A restoration of Yawunik kootenayi, an early arthropod.
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Art by Lars Field/Phlesch Bubble.
A restoration of Yawunik kootenayi, an early arthropod.

Scientists Uncover Yet Another Cambrian Weirdo

There is nothing wrong with your monitor. Do not attempt to adjust the picture. The creature at the top of this post isn’t an April Fool’s joke, nor is it a Lovecraftian nightmare. Named Yawunik kootenayi, the archaic arthropod is a real animal that undulated through Earth’s seas 508 million years ago.

Following hot on the heels – or is that fins? – of the filter-feeder Aegirocassisthe filter-feeder AegirocassisYawunik is the latest ancient invertebrate to make us ask “What the heck is that thing?” Described by paleontologists Cédric Aria, Jean-Bernard Caron, and Robert Gaines from 42 fossils found in Canada’s Kootenay National Park, the Cambrian critter adds to the wonderful and perplexing spread of body plans that had evolved by this chapter in Earth’s history – jutting out from beneath the invertebrate’s tough exoskeletal hood are paired, pinching appendages arrayed with long wisps. The overall effect is of a lobster tail that’s out for revenge on those who drew butter against it.

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A specimen of Yawunik embedded in stone. Image via the University of Toronto.

At the time that Yawunik swam around delivering deadly pinches to worms and other small prey, though, there weren’t lobsters yet. Aria, Caron, and Gaines propose that Yawunik belonged to a lineage of invertebrates called leanchoiliids – a group so obscure they don’t even have a Wikipedia page summarizing what they are – that fit near the base of the arthropod family tree. This doesn’t mean that Yawunik was an ancestor to today’s insects, crustaceans, and arachnids, but rather that it was part of an evolutionary explosion from which the true arthropod ancestors emerged.

Fossils provide the only views of such startling species. Without the exquisite preservation of the Burgess Shale, we wouldn’t be able to puzzle over Yawunik and its bizarre neighbors. That’s the wonderful thing about paleontology. You can’t make this stuff up.


Aria, C., Caron, J., Gaines, R. 2015. A large new leanchoiliid from the Burgess Shale and the influence of inapplicable states on stem arthropod phylogeny. Palaeontology. doi: 10.111/pala/12161