Study: Mammals may get smaller as world gets warmer

ANN ARBOR, Mich., Nov. 4 (UPI) -- A decrease in mammal body size during at least two ancient global warming events is possible again with human-caused climate change, a U.S. paleontologist says.

Researchers studying fossils have long known mammals such as primates and the groups that include horses and deer became much smaller during a period of warming called the Paleocene-Eocene Thermal Maximum about 55 million years ago, and again 53 million years ago.

Such mammalian "dwarfing" could happen again in a warming world, University of Michigan paleontologist Philip Gingerich said.

"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," he said.

Gingerich and colleagues at a number of U.S. universities said at a meeting of the Society of Vertebrate Paleontology in Los Angeles they've concluded decreased body size "seems to be a common evolutionary response" by mammals to extreme global warming events, known as hyperthermals, "and thus may be a predictable natural response for some lineages to future global warming."

Parallels between ancient hyperthermal events and modern-day warming make studies of the fossil record particularly valuable, researchers said.

"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," Will Clyde of the University of New Hampshire said.