A new study by researchers at the American Museum of Natural History presents the oldest known example in the fossil record of an evolutionary arms race. These 517 million year old predator-prey interactions occurred in the ocean covering what is now South Australia between a small shelled animal distantly related to brachiopods and an unknown marine animal capable of piercing its shell. Described today in the newspaper Current biologythe study provides the first demonstrable record of an evolving arms race in the Cambrian.
Predator-prey interactions are often presented as one of the main drivers of the Cambrian Explosion, particularly with regard to the rapid increase in the diversity and abundance of biomineralizing organisms at this time. Yet there is little empirical evidence showing that prey respond directly to predation, and vice versa. »
Russell Bicknell, postdoctoral researcher, Division of Paleontology, American Museum of Natural History and lead author of the study
An evolutionary arms race is a process in which predators and prey continually adapt and evolve relative to each other. This dynamic is often described as an arms race, as the enhanced capabilities of one species lead the other species to improve their capabilities in response.
Bicknell and colleagues from the University of New England and Macquarie University—both in Australia—studied a large sample of fossilized shells from an Early Cambrian tommotiid species, Lapworthella fasciculatefrom South Australia. More than 200 of these extremely small specimens, ranging in size from a little larger than a grain of sand to a little smaller than an apple seed, have holes that were likely dug by a boring predator – probably some kind of soft body. mollusk or worm. The researchers analyzed these specimens based on their geological age and found an increase in shell wall thickness that coincides with an increase in the number of perforated shells in a short period of time. This suggests that a microevolutionary arms race was underway, with L. fasciculée finding a way to fortify its shell against predation and the predator, in turn, investing in the ability to pierce its prey despite its increasingly bulky armor.
“This critically important evolutionary record demonstrates, for the first time, that predation played a central role in the proliferation of early animal ecosystems and shows the rapid speed at which such phenotypic changes emerged during the Cambrian Explosion ” said Bicknell.
This research was supported in part by the University of New England, the American Museum of Natural History, and the Australian Research Council (Grant Nos. DP200102005 and DE190101423).
