Bizarre, Spiked, Worm-Like Creature from Prehistory Discovers Its Place in Evolution

A bizarre, worm-like creature with legs, spikes and a head difficult to tell apart from its tell has officially found its place in the evolutionary Tree of Life. Scientists have taken a closer look at a fossil of this ancient animal and have linked it to modern velvet worms.

The animal in question is known as Hallucigenia. Long considered an "evolutionary misfit," researchers have wondered exactly where to place it in the grand scheme of evolution. Until now, this animal and other "legged words," or lobpodians, have lacked an evolutionary home to do a dearth of evidence.

Hallucigenia lived about 505 million years ago during the Cambrian Explosion, a period of rapid evolution when most major animal groups first appeared in the fossil record. It possesses a row of rigid spines along its back and seven or eight pairs of legs ending in claws. They lived on the floor of the ocean and are actually related to modern velvet worms.

"It's often thought that modern animal groups arose fully formed during the Cambrian explosion," said Martin Smith, lead author of the new paper, in a news release. "But evolution is a gradual process: today's complex anatomies emerged step by step, one feature at a time. By deciphering 'in-between' fossils like Hallucigenia, we can determine how different animals groups built up their modern body plans."

The researchers analyzed both prehistoric and living creatures, examining Hallucigenia and velvet worms. In the end, they found that the claws on Hallucigenia were the connection joining them to velvet worms.

"An exciting outcome of this study is that it turns our current understanding of the evolutionary tree of arthropods-the group including spiders, insects and crustaceans-upside down," said Javier Ortega-Hernandez, co-author of the new paper. "Most gene-based studies suggest that arthropods and velvet worms are closely related to each other; however, our results indicate that arthropods are actually closer to water bears, or tardigrades, a group of hardy microscopic animals best known for being able to survive the vacuum of space and sub-zero temperatures-leaving velvet worms as distant cousins."

The findings are published in the journal Nature.