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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 . . ."
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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