Giant prehistoric shrimp had the weirdest mouth of the Cambrian periodS

500 million years ago, the meter-long Anomalocaris roamed the Cambrian seas. Researchers once thought that Anomalocaris crushed trilobites with their teeth, but recent fossil analysis suggests something a lot stranger.

When paleontologist James Hagadorn of the Denver Museum of Nature & Science noticed that Anomalocaris remains lacked fossilized digestive remains or feces, his team began investigating how the Anomalocaris' jaws worked. Hagadorn's team studied 400 Anomalocaris specimens — not only did these fossilized mouths lack wear and tear, they also suggested that Anomalocaris could barely crack shelled prey. From the Geological Society of America:

"It was supposed to roam around the Cambrian seas gobbling up trilobites and everything else," said Hagadorn. But the pineapple-like whorl of mouth parts and the associated whisker-like appendages of Anomalocaris all appear to have been bendable, in the fossil remains, he said. They are not mineralized like the exoskeletons of the trilobites they were supposedly eating.

His suspicions prompted Hagadorn to develop a 3-D, finite element analysis model of the Anomalocaris mouth. This allowed for testing just how the mouth worked and how much force it could create – in other words, how strong a bite it had. The model turned up some surprises.

"It couldn't even close its mouth," said Hagadorn. And there was no practical way these mouth parts could create the force needed to break open a modern lobster shell nor a shrimp shell, which were used as analogues for a trilobite carapace in the model.

It's unclear how Anomalocaris fed, but researchers now suspect that the creature either ground up its food or regurgitated it. In any case, this nightmare of the primeval oceans has been knocked down a peg.

[Via The Geological Society of America. Top image is Anomalocaris by John Sibbick via Paleo King.]