Researchers have uncovered the oldest known example of an evolutionary arms race in the fossil record, dating back 517 million years. These ancient predator-prey interactions took place in the ocean that once covered what is now South Australia.
The study, led by the American Museum of Natural History, reveals the dynamic between a small, shelled creature known as Lapworthella fasciculata and an unknown marine predator capable of piercing its hard shell. The interactions between these species provide the first demonstrable record of an evolutionary arms race during the Cambrian period, a time of rapid diversification in early animal life.
"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," said Russell Bicknell, a postdoctoral researcher in the museum's Division of Paleontology and lead author of the study. "Yet, there has been a paucity of empirical evidence showing that prey directly responded to predation, and vice versa."
An evolutionary arms race occurs when predators and prey continuously adapt and evolve in response to each other. As one species develops improved abilities, the other evolves countermeasures, leading to ongoing cycles of adaptation.
Bicknell and colleagues from the University of New England and Macquarie University examined more than 200 fossilized shells of Lapworthella fasciculata. The specimens, ranging in size from slightly larger than a grain of sand to just smaller than an apple seed, displayed holes likely made by a hole-punching predator, possibly a soft-bodied mollusk or worm.
Analyzing the specimens' geological ages, the researchers found that as the number of perforated shells increased over a short period, so did the thickness of the shell walls. This suggests that Lapworthella fasciculata developed thicker shells to fortify against predation. In turn, the predator invested in the ability to puncture the thicker armor, indicating that a microevolutionary arms race was underway.
"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 said.
The findings, described in the journal Current Biology, offer new insights into how early animal life evolved through interactions between predators and prey. The study highlights the significant role predation played in driving evolutionary changes during a pivotal time in Earth's history.
The research was funded in part by the University of New England, the American Museum of Natural History, and the Australian Research Council.
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