Sea cows, or sirenians, make up the group of marine mammals that includes slow-moving manatees and dugongs.

"They're one of the forgotten groups of marine mammals," said study co-author Mark Clementz, a biologist at the University of Wyoming. "Whales get all of the attention."

Like all mammals, the gentle giants can maintain a constant core body temperature. This makes sea cows ideal for measuring Earth's past climates, because their fossils' chemical makeup isn't distorted by varying temperatures in their surroundings.

(See "Prehistoric Pygmy Sea Cow Discovered in Madagascar.")

Clementz and his colleague, Jacob Sewall of Pennsylvania's Kutztown University,