Big-Headed Turtle: Platysternidae

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BIG-HEADED TURTLE: Platysternidae

PHYSICAL CHARACTERISTICS

The family Platysternidae has only one member, the bigheaded turtle, which has the scientific name Platysternon megacephalum. This small to medium-sized 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 (SCOOT). The upper shell, or carapace (KARE-a-pays), is quite flat and sometimes has a single ridge running down the middle from front to back. The carapace is yellow to dark-brown and may have a pattern on it. A few big-headed turtles have red or pink markings on the carapace. Like that of many other turtles, the lower shell, or plastron (PLAS-trun), of the big-headed turtle is yellow and covers most of the underside. Unlike those of many other turtles, the upper and lower shells of the big-headed turtle are not connected by a bony bridge, but by softer, more flexible tissue, called ligaments (LIH-guh-ments). The upper jaw, also known as the beak, comes to a sharp point in the front. The big-headed turtle has a scaly tail that is nearly as long as the upper shell. The feet have obvious claws and just a bit of webbing between the toes. Turtle size is measured by the length of the carapace. The carapace length of the big-headed turtle reaches about 8 inches (20 centimeters). Males and females are similar, but the males have a more indented plastron.

GEOGRAPHIC RANGE

The big-headed turtle lives in China, Laos, Myanmar, Thailand, and Vietnam.

HABITAT

The big-headed turtle is rare and has been found only in small mountain streams from southern China to Thailand and southern Myanmar. These turtles appear to be very particular about the type of stream, living only in rock-bottomed, cool waters and only in mountainous regions up to 6,600 feet (2,000 meters).

DIET

Because the big-headed turtle is so rare, scientists have been able to learn about its diet only by observing captive, rather than wild, turtles. In captivity, the turtles eat meat, fish, and insects. The big-headed turtle is probably a meat-eater in the wild and may eat no plants at all. The turtle most likely gets most of its meals by gathering insects, mollusks, crustaceans, and other small invertebrates from the stream bottom, but it also may crawl out of the water onto shore and search for food on land. Invertebrates (in-VER-tehbrehts) are animals without backbones. Both mollusks (MAH-lusks) and crustaceans (krus-TAY-shuns) are invertebrates with shells. Mollusks, such as snails and clams, have an unsegmented body, and crustaceans, such as crayfish and shrimp, have a segmented body.

CHANGES IN CLOSEST RELATIVES

Big-headed turtles are the only species in the family Platysternidae. Scientists once believed these turtles were most closely related to New World pond turtles, including the painted turtles that are common in much of North America. That idea has faded, however. Now many people believe the closest relatives are the snapping turtles, which are in the family Chelydridae, or possibly the Eurasian pond and river turtles and neotropical wood turtles of the family Geoemydidae. A few scientists believe the big-headed turtles should be included in the snapping turtle family, but most argue that these turtles are different enough to be in a separate family.

BEHAVIOR AND REPRODUCTION

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 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.

BIG-HEADED TURTLES AND PEOPLE

Some people consider the meat of the big-headed turtle a delicacy, so the turtles face threats from hunters. Other people collect the turtles for use in folk medicines. Despite their tendency to bite, these turtles are fairly popular pets.

CONSERVATION STATUS

According to the World Conservation Union (IUCN) the bigheaded turtle is Endangered because of overcollection. Endangered means that this species is facing a very high risk of extinction in the wild in the near future.