When a pesky pest is trying to bore its way into your home, the natural reaction is to build a stronger defense to keep it out.
According to a new study based on fossils from the Cambrian, this is what evolved to happen between two species of sea creature in the ocean covering what is now South Australia over 500 million years ago, making it the oldest known example of a predator-prey “arms race".
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Researchers from the American Museum of Natural History say the fossil record reveals a 517-million-year-old predator-prey relationship that occurred between a small shelled animaldistantly related to brachiopods and an unknown marine animal capable of piercing its shell. It is the earliest demonstrable record of an evolutionary arms race.
What is an evolutionary arms race?
An evolutionary arms race is a process in which predators and prey continually adapt and evolve to outsmart each other. In this case, it was a shelled marine creature versus a predatory soft-bodied worm or mollusk.
“Predator-prey interactions are often touted as a major driver of the Cambrian explosion, especially with regard to the rapid increase in diversity and abundance of biomineralizing organisms at this time. Yet, there has been a paucity of empirical evidence showing that prey directly responded to predation, and vice versa,” said Russell Bicknell, a postdoctoral researcher in the Museum’s Division of Paleontology and lead author of the study.
Bicknell and colleagues from the University of New England and Macquarie University – both in Australia – studied a large sample of fossilised shells of an early Cambrian tommotiid species, Lapworthella fasciculata, from South Australia. More than 200 of these extremely small specimens, ranging in size from slightly larger than a grain of sand to just smaller than an apple seed, have holes that were likely made by a hole-punching predator—most likely a kind of soft-bodied mollusk or worm.
How did the shell develop better defenses?
The researchers analysed these specimens in relation to their geologic ages, finding an increase in shell wall thickness that coincides with an increase in the number of perforated shells in a short amount of time. This suggests that a microevolutionary arms race was in place, with L. fasciculata finding a way to fortify its shell against predation and the predator, in turn, investing in the ability to puncture its prey despite its ever-bulkier armour.
“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 modifications arose during the Cambrian Explosion event,” Bicknell says.