517-Million-Year-Old Cambrian Fossils Indicate Earliest Known Example of Predator-Prey 'Arms Race'

Scientists have found evidence of the most ancient evolutionary arms race, 517 million years old, and a study about it was published in Current Biology. That remarkable finding brought to light very ancient predator-prey interactions between a small, shelled marine creature and an unknown predator that was able to pierce its protective armor.

The lead researcher of this study, Russell Bicknell from the American Museum of Natural History, and his colleagues studied hundreds of these fossilized shells found in South Australia's Flinders Ranges. These tiny creatures, known as Lapworthella fasciculata, were the first tangible evidence of predation as one of the drivers of evolutionary innovation during the Cambrian period. This discovery demonstrates that "predation played a pivotal role in the proliferation of early animal ecosystems," said Bicknell, a postdoctoral researcher in the Museum's Division of Paleontology, as per Cosmos. The researchers found more than 200 shells bearing the telltale signs of the predators' work in the form of circular holes likely made by a soft-bodied mollusk or worm.

This pattern is important because a clear trend of adaptation is observed in the fossil record. As the number of punctured shells increased over time, the scientists found that L. fasciculata developed thicker shell walls to ward off the attacks. In turn, the predator evolved stronger methods to breach the tougher shells, creating a textbook example of an evolutionary "arms race." This finding agrees with the Cambrian explosion—a period between 541 and 485 million years ago that saw an unparalleled rise in evolutionary diversity. Although scientists had long suspected that predator-prey dynamics fueled this diversification, actual proof had been scant until recently.

These fossils, which range in size from that of a grain of sand up to just smaller than an apple seed, offer a fascinating glimpse into ancient survival strategies. The fact that the diameter of the holes generated by the predator is consistent implies that while the predator did not grow larger, it developed its facility to punch through more robust defenses. This ancient arms race parallels better-known modern examples in nature, such as the coevolutionary race between venomous snakes and resistant prey or the evolution of drug resistance among bacteria.

This research, in collaboration with the University of New England and Macquarie University in Australia, used scanning electron microscopy to closely gauge shell thickness, damage patterns, and other aspects associated with predation. The study was funded by the University of New England, the American Museum of Natural History, and the Australian Research Council.

More than just shining a light into ancient ecological processes, these findings give quite a lot of insight into how predation pressures shape life on Earth continuously up to the present. The findings represent new pathways through which one can come to understand the complicated dynamics that drove the Cambrian explosion, which was able to pave the way for today's rich biodiversity in oceans.