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X-ray of a fossil finds other fossils inside

An X-ray scan of a fossilized sea urchin revealed a large number of fossilized clams inside.

Detail of the CT scan: a sea biscuit full of clams. Imran Rahman/University of Bristol

X-ray computer tomography has been doing fantastic things for archaeology and paleontology, allowing researchers to look inside fragile fossils without damaging them.

Recently, an international team of researchers has used the technology to peer inside a 10 million-year-old fossil of a sea urchin, revealing a large number of fossilized boring bivalves (bivalves that bore holes, not bivalves that send you to sleep with stories about potatoes) inside.

Moreover, the scan was so precise that the researchers were able to determine that the bivalves were of the genus Rocellaria, a type of saltwater clam that still exists today and is known to burrow into rocks and shells. The team's research will be published in the November issue of Palaeogeography, Palaeoclimatology, Palaeoecology.

The clams did not eat the living urchin, which was determined to be a Miocene-era Clypeaster, or sea biscuit. According to study's co-author Zain Belaústegui of the University of Barcelona, they would have been using the skeleton of the already deceased animal as a home.

"The study confirms that the skeletons of dead animals, such as sea urchins, have been important island habitats for boring and encrusting organisms for tens of millions of years," he said.

"This work also highlights how studying the traces left behind by animals, coupled with the processes that led to the formation of fossils in deep time, can provide new insights into the biology of ancient organisms and past environments."

Lead author Imran Rahman of the University of Bristol's School of Earth Sciences believes that, as well as revealing something of the behaviour of these ancient animals, the research demonstrates the value in CT scanning fossils.

"We had no idea there would be so many bivalves inside the sea urchin," he said. "This goes to show the importance of CT scanning for understanding long-dead organisms and their ecosystems."