Reptiles
Sailfin Dragon
Hydrosaurus pustulatus · also called sailfin dragon, philippine sailfin lizard, sailfin lizard
The sailfin dragon is a big, semi-aquatic lizard of Southeast Asian rivers, and the feature that names it is a tall, skin-covered sail running along the base of its tail. It swims and dives like an otter, basks its sail toward the sun to warm up, and — while it is still young and light — can bolt several metres across the surface of a river on its hind legs.
Overview
The sailfin dragon covered here, the Philippine sailfin lizard, lives along rivers, streams, and mangrove edges throughout the Philippine islands. It is one of the largest agamid lizards, reaching about 1 m in total length, heavy-bodied, and greyish-green flecked with turquoise and purple. Other sailfin dragons live in Sulawesi, the Moluccas, and New Guinea.
The sail
A crest of tall, skin-covered spines rises along the tail base, largest in mature males. It is used in display to rivals and mates, and it works as a solar panel, letting a lizard warm quickly after time in cool water.
Running on water
Startled juveniles drop into the river and sprint across the surface on their hind legs for a few metres before sinking, using slapping strides and fringed toes — the same trick as the American basilisk. The ability fades as the lizard grows heavy, and adults simply dive and swim, sometimes staying submerged for many minutes.
Breeding
The female digs a shallow pit in a sunny sandbank near water, lays several eggs, covers them, and leaves them to incubate alone.
Status
The Philippine sailfin dragon is Vulnerable and declining, hit by capture for food and the pet trade and by clearance of the riverside forest it depends on.
Sailfin Dragon: common questions
Can a sailfin dragon really run on water?
Yes, when it is young and light. Juvenile sailfin dragons that are startled near a river will often flee straight into the water and run across the surface on their hind legs for a few metres before dropping in and swimming. They do it much as a basilisk lizard does, by slapping the water hard with fringed hind feet fast enough that the pocket of air trapped by each slap supports the foot before it can sink. As a sailfin dragon grows into a heavy adult of up to a metre long, it becomes too massive for this to work, and older animals simply dive and swim instead.
What is the sail on its back for?
The sail, a fin of tall spines covered in skin along the base of the tail, has more than one function. It is largest and most impressive in adult males, and it plays a role in display, making a male look bigger and more striking when he faces a rival or courts a female along a riverbank. It also acts as a solar panel. Sailfin dragons spend a lot of time in and around cool water, and turning the broad surface of the sail toward the sun lets a lizard absorb heat and raise its body temperature quickly after a swim.
How is a sailfin dragon different from an iguana?
They look somewhat alike, with a crest along the back, a long tail, and a partly plant-based diet, but they are not close relatives. Iguanas are New World lizards in the family Iguanidae. Sailfin dragons are Old World lizards in the family Agamidae, the same broad group as bearded dragons and water dragons, and they are native to Southeast Asia and the western Pacific. Differences include tooth attachment, the structure of the crest, which in the sailfin dragon becomes a distinct tail sail, and the water-running ability of young sailfin dragons, which iguanas do not share.
Do sailfin dragons make good pets?
They are kept by experienced reptile keepers but are demanding and not suited to beginners. They grow large, are fast and nervous, and need a very big enclosure with a large water area for swimming, strong heating and UV lighting, high humidity, and a varied diet of greens, fruit, and animal prey. Wild-caught imports, which have made up much of the trade, often arrive stressed and carrying parasites, and buying them adds pressure to declining wild populations. Captive-bred animals are preferable where available, but the space and care requirements still put this species beyond most households.