Evolutionary Misfit Finds a Home

I like to imagine Hallucigenia, a tiny, um, thing-like prehistoric animal that scientists first found baffling fossils of in the 1970s, singing a jaunty personalized version of “We’re a Couple of Misfits” from Rudolph the Red-Nosed Reindeer as it went about its underwater day 505 million years ago during the Cambrian Explosion.

Why am I such a misfit?
I am not just a nit wit!
I’m an adorable something
Why don’t I fit in?

I imagine this because I am much too prone to whimsy. But also because try as they might, scientists could not place this evolutionary weirdo anywhere that made sense with modern animal groups. But now Hallucigenia has found a home, and is a misfit no more.

Scientists at the University of Cambridge have found a link between the ocean-dwelling Hallucigenia and modern velvet worms, a small group of animals that live in tropical rain forests.

Hallucigenia was discovered in Burgess Shale in Canada’s Rocky Mountains and was so named because it looked weird and people did a lot of acid in the 70s. Part of the confusion about its origins is because when scientists first discovered Hallucigenia they read the fossils upside down. Hallucigenia has a row of spines on its back that were mistaken for legs, clawed legs that were mistaken for tentacles, and a head that was mistaken for a tail.

But the new study for the first time looked closely at Hallucigenia’s claws, and found them very similar to the jaws of velvet worms. Velvet worm jaws are simply legs modified for chewing, and they share with Hallucigenia legs a similar structure in which layers of cuticle, a hard substance like your fingernails, are built up in a “Russian nesting doll” pattern.

And just like that, Hallucigenia finds a place to fit in the evolutionary tree.

“It’s often thought that modern animal groups arose fully formed during the Cambrian Explosion,” said Dr Martin Smith of the University’s Department of Earth Sciences, the paper’s lead author. “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 animal groups built up their modern body plans.”

[Source: University of Cambridge]

Images: Recreation of Hallucigenia sparsa by Stanton F. Fink via Wikimedia Commons, Hallucigenia sparsa fossil via University of Cambridge; Velvet worm posted by chvictor on photography-on-the.net/