Global Warming Led to Dwarfism in Mammals: Impacts of Climate Change

Climate change continues to impact our globe. The warming temperatures in particular have caused species to change their behaviors in an attempt to adapt. Yet mammals don't just change their behaviors when things heat up; they may also change their sizes. Scientists have discovered that mammal body size decreased significantly during at least two ancient global warming events--and a similar outcome may be possible for current warming trends.

During the Paleocene-Eocene Thermal Maximum (PETM), there was a period of warming. Occurring about 55 million years ago, this period hosted mammals that included the ancestors of horses and deer and primates. Yet these mammals seemed to undergo a process called "dwarfing" during this time. Not only that, but the same thing happened during a smaller global warming event that occurred just 2 million years after the PETM.

The PETM lasted about 160,000 years. Global temperatures rose about 9 to 14 degrees Fahrenheit at its peak--much warmer than current conditions. During the smaller event, known as ETM2 (Eocene Thermal Maximum 2), the warming lasted just 80,000 years and resulted in a peak temperature increase of about 5 degrees Fahrenheit.

In order to study these time periods a bit more closely, the researchers examined teeth and jaw fossils of early hoofed mammals and primates. They used molar teeth as a proxy for body size. After studying these fossils, the researchers noted that body size decreased during both periods, though this dwarfism was less pronounced during the ETM2.

"The fact that it happened twice significantly increases our confidence that we're seeing cause and effect, and one interesting response to global warming in the past was a substantial decrease in body size in mammalian species," said Philip Gingerich, one of the researchers, in a news release.

As our modern climate continues to warm, it's very possible that this same type of dwarfism may possibly occur. Yet scientists need to investigate a bit further in order to learn more about the changes that might be expected.

"Developing a better understanding of the relationship between mammalian body size change and greenhouse gas-induced global warming during the geological past may help us predict ecological changes that may occur in response to current changes in Earth's climate," said Will Clyde, one of the researchers, in a news release.

The findings were presented on Nov. 1 in Los Angeles at the annual meeting of the Society of Vertebrate Paleontology.