Ancient Shellfish Body Revealed


By Rossella Lorenzi, Discovery News

Aug. 23, 2005— A team of British and American scientists has digitally resurrected the forerunner to modern clams and mussels — an "articulate brachiopod" not seen for 425 million years.

Found in a quarry on the border between England and Wales, buried in volcanic ash, the shellfish fossil is the first of its kind to be preserved with the fleshy parts intact.

"It is something we never dared to dream we might see: an ancient fossil articulate brachiopod with its fleshy parts intact, and preserved in three-dimensions to boot," said Mark Sutton of Imperial College at the University of London, who made the discovery.

"Up to now, in all the millions of articulate brachiopod fossils scientists have examined, no-one has ever found anything except empty shells."

Brachiopods, clam-like creatures also known as "lamp shells," populated the Paleozoic oceans 542 million to 251 million years ago.

Named Bethia serraticulma after Sutton's wife Bethia, the brachiopod was brought into digital life by shaving away the rock encasing the fossil layer by layer. Scientists photographed each layer, reducing the brachiopod to dust, but converting it into a high-fidelity 3-D virtual fossil.

The digitally reconstructed brachiopod most probably belonged in the order Orthida, the most primitive of all brachiopod orders, Sutton and colleagues from the universities of Yale, Oxford and Leicester report in the current issue of Nature.

The fossil was found complete with a robust, ridged pedicle together with a lophophore, or feeding organ, and other soft tissue structures.

Showing the internal structure of the brachiopod as well as the stalk and rootlets that kept it tethered in place, the digital model challenges assumptions that the extinct creatures are similar to their living descendents.

"This finding adds crucial new information about the soft anatomy of this type of brachiopods. The authors are absolutely correct in that we sometimes are overly confident in using what is known of the anatomy of the few living representatives in interpreting the soft anatomy of extinct forms," Lars Holmer, professor in historical geology and palaeontology at the University of Upsala, Sweden, told Discovery News

Indeed, the fossil's rootlets are physically tied onto a stick-like object on the sea-floor, most likely to be debris from a dead sea-lily.

On the contrary, rootlets of modern brachiopods spread out into soft sediment, just as plant roots do.

"Those brachiopods that stick to a hard object do it chemically, rather than tying themselves on. Bethia's stalk is also much chunkier than in any modern brachiopod, and has strange ridges on it. It clearly didn't work in the same way at all," Sutton said.

The site of the discovery has revealed several spectacularly well-preserved creatures, including an ancient sea spider and the oldest fossil of a male animal. Both have been digitally reconstructed.

"Every new fossil we find casts new light on a different area. We have found a mine of information, and we are extracting a series of valuable nuggets," Sutton told Discovery News.