The penis worm, also known as Ottoia prolifica, is infamous in the animal kingdom for its gruesome features, not least of which is the worm's razor-like teeth located around its throat.

This unique dental structure is what scientists are now trying to study in order to identify fossil specimens dug up from the time when animals first evolved.

In a research published in the journal Palaeontology, scientists from the University of Cambridge and the University of Leicester in the United Kingdom studied the internal structure of the penis worm's teeth through the use of electron microscopy.

The researchers believe this dental structure first developed during what was called the Cambrian explosion, wherein many animal groups experienced a rapid period of evolution.

The penis worm's ancestors during the Cambrian period, called priapulids, had different shapes of teeth formed for different functions. Some teeth were shaped like bear claws, while others looked like cones. Scientists have also seen teeth in various sizes that resembled the skyline of a city.

The researchers analyzed Ottoia fossils recovered from the Burgess Shale in Canada. The area is known to be the richest source of fossils from the Cambrian period in the world.

According to their findings, many of the animals that existed during the Cambrian period had soft bodies, which is why only a few fossils have been included in the fossil record. This makes it difficult for researchers to figure out the total extent of the species distribution across the world at that period.

Dr. Martin Smith, one of the researchers from the Department of Earth Sciences in Cambridge, explained the difficulty in recovering fossils of soft-bodied specimens.

He said that the teeth of animals are the most common fossils since they are the hardiest and most resilient part of their bodies. Scientists, however, often misidentify these fossils as algal spores because the teeth only measure about one millimeter long.

Smith added that the study of the penis worm's dental structure has allowed the researchers to better identify a wide range of mysterious fossils.

"Teeth hold all sorts of clues, both in modern animals and in fossils," the Cambridge researcher said.

"It's entirely possible that unrecognized species await discovery in existing fossil collections, just because we haven't been looking closely enough at their teeth, or in the right way."