Form and Function of Sharks 31
mals when it grows to over 3 m in length. Fish-eating sharks (makos, Sand
Tigers) often have long, slender teeth for grasping, whereas sharks that
cut chunks from their prey have broader, serrated-edge teeth for cutting.
The teeth of White Sharks, especially in the upper jaw, reflect this dietary
switch, being more slender and spiky in young sharks and more triangular
in older, larger individuals. When a shark switches from low-energy fish to
high-energy whales, its growth rate accelerates (see “How fast do sharks
grow?” in chapter 6).
One might think that being a successful yet inefficient forager on dead
whales would be worth a little extra work, even if your teeth weren’t quite
up to the job. Recent biomechanical studies provide additional insight.
The jaw cartilage of White Sharks becomes stiffened (more mineralized)
after these animals reach 3 m in body length. Before that, their jaws, not
their teeth, might be damaged if they chomp down on tough, hidebound
prey. Spiky teeth and a fish diet may be the way they compensate for inad-
equate jaw strength while youngsters (although we’ve recently learned that
even young White Sharks will feed on marine mammals if the opportunity
arises).
The lamnoid White Sharks and their relatives have another type of
tooth before they are born, analogous to the baby teeth of mammals. As
embryos, their teeth are peglike and blunt, without cutting edges or ser-
rations. Most embryonic lamnoid sharks feed on eggs produced by the
mother while developing in the mother’s uterus. It is thought that their
blunt teeth prevent them from damaging the mother’s uterus while being
sufficiently functional to handle the eggs the mother produces. The excep-
tion in the group is the Sand Tiger, which actually cannibalizes its siblings
The teeth of young White Sharks
in both upper and lower jaws are
slender and sharp. Only later do the
upper jaw teeth take on the classic
triangular shape. Slender teeth are
better suited for capturing slippery
prey such as the fishes that make up
the diet of young White Sharks. Photo
by Gene Helfman