What's the Difference?

"I give you now Professor Twist,
A conscientious scientist,
Trustees exclaimed, "He never bungles!"
And sent him off to distant jungles.
Camped on a tropic riverside,
One day he missed his loving bride.
She had, the guide informed him later,
Been eaten by an alligator.
Professor Twist could not but smile.
'You mean,' he said, 'a crocodile.'"

- The Purist, by Ogden Nash

Even more common than the "You gonna wrestle them?" line when I service our alligator exhibit is the ever-popular, "Aren't you scared to be in there with them?"   I generally respond in the negative, saying something along the lines that the alligators and I are very used to one another, and I make sure to pay attention and be careful when working around them.  That satisfies many people... but I also get a fair number of people who nod knowingly and then say, "But I bet you wouldn't do that with a crocodile, would you?"

Unless you are in southern Florida (or a zoo or aquarium), it should be easy to know if you are looking at a crocodile or an alligator - that's the only place on earth you'll naturally find both in the wild.

A lot of visitors are a little hazy on the differences between alligators and crocodiles.  Some seem to latch onto the idea that alligators are docile and crocodiles are savage - not necessarily the case.  Sure, the crocodile label encompasses potential man-eating behemoths like the Nile crocodile of Africa and the saltwater crocodile of Asia and Australia... but it also includes several fairly shy, inoffensive species.  Other guests say that crocodiles are bigger... but a full grown American alligator is a giant compared to a African dwarf crocodile, or a Philippine crocodile.

The differences are less exciting.  Alligators have something of an overbite - when their mouths are closed, you see the top teeth, whereas with crocs you might see both.  Also, alligators have a more rounded snout, compared to the more pointed snout of a crocodile.  Alligators tend to be more tolerant of the cold, less tolerant of salt than crocodiles.  Closely related to the alligators are the Central and South American caimans, which differ from the alligators in their belly scales and the absence of a bony septum. 

This is the exact sort of description which makes many zoo visitors nod for a moment, than wander off in mid-sentence to look at the monkeys.

The fact is, it's hard to come up with hard and fast rules to describe what animals are part of which group.  There's over a dozen species of crocodile scattered over five continents (there are, in contrast, only two alligators - the American and the Chinese) - some are big, some are small, some have broad snouts, some have very narrow ones.  It's easy to say that monkeys have tails and apes don't... but Barbary macaques don't, either, and they're monkeys.  Mammals give live birth... except for those pesky echidnas and that irksome platypus.

Ultimately, what defines an animal's place on the tree of life is who it is actually related to, it's common ancestors.  You might not look a thing like your sibling - you may have much more in common with your best friend - but that doesn't change the fact that your sibling is, in fact, who you are more related to, based on the fact that you share parents.

So, Mr. Zoo Visitor, I can give you some generalities on what makes animal A an alligator and animal C a crocodile, but they will just be that - generalities.  Nature never read a rule book... and she certainly never wrote one.

"It's not so hard to tell if it's an alligator or a crocodile.  An alligator will see you later, a crocodile will see you in a while."