Friday, January 01, 2010

Convergent crocodilians

This attractive individual lives in the Zoo Basel. It shares a large enclosure with these two:

As we gazed upon their toothy serenity, my wife asked me what species they were. I had to admit I didn't know. There may have been a placard somewhere, but in the crowd of humans I didn't notice it. Clearly crocodillians, and not alligators or caimans, but beyond that I couldn't say. Gharials have longer, skinnier snouts for catching fish, and most crocodiles have thicker, heavier snouts for pulling down large terrestrial animals. These seemed to be somewhere in between.

I've looked up what species of crocodilians have snouts like this, and was pleasantly surprised to find out that there are three candidates: the Slender Snouted Crocodile, the False Gharial and the Freshwater Crocodile. All three have similarly shaped snouts and eat a mixture of fish and terrestrial prey. All three are said to bite humans only when harassed, and all three live in fresh water. Each is found on a different continent and they are not closely related to each other. The African Slender Snouted Crocodile, the South Asian False Gharial and the Austrailan Freshwater Croc have apparently evolved into similar niches and therefore converged on similar morphology. Interestingly, despite its numerous crocodilians, the Western Hemisphere seems to lack a similar species.

I found out that these are Australian Freshwater crocs only by looking up which of these three species the Zoo in Basel keeps.

They also hold three of these, Nile Crocodiles:
That's what the above water part looks like. The below water part of the same individual in the same position looks like this:

Notice the much wider, more typical crocodilian snout.

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