Rub
My Tusk, Baby - Narwhal Tooth Explained
Reprint
of a Harvard Medical School Office of Public Affairs Press Release
Function
of "Unicorn" Whale's 8-foot Tooth Discovered
Harvard School of Dental Medicine Researcher Announces Findings
Today
SAN DIEGO-Dec. 13, 2005-Today, Harvard School of Dental Medicine
(HSDM) researcher Martin Nweeia, DMD, DDS, answers a marine science
question that has eluded the scientific community for hundreds
of years: why does the narwhal, or "unicorn," whale
have an 8-foot-long tooth emerging from its head, and what is
its function? Nweeia, a clinical instructor in restorative dentistry
and biomaterials sciences at HSDM, will be presenting his conclusions
at the 16th Biennial Conference on the Biology of Marine Mammals
in San Diego.
The narwhal has a tooth, or tusk, which emerges from the left
side of the upper jaw and is an evolutionary mystery that defies
many of the known principles of mammalian teeth. 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. The narwhal is usually 13 to
15 feet in length and weighs between 2,200 and 3,500 pounds. Its
natural habitat is the Atlantic portion of the Arctic Ocean, concentrating
in the Canadian High Arctic: Baffin Bay, Davis Strait, and northern
Hudson Bay. It is also found in less numbers in the Greenland
Sea, extending to Svalbard to Severnaya Zemlya off the coast of
Russia.
Nweeia
has discovered that the narwhal's tooth has hydrodynamic sensor
capabilities. 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.
"Why
would a tusk break the rules of normal development by expressing
millions of sensory pathways that connect its nervous system to
the frigid arctic environment?" says Nweeia. "Such a
finding is startling and indeed surprised all of us who discovered
it." Nweeia collaborated on this project with Frederick Eichmiller,
DDS, director of the Paffenbarger Research Center at the National
Institute of Standards and Technology, and James Mead, PhD, curator
of Marine Mammals at the National Museum of Natural History of
the Smithsonian Institution.
Nweeia
studied the whales during four trips to the Canadian High Arctic.
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.
Nweeia's findings point to a new direction of scientific investigation.
Fewer than 250 papers have been published about the narwhal, and
many offer conflicting results. Because of its Arctic habitat
and protected status in Canada, the whale is difficult to study.
Nweeia has brought together leaders from the fields of marine
mammal science, dental medicine, engineering, mathematics, evolutionary
biology, anatomy, and histology.
The
sensory connections discovered by Nweeia and his colleagues also
are capable of tactile ability. Narwhals are known for their "tusking"
behavior, when males rub tusks. Because of the tactile sensory
ability of the tusk surface, the whales are likely experiencing
a unique sensation.
Results
from the team's research already has practical applications; studies
about the physical makeup of the tusk, which is both strong and
flexible, provide insight into ways of improving restorative dental
materials. (An 8-foot-long tooth can yield one foot in any direction
without breaking). Nweeia also leads the Narwhal Tooth Expeditions
and Research Investigation, founded in 2000, which combines scientific
experts with Inuit elders, who have collected notes for hundreds
of years, to discover the purpose and function of the narwhal
tusk.
"Now
that we know the sensory capabilities of the tusk, we can design
new experiments to describe some of the unique and unexplained
behaviors of this elusive and extraordinary whale," said
Nweeia.
This
work was funded by Harvard School of Dental Medicine; the National
Geographic Society; Sunstar Butler; the Smithsonian Institution
Center for Arctic Studies; Astro-Med, Inc.; and Fisheries and
Oceans, Canada.
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