Alligators have a number of special features that have allowed them to stick around for 180 million years.
For example, alligators are armor-plated. Bony plates inside the skin, called osteoderms or scutes, make the skin very hard to penetrate. When you look at the ridges on the back of an alligator, each little spike is made by a piece of bone in that section of skin. Click here to see a photo of typical osteoderms.
Even though alligators are huge and cold-blooded, they can be quite fast, with a top speed of 11 MPH (17 KPH) over short distances. For comparison, the fastest humans running at world-record times in a 100 meter dash, are running about 20 MPH (32 KPH), but a typical adult human is no faster than an alligator. This makes it possible for an alligator to escape from most situations on land and get into the water.
Alligator eyes have two sets of eyelids. The outer lids are like human eyelids. They are made of skin and close top-to-bottom. The inner lids are clear and close back-to-front. While an alligator is sitting about or swimming, these inner eyelids protect the alligator's eyes and provide clearer vision in the underwater environment.
When swimming underwater, alligators are water tight. Flaps close off the ears and nostrils, the inner eyelids protect the eyes and a special flap called the palatal valve closes at the back of the throat to keep water out of the throat, stomach and lungs. Alligators can stay underwater for quite a while. A typical dive might last 10 to 20 minutes. In a pinch, an alligator can stay underwater for two hours if it is at rest. And, in very cold water, an alligator can last up to eight hours submerged.