Commonly called the tailbone, what is the biological name for the small triangular bone at the base of the spinal column?

The formal biological name for this structure is derived from the ancient Greek word for "cuckoo," which is "kokkyx." Early anatomists noted that the bone’s curved shape resembled the beak of a cuckoo bird, and the name stuck. This small, triangular bone is the final segment of the human vertebral column, typically composed of three to five separate or fused vertebrae that sit just below the sacrum.

While it is commonly called the tailbone, the coccyx is actually a vestigial structure—an evolutionary remnant of the tail that our distant primate (Review) ancestors possessed. In those ancestors, a tail was crucial for balance, movement, and even communication. As humans evolved to walk upright, the need for a tail diminished, and it eventually receded into the small bone we have today.

Far from being useless, the modern coccyx serves as an important anchor point for numerous muscles, tendons, and ligaments within the pelvic floor. It also works together with the bones you sit on (the ischial tuberosities) to help support and balance your weight, particularly when you are seated and leaning back.