Coming face to face with a crocodile or an alligator, you'd likely see a mouth full of serrated teeth that would likely scare the bejeezus out of you.
Upon closer inspection, not recommended out in the wild, you'd spot glaring differences:
Snout shape: Alligators have wider, U-shaped snouts, while crocodile front ends are more pointed and V-shaped.
Toothy grin: When their snouts are shut, crocodiles look like they're flashing a toothy grin, as the fourth tooth on each side of the lower jaw sticks up over the upper lip. For alligators, the upper jaw is wider than the lower one, so when they close their mouths, all their teeth are hidden.
Home base: Crocodiles tend to live in saltwater habitats, while alligators hang out in freshwater marshes and lakes.
The two reptile groups are close relatives, so their physical similarities are expected.
They belong to the subgroup Eusuchia, which includes about 22 species divided into three families: the fish-eating gavials or gharials, which belong to the Gavialidae; today's crocodiles or the Crocodylidae; and the Alligatoridae, or alligators. Eusuchians appeared on the scene during the late Cretaceous some 100 million or so years ago.