SCIENCE LAB SCHEME : THE NAKED TRUTH

Did all ancient sloths wear fur? Or did one go without : Ground sloths emerged in South America tens of millions of years ago, eventually ranging as far north as Canada.

While their modern relatives dwell in trees and can be the size of smaller dog breeds, ground sloths also occupied land and seashores and, at their largest, rivaled today's elephants in size.

Some ground sloths had lots of fur. But did other sloths evolve to be nearly hairless?

Research published in The Journal of Mammalian Evolution offers insights into what the extinct sloths may have looked like. Their habits varied between tropical and cold climates across the Americas.

And the sloths came in a variety of sizes. The megatheres, known as Eremotherium and Megatherium, were among the biggest terrestrial mammals of their time.

Researchers started by determining sloth body temperature. Using three megathere teeth and two teeth from smaller ground sloths they measured the abundance of certain isotopes [ used to show the body temperature of extinct species ] within minerals inside the sloth teeth.

At 84 to 89 degrees Fahrenheit [ 28 to 31 degrees Celsius], ground sloths had lower core body temperatures than that of most large land mammals today.

Eremotherium was the only sloth whose fur coverage might have changed depending on its habitat -without at least a centimeter of fur, it would have been too cold in northern habitats.

But in tropical climates, sparse fur might have suffered. Eremotherium may have had either varied fur coverage depending upon region or it may have shed its coat during warmer seasons.

The World Students Society thanks Jeanne Timmons.