes, like gibbons, and the great apes, such as gorillas, chimpanzees, and orangutans.
In contrast, almost all species of monkeys possess a tail, which they use for various purposes. New World monkeys, like spider monkeys, often have prehensile tails that can grasp branches like a fifth limb. Old World monkeys, such as baboons, have non-prehensile tails used primarily for balance. Apes evolved a different mode of movement, characterized by a broader chest and more flexible shoulder joints, which made a tail unnecessary.
Why Gorillas and Other Apes Evolved Without Tails
The loss of the tail in the ape lineage is directly connected to a major shift in locomotion that occurred millions of years ago. Early primates used their tails for balance while running quadrupedally along the tops of tree branches. As the ancestors of apes began to move differently, favoring vertical climbing and swinging beneath branches, the tail became redundant.
This form of movement, known as brachiation, did not require the tail for balance or grasping. A tail could have become a hindrance in this new environment, potentially interfering with movement or becoming an energy drain.
Recent scientific research suggests that the loss of the tail may have a specific genetic cause, occurring around 25 million years ago. A small piece of repetitive DNA, called an Alu element, was inserted into the Tbxt gene, which plays a role in tail development. This genetic change is thought to have shortened the tail in the common ancestor of all apes. The resulting taillessness simplified life on the ground and may have paved the way for the upright movement seen in modern humans.