An Arthropod With Vision

The eyes set an ancient crab apart as a probable predator.

Modern crabs are not renowned for their swimming ability or their vision. They scuttle across floors of silent seas, getting little help from their small eyes as they scavenge or graze.

But 95 million years ago, a crab flitted with unusual grace through the tropical waters of what is now Colombia. The species, Callichimaera perplexa, looked a bit like spider, with flat, oatlike legs and keeled body. And it had enormous eyes.

The species was discovered in 2005 by Javier Luque, a paleontologist from Colombia and now a research fellow at Harvard. He was exploring rocks in Colombia, when he stumbled upon an outcrop full of fossil arthropods.

The eyes took up around 16 percent of the bodies of the adult crabs, which would be like a human around with eyes the size of soccer balls.

''Whatever this animal was doing, it must have used such big eyes actively,'' Dr. Luque said. ''They're a huge drag in the water, and they're vulnerable. So whatever drawbacks that are there for such big eyes, they must have been nothing, compared to the advantages.''

When combined with the paddle legs and streamlined body, Dr. Luque said, these powerful eyes suggested that adult Callichimaera preyed on smaller creatures. [ Asher Elbein ]


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