Australian-led team discover reasons behind snakes' 'shrinking heads'

A small-headed sea snake foraging in waters off the
Ryuku Islands. Photo by Yoshitaka Tahara.

An international team of scientists led by Dr Kate Sanders from the University of Adelaide, and including Dr Mike Lee from the South Australian Museum, has uncovered how some sea snakes have developed 'shrunken heads' - or smaller physical features than their related species.

Their research is published today in the journal Molecular Ecology.

A large head - "all the better to eat you with" - would seem to be indispensable to sea snakes, which typically have to swallow large spiny fish. However, there are some circumstances where it wouldn't be very useful: sea snakes that feed by probing their front ends into narrow, sand eel burrows have evolved comically small heads.

The team has shown normal-shaped sea snakes can evolve such "shrunken heads" very rapidly. This process can lead to speciation (one species splitting into two).

The small-headed populations are also much smaller in absolute size than their ancestors, and these shape and size differences mean they tend to avoid interbreeding with their large-headed ancestors.

Dr Lee says, "A team led by my colleague Dr Kate Sanders (University of Adelaide) has been investigating genetic differences across all sea snakes, and we noticed that the blue-banded sea snake (Hydrophis cyanocinctus) and the slender-necked sea snake (Hydrophis melanocephalus) were almost indistinguishable genetically, despite being drastically different in size and shape.

"The slender-necked sea snake is half the size, and has a much smaller head, than the blue-banded sea snake.

"This suggested they separated very recently from a common ancestral species and had rapidly evolved their different appearances.

"One way this could have happened is if the ancestral species was large-headed, and a population rapidly evolved small heads to probe eel burrows - and subsequently stopped interbreeding with the large-headed forms."

Dr Sanders says the research could have wider implications in other scientific studies: "Our results highlight the viviparous sea snakes as a promising system for studies of speciation and adaptive radiation in marine environments."

New species discovered off Australian coast

A new species of venomous sea snake mysteriously covered head to tail in spiny scales has been discovered in treacherous seas off northern Australia, according to a new study.

Though some other sea snakes have spiky scales on their bellies, "no other [known] sea snake has this curious feature," study leader Kanishka Ukuwela, an ecologist at the University of Adelaide, said by email.

Normally snakes have smooth scales, but each of the newly named Hydrophis donaldi's scales has a spiny projection, he said.

Scientists cruising shallow seagrass beds in the Gulf of Carpentaria (map) recently captured nine of the rough-scaled reptiles, National Geographic reported.

"The minute the first one landed on the deck, I knew we had something special," study co-author Bryan Fry of the University of Queensland in Brisbane, Australia, said by email. "It was quite unlike any of the sea snakes I have seen."

Each of the specimens was found on the rocky seafloor, a habitat that could explain the new species' uniquely strong scales, Fry noted.

Overall, though, "we don't know why this interesting feature evolved in this species, or what they are used for," study leader Ukuwela said.

The new Hydrophis—literally "water serpent"—likely eluded notice for two reasons. The species is apparently rare, and it lives in coastal habitats largely avoided by fishers, Ukuwela said. Many Australian sea snake species live in the open ocean and are often accidentally caught in prawn trawls. (See snake pictures.)

Little is known about the yellowish brown reptile, other than that it gives birth to live young and, like nearly all live-bearing sea snakes, is "venomous and potentially dangerous to humans," according to the study, published February 21 in the journal Zootaxa.

Furthermore, venom is just one obstacle to unraveling the new species' mysteries, the University of Queensland's Fry noted.

"Field observations are impossible, because the water is very murky and filled with lots of very large bull sharks and saltwater crocodiles, in addition to [highly poisonous] box jellyfish," he said.

"If we tried to dive there, our life expectancy would be measured in minutes. The only question is which animal would kill us.

"My money is on the bull sharks."

The Mystery of the Beast of Bowen (1934)

Fishermen have been reporting run-ins with strange sea creatures for centuries, even right here in Australian waters.

A giant seafaring snake 30-35ft long with a "head like a turtle" alarmed a party of fishermen in 1934, who described the aquatic anomaly as having "a body like a big-ribbed hose". So what was it?

Most sea snakes only grow to lengths of 3-5m, with the exception of the Yellow Sea Snake (below) which can reach almost 10ft in length. 

Responding to the claims in the newspaper, a letter writer observed:

I do not wish to compete against your well known contributor, 'BUI Bowyang,' in the telling of a tall yarn, but 'the sensational report ot the sighting of a huge sea serpent by the crew at the steamer 'St. Francois Xavier,' at Port Stephens (N.S.W.) prompts me to state that there is no reason to ridicule the story.

Some time back when Mr T. Murray, a well known local angler, was fishing In a boat off King's Beach, his attention was attracted by a loud thumping sound some distance out at sea. Suddenly a huge serpent-like creature reared itself, about 30 feet out of the water, and Mr Murray could distinctly see a spike-like fin, resembling that of a shark, sticking out of its back.

Each time the creature rose in the air it threw itself on the surface of the sea 'with terrific force. After a time it proceeded towards Holbourne Island and disappeared from view. Some months back a lady residing on Queen's Beach sighted a similar creature.

Be it myth or reality the fact remains that there must still be many denizens of the deep unknown to man, and one cannot believe that all people who claim to have seen the sea-serpent were romancers, seeking notoriety.

Could these accounts be referring to the rare so-called 'eel sharks' (frilled sharks)? Certainly the head could at some angles look turtle-like, but they certainly don't grow any larger than 6-7ft - but then again some fishermen's licence may have been taken when exaggerating the size!