14 December 2005

Tusk, tusk

Narwhals have often piqued my curiosity. Their “horns” are pretty much unique — there are no “nearwhals” with shorter “horns” (actually, they’re teeth) or anything else like them either living or fossil from which to extrapolate development or a purpose.

Like the turtles and so many other species, they stand quite alone and distinct in the underground bony “audit trail” we call The Fossil Record:

The tooth’s unique spiral, the degree of its asymmetry to the left side, and its odd distribution among most males and some females are all unique expressions of teeth in mammals. [...]

In the past, many theories have been presented to explain the tooth’s purpose and function, none of which have been accepted as definitive. One of the most common is that the tooth is used to display aggression between males, who joust with each other for social hierarchy. Another is that the tooth is a secondary sexual characteristic, like a peacock’s feathers or a lion’s mane.

“Secondary sexual characteristic” seems to be biologists’ code for “We don’t have a —ing clue what this is really for, but we needed something to fill the gap in our report”.

Now a Harvard Medical School researcher thinks that he knows what the tusks do:

Ten million tiny nerve connections tunnel their way from the central nerve of the narwhal tusk to its outer surface. Though seemingly rigid and hard, the tusk is like a membrane with an extremely sensitive surface, capable of detecting changes in water temperature, pressure, and particle gradients. Because these whales can detect particle gradients in water, they are capable of discerning the salinity of the water, which could help them survive in their Arctic ice environment. It also allows the whales to detect water particles characteristic of the fish that constitute their diet. There is no comparison in nature and certainly none more unique in tooth form, expression, and functional adaptation.

Finally, something which makes sense!

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