Mystery solved around the "horn" of the narwhal

Tooth serves the "unicorn of the seas" as a sensory organ

Narwhal Harvard Medical School
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Why does the narwhal - the unicorn of the sea - have its horn? This question has so far been largely unexplained. Now, however, American scientists have investigated the function of the up to two and a half feet long, protruding from the head projection.

The narwhal, a marine mammal up to 4.5 meters long, lives in the Arctic North Atlantic. His "horn" is actually a "tusk" that extends from the left side of the upper jaw and extends forward. Its spiraling structure, its asymmetric origin and the seemingly irregular distribution between the sexes - most males also own it but some females - are considered to be one of the mysteries of evolution and unique among mammalian teeth.

So far, several theories circulated about the function of these teeth, none of them could prevail, however. Some researchers believed that the protrusion could be a secondary sex feature such as the lion's mane or a peacock's wheel, while others suggested that the males use the tooth to compete in rank fights.

Millions of nerve tracts

Martin Nweeia, an expert in biomaterial science and restorative dentistry at the Harvard School of Dentistry (HSDM), studied the whales and their teeth during four Arctic expeditions. He is the director of a Narwhalahn study, which since 2000 has brought together researchers and experienced Inuit elders to combine the centuries-old experiences of Arctic people with modern scientific methods and approaches.

With success: He and his colleagues came to a completely new conclusion. They discovered that the tooth of the whale apparently acts as a hydrodynamic sensor. Ten million tiny nerve connections connect the central nerve of the tooth with its surface and make the outgrowth a sensitive sensor. Although seemingly hard and massive, the tusk works like a membrane with a sensitive surface that can detect changes in water temperature, pressure, and the concentration of chemical substances. display

"Why could a tusk break the rules of normal development by creating millions of sensory nerves that connect its nervous system with the icy arctic environment, " Nweeia asks. "Such a find is amazing and has surprised all of us."

Sensors help to survive in extreme environments

The ability to detect chemical gradients with the help of the tooth helps the narwhals, on the one hand, to measure the salinity of the water and thus better survive in the Arctic Ocean. On the other hand, it also allows the animals to better find their fish, which make up the bulk of their diet, on the basis of their characteristic "chemical trail". Nweeia and his colleagues also found that the tooth also transmits tactile stimuli and therefore plays an important sensory role in the typical "horndriving" of the male.

A tooth as a sense organ in this complex form and combination has not yet existed, so the researchers. "Now that we know the sensorial capabilities of the bump tooth, we can design new experiments to better explore some of the unique and previously unexplainable behaviors of these rare and shy whales."

(Harvard Medical School, Dec 14, 2005 - NPO)