A fossil considered one of the oddest ever found may finally have its proper place in evolutionary history. New research conducted at the University of Cambridge in England links the weird legged worm known as Hallucigenia to modern velvet worms, wormlike animals that live in tropical forests.
The research comes after decades of confusion and may settle a longstanding debate over how to classify Hallucigenia, which lived on the ocean floor more than 500 million years ago before becoming extinct. When Hallucigenia fossils were first discovered in the 1970s, scientists had a hard time figuring out just what they were looking at. The appendages now known to have been spines along the creature's back were originally thought to have been legs, and the animal's actual legs were believed to have been tentacles along its back.
How did scientists manage to link a creature long considered an "evolutionary misfit" to velvet worms?
Hallucigenia's claws were the "smoking gun," Dr. Martin Smith, a scientist in the university's department of earth sciences and the lead author of a paper describing the new research, said in a written statement. The claws are similar to those of velvet worms, with layers of cuticle stacked together like Russian nesting dolls.
"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," study co-author Dr. Javier Ortega-Hernandez, said in the statement. "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," microscopic water-dwelling animals.
Now you know.
The paper was published online in the journal Nature on August 17, 2014.