As the planet faces rising seas, killer storms, droughts, and extinctions, a new concern emerges: the potential for shrinking species.
Research suggests that climate change could potentially lead to a reduction in the size of some mammals, including horses, reminiscent of ancient species that adapted to warmer temperatures.
Historical Context
During the Paleocene-Eocene Thermal Maximum approximately 56 million years ago, global temperatures rose significantly, prompting evolutionary changes in various species. Notably, the early horse known as Sifrhippus shrank to the size of a house cat—around four kilograms—as a response to these warmer conditions. This adaptation was likely driven by natural selection, as smaller animals can dissipate heat more effectively due to their larger surface area relative to their volume.
A recent study published in the journal Science reveals that climate change has historically influenced mammal sizes, exemplified by the first horse, Sifrhippus, which lived 56 million years ago.
Climate-Induced Size Reduction
Sifrhippus, which inhabited what is now the Bighorn Basin in Wyoming, shrank from an average weight of about 12 pounds to approximately 8.5 pounds during a significant warming period known as the Paleocene-Eocene Thermal Maximum (PETM). This transformation occurred over thousands of years as temperatures rose by an estimated 9 to 18 degrees Fahrenheit.
A Glimpse into Prehistoric Life
The early horse was quite different from modern equines; it was roughly the size of a cat and primarily fed on leaves rather than grass. Fossils of Sifrhippus provide a detailed record of its size changes throughout this warm period, which lasted around 175,000 years.
Bergmann’s Rule in Action
The phenomenon observed in Sifrhippus aligns with Bergmann’s rule, which posits that mammals tend to be smaller in warmer climates. While this rule typically applies to geographic variations, the findings suggest it also holds true for temporal changes in climate.
Research Findings
The research team, led by Ross Secord from the University of Nebraska-Lincoln and Jonathan Bloch from the Florida Museum of Natural History, analyzed numerous fossils from the Bighorn Basin. They discovered that Sifrhippus experienced a size reduction of about 30% over the first 130,000 years of warming before rebounding to a larger size over the next 45,000 years.
Implications for Future Climate Change
This study not only enhances our understanding of ancient ecosystems but also raises questions about how modern species might respond to ongoing climate change. As temperatures continue to rise globally, researchers are keen to explore whether similar patterns of size reduction could occur in contemporary mammals.
Will Humans Shrink to Hobbit Size Again?
While it is theoretically possible for humans to experience size reduction in response to climate change over long timescales, current evidence suggests that immediate adaptations would more likely involve behavioral and technological changes rather than significant physical alterations. The rapid pace of climate change poses challenges that may not lead to the same evolutionary responses seen in the past.
