Tehran- More than 200 million years ago, mammals and reptiles lived in their own separate worlds on the supercontinent Pangaea, despite little geographical incentive to do so. Mammals lived in areas of twice-yearly seasonal rainfall; reptiles stayed in areas where rains came just once a year. Mammals lose more water when they excrete, and thus need water-rich environments to survive. Results are published in the Proceedings of the National Academy of Sciences
Aggregating nearly the entire landmass of Earth, Pangaea was a continent the likes our planet has not seen for the last 200 million years. Its size meant there was a lot of space for animals to roam, for there were few geographical barriers, such as mountains or ice caps, to contain them.
Yet, strangely, animals confined themselves. Studying a transect of Pangaea stretching from about three degrees south to 26 degrees north (a long swath in the center of the continent covering tropical and semiarid temperate zones), a team of scientists led by Jessica Whiteside at Brown University has determined that reptiles, represented by a species called procolophonids, lived in one area, while mammals, represented by a precursor species called traversodont cynodonts, lived in another. Though similar in many ways, their paths evidently did not cross.