Around 54 million years ago, when Earth suddenly got really hot, an ancient horse was about the size of a dog. Then it dwarfed, going down to the size of a cat.

This is no longer a distant possibility, as global warming continues on its course and affects various life forms on the planet, new research concludes.

Animals Could Shrivel In Extreme Heat

University of New Hampshire researcher Abigail D’Ambrosia, who led the study, warned that mammals could shrink in the future under even more accelerated man-made warming.

“It’s something we need to keep an eye out for. The question is how fast are we going to see these changes,” D’Ambrosia said in a statement.

The results are based on an analysis of fossilized teeth and jaw fragments obtained from northwestern Wyoming’s Bighorn Basin, located around 80 miles east of Yellowstone National Park. Measuring teeth is a good way to determine body size of adult mammals from bygone eras, D’Ambrosia explained.

She discovered mammal dwarfing during the largest ancient warming event that took place about 56 million years ago, which saw a temperature rise of 9 degrees Fahrenheit or more. Warm-blooded creatures shrank when carbon dioxide levels climbed and temperatures spiked to unprecedented levels.

The earliest squid, Sifrhippus, shrank by 30 percent at a minimum in the first 130,000 years of the warming event, but as the temperature gradually returned to normal levels, its body size was able to rebound by 76 percent.

An early compact horse called Arenahippus pernix became 14 percent smaller, moving from 17 pounds to just 14.6 pounds. From being approximately dog-like in built, it shrank to the size of a cat. The lemur-like primate Cantius abditus, on the other hand, shriveled around 4 percent — despite studies showing that the species typically got bigger over time.

Heating-Shrinking Relationship

The findings suggested that shrinking response to heightened climate change proportionately scales with the magnitude of the warming.

The small horse decreased by about 30 percent in the first warming event, while a different small horse shrank by 14 percent in the second event, which was approximately half as intense.

Scientists believe that body size plays a role in climate adaptation. Since they have more skin or fur per pound than their bigger counterparts, smaller animals can let more heat escape, thus they are better adapted for warmer environments. Larger animals, meanwhile, fare better in the cold since they have less skin per pound and better retain heat.

The finding that mammals shrink in warmer climates is no longer strange or surprising. As an example of the so-called Bergmann’s Rule, red foxes living in higher and cooler latitudes are larger in size compared to those residing closer to the equator.

Other reasons, however, may play a part in dwarfing. These could include the inability to get enough food or water.

Jonathan Bloch, Florida Museum of Natural History’s curator of vertebrate paleontology, said the results prove significant.

“If we start to see patterns repeat themselves, we can learn from that,” said Bloch, who wasn’t part of the research.

The findings were discussed in the journal Science Advances.

A separate study warned that climate change impact on birds and mammals are largely underreported. A team from University of Queensland in Australia found that nearly 700 birds and mammals have already responded to the changes in a negative way.