The Great Grand Daddy of All Sea Snakes
Text by Jay Maclean
Photography by Juergen Freund

There's a website you can visit that provides the experience of being on a jurassic reef (www.paleo.de/edu/jrp). Actually it's rather dull, and basically lets you know there were coral and sponge reefs present in the late jurassic, 160-135 million years ago. None of the wonder and thrills the diver experiences. I wondered how scuba diving would be then—what perils would enliven the scene? One you might not expect would be the probable ancestor of snakes—no, not just sea snakes, all snakes. Scientists agree that snakes evolved from lizards but have not found any convincing intermediate stages between them, probably because the scientists were looking in the wrong place. A recent article in the journal Nature makes a good case for pinpointing a group of marine lizards called mosasaurs as the precursors of all modern snakes. Sea snakes are 'new', having evolved in the last few dozen million years or so from land snakes. Divers should be grateful that this circuitous evolutionary route included great reduction in size.

Sea snakes are deadly and they mostly occur in the waters of Southeast Asia. There are about 60 estuarine or marine species, 47 of which, the family Hydrophiidae, are known as true sea snakes. Some live in muddy bottoms, mangrove areas or salt marshes. Divers generally see reef species weaving amongst the coral minding their own business. I know of no fatality amongst divers from them, although it can come as a shock to find one right beside you on the surface as happened to me a little while ago while snorkeling. Fishers on shrimp trawlers in northern Australia used to handle them carelessly, presuming that the snakes, having come up in the trawl net, had bitten everything within range and exhausted their venom; not always though—serious bites to these fishers are common! Sea snakes have small mouths and can only bite on a finger or an ear, but don't tempt them; they have the most powerful venom of all snakes!

True sea snakes are live-bearers, giving birth to tiny offspring, usually 6 or less, underwater. The first move the young make is to the surface to take their first breath. Some, such as sea kraits, come ashore to lay eggs and often just to rest.

Marine lizards are rare now; the small marine iguanas of the Galapagos Islands are the only truly marine species left, although some skinks splash around in the intertidal zone. But in cretaceous times, marine lizards, mosasaurs, were large to gigantic, reaching maybe 50 feet long, making them the largest marine reptiles of all time. They were definitely not herbivores and ate other marine reptiles including turtles, birds and even other mosasaurs! Mosasaurs were the top marine predators of their day, distributed widely around the oceans including the tropics.
Next time you see a sea snake while scuba diving, relax and take comfort that it is not one of their mosasauran ancestors. Believe me, it would not have to spit out your tank.

With thanks to Michael Lee. Source: M.S.Y. Lee, G.L. Bell Jr., and M.W.Caldwell. 1999. Nature 400:655-659.

Jay Maclean is a marine biologist and artist living in Manila and Anilao, Philippines.