An extinct, cone-shaped creature of the deep that lived some 540 million years ago now has a definitive place on the tree of life, 175 years after it was first discovered.

Researchers from the University of Toronto (UT), in a new study in the journal Nature, say they have found a taxonomic home for the hyolith, a cone-shaped marine animal that had stubbornly resisted definitive classification.

Hyoliths were part of the "Cambrian Explosion" of animals that took place more than 500 million years ago. They diversified and spread themselves out to marine ecosystems everywhere, holding on until about 252 million years ago, when they went extinct.

The animals had long, conical shells and a smaller shell that functioned as a kind of cap to cover the long shell's opening.

The creature was commonly considered to be within the same family as squid and snails, until more than 1,500 specimens from the famed Burgess Shale fossil site in British Columbia showed otherwise.

The specimens examined by the UT researchers had something in their favor that allowed the animal to finally be classified, something characteristic of Burgess Shale fossils: well-preserved soft tissue.

The tissue allowed the scientists to identify a feeding structure on the animal that featured a group of tentacles protruding out from the mouth. The feeding apparatus is called a lophophore, and the scientists say it is found in only one other place today: brachiopods, small marine animals – 0.04 to just under 4 inches long – with hard shells (valves) top and bottom and a hinged opening for feeding time.

"Only one group of living animals - the brachiopods - has a comparable feeding structure enclosed by a pair of valves. This finding demonstrates that brachiopods, and not mollusks, are the closest surviving relatives of hyoliths," said study lead Joseph Moysiuk in a statement.

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The find also told the scientists how the creature ate its meals. "It suggests that these hyoliths fed on organic material suspended in water as living brachiopods do today, sweeping food into their mouths with their tentacles," Moysiuk said.

Now, a marine animal that was once "an orphaned branch on the tree of life," according to co-author Jean-Bernard Caron, has found its place.

"Resolving the debate over the hyoliths adds to our understanding of the Cambrian Explosion, the period of rapid evolutionary development when most major animal groups emerge in the fossil record," said co-author Martin Smith.

Top Photo: This illustration shows the hyolith Haplophrentis extending the tentacles of its feeding organ (lophophore) from between its shells. The paired spines, or "helens," are rotated downwards to prop the animal up off the ocean floor. Credit: Artist: Danielle Dufault. © Royal Ontario Museum

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