A half-a-billion-year-old fossil of an ancient creature with sharp claws, a hinged shell, and more legs than usually deemed necessary has been discovered in the Rockies of Canada. An early representative of mandibulates – the hyper-diverse group that contains not only insects, but crabs and millipedes – Tokummia katalepsis could help explain the origin of this wildly successful clade of arthropods.
Even though mandibulates are a vastly diverse group of animals in modern times, their evolutionary origin has largely remained shrouded in mystery. This latest find could help shed light on what the first arthropods with mandibles looked like and how they behaved as they swam through the warm tropical seas of the Cambrian period, picking off the early complex lifeforms with which they shared the waters.
The fossils were discovered in the rich Burgess Shale formation in the Canadian Rockies, which have turned out to be an incredible window into life 508 million years ago. The rocks have preserved in exquisite detail the soft tissue of a whole host of creatures that were swimming in the seas during the period of vast diversification called the Cambrian Explosion. Many of the fossil creatures uncovered represent the first examples of groups prevalent today.
With around 50 pairs of legs and subdivided limb bases displaying features called “endites”, the researchers suspect that the creature was mainly a bottom-dwelling animal that occasionally swam up into the water column, not unlike lobsters and mantis shrimps today. The creature was covered with a bivalved carapace, or a shell-like structure that split into two pieces. But the stand out features are the two pointy pincers projecting from the front.
How Tokummia fits into the evolutionary tree of arthropods. Royal Ontario Museum
“The pincers of Tokummia are large, yet also delicate and complex, reminding us of the shape of a can opener, with their couple of terminal teeth on one claw, and the other being curved towards them,” explains Cédric Aria, who led the study published in Nature, in a statement. “But we think they might have been too fragile to be handling shelly animals, and might have been better adapted to the capture of sizable soft prey items, perhaps hiding away in mud.”
Once the prey had been captured, the researchers think that the soft flesh would have been passed under the shell, to be torn apart and consumed by the mandibles – a revolutionary tool that may have helped the creatures go on to dominate the diverse range of environments they still inhabit today.
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