Well, it may not be one of those questions that keeps you awake at night, but if you’ve ever been to a zoo with a large, scaly, toothy,  primitive-looking,  grinning aquatic creature that may not move a muscle, you may have wondered whether it was an alligator or a crocodile.  These two are frequently confused, but really are separate species, and have been for the last 70 million years or so.   And one deserves their shared fearsome reputation way more than the other!


According to the Crocodile Specialist Group of the International Union for the Conservation of Nature (IUCN), there are 24 distinct species of crocodilians living on earth, and they’re classified into three families:   the Alligatoridae, the Crocodylidae (also called “true crocodiles”), and the Gavialidae, which only include two species, Gharials and Tomistoma.  The Alligatoridae family includes Caimans, too, and there are really only two types of actual alligators, the American Alligator and the Chinese Alligator.  The Crocodylidae is a much bigger family, because these creatures live all over the world – there are 14 distinct species.  

Back to the question!   Alligator or Crocodile?

First of all, there are some well-known differences between these species.  If you see one in the wild, you can probably identify it just based on your own location – Alligators live in the southeastern U.S. and in eastern China; Crocodiles live in Africa, Australia, Southeast Asia, North America (one teeny area), South America, and Central America.   And if you’re near salt water, then it’s most likely a Crocodile.   

Unless you happen to be in Dade or Monroe Counties in Florida, or in the Florida Keys, where the American Alligator and the American Crocodile coexist, pretty peacefully in general.  In fact, this is the only area in the world where the two species comingle, but they never breed because they are too genetically different.       

Let’s say you see an American Alligator and an American Crocodile side by side (from a safe distance, of course):   there are a few sure-fire ways to tell them apart.

Head shape:   Alligators have a u-shaped nose.   Crocodiles’ heads are shaped like a long-skinny V.  If you have great binoculars or a zoom lens, you may also be able to see their

Teeth:   When alligators close their jaws, their upper teeth are visible outside their mouths.   When crocodiles do the same, you can see both the upper and lower teeth outside their jaws.   Now, if the light is good, you may be able to see different

Color:  Alligators are usually dark gray – and Crocodiles are mostly light tan or olive color.   But this is affected by their environment, since concealment is an important hunting and survival strategy for them.

General Differences

Size:   Though the two species are similar in size in South Florida, in general crocodiles are larger, growing to about 19 feet, while alligators can reach around 14 feet in length. Record weight for a crocodile is 2,000 pounds, and for an alligator, only half that.    Again, a lot depends on the environments in which they live.

Speed:   Because of their long, muscular tails, both are quick and efficient swimmers.   Alligators can reach about 20 mph in the water, while crocodiles have been clocked at a maximum of 9 mph.  On land, both can “sprint” for a short time, but again the Alligator wins the race, barely:  gators can run about 11 miles per hour, while the consistent crocs run like they swim, at 9 mph.

Strength:  Since crocodiles (especially huge ones like those in Africa and Australia) are so big, they definitely are stronger than alligators.   A good measure of this is the “bite force” of the two species.  The record psi (pounds per square inch) bite force for a croc is 3,700 pounds.   The Alligator record is 2,900 psi – but you wouldn’t want to be in range of either of those sets of jaws!  Which brings us to the matter of…..

Aggression:   We know that both alligators and crocodiles have a reputation as fierce predators and scary, aggressive creatures that would love to hunt you down.    The truth is that Crocodiles are far more dangerous to humans than their smaller cousins the alligators.   In fact, most American Alligators would prefer to be as far from humans as possible – they might only attack a human if they mistook one of us for prey, or if they were defending a nest or their young.  The best advice is to give them space!   

Crocodiles, especially Australian saltwater varieties and the infamous Nile Crocodile, are more aggressive  – and as they are so large with those scary, powerful jaws, are much more to be feared by humans.   In fact, there’s actually a website called CrocBITE which keeps a database of crocodilian attacks worldwide, and they have found definitively that the Nile Crocodile is the one we should give the MOST space.      

But this is good advice for any kind of encounter with a wild animal!  Whether you happen upon a rattlesnake here in the desert, a bear in the mountains, or a gator or croc in the wetlands, the best advice is to calmly steer clear and respect the animal’s territory and space.   


So come to the Reid Park Zoo and meet their American Alligator –  but when the Reid Park Zoo expansion opens and you rush to see the Komodo Dragon, please keep in mind that he is not as closely related to the alligator as you think!    Read on if you’d like to know why crocodilians are more closely related to birds than to lizards………

The Very Beginning – The Archosaurs

Common sense tells us that two types of reptiles, such as alligators and crocodiles, that look so similar, surely have a common ancestor, and they do.   Surprisingly, this is also a common ancestor of BIRDS, so that same common sense will fail you if you assume that the alligator or crocodile you’re wondering about is just a giant aquatic lizard.  

Though crocodilians ARE reptiles, they are much more closely related, genomically speaking, to birds.    Oh, and to the delight of children especially, who can guess this without being told, they are also closely related to dinosaurs, which may account for their uniquely primordial charm.  Reptiles evolved from amphibians approximately 320 million years ago, and mammals and birds evolved from reptiles about 120-180 million years later.

Archosaurs, also called “The Ruling Reptiles,” exist in the fossil record from the early Triassic period, 245 million years ago.  They were classified by scientists in part because of their unique skull structures (with teeth in sockets and room for lots of jaw musculature).  The best-known Archosaurs were the dinosaurs, of course, some of whom had beaks and could fly.    When the late Cretaceous period ended, about 65 million years ago, most of the dinosaurs and some of the crocodilians disappeared, and it’s around this time that alligators and crocodiles had an evolutionary parting of the ways.  But it’s fair to say that today’s birds and crocodilians are not “living fossils,” as they’re often called,  but living Archosaurs.