Science Standards by State
animals that have backbones have jaws. Some, such as birds, frogs,
and snakes, don't chew their food as you do. But most animals that
have bony skeletons do have jaws and chew their food. Dogs, cats,
horses, cows, and people chew their food before they swallow it.
Imagine that the fingers of your right hand were your upper jaw.
And the thumb of that hand was your lower jaw. Show, by moving fingers
and thumb, how upper and lower jaws would work in chewing a cracker.
Using only your right hand, how would you show how a dog chews? How
about a cat? A cow?
Now put a small cracker in your mouth. Rest your nose on the edge of your desk or a table as you chew. Does your lower jaw go up and down when you chew? Does your upper jaw go up and down the way your lower jaw does? Put another cracker in your mouth, but this time rest your chin on the table as you chew. Now show again by using your hand how jaws work as you chew. What part of your head moves in chewing? What part of your head does not move at all? Show once more, using only one hand, how your jaws work as you chew. If your eyes moved up and down as you chewed, wouldn't everything look blurred when you ate?
Some animals have jaws that don't work the same way yours do. Snakes, for example, have heads that are way too small to swallow large prey. So their lower jaw is in two halves, connected by rubbery ligaments that can stretch. When a snake grabs food such as a frog or a mouse, its sharp teeth, sloped backward, hold the food. Then the two halves of the lower jaw slowly separate and the jaws slowly "walk their way" over the prey. Pretty neat - if you are a snake!
Imagine what it would be like for you to try to eat a hamburger if you had no hands and if your lower jaw were in one single piece. You could "grab" it with your teeth, but that's as far as you could go. Yet if your lower jaw were in two halves, connected by ligaments, and your teeth were pointed and sloped backward, you could "walk your way" over the hamburger like a snake. Not easy, not much fun, and no talking while eating, but it might work. It does for snakes! If you ever get a chance to watch a harmless snake such as a garter snake swallow prey such as a frog or small mouse, do so. You might be surprised to see how so small a head can swallow such a large object.
Remember what happened when you chewed with your nose resting on the table or desk? Only your lower jaw moved up and down. But the lower jaws of alligators and crocodiles rest almost on the ground. They cannot drop their lower jaw as they gulp food. So for them, it's often their upper jaw that moves when they eat.
In insects that chew leaves, their jaws work sideways instead of up and down. A grasshopper, for example, chews a leaf while holding onto its edge. It would be nearly impossible for a grasshopper to sit on the surface of a leaf and chew it with jaws that worked from side to side.
It's fun to think about how the
jaws of various animals work. But it's not much fun to be fed on
by insects whose jaws are modified into a tube that has tiny cutting teeth
at the tip. You can't see how the jaws of a mosquito or of a biting
fly work. But they do work - better than I wish they did!