Climate Fact Of The Day – Evolution of Earliest Horses Driven by Climate Change

ScienceDaily (Feb. 23, 2012) — When Sifrhippus, the earliest known horse, first appeared in the forests of North America more than 50 million years ago, it would not have been mistaken for a Clydesdale. It weighed in at around 12 pounds — and it was destined to get much smaller over the ensuing millennia. Sifrhippus lived during the Paleocene-Eocene Thermal Maximum, a 175,000-year interval of time some 56 million years ago in which average global temperatures rose by about 10 degrees Fahrenheit, caused by the release of vast amounts of carbon into the atmosphere and oceans. About a third of mammal species responded with significant reduction in size during the PETM, some by as much as one-half. Sifrhippus shrank by about 30 percent to the size of a smallhouse cat (about 8.5 pounds) in the PETM’s first 130,000 years and then rebounded to about 15 pounds in the final 45,000 years of the PETM. Read Article