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5 December 2013 11:26 am ,
Vol. 342 ,
Dyslexia, a learning disability that hinders reading, hasn't been associated with deficits in vision, hearing, or...
Exotic, elusive, and dangerous, snakes have fascinated humankind for millennia. They can be hard to find, yet their...
Researchers have sequenced and analyzed the first two snake genomes, which represent two evolutionary extremes. The...
Snake venoms are remarkably complex mixtures that can stun or kill prey within minutes. But more and more researchers...
At age 30, Dutch biologist Freek Vonk has built up a respectable career as a snake scientist. But in his home country,...
Since arriving on the island of Guam in the 1940s, the brown tree snake ( Boiga irregularis ) has extirpated native...
An animal rights group known as the Nonhuman Rights Project filed lawsuits in three New York courts this week in an...
Researchers have been hot on the trail of the elusive Denisovans, a type of ancient human known only by their DNA and...
- 5 December 2013 11:26 am , Vol. 342 , #6163
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Looking a Trilobite in the Eye
14 March 2013 11:30 am
Hundreds of millions of years ago, the Earth's seas teemed with trilobites, hard-shelled critters that resembled spiny aquatic cockroaches. Because their exoskeletons lent themselves to fossilization, scientists know a lot about what the outside of their bodies looked like. Their inner workings, however, have remained mysterious. Now, a new study has revealed the structure of the trilobite eye, bringing researchers one step closer to understanding the evolution of vision.
Like today's insects and crustaceans, trilobites had compound eyes, with many different lenses focusing light onto clusters of sensory cells lying below them. The resulting image was put together a lot like a picture on your computer screen, with each lens producing one "pixel" of the whole. Because the lenses themselves were made of the mineral calcite, they often fossilized along with the rest of the trilobite's tough exoskeleton. The sensory cells underneath the lenses, however, were ephemeral, and scientists had always assumed that they had decayed without a trace.
So imagine Brigitte Schoenemann's surprise when she spotted fossilized versions of these delicate sensory cells while x-raying a long dead trilobite with a computed tomography (CT) scanner. "I expected that we would see [something] in the lens of trilobites, but then suddenly we saw structures of cells below the lens," recalls Schoenemann, a physiologist at the University of Bonn and the University of Cologne, both in Germany. Inspired, she applied to take more fossils to the European Synchrotron Radiation Facility in Grenoble, France, where she could use a particle accelerator's high energy x-rays to peer deeper into the trilobites' eyes. Now, she says, she's created images of the extinct animal's entire visual system, down to the level of fossilized individual cells.
So what does the inside of a trilobite eye look like? A bit like a flower, Schoenemann and a co-author report online today in Scientific Reports. Beneath each lens, round sensory cells are arranged like petals around a diamond-shaped photoreceptor able to pick up the dim light that filtered down through the Earth's ancient oceans. Pigment cells filled in the space between the blooms and likely made trilobite eyes appear brownish-black.
This bouquet of light sensitive blooms buffered by pigment cells is very similar to the structure seen in the eyes of today's horseshoe crabs (Limulus). "If you have an optical system that works, it can last," says Richard Fortey, a paleontologist at the Natural History Museum in London. He hopes the x-ray techniques used in this study will soon be applied to more trilobite species—which may have evolved different visual systems—as well as other types of well-preserved fossils. Modern techniques like synchrotron radiation "produce details you wouldn't have dreamed could be seen a few years ago," he says.
"It's fantastic to see" this new tool being adopted, agrees physicist Uwe Bergmann of the SLAC National Accelerator Laboratory in California, who has also used x-rays from a synchrotron there to study fossils. "It seems as if these x-ray tomography techniques have brought out really new knowledge … about the early evolution of eyes."