Though the earth is experiencing its first bout of human-induced climate change, the planet has faced massive global warming events in the past. For instance, 56 million years ago, the earth was 46 degrees hotter on average than it is right now. And in response, mammals literally shrank. Imagine an early horse ancestor the size of a cat.

Abigail D’Ambrosia, a researcher at the University of New Hampshire, did a study with scientists at the University of Michigan to see if mammals experience this kind of “dwarfing” during other, less-intense periods of warming — like the one happening now. The short answer: “Yup — there’s definitely dwarfing in a couple of the mammals we found,” D’Ambrosia says. “There is the red deer that’s showing a decrease in body size. And there is the California squirrel that is showing a reduced body size, more in correlation to reduced precipitation.”

D’Ambrosia has a few theories about why this might be the case. Maybe it’s easier for animals to cool themselves off if they’re smaller. Or maybe global warming killed off so many plants, the animals didn’t get enough food.

Whatever the reason, she says it’s happening again. However, there is one important difference between this and past periods of climate change. Today, the warming is happening at a faster rate. D’Ambrosia says during the last massive global warming period, few mammals actually went extinct. But now, some animals might not have enough time to adapt.

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This story comes from our partners at Michigan Radio's Environment Report, a program exploring the relationship between the natural world and the everyday lives of people in Michigan.