Ancient horses shrunk during hot period: Recovered teeth provide clues about effects of global warming on mammals
Imagine horses the size of housecats. They were called Sifrhippus, and they lived 56 million years ago.
Weighing in at a tiny 12 pounds and eating mostly leaves, Sifrhippus didn’t look or act much like modern horses. They’re really only related through name and an ancient common ancestor. In fact, Sifrhippus got smaller before it got bigger, evolving eventually into the Arabians and Clydesdales and Mustangs we know today.
Scientists from across the U.S. reported last week that the ancient horse was one of many mammals that shrunk during the Paleocene-Eocene Thermal Maximum, a time span of about 175,000 years where the oceans released massive amounts of carbon into the atmosphere and global temperatures increased by between 9 and 18 degrees Fahrenheit.
The tiny horse, which lived in what is now the Bighorn Basin in north-central Wyoming, shrank about 30 percent to an average of eight-and-a-half pounds. Near the end of the warming period, when the temperature started decreasing, they began bulking up again. They eventually became larger than they had been before.
A principle that states species of a widely distributed genus generally tend to be smaller in hotter temperatures was already well known in the scientific community—it’s called Bergmann’s rule—but teeth from the horses reveal new evidence about global warming’s effect on evolution. Oxygen isotopes in the teeth, which were recovered from the Bighorn Basin, show conclusively that as temperature went up, the size of the horses went down.
Scientists believe these findings could help to predict the evolutionary response of mammals to future global warming. With the Intergovernmental Panel on Climate Change predicting a 2 to 11.5 degree Fahrenheit increase in global surface temperature this century, one question comes to mind.
Will mammals keep up?
Groups like the IPCC and the Sierra Club have been pushing the government to act on issues like climate change for years. But they might soon find themselves with a partner that has not traditionally spoken out in favor of science—the church.
The Clergy Letter Project is a group of American Christian, Jewish and Unitarian Universalist clergy that supports teaching evolution in public schools and is opposed to teaching creationism.
“Within the community of Christian believers there are areas of dispute and disagreement, including the proper way to interpret Holy Scripture. While virtually all Christians take the Bible seriously and hold it to be authoritative in matters of faith and practice, the overwhelming majority do not read the Bible literally, as they would a science textbook,” the letter states.
“We the undersigned, Christian clergy from many different traditions, believe that the timeless truths of the Bible and the discoveries of modern science may comfortably coexist.”
The group just wrapped up its seventh annual Evolution Weekend, a group of events where clergy and congregations learn about and discuss evolution. The relevant story of the shrinking Sifrhippus horse might have been a topic of conversation at many of the group’s events.
And just so. With global temperatures up 1.4 degrees Fahrenheit since the early 20th century, science needs to be taken more seriously than ever.
Hidden in the teeth of these tiny horses is a lesson that humanity needs to quickly learn.