Sirenians, or seacows, are a group of marine mammals that include manatees and dugongs. Currently, only a single species of seacow is found anywhere in the world. However, the fossil record of seacows, which dates back 50 million years, tells a different story.
Researchers from Howard University and the Smithsonian's National Museum of Natural History documented three instances in the geologic past when it was more common to find three -- or maybe more -- different species living together at one time. Their research has shown that each instance of such communities with many species was distinct, including unrelated species of extinct seacows.
This illustration shows multispecies communities of seacows from three different time periods and ocean basins. Each seacow represents a different extinct species of dugong. Florida, ~26 million years ago (upper left); India, ~18 million years ago (upper right); Mexico, ~4 million years ago (lower right).