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WHAT BIG AMPULLAE OF LORENZINI YOU HAVE,
GRANDMA . . .
The better to sense your electrical field, my
dear little Red Riding Hood! The GW is equipped with two
of the most powerful sensing mechanisms in Nature, a
highly developed sense of "smell" and the ability to
sense the electrical fields radiating from living
creatures.
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As anyone familiar with the 'Jaws'
movie posters can tell you, GW's have a pair
of nostrils near the tip of their snout.
Since "breathing" takes place in the gills,
the nostrils of a shark are used solely for
olfactory purposes - to sniff
out their prey. Each nostril is divided by a
small skin flap that separates the water the
shark is swimming through into two flows, one
incoming and one outgoing. This flow passes
through an area that contains a large number
of small sensory organs known as
lamellae. These lamellae are
shaped like tiny flower petals and are in
turn covered with millions of olfactory
cells. These cells are in turn directly
connected to the center of the brain
responsible for detecting odors, turning the
shark into a swimming nose. |
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The second system is the more
specialized of the two and warrants a
closer look due to its unusual nature.
Notice in this picture the large number of
tiny black dots marking the snout of the
GW. These pore-like markings are the
ampullae of Lorenzini, the
secret weapon in the GW's arsenal of
predation. Each is a minute capsule
filled with a gel-like substance excreted
by the shark, sensitive to electrical
discharges as small as .005 microvolts. Dr.
John McCosker and Richard Ellis point out
in their book 'The Great White Shark' that
these ampullae collectively give the GW the
ability to sense the electrical field
distributed by a copper wire 1000 miles
long hooked up to a D-sized battery! This
amazing sensitivity is due to both the
large number of ampullae present and also
the fact that like the lamellae, each
ampulla utilizes a large number of sensory
cells to "pick up" the signal. These
sensory cells lie inside
alveoli, small sacs within
each ampulla which are in turn connected
directly to the brain of the shark - no
muss, no fuss . . . just a straight signal
to Eating Central that prey lies dead
ahead, if you'll excuse the pun.
So what good does a built-in
electrical field detection system do the
GW? Plenty, it turns out. Every creature
in the briny blue generates a small
electrical field from where their skin
meets the water. The mucous
membranes that coat the mouth and gills
of fish also create steady current fields
which are affected by their breathing
patterns. Furthermore, a wounded animal
bleeds, producing yet another set of
electrical information. By honing in on
this information, the GW can detect and
distinguish between prey items who are
swimming along peacefully, who are moving
quickly about in a panic, and better yet,
who might be bleeding and incapacitated -
making them a hassle-free
lunch.
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In summary, these two sensory packages, the
nasal lamellae and the ampullae of Lorenzini, have
evolved over millions of years into detection systems for
the very things that make prey more attractive to our
friend the GW - blood, indicating animals that are
injured and thus easier to catch and movement, telling
the GW both where their prey is and what state it might
be in when the shark catches it.
CHECK OUT THE BOD ON THAT ONE . . .
The form of the GW is evolution at its best.
Nearly every aspect of its physical makeup from the
conical snout to the large, nearly symmetrical tail fin
contributes to its efficiency as a hunter. As one of the
Earth's oldest species, sharks represent millions of
years of Mother Nature's poking and prodding - and
judging from the GW, Mother Nature certainly seems to
have a mean streak!
"OH THE SHARK HAS PRETTY TEETH, DEAR . .
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Much has been made of the infamous jaws of the
GW and rightly so. Each upper tooth is a marvel of
compact engineering with hundreds of tiny serrations.
This coupled with their enormous jaw strength enables the
GW to cut through just about anything they feel needs
cutting. The bottom teeth are not as large but serve the
purpose of skewering the shark's prey, holding it in
place for the upper teeth to do their work - which is to
remove as much flesh from the shark's prey as possible!
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