This Ancient Crab Had Unusually Huge Eyes

Adult crabs are not renowned for their swimming ability or vision. They scuttle across the floors of silent seas without relying on small eyes.

95 million years ago, an unusual crab flew around the tropical waters of what is now Colombia. The quarter-size species, Callichimaera perplexa, looked a bit like a spider, with flat, oarlike legs and a keeled body. It had a large set of eyes as well.

A group of paleontologists have shown in a study that Callichimaera had sharp eyes and was a free-swimming predator.

A research fellow at Harvard University, Luque discovered the species in 2005. He stumbled upon an outcrop full of fossil arthropods while he was an undergrad in the Boyac department.

Many of the specimen that Dr. Luque and his colleagues collected are extremely well-preserved. Dr. Luque said it was a huge sample size. Do you have 100 specimen?

Detailed eyes were preserved in seven of the specimens. Dr. Luque said that living crabs usually have tiny compound eyes, which are at the end of a stalk and covered by a protective orbit. The compound eyes of Callichimaera were large.

It is a image.

A Callichimaera fossil, one of several well-preserved arthropods, was found in 2005.

Crabs go through multiple stages of growth, beginning life as small shrimplike creatures before becoming armored forms. Young crabs with big eyes are free-swimming in the last stage. Dr. Luque and his colleagues thought that the fossil was a crab in its last stage, even though it was a large one.

According to a co-author on the paper, no other crab has these huge eyes. avier wanted a more in-depth look at the animal.

To figure out how Callichimaera used its eyes, Ms. They compared this with other crab species. They were surprised to find that Callichimaera retained its large eyes into adulthood.

Their calculations showed that Callichimaera's compound eyes grew faster than those of the modern crabs. Their eyes took up around 16 percent of their body, the same amount as a person walking around with eyes the size of soccer balls.

Animals with compound eyes have a view of the world that is very small. The sharper the vision, the higher the count. The analysis of Callichimaera's eyes shows that it had a very clear vision for a crab.

Dr. Luque said that the animal must have used big eyes. They are a drag in the water and vulnerable. The drawbacks of having big eyes must have been nothing compared to the advantages.

Dr. Luque said the eyes suggested that Callichimaera preyed on smaller creatures. They did this by maintaining their predatory form into adulthood, rather than making the final transformation into the flat and scuttling shape favored by other crabs.

Callichimaera has both eyes and preserved neural tissue. It is rare to get a good look at an animal's visual processing system when it is half a billion years old. You can find parts of the brain, but not the eyes. Dr. Luque said that Callichimaera has both.

The site that produced Callichimaera is likely to have more secrets.

There is a huge gap in the fossil record because we are not doing much fieldwork in the tropics. The places are usually covered in vegetation and the rocks are very fast. New avenues to study the fossil record are opening because of the preservation. No pun intended.