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Shell-Crushers Perfected Feeding During the Cambrian

Evolution has explored many approaches to eating prey, and discarded almost as many, but one group of marine arthropods optimised the biomechanics of their feeding structures more than half a billion years ago according to a study published in Proceedings of the Royal Society B (

Scientists at the University of New England used advanced computational 3D modelling to compare a modern shell-crushing arthropod, the American horseshoe crab, with a 508-million-year-old fossil species (Sidneyia inexpectans) that also fed on shelled organisms found on the ocean floor. Study leader Dr Russell Bicknell says that “the biomechanical performance of their feeding structures is very similar. If anything, the modern horseshoe crab has slightly reduced performance over its ancient relative.

“The rapid emergence of a species so well-adapted to eating shelly animals shortly after shell-bearing creatures appeared is evidence of one of evolution’s earliest arms races – one in which evolution converged upon an optimum shell-crushing solution very early on, during the Cambrian Explosion.”

The team employed 3D Finite Element Analysis to predict how stresses and strains are distributed through appendages used for mastication, such as the gnathobases, which function like teeth and are capable of crushing shelled prey.

After modelling the fossil species’ shell-crushing ability, and noting that Sidneyia fossils sometimes preserve the shelly gut contents of juvenile trilobites and other thin-shelled creatures, the researchers proposed that Sidneyia was one of the Earth’s first shell-crushers and “potentially drove selection for more fortified shells or other novel defences in biomineralized prey” during the Cambrian Explosion.