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alligator and crocodile Anonymous asked this question on 5/23/2002: What's the difference between an alligator and crocodile?

beainsc gave this response on 5/23/2002: This is probably the most commonly asked question when it comes to crocodilians! However, although the answer is relatively straighforward, there's a bit more to it than the question might suggest. There are three groups (subfamilies) of crocodilians: the alligatorinae, which includes the alligator and the caimans; the crocodylinae, which includes the "true" crocodiles; and the gavialinae, which contains only the gharial. So, the first difference is that alligators and crocodiles are actually in different subfamilies. The easiest way of telling them apart, though, is to 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 the alligators is very strong, and capable of withstanding the great crushing power which alligators and caimans use for cracking open turtles and hard-shelled invertebrates - even though they eat softer prey too! The pointed snout of a crocodile, however, isn't quite as strong as the alligatorine shape, but the crocodile is still capable of exerting massive biting power. The crocodile shape can be thought of as being more generalised - ideal for a wide variety of prey. Nobody really knows the extent to which these differences in shape may be important, but it's obvious that a very thin nose like a gharial's is much better at dealing with a fish than a turtle! There are 23 species of crocodilians, though, and this simple broad vs. narrow rule doesn't always work. Another difference comes in the placement of the teeth. In alligators, the upper jaw is wider than the lower jaw and completely overlaps it. Therefore, the teeth in the lower jaw are almost completely hidden when the mouth closes, fitting neatly into small depressions or sockets in the upper jaw. This is particularly apparent with the large fourth tooth in the lower jaw. In crocodiles, the upper jaw and lower jaw are approximately the same width, and so teeth in the lower jaw fit outside the upper jaw when the mouth is closed. The upper teeth also fit outside the lower jaw, giving the teeth an "interlocking" appearance when the mouth shuts. The big fourth tooth in the lower jaw also fits outside the upper jaw, and there's a constriction in the upper jaw behind the nostrils to accommodate it when the mouth is closed. Crocodiles differ from alligators and caimans in having functioning salt glands (modified salivary glands) on their tongue. Although similar modified salivary glands are present on the tongue of alligators and caimans (and also gharials), they have lost their ability to secrete significant amounts of salt. It has been suggested that crocodiles had a more recent marine ancestry, with only the modern crocodiles colonising more freshwater habitats. They still retain a relatively high tolerance to salt water, however, and some species such as saltwater crocodiles (C. porosus) can survive for extended periods in quite saline environments. Alligators and caimans have lost much of this osmotic ability to secrete excess salt through the tongue glands, and can only tolerate it for short periods of time, prefering to remain in freshwater areas when possible. There's more! Both crocodiles and alligators have small, sensory pits around the upper and lower jaws - take a close look on a photograph, and you'll see small, black speckles almost like unshaven stubble. These are capable of detecting small pressure changes in water, and assist in locating and capturing prey. Crocodiles have similar organs covering virtually every scale on their body, but alligators and caimans have none except those around the jaws. Nobody is quite sure what these sense organs actually do - they may help to extend a sensory surface all over the crocodile, they may play some role in chemical reception, and there has even been the suggestion that they are involved in detection of salinity. Regardless of what they do, they're very good at telling apart crocodile skin from alligator skin. If the scales of a crocodile or alligator skin product (e.g. handbag, wallet) have a small spot or dimple close to the edge, you know the skin is from a crocodile and not an alligator or caiman. The alligator does not have any sense organs, but the crocodile does. These are probably the most obvious differences between crocodiles and alligators in terms of external appearance. However, each species is unique, and to list all the possible differences would be like comparing a jaguar with a lion. Differences in behaviour are also apparent. Most people regard crocodiles as more aggressive than alligators, and this is true of some species. For example, alligators are relatively docile next to saltwater crocodiles, but there are many species with many differerent kinds of behaviours and temperaments. Alligators can often reach at least 14 or 15 feet in length, which is larger than some crocodile species, but not others. The largest crocodile species is the saltwater crocodile, which can get to at least 17 or 18 feet - some rare individuals exceeding 20 feet after many years. The African dwarf crocodile, as a contrast, doesn't grow larger than 4 or 5 feet. The Indian mugger (Crocodylus palustris) breaks the crocodile convention of having narrow jaws - its jaws are superficially very similar in shape to those of an alligator, although the fourth lower tooth is still visible. When all the above criteria are considered, the mugger is definitely a crocodile. • beainsc recommends buying a book with the title, author, or subject: Evolution of Crocodiles

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