Real Monstrosities: Sailfin Lizard

Just because the dinosaurs died out doesn't mean reptiles of today can't benefit from some of those ancient ideas!

Oh, alright. You got me. I can't fool you, can I? Obviously a whole bunch of dinosaurs didn't die out at all; they became today's birds, instead. And the Sailfin Lizard is clearly borrowing from the Dimetrodon, which went extinct some 40 million years before the first dinosaur ever appeared. And it was a synapsid, which means it was more closely related to mammals than to any reptile.

Just don't tell the Sailfin Lizard that, OK?

Image: ell brown

And anyway, if the best we mammals can do is a camel's hump, we simply must open our warm-blooded arms for the Sailfin Lizard and his wonderful tail-sail.

There are three species of Sailfin Lizard, all belonging to the superbly named genus Hydrosaurus.

Image: Wilfried Berns
The Giant Indonesian Sailfin Lizard (H. amboinensis) reaches 3 or 4 ft long and comes from Papua New Guinea, Indonesia and the Philippines

At a metre (3 feet) or more in length, Hydrosaurus amboinensis is slightly longer than the other Sailfins and is thus the biggest of all agamids. Agamidae is a family of lizards closely related to the iguanids, which is proabably why Sailfins look a bit like iguanas.

Image: Sylfred1977
Female Sailfins are a little smaller than the males and have a less prominent fin

Sailfins spend most of their time climbing around in trees. They're omnivorous, feeding on fruit, vegetation, insects, frogs and any other creatures they happen upon.

Image: Neil Saunders
The Philippine Sailfin Lizard (H. pustulatus) comes from the Philippines and is about as long as H. amboinensis, but slimmer.
This one is beautiful with those big, soft eyes. I hope it's a female...

Sailfins don't usually stray far from the damp embrace of a good river and, despite their impressive size, they are always ready to leap into the water at the first sign of trouble. They can even stay submerged for over 15 minutes! Hydrosaurus means "water lizard", after all.

Image: Wilfried Berns
Weber's Sailfin Lizard (H. weberi) is only 2 or 3 feet long and lives on a few islands in Indonesia

Sailfins are the proud owners of a whole host of adaptations for a good time swimming...

Image: OZinOH

The most obvious of which are the bright orange arm bands which ensure... Oh, wait. That's some kind of fin, right? A "sailfin", maybe. This thing can get up to 9 cm (3.6 in) tall in some males, which is probably a bit much just for swimming. I assume it's used for display. Weird, sticky-out bits on males are usually for display. Also there's no bone in there, unlike the massive frill on Dimetrodon.

More useful in water is the incredibly long, slightly flattened tail and long toes lined with extra flaps of skin.

Image: Superstringphysics

Big legs, long toes and flaps of skin obviously make it difficult to find good footwear, but it does allow Sailfins to power their through rivers. It also allows younger Sailfins to run across the water's surface for a bit! Bright orange arm bands really don't figure in this at all. I don't know what I was thinking.

Females lay a few eggs in a nest dug out in soil near water. They hatch in a couple months and the youngsters that emerge are active, energetic and can immediately run, swim and climb all over the place.

It's amazing the range of colours these lizards can acquire...