Big-Headed Turtle: Platysternidae

All turtles fall into one of two groups: the Cryptodira or the Pleurodira. The difference between the two is the way each pulls its neck and head back toward or into the shell. The Cryptodira, also known as hidden-necked turtles, can pull their heads and necks straight back and are usually able to tuck both into the shell. The Pleurodira, also known as side-necked turtles, can only pull their necks sideways rather than straight back, so most tuck their head and neck along the side of the shell. The big-headed turtle is unusual because it is a Cryptodira in that it can pull its neck backward, but it cannot draw its head into the shell because its head is so large.

Most hidden-necked turtles are shy animals that pull their heads, limbs, and tails into the shell whenever they feel threatened. Attacking animals, called predators (PREH-duh-ters), find it difficult, if not impossible, to get past the shell, and the turtle usually survives with little if any injury. The big-headed turtle cannot hide this way and instead defends itself by drawing its legs and tail into the shell and then ducking down its head so that the chin is on the ground and only the hard top shows. Sometimes the turtle may lash out with a quick bite. It may continue biting, and biting quite hard, until the predator leaves. Captive turtles also squeal when threatened. In addition, this turtle has glands, or sacs, on the sides of the shell that squirt out a bad-smelling musk, which may be used to scare off predators.

The big-headed turtle is a surprisingly good climber and uses its long tail for balance. The turtle may also use its beak to grab vertical surfaces when climbing. When placed in a fenced-in, indoor area, the turtle is able not only to climb over the fence The big-headed turtle is most known for its huge head, which is about half as wide as the upper shell. The head is shaped like a triangle and covered with a single, large, hard scale, known as a scute. (©Tom McHugh/Photo Researchers, Inc. Reproduced by permission.) but also to grab onto window curtains and scramble all the way to the ceiling. In the wild, the turtles likely put this climbing ability to good use for crawling over rocky stream bottoms and against fast current. Some people report seeing the turtles climbing trees and bushes in the wild.

Big-headed turtles appear to be nocturnal (nahk-TER-nuhl) and crepuscular (kreh-PUS-kyuh-lur) in the wild. Nocturnal means they are active at night, and crepuscular means they are active at dusk and dawn. During the day, these turtles take cover and relax underwater beneath logs or rocks and wedged into cracks in boulders. Big-headed turtles that live in colder waters disappear in the winter. Although no one knows where the turtles go, scientists believe they probably hibernate (HIGH-bur-nayt), which means they enter a deep sleep. Some people think the turtles may hibernate in a protected spot on land.

Little is known about the courtship, or mate-attracting activities, of big-headed turtles or about their mating and nesting behaviors. In the wild the females probably nest sometime from May to August. The only egg ever seen hatching did so in captivity, and it hatched in September. In each clutch, or nest of eggs, females lay one or two eggs, sometimes as many as four. The eggs are 1.5–1.7 inches (3.8–4.3 centimeters) long and are about 0.9 inches (2.3 centimeters) wide. The eggs are quite large considering that the turtle's carapace length only reaches 8 inches (20 centimeters). No one knows whether the turtle lays one or more than one clutch a year. In captivity these turtles can live to be as old as twenty-five years.