Ancient Fossil Termed 'Evolutionary Misfit' Was An Ancestor Of Velvet Worms: Study

An ancient fossil, discovered in the early 1900s and long considered an “evolutionary misfit,” finally found its rightful place in the tree of life after a team of scientists at the University of Cambridge linked it to the modern-day velvet worm, which is commonly found in tropical forests.

The aptly named Hallucigenia belonged to a group of animals that roamed the ocean floor over 500 million years ago. The earliest fossils of the creature, discovered in the Burgess Shale -- one of the richest fossil deposits in the world -- in Canada’s Rocky Mountains, depicted animals about 5 millimeters to 35 millimeters long, with a row of rigid spines along their backs and seven or eight pairs of legs ending in claws. The spines were originally thought to have been legs, and its actual legs were believed to have been tentacles along its back.

Due to its bizarre appearance, scientists had a hard time classifying Hallucigenia and it was initially placed both backwards and upside down so that its head was mistaken for its tail. It was also misidentified as an annelid worm, similar to today’s earthworms and leeches.

However, scientists from the University of Cambridge claim to have settled the long-standing debate over the animal’s classification in a paper published in the journal Nature.

“The peculiar claws of Hallucigenia are a smoking gun that solve a long and heated debate in evolutionary biology, and may even help to decipher other problematic Cambrian critters,” Martin Smith of the university’s Department of Earth Sciences and the paper’s lead author said, in a statement.

The statement added that though it was long suspected that Hallucigenia was an ancestor of velvet worms, definitive characteristics linking them together had been hard to find because their claws had never been studied in detail.

“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 animal groups built up their modern body plans,” he added.

Javier Ortega-Hernandez, the paper’s co-author, said that the outcome of the study “turns our current understanding of the evolutionary tree of arthropods – the group including spiders, insects and crustaceans – upside down...our results indicate that arthropods are actually closer to water bears, 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.”