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Global Warming Led to Shrinkage of Early Mammals—Twice

About 55 million years ago, the Earth went through a series of global warming events—within 20,000 years, global temperature raised up for 6°C. During this period, the early horses called Hyracotherium, experienced a body-size decrease of about 30%. Scientists believe that the shrinkage in body size results in an increase in surface area to volume ratio and hence it can accommodate an enhanced heat dissipation.


An image of modern-day Morgan horse with height of 145~157 cm. *Image source: Wikipedia.


An image illustrating the body size comparison between the early horse Hyracotherium (right) and a modern-day Morgan horse (left). *Image source: Danielle Byerly/University of Florida

Now, another study has proved that mammalian “dwarfing” was not occurred solely on horses. Recently, researchers from the United States noted that around 53 million years ago, there was a separate, smaller global warming event, comparing with that occurred 200 million years ago. This new finding was presented at the annual meeting of the Society of Vertebrate Paleontology.

Researchers investigated and collected teeth and jaw fossils of early hoofed mammals and primates that spanned this later climatic event in Wyoming’s Bighorn Basin. Using the size of molar teeth as an evaluation standard, researchers found that during that period, mammals including deer and some small primates had decreased body size and Hyracotherium experienced another shrinkage—its body size decreased by approximately 22%. When the Earth stopped heating, these mammals recovered to their original body size again.

It should be noted that these two global warming were both initiated by the dramatic increase in carbon dioxide in the atmosphere—a situation we are facing in the present day. Maybe it is time for our body to shrink, are you ready?


PS:  Future human: What? It’s HOT!

Source: University of New Hampshire