A new study has revealed that the size of prey has remained the same even though the size of marine invertebrates has increased over the last 500 million years.
By analyzing the attack marks on fossilized shells of marine prey, researchers discovered that the size of predators have increased over the last 500 million years, even though the size of their prey has stayed constant.
Nevertheless, the prey species evolved by developing new behavioral trends, like becoming more mobile and increasing their motility, burrowing or defensive abilities. This finding supports the escalation hypothesis, which proposes that top-down pressure from increasingly powerful predators can lead to evolutionary trends in the prey.
The research team, with lead author Adiël A Klompmaker from the University of California, Berkeley, arrived at this finding after studying the attack marks (or drill holes) in fossilized shells of various species of prey from the Phanerozoic period, which spans the past 540 million years. They discovered that although the median shell size of prey remained more or less constant, the median drill-hole diameter increased from 0.35 to 3.25 millimeters, indicating a significant increase in the size of predators.
According to the researchers, the increase in the predator-prey size ratio is driven by changes in the energetic structure of marine ecosystems, where marine predators had to eat more to satisfy their growing body size and appetites.