The Biggest Prevail. New Research Shows Marine Animals Keep Evolving to Larger Sizes

Survival of the fittest? More like survival of the biggest. New research is out this week showing the average size of marine animals has increased 150-fold over the past 542 million years.

This new research supports Cope’s rule, a theory that says animal lineages tend to evolve to be bigger over time. So, I’m just evolving too right?

“We’ve know for some time now that the largest organisms alive today are larger than the largest organisms that were alive when life originated or even when animals first evolved,” said Jonathan Payne, a paleobiologist at Stanford.

Noel Heim, a postdoctoral researcher who assisted Payne, used a sea urchin as an example for describing the 150-fold increase in average size. “That’s the size difference between a sea urchin that is about 2 inches long versus one that is nearly a foot long,” said Heim. “This may not seem like a lot, but it represents a big jump.

Scientists had to figure out if this increase in size was part of a larger trend in body size evolution. Payne said a complete look at marine species was necessary to determine if evolution was responsible. Just looking at today’s specimens or looking back over shorter periods of time would not be enough. “You will absolutely be wrong about the rate, and possibly also the direction,” according to Payne.

Researchers found the increase was not due to every species getting bigger. Groups of marine organisms that became more diverse were the ones that saw the biggest growth.

Heim and his fellow researchers looked at more than 17,000 samples. A Stanford press release highlights what they found:

A pattern soon became apparent: Not all classes – groups of related species and genera – of animals trended toward larger size, but those that were bigger tended to become more diverse over time. The team suspects this is due to advantages associated with a larger size, such as the ability to move faster, burrow more deeply and efficiently in sediment, or capture larger prey.

“It’s really a story of the survival and diversification of big things relative to small things,” Heim said.

You can check out the full study in the journal Science.

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