When an international team of researchers CT-scanned a 100-million-year-old sea urchin fossil (Clypeaster), they made a surprising discovery. It was choc-a-block with around 50 fossilised bivalves (a class of molluscs).
"We found an interesting fossil specimen in Spain, which showed some evidence on the outside of borings, which are structures that might be produced by tiny shelled invertebrates called bivalves," Imran Rahman, a palaeontologist at Bristol's School of Earth Sciences, told me over the phone. "This suggested that the bivalves were using this fossil sea urchin as a kind of habitat on the seafloor."
Suspecting that there might be a real rave going on inside the fossilised sea urchin, the researchers decided not to break it open (the traditional method), but to use a CT scan to virtually peer inside the specimen. This, explained Rahman, preserved the quality of the fossil for future researchers.
Once the researchers had CT-scanned the fossil, they produced a 3D digital reconstruction of its innards that revealed that it had become the resting place for as many as 50 little bivalves. "It was quite a shock," said Rahman. "We expected to see something inside the fossil but we never expected to see so many bivalves so tightly meshed together."
Describing the sea urchin fossil's innards as a "crowded habitat," Rahman said that his team found that the bivalves from 100-million years ago shared many similarities with their contemporaries.
explained that the discovery of so many bivalves allowed them to link that genus (Rocellaria) with a more contemporary bivalve species of the same genus.
"We were able to work out what type of bivalve it was and assign it a genus," said Rahman. "We found that it was a genus of a bivalve that occurs today that has a similar mode of life."
CT scanning fossils isn't a new practice, with paleontologists already scanning larger dinosaur and mammal fossils. But Rahman explained that finding out that there was an "intensive colonization" of their sea urchin fossil with so many bivalves in a non-destructive way was pretty new for the fossil community.
Next up, Rahman will be heading out to the Swiss Light Source, which is a massive particle accelerator used to produce X-rays and perform CT scanning at much higher resolutions.
"We'll be using that to study some very tiny fossils again by looking inside them, non-destructively. These fossils will be hundred of millions years old," said Rahman.