|The 510 million year old fossil of Wiwaxia. The dark |
mouth parts are just visible at the top o0f the fossil
A defining feature of nearly all molluscs is a structure called a radula. Homologous to a tongue, a radula consists of hundreds of sharp, interlocking teeth used to feed. In slugs and snails, its purpose is to simply grind its way through vegetable matter. In larger creatures such as the squid, its purpose is a little more gruesome: scraping the flesh and muscle from prey. Such a distinctive organ must have been present in the earliest molluscs.
It is likely that Kimberella, one of those strange organisms which are part of the Ediacara biota, was the first of its kind. Scratch marks found close to the head in some fossils suggest that it may have had a scraping structure similar or possibly even a precursor to a radula. Yet no actual organ has been preserved on account of the owner's soft-bodied nature. As a result, the origin of the radula remained quite mysterious until recently.
|The electron micrograph image of the radula of Wiwaxia|
'You could see details you'd never guess were there if you just had a normal microscope.' Previously, it was impossible to analyse complete fossils, only small samples of a material. Despite the fact that the fossils of Wiwaxia, a gumdrop shaped creature covered in armor plates and spines, and Odontogriphus, lozenge shaped with a shell on its back and a single muscular foot, were tiny, they were still too large to analyse as a whole.
|The final model of the radula of Wiwaxia|
To feed, the teeth moved back and forth along to scrape algae and detritus from rocks and the sea floor. 'When I set out, I just hoped to be a bit closer to knowing what these mysterious fossils were,' said Smith. 'Now, with this picture of the earliest radula, we are one step closer to understanding where the molluscs came from.'