Cambrian Carnivore was Just an Old Softy

Drat. Another prehistoric predator loses the vicious duende required to inspire a Syfy Original monster movie.

Anomalocaris canadensis, the top predator from the middle Cambrian Burgess Shale of British Columbia, pencil drawing, digital coloring. The "tail fins" in this reconstruction should be placed ventrally (on top of the organism), and not at the rear as illustrated. (Credit: Nobu Tamura)

Pictured is Anomolacaris canadensis, the “unusual Canadian shrimp,” one of the more memorable Cambrian critters fossilized in the Burgess Shale and beloved to many of us who came to learn about it through Stephen Jay Gould’s book Wonderful Life. This proto-arthropodal creature undulated through shallow seas more than a half-billion years ago, and at nearly a meter in length was a giant of its time. It has sometimes been called the “first super predator” because Anomalocaris was commonly imagined to swoop in on trilobites crawling across the seabed, sweeping them up with that front pair of limbs and stuffing them into its circular jaws on the bottom, where its plated esophagus would crunch the prey’s shells bits. (Visit The Anomalocaris Homepage, now out of date, for more.)

Unfortunately, the latest analysis pokes a serious hole in this picture: it turns out that Anomalocaris lacked mouthparts hard enough to chew up trilobites or other arthropods. James Hagadorn of the Denver Museum of Nature & Science examined the fossilized mouthparts of more than 400 specimens of Anomalocaris and noticed that none of them showed any signs of wear, which was odd because a lifetime of grinding through trilobites should have left plenty of scratches, chips and abrasions. Moreover, unlike trilobite shells, the Anomalocaris mouthparts were not mineralized, suggesting that they were relatively soft and flexible, and not at all up to the job of helping the animal eat such hard prey. (Imagine trying to gum your way through a live lobster.)

A clincher was that when Hagadorn created a 3-D computer model of Anomalocaris‘s sphincter-like mouth, he found that although it was capable of generating a suction force, the mouth couldn’t even fully close. Hagadorn notes that Anomalocaris might have been able to suck and consume some very small trilobites whole, or to eat freshly molted trilobites whose cuticle had not yet hardened, but for the most part, this supposed super predator would have been unable to chew its food.

Hagadorn presents his work today at the Geological Society of America’s annual meeting. (GSA press release here; abstract for Hagadorn’s presentation here.)

So… feh. There go my dreams of convincing monster-movie schlockmeister Roger Corman, the man behind Sharktopus, to make a movie about giant predatory anomalocarids. Naturally, we would have needed to call them something different in the title. I was leaning toward Roger Corman’s Trilobiter! But maybe I can still salvage something. If they were shiny and sucked at their prey, like romantic Cambrian vampires, and if a mopey teenage paleontologist fell in love with one… hmm….

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