Reptiles
Big-headed Turtle
Platysternon megacephalum · also called big-headed turtle
The big-headed turtle is built wrong for a turtle. Its head is far too big to pull inside its shell, its tail is nearly as long as its body, and it spends its time not swimming but climbing over boulders and waterfalls in cold mountain streams.
Overview
Platysternon megacephalum lives only in cool, clear, fast rocky streams in the hills and mountains of southern China and mainland Southeast Asia. It is a nocturnal hunter of snails, insects, fish, and frogs, crushing them with powerful hooked jaws. It is the sole member of its family, Platysternidae.
Armoured head, climbing tail
Its oversized head cannot retract, so the top is protected by a solid helmet of bony scales, and the turtle defends itself by biting. Its long heavy tail works as a fifth limb, bracing against rock as it clambers over boulders and up waterfalls, and it is regularly seen climbing logs and low streamside trees.
Status
Critically Endangered. It has been collected in enormous numbers for the Asian food, medicine, and pet markets, and its mountain streams are being dammed and polluted. It is now protected under international trade rules and bred in captivity for conservation.
Big-headed Turtle: common questions
Why can't the big-headed turtle pull its head into its shell?
Its head is simply too large. In most turtles the head, limbs, and tail can be drawn inside the shell for protection, but the big-headed turtle has evolved a head so massive, with heavy jaw muscles for crushing hard-shelled stream prey, that there is no room for it inside the carapace. The trade-off is that the top and sides of the head are covered by a single large shield of bone-reinforced scales, effectively a helmet, and the turtle relies on that armour plus an aggressive, snapping defence rather than on retreating. The tail is likewise too long and thick to withdraw fully.
Can it really climb trees?
It is a genuine and unusual climber, though how high it goes is debated. There is no doubt that the big-headed turtle scrambles over large boulders and up small waterfalls and cascades within its streams, using its clawed limbs, its hooked beak, and especially its long muscular tail as a fifth limb to hook and brace against rock. Numerous field and captive observers also report it climbing onto logs, up sloping tree trunks, and into low streamside vegetation, sometimes well above the ground. It is one of the very few turtles for which climbing is a normal part of getting around.
Is the big-headed turtle dangerous to handle?
It will defend itself hard. Because it cannot hide in its shell, a cornered big-headed turtle faces the threat, opens its mouth wide, and strikes with a fast, strong bite from sharp hooked jaws that can draw blood and hold on, and it may also scratch with clawed feet and lash the tail. It has no venom and is not a danger to anyone who leaves it alone, but it should never be picked up casually. In its native range this fierce temperament has not saved it, because most collection is done with baited traps rather than by hand.
Why is it so endangered?
A combination of heavy exploitation and a narrow habitat. The big-headed turtle is sought for the food and traditional medicine trade in China and neighbouring countries and is one of the more expensive turtles in the international pet market, so trappers work the streams intensively. At the same time it can only live in cool, clean, fast headwater streams, and those are being dammed for hydropower, silted by logging and farming, and polluted. A slow-maturing turtle in a shrinking, accessible habitat cannot withstand that pressure, and it is now considered one of the most threatened turtles in Asia.