Carroll said it wouldn't surprise her if free-roaming horse populations began to show signs of decreased body size as scientists have already documented climate-induced body size change in some wild mammal populations, from the red deer in Europe to the California squirrel. | Photo: iStock

As far back as 50 million years ago, horses figured out that bigger isn’t always better. Researchers have learned that many mammals—horses included—adapted to climate change by getting smaller.

By requiring less nutrition and water to survive and by having more surface area compared to their general size to better “air themselves out,” smaller horses and other mammals can adapt to hotter climates, said Abigail (D’Ambrosia) Carroll, a PhD candidate in the Earth and Environmental Sciences Department at the University of New Hampshire, in Durham.

During recent periods of global warming (56 and 53 million years ago) horses either migrated or evolved to exist as smaller species, Carroll said. In fact, the greater the temperature increase, the smaller the horses got. They might have adapted over many generations to become smaller than their predecessors. Or, already existing smaller horses might have migrated into areas once inhabited by larger horses