英語(yǔ)聽力：冰河綠洲—4

At first sight, manatees might look like seals or dolphins. But in fact, some of their closest relatives live on land. These toenails are the giveaway, remarkably similar to those of elephants.

13,000 years ago, two other members of the elephant family roamed this land. The manatees that swim in Florida's springs today are living relatives of ice age mammoths and mastodons.

Some of the bones found in these springs are easy to identify, but scattering among them are some more obscure remains. What kind of animal could this belong to? These rosettes are bony scales or scutes, similar to those that cover some reptiles today. But this is only one piece of the jigsaw. Imagine what the creature would have looked like when all these pieces were fitted together.

The scutes, around 2,000 of them, once formed the shell of a huge animal called the glyptodont. With its heavy weight exterior, the glyptodont looks like a reptile, like the alligator, which has been around for millions of years, long before the last ice age.