Fossilized shells show big predators kept picking on small prey

Predators in the oceans grew significantly bigger 540 million years ago, while their prey became faster and trickier, according to a new study in Science.

It's one of the first pieces of evidence to support a popular evolutionary hypothesis that's been difficult to prove: the notion that, as predators evolve to become bigger and more powerful, the entire predator-prey relationship up and down the food chain also changes. Researchers were able to observe in the fossilized record how ocean predators increased in size over millions of years and how that drove more changes down the food web.

How they did it: Researchers studied the attack marks - known as "drill holes" - in 7,000 different fossilized shells from the Phanerozoic period 540 million years ago. During that era, they found that that the predators of these prey had all grown significantly bigger. Meanwhile, the prey had all remained the same size – though they had also become more mobile and better able to burrow in order to escape the ever-growing predators. Over the last 500 million years, the ratio between the size of marine predators and their prey increased 67-fold.