Form and Function of Sharks 27
usual teeth. In some squaloid sharks, such as the 40-cm-long (15.7-in)
Cookiecutter Shark, Isistius brasiliensis, the lower teeth are arranged in a
flat band across the lower jaw and are more bladelike than the upper-jaw
teeth. Cookiecutters are somewhere between parasites and predators, tak-
ing (relatively) small pieces out of large prey. Cookiecutter Sharks get their
name from the wounds they leave on tunas, dolphins, whales, and even
Megamouth and White sharks and humans. These wounds are circular and
craterlike and about 4 cm (1.6 in) across, an exact match to the mouth size
of the Cookiecutter Shark. The shark apparently attaches to the side of
its victim via suction created by its movable tongue, fleshy lips, and spe-
cial throat, jaw, and gill muscles. It then sinks its hooklike upper teeth and
sawlike lower teeth into the prey and twists and spins about its long axis,
removing a flat, craterlike cone of tissue. Similar, larger wounds have been
found on seals and beluga whales and may result from attacks by large
Greenland Sharks, a squaloid with a tooth type and distribution similar to
a Cookiecutter’s.
Sharks and rays that feed on hard-shelled prey such as clams and snails
and on large crustaceans such as lobsters and crabs have broad teeth de-
signed more for crushing than for piercing. Instead of just the outer row
contacting the prey, these crushing teeth occur in bands that bring several
rows into action at a time, forming a broad crushing plate. Nurse Sharks eat
both invertebrates and fishes, and their teeth are broad with small points
and with several rows functioning in the bite. In many rays, the teeth are
entirely flattened and arranged like paving blocks on a roadbed, providing
the perfect crushing surface.
The Cookiecutter Shark (Isistius
brasiliensis) is a small tropical spe-
cies that parasitizes tunas, sharks,
and marine mammals, gouging out
plugs of flesh with specialized teeth.
A White Shark photographed near
Guadalupe Island, Mexico, in 2011
had a fresh Cookiecutter bite mark
just behind its jaws. Photo by C. S. John-
son, from Springer and Gold ( 1989 ); used with
permission of the Smithsonian Institution
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