On Pangaea, the mammals needed a water-rich area, so the availability of water played a decisive role in determining where they lived. "It's interesting that something as basic as how the body deals with waste can restrict the movement of an entire group," Whiteside said.
In water-limited areas, "the reptiles had a competitive advantage over mammals," Whiteside said. She thinks the reptiles didn't migrate into the equatorial regions because they already had found their niche.
The researchers compiled a climate record for Pangaea during the late Triassic period, from 234 million years ago to 209 million years ago, using samples collected from lakes and ancient rift basins stretching from modern-day Georgia to Nova Scotia. Pangaea was a hothouse then: Temperatures were about 20 degrees Celsius hotter in the summer, and atmospheric carbon dioxide was five to 20 times greater than today. Yet there were regional differences, including rainfall amounts.
The researchers base the rainfall gap on variations in the Earth's precession, or the wobble on its axis, coupled with the eccentricity cycle, based on the Earth's orbital position to the sun. Together, these Milankovitch cycles influence how much sunlight, or energy, reaches different areas of the planet. During the late Triassic, the equatorial regions received more sunlight, thus more energy to generate more frequent rainfall. The higher latitudes, with less total sunlight, experienced less rain.
The research is important because climate change projections shows areas that would receive less precipitation, which could put mammals there under stress.
"There is evidence that climate change over the last 100 years has already changed the distribution of mammal species," said Danielle Grogan, a graduate student in Whiteside's research group. "Our study c
|Contact: Richard Lewis|