Early horses shrunk in size due to warming climate

Direct evidence has been discovered about how mammals’ sizes respond to rise in temperatures.

Washington: Direct evidence has been discovered about how mammals’ sizes respond to rise in temperatures.

In a study, researchers from eight institutions, led by scientists from the University of Florida and University of Nebraska, followed the evolution of the earliest horses about 56 million years ago and found a correlation between temperature and body size in mammals. They saw that as temperatures increased, the animals’ sizes decreased.

“Horses started out small, about the size of a small dog like a miniature schnauzer,” said co-author Jonathan Bloch, associate curator of vertebrate paleontology at the Florida Museum of Natural History on the UF campus.

“What’s surprising is that after they first appeared, they then became even smaller and then dramatically increased in size, and that exactly corresponds to the global warming event, followed by cooling.

“It had been known that mammals were small during that time and that it was warm, but we hadn’t understood that temperature specifically was driving the evolution of body size,” he said.

Bloch said the project began about seven years ago when former UF student and study co-author Stephen Chester, now an anthropology doctoral candidate at Yale University, measured horse teeth that seemed to be too large for their age and became smaller through the geologic section. The findings raise important questions about how animals might respond to future rapid climate change.

Lead author Ross Secord began geochemical analysis of the horse teeth and other mammals as a postdoctoral researcher with Bloch before joining the University of Nebraska-Lincoln in 2008.

“When Jon and I started plotting oxygen data from the mass spectrometer, we could immediately see that the shifts in size of horses and temperature were mirror images of each other,” he said.

“We’re seeing about a third of the mammals getting smaller and some of them getting a lot smaller, by as much as half of their original body size,” Secord added.

The study was published in the journal ‘Science’ on February 24.


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