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UV Light Reveals the Colors of Fossil Shells

Patterns made visible help a researcher discover 13 new species of ancient cone snails

Three new proposed cone snail species (L-R): Conus carlottae, Conus garrisoni and Conus bellacoensis, under regular light (top) and ultraviolet light (middle) and with colors reversed to approximate how they would have appeared (bottom) (Jonathan Hendricks, via PLOS ONE)
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Rays of ultraviolet light—the same wavelengths that stream from black lights to give funky fluorescence to a rave—can be used to uncover secrets usually invisible to human eyes. A UV camera can expose sun damage to skin, show how carnivorous plants lure ants and highlight hints of feathers still clinging to dinosaur fossils. Now researchers are using UV light to coax color from porcelain white seashell fossils.

Just as age and weathering have washed the colors from classic Greek statutes, so has time leached pigments from cone snail fossils, found in the Dominican Republic and ranging from 4.8 million to 6.6 million years old. Modern cone snails are predatory, widespread and often colorful. But researchers studying ancient cone snails sometimes have trouble distinguishing species without the aid of their distinct markings — all are roughly cone-shaped.

But traces of those pigments still linger, and UV light makes them glow, found geologist Jonathan Hendricks of San Jose State University, according to research in PLOS ONE. He looked at more than 350 shells originally found in the 1970s under UV light and characterized them by their stripes, spots and colors. For The Washington Post, Rachel Feltman writes:

By drawing out the patterns of the fossils, he was able to classify them by species. In many cases he found their patterns to be quite similar to surviving species. But in other cases -- like the proposed new species Conus carlottae -- patterns were strikingly unfamiliar. This species had large polka dots all over its shells, which isn't a pattern seen in cone snails today.

This shell shows the effects of oxidation -- darker colors in the right-hand portion. By Jonathan Hendricks, via PLOS ONE

Hendricks proposes 13 new species based on his UV work. Next, he writes, scientists need to figure out what compound the UV light picks up and fluoresces. Some shells have patches of more vivid patterning where it appears they were exposed to sunlight (the other side was buried in the sand), so Hendricks thinks that some reaction triggered by exposure to oxygen, aided by the sun’s rays, makes the pigment respond to UV light better. But they still don’t know why. 

Still, now we have some fantastic images that make imagining the sea life of millions of years ago a little more colorful.

By Jonathan Hendricks, via PLOS ONE
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