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"Heat Shrink" -- The Discovery Files

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Mammal body size decreased significantly during at least two ancient global warming events, a finding that suggests a similar outcome is possible in response to human-caused climate change, according to a University of New Hampshire paleontologist and his colleagues.

Credit: NSF/Karson Productions

Audio Transcript:

Global dwarfing?

I'm Bob Karson with the discovery files--new advances in science and engineering from the National Science Foundation.

As we size up the possible effects of global warming, size could be one of them. Scientists know that mammals became much smaller during a period of warming about 55 million years ago, when global temperatures spiked about 9 to 14 degrees. Now, a team led by the University of New Hampshire has found evidence of another shrinking--two million years later, when temps jumped about five degrees.

The researchers studied teeth and jaw fossils of early hoofed mammals and primates from this second warming period. They found that significant dwarfing occurred, though not as much as in the previous, more intense warming. An example, in an early horse, a body-size decrease of 30 percent during the first warming, and 19 percent during the more mild one (Sound effect: tiny horse sound) whoa, my little pony!

The scientists believe that since the shrinking occurred during both periods, there's a likely cause-and-effect relationship. As the warming subsided, species rebounded to their earlier sizes. The team theorizes that dwarfing could be an evolutionary response to the warm periods' elevated CO2 levels, which cause plants to grow quickly but be less nutritious.

They say the findings suggest the possibility of a similar response to modern-day global warming. It's kind of like looking in a rear-view mirror: "Mammals are smaller than they appear."

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