Thursday, February 26, 2009

Ally gator or a crocodile?

Alligators are often confused with crocodiles (I don’t know how can people do that but they do). They do share many similarities but they are two different animals.

So how do you tell them apart?

Firstly, they are a different family. There are three families of crocodilians: the alligatoridae, which includes alligators and caimans; the crocodylidae, which includes the “true” crocodiles; and gavialidae, which contains only the Gharial.

Shape of the snout: Alligators (and caimans) have a wide “U” shaped, rounded snout, whereas crocodiles tend to have a longer and more pointed “V” shaped snout.

Placement of teeth: In alligators, the upper jaw completely overlaps the lower jaw. Therefore the teeth in the lower jaw are almost hidden when the mouth closes. While in true crocodiles, the large “fourth tooth” in the lower jaw fits into a constriction in the upper jaw making it clearly visible. 


In the top photo you can see a fourth tooth coming out from the lower jaw of a Crocodylus niloticus (Nile crocodile) and in the bottom photo you can see no fourth tooth in an Alligator mississippiensis (American alligator).

Lingual salt glands: Crocodiles and gharials also differ from alligators and caimans in having functioning salt glands on their tongue. Structurally, these are actually modified salivary glands, and while alligators and caimans also have these structures they appear to have lost the ability to use them for excreting significant amounts of salt. This makes crocodiles more tolerant to life in saline water, including sea water in some species. 

Integumentary sense organs: Both crocodiles and alligators have small, sensory pits dotted 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. These were originally called ISOs, or Integumentary Sense Organs, although recent research has renamed them DPRs (Dermal Pressure Receptors). Crocodiles have similar organs covering virtually every scale on their body, but alligators and caimans only have those around the jaws.

The fourth-tooth feature is one of the most reliable external differences apart from the snout shape that allow easy identification.

Now comes the interesting stuff..

“Ally” – an American alligator at the Madras Croc Bank (She is one of my favourite crocs! Such a sweetheart.) has fourth tooth like a true crocodile!

This just may be a weird case of some unusual formation of teeth structure and is not of much importance morphologically but it surely is a pretty interesting thing to happen!

1 comment:

shafeeq said...

She's an ABSOLUTE sweet heart!!!