|
Sci Tech
Giant sea scorpion discovered
Sea scorpions do not usually grow a single huge claw Their size is due to lack of competition from vertebrates
Those who are unnerved by creepy crawlies should stop reading now — a newly discovered two-and-a-half-meter monster arthropod, the largest yet discovered, is being unleashed on the world. Luckily for those of a nervous disposition, the release of this long-extinct relative of sea scorpions is limited to the pages of the journal Biology Letters.
Giant example
There, Simon Braddy of the University of Bristol, U.K., and colleagues report finding a 46-centimetre claw from a Jaekelopterus rhenaniae — from which they infer the existence of a giant example of this species.
Although called a ‘sea’ scorpion, the 400-million-year-old beast probably terrorized lakes and rivers, and rarely, if ever, ventured into the oceans.
“This huge monster lived alongside other sea scorpions and fish,” says Braddy. “They would probably lie in wait. When another animal went in front of it, it would lurch forward and capture it. ... These things would tear their prey to shreds and then eat the little pieces.”
Amazing
The J. rhenaniae claw was found near Prum in Germany. To work out the size of the arthropod it belonged to, Braddy and colleagues collected information on other sea scorpions and the ratio between their claw size and body length. This turned out to be relatively constant, leading the researchers to conclude that a creature with a 46-centimetre claw probably had a body length of between 233 and 259 centimetres, or 333 and 359 centimetres including the claws and arms.
“I was amazed,” says Braddy. “Whenever I’ve shown the picture to people they’re equally amazed.
When you work out how big this beast was you’re staggered by the size of it.”
Unlike some crabs, sea scorpions are not known to grow a single enormous claw, so extrapolation is reasonably straightforward, says Braddy.
Safe grounds
Greg Edgecombe, a palaeontologist at the Natural History Museum in London, said the researchers were “on pretty safe grounds” with their calculations.
A previous sea scorpion find had been reported as being 250 centimetres long based on a similar extrapolation from its claw size, Braddy says.
But Braddy’s new analysis indicates that this beast was actually a puny 210 centimetres long, leaving J. rhenaniae the arthropod crown-holder for size. “It changes our ideas about what is possible,” says Edgecombe of these creatures. “It forces us to modify our ideas about how large arthropods can be.” Exactly how or why this animal grew to the size it did is unclear.
Oxygen increase
Giant arthropods, including huge millipedes and dragonflies, are known to have existed on land during the Carboniferous, some 359 million to 299 million years ago. Their existence is sometimes explained by an increase in the levels of atmospheric oxygen at that time.
This could have allowed creatures with breathing systems that relied on the diffusion of oxygen into tissues, rather than a full-blown respiratory system, to grow much larger.
Evolutionary race
But giant aquatic sea scorpions existed before this oxygen boost, notes Braddy. Another theory holds that the size of these animals is the result of an evolutionary arms race with their prey, which included armored fish. Braddy speculates that they grew so big because of a lack of competition from vertebrates.
When vertebrates arrived, it could have spelled the end for the giant scorpions. “It’s a case of the vertebratescoming along and spoiling the arthropod party,” he says.
DANIEL CRESSEY
Nature News Service
Printer friendly
page
Send this article to Friends by
E-Mail
Sci Tech
|
