Alligator and Crocodile heads. The left one is an alligator, and the right one is a crocodile. Photo: animalsunlimited.co.uk
The shape of the head (jaw) is the most obvious difference between a crocodile and an alligator. Crocodiles have a longer, more V-shaped head then alligators. Look at their noses: alligators (and caimans) have a wide “U”-shaped, rounded snout (like a shovel), whereas crocodiles tend to have longer and more pointed “V”-shaped noses.
The broad snout of alligators is designed for strength, capable of withstanding the stress caused to the bone when massive force is applied to crack open turtles and hard-shelled invertebrates which form part of their diet. Of course, alligators eat softer prey too, but hard-shelled prey are ubiquitous in their environment and it’s a big advantage to be able to eat them. Conversely, the pointed snout of a crocodile looks not quite as strong as the alligatorine shape, but the crocodile is still capable of exerting massive biting power, even more than alligators. Crocodile jaws can be thought of as being more generalized – ideal for a wide variety of prey. The full extent of the way jaw shape influences diet isn’t particularly well studied in crocodilians, but it’s obvious that a very thin nose like a gharial’s is much better at dealing with a fish than a turtle. The Indian Mugger Crocodile (Crocodylus palustris), however, breaks this general rule as its jaws are superficially very similar in shape to those of an Alligator, that said other characteristics mark it as a Crocodile, for example, it’s teeth (see the placement of teeth below).