Monday, December 26, 2011

Cambrian predator had killer eyes

A fearsome predator that swam in the Cambrian oceans was in fact a metre-long arthropod with killer vision, say researchers.

Palaeontologist Dr John Paterson, from the University of New England, and colleagues, have discovered the fossilised remains of compound eyes from a creature called anomalocaris.

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"The fact that each eye in anomalocaris would have had over 16,000 lenses, means it would have very, very good resolution," says Paterson, whose work is published today in the journal Nature.

"When you consider that a modern housefly, for example, has about 3000 lenses, it's pretty impressive that an animal half a billion years old already has remarkable vision like this."

Around 500 million years ago, during the Cambrian, large alien-like creatures began to resemble modern animals, says Paterson.

"But you still had the odd freak swimming around," he says, referring to the metre-long free-swimming anomalocaris.

"It's an animal that's on its way to becoming an arthropod from an evolutionary point of view," says Paterson.

The creature would have propelled itself through the water by moving flaps down the length of its body in a wave-like pattern, he says.

It had a soft shrimp-like exoskeleton and fierce grasping claws and would have dined on soft-bodied organisms such as worms.
Missing attributes

But anomalocaris has presented a bit of puzzle to scientists because while it looked like it might be an arthropod, it was missing certain attributes.

Arthropods include animals with jointed legs such as insects, spiders, crustaceans and millipedes.

"But when you look at anomalocaris, it doesn't actually have any jointed legs," says Paterson.

Now, the discovery of fossilised compound eyes belonging to the animal has confirmed it is indeed an arthropod.

"Compound eyes are actually a definitive arthropod characteristic or trait," says Paterson.

The fossilised eyes were discovered alongside remains of the grasping claws and the body flaps in shale at Emu Bay on the northern coast of Kangaroo Island, off South Australia.

The soft tissue of the compound eyes were slowly replaced by a mineral called pyrite in a low oxygen sediment, says Paterson.

The discovery supports the idea that compound eyes evolved very early on in arthropod evolution, before the evolution of jointed legs or hardened exoskeletons.

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