Animals came about 600 million years ago. But they weren’t like the animals we typically envision today—the first animals were microscopic and gleaned their energy for life by simple means. The amount of diversity existing on Earth for the first 200 million years of animal existence couldn’t hold a candle to the kind we see today.
But 540 million years ago, an intense eruption of diversity occurred on Earth: the Cambrian Explosion. A novelty came about during this period for which scientists have long pondered the origin: the carnivore.
A new study in Proceedings of the National Academy of Sciences offers an explanation for the origin of carnivores.
Erik Sperling from Harvard University led the study, which analyzed modern environments with varying levels of oxygen and compared them to what scientists believe Precambrian and Cambrian ocean habitats looked like in terms of oxygen levels. Right before the Cambrian Explosion, the oxygen levels on earth were only about 1 to 10 percent of those that exist now. But soon after, atmospheric oxygen levels shot up.
Sperling’s team found that the amount of oxygen in modern environments is directly related to the abundance of carnivores– environments low in oxygen have few carnivores, some none at all. The areas with the least amount of oxygen have the lowest amount of biodiversity. These regions house very basic life forms—microbes and small animals that feed on detritus or bacteria that resemble fossils from the Precambrian.
Not only do the numbers of carnivores correlate with the presence of oxygen—so do the size of meat-eating animals. The more oxygen molecules floating around in the atmosphere, the bigger the carnivores in that area are.
When oxygen levels rose during the Cambrian, larger animals could retain more energy and developed the ability to stalk down, catch, and consume smaller animals. Carnivorous behavior began when small animals started chomping down on even smaller plankton. Bigger carnivores soon evolved, with more complex body forms and specialized predator characteristics—such as jaws and teeth for biting and stronger and faster limbs for catching prey. The prey, lagging just a bit behind carnivores, began evolving too: hard shells, spikes, needles, poisonous appendages, and bad-tasting exteriors developed.
Read the entire study in the journal Proceedings of the National Academy of Sciences.
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