Scientists have compiled a 'dentist's handbook' of prehistoric penis worm teeth

Hidden deep in the Canadian Rockies of British Colombia, the Burgess Shale is the cradle of life for almost every animal that has ever existed. At over 500 million years old, it's a fossil field that preserves the tissue remains of some of the first complex organisms that ever inhabited the oceans.

With most of its body concealed, the Ottoia worm would lurk with just its enlarged head sticking out to ensnare passing prey. Image: Wikimedia Commons

Ottoia

Discovered by the palaeontologist Charles Walcott in 1909, the site is a treasure trove of weird and wonderful fossils that continues to surprise modern-day palaeontologists. One of the more common – and certainly one of the weirdest – organisms preserved here was Ottoia, a burrowing predator that belonged to a group of marine worms known as priapulids. Scientists also refer to these animals as penis worms, because, well, it's not hard to see why.

The predatory Ottoia would lurk with most of its body concealed in the seafloor, its enlarged head sticking out just enough to ensnare passing prey. Its mouth could evert (much like a goblin shark's), exposing a throat lined with tooth-like structures called sclerites, like a miniature cheese grater. We know that in modern priapulid worms, these toughened sclerites serve the animals during feeding, sensory activities and movement. They can even help scientists differentiate between different kinds of worms. But as it turns out, with a bit of help from a high-powered microscope, these tiny "teeth" (many of which are just several thousandths of a centimetre across!) can also tell us a lot about prehistoric life.

Thanks to the latest imaging techniques, a team of researchers led by Dr Martin Smith has been able to examine Ottoia "teeth" in unprecedented detail, revealing that these structures had a scaly base and were fringed with tiny prickles and hairs. Their research has resulted in something of a "dentist's handbook" for worm fossil hunters. "Taken together, it will help palaeontologists recognise a range of early teeth," Smith says. The study was published today in the journal Paleontology. "[In the past], these teeth were easily misidentified as algal spores, rather than as parts of animals. Now that we understand the structure of these tiny fossils, we are much better placed to find them."



The new research has revealed the "teeth" of the Ottoia worm in unprecedented detail. Image: Tom Harvey

Based on the features of various Ottoia "teeth", Smith was able to show that predatory worms like this were actually much more common in primeval Cambrian ecosystems than we thought. What's more, the team also confirmed that there was more than one species wriggling about: distinguished by three distinctive peaks on its teeth, a new species, Ottoia tricuspida, has now joined the long-known Ottoia prolifica, which was discovered over a century ago.

"Our new observations emphasize the importance of [studying] sclerites," says Smith, noting that even when the most advanced technology is at your fingertips, the soft bodies of worms are rarely preserved in enough detail to allow experts to distinguish one species from another. Unlike soft tissues that deteriorate quickly, the hard tooth-like sclerites stand up to the test of time, giving scientists information that would otherwise be impossible to deduce.

The new research also highlights how technology can provide insight into the diversity of prehistoric ecosystems – even ones we have studied for years. By applying what they had learned from their Burgess Shale finds to fossils unearthed in other parts of the world, the researchers were able to uncover previously unidentifiable specimens of these “toothed” worms. It turns out that rather than being restricted to ecosystems like the one preserved at Burgess Shale, Ottoia worms were more cosmopolitan, able to live in a range of very different environments, including localities in Australia and China.

"Unrecognized fossil species may well await discovery in [other] existing fossil collections," adds Smith.