Splitjaw Snake: Bolyeriidae

The splitjaw snake has an upper jaw bone split into front and back halves that are hinged together at a point just below the eye. With this unusual split in the jaw, the bone holding the upper teeth in the front of the mouth can bend up and down, while the bone holding the back teeth can stay in place. No other bird, mammal, reptile, amphibian, or fish has such a strangely jointed jaw. For many years, this snake was considered to be a member of the boa family, but its odd jaw was so unusual that scientists felt it should be in its own family. Despite its listing in its own family, the splitjaw snakes often go by common names that still include the word "boa."

Two members of this family existed in the 20th century, but only one has survived to enter the 21st century. The smooth-scaled splitjaw, also known as the smooth-scaled Round Island boa, is now believed to be extinct. The other species, the keel-scaled splitjaw, still exists today. The main difference between the two snakes is the presence or absence of small ridges, or keels, on the scales. Only the keel-scaled splitjaw has the ridges. In the splitjaws, as in other snakes, the ridges make the skin look a bit dull. Smooth scales, on the other hand, usually give snakes a shiny appearance.

The keel-scaled splitjaw is a thin snake with six-sided, or hexagonal (HEHK-SAE-guh-nuhl), scales running down its back. In many snake species, the back scales overlap, but the splitjaw's back scales barely touch each other, if at all. The snake has a long tail that makes up at least one-quarter of its entire body length. In snakes, the tail begins at the vent, a slitlike opening on the belly side. Its head is wider and flatter than the neck and is quite long, with an often noticeable black stripe behind the eye. Sometimes a white stripe lies alongside the black face stripe. The snake has a catlike pupil, but since its eye color is quite dark, the pupil is usually difficult to see. The upper body is light-to-dark brown, and the cream-colored belly is speckled with brown.

Some snake species have bits and pieces of leftover hip bones. In humans and other walking animals, the hip bones link to the leg bones, but since snakes have no legs, they do not need them. In splitjaws, no bits of hip bone remain. Adult keel-scaled splitjaws generally reach about 4 feet (1.3 meters) in length.