The carnivorous penis worm, or Ottoia, known from 500-million-year-old fossils, was a fearsome beast: it could turn its mouth inside out to reveal a tooth-lined throat that looked like a cheese grater. Scientists have discovered that the unfortunately-named penis worm could actually drag itself around by its teeth.

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All species of the tubular animals, which can reach lengths of 39 cm, have an extensible mouth called a proboscis that is lined with sharp hooks, teeth and spines.

Investigators discovered that the teeth had a scaly base and were fringed with tiny prickles and hairs. By reconstructing what the penis worm's teeth looked like, the researchers discovered fossil teeth from a number of previously unrecognised penis worm species all over the world. Because its teeth are less than a millimetre in size, researchers used high-powered microscopes to find out more about their structure.

The research has allowed scientists to compile a 'dentist's handbook', which will help paleontologists recognise a range of early teeth preserved in the fossil record, according to lead author of the palaeontology study Dr Martin Smith.