Global Warming Led to Dwarfism in Mammals Twice: Study

Global warming led to a significant decrease in the mammal body size millions of years ago, a new finding suggests.

In a new finding, a paleontologist at the University of Michigan claims that during the last two ancient global warming events, the mammal body size decreased significantly. He also claims that a similar outcome is possible in response to human-caused climate change.

It was already known that mammals like primates and other groups that include horses and deer became much smaller during the Paleocene-Eocene Thermal maximum (PETM)-a warming period about 55 million years ago.

In this current study, paleontologist Philip Gingerich along with his colleagues found a strong evidence that supports the fact that mammalian dwarfing took place in a separate event of small global warming called ETM2 (Eocene Thermal Maximum 2) that took place some 2 million years after the PETM period, i.e. 53 million years ago.

For nearly 160,000 years that PETM lasted, the temperatures soared from 9-14 degrees Fahrenheit. Whereas the ETM2 lasted for 80,000-100,000 years during which the temperatures increased by 5 degree Fahrenheit.

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

Based on the observations, the researchers concluded that the shrinking of mammalian body size seems to be a common evolutionary response by the mammals to the extreme global warming events called as 'hyperthermals'. This may be useful in predicting some of the natural response of some lineages to future global warming.

From the Wyoming's Bighorn Basin, a geological structural basin filled with more than 20,000 feet of sedimentary rocks of the Miocene era, the researchers collected the fossils of teeth and jaw of early hoofed animals and primate that lived the ETM2 era. The approximate body size of the mammal was estimated based on the size of the molar teeth. They noticed the mammals body size decreased during the ETM2 period but not as much as dwarfism that was noticed in PETM fossils.

The researchers stated the example of the lineage of early horses that were the size of a small dog known as Hyracotherium, they saw a 19 percent decrease in the body size during ETM2. Whereas during the PETM the same horse lineage witnessed a 30 percent decrease in body size.

"Interestingly, the extent of mammalian dwarfism may be related to the magnitude of the hyperthermal event," said team member Abigail D'Ambrosia of the University of New Hampshire.

The present day climate change is due to the high rate of burning fossil fuels that results in the release of greenhouse gases mainly carbon dioxide. Whereas in the ancient times climate warming took place due to the seabed methane clathrates- methane present in ice that is found in ocean sediments.

"The parallels between ancient hyperthermals and modern-day warming make studies of the fossil record particularly valuable, said team member Will Clyde of the University of New Hampshire. "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."

The study findings Friday was presented on Nov. 1, in Los Angeles at the annual meeting of the Society of Vertebrate Paleontology.