Wednesday, January 10, 2007

The Nose Knows

Adult male elephant seals are the largest of the pinnipeds, which include seals, sea lions, and walruses. These colossal mammals can grow up to 15 feet long and weigh up to 5,000 pounds! As males get older, they develop a chest shield of wrinkled skin that is bright pink, rough, and deeply fissured like the bark on a tree.

But the inflatable proboscis is without doubt the most exceptional feature of the male elephant seal. Its full size is reached when the male is about eight years old. This peculiar proboscis is an enlargement of the nasal cavity that hangs down about a foot over the mouth when the animal is relaxed (much like the trunk of an elephant, thus the name).

But when that nose inflates…watch out!

A combination of muscle action and blood pressure causes it to form a large cushion on top of the snout, with the tip hanging down so that the nostrils open immediately in front of the mouth. The seal then forces air from his lungs into the nostrils at about 3 to 5 pulses per second. The inflated proboscis acts like as a resonating chamber, projecting the rhythmic, metallic-sounding snorts for nearly a quarter of a mile.

The male elephant seal’s proboscis is a classic example of sexual selection, in which females select males with a certain characteristic that communicates the male’s fitness such that it evolves to extreme proportions. The nose does not appear to perform any particular function for the male other than to attract females and repel males with its enormous size and resulting deep bellow, and is known as a “secondary sexual characteristic.” This is similar to the large showy tail on a peacock or the massive antlers on an elk.

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