Imma Perfetto
Cosmos science journalist
The oldest-known fossil evidence of a predator-prey arms race has been discovered in shells dating back to the early Cambrian.
The species, Lapworthella fasciculata, was a small, shelled animal distantly related to brachiopods. It lived in an ocean covering what is now South Australia and was hunted by a mysterious predator that could punch holes its shell.
A new study in the journal Current Biology has revealed that L. fasciculata adapted to this predation by reinforcing its shell. In turn, its killer – most likely a kind of soft-bodied mollusc or worm – responded by increasing its own ability to pierce shells.
“Predator-prey interactions are often touted as a major driver of the Cambrian explosion,” says Russell Bicknell, a researcher at the American Museum of Natural History and Australia’s University of New England and Macquarie University.
“Especially with regard to the rapid increase in diversity and abundance of biomineralising organisms at this time,” he says. Biomineralisation is the process by which living organisms form hard mineral structures, such as teeth, bones, coral and shells.
But there has been a lack of empirical evidence showing that prey directly responded to predation, and vice versa, during the Cambrian explosion until now.
The new study provides the first evidence of an early Cambrian “evolutionary arms race” where predators and prey continuously adapted to and evolved in response to each other.
Bicknell and collaborators studied a sample of L. fasciculata specimens from South Australia’s Flinders Ranges. The shells range in size from slightly larger than a grain of sand to just smaller than an apple seed. More than 200 of them had circular holes punched into them.
Analysing the shells’ ages reveals an increase in thickness of the shell wall over a short period of time, which coincided with an increase in the number of perforated shells.
Because the diameters of the holes remained consistent, this suggests that the body size of the predator remained unchanged. Instead, increasingly effective hole-punching capabilities would have driven the shell thickening in L. fasciculata.
“This critically important evolutionary record demonstrates, for the first time, that predation played a pivotal role in the proliferation of early animal ecosystems and shows the rapid speed at which such phenotypic [physical] modifications arose during the Cambrian Explosion event,” says Bicknell.
