国家地理:Explorer: Ultimate Shark 终极者——鲨鱼

（单词翻译）

What exactly is the power that drives nature's most famous jaws²? In New Zealand, this great white shark drowned in a fisherman's net. And scientists Kara Yopak and Clinton Duffy are preparing an ultra-rare great white shark dissection³.

"Ah, I've never dissected⁴ one that is the size before."

It's a unique opportunity to study a great white's near-perfect design, including its fearsome jaws.

"The jaws of great white are really, really valuable. So most of the time, if we do get a specimen⁵ to measure, it looks a little bit more like this. Not nearly as pretty. That fishermen know pretty much. We're catching⁶ animal of, yes, for, um, a fishing competition or even just in its net. Um, we'll remove the jaws and quite often its fins⁸ as well. The jaws are amazingly valuable. Uh, they can go anywhere, from ten to twenty thousand dollars. Um, you can see them, I mean, being sold on eBay. It's kind of such a status symbol. Everybody knows the great white shark. When you have an idea of shark in your head, it's gonna be this one."

Look at the jaws.

The jaws of a great white are evolutionary⁹ marvel¹⁰. They actually burst forward, allowing for a bite that shears¹¹ up to 30 pounds of flesh in a single mouthful. About 50 teeth lie in the front of a great white's jaws. The lower teeth act like daggers¹², stabbing and holding prey¹³ in place. The larger upper teeth are like steak knives, slicing off giant mouthfuls of a victim. And behind this front row of teeth are literally¹⁴ hundreds of others, ready to be pressed into service. But to truly understand this extreme design, you have to go beneath the skin.

Unlike human beings, the great white's jaws aren't fused to the skull¹⁵. They hang loosely underneath¹⁶ the braincase, ready to execute their signature bite. First, the snout rises and opens the mouth. At the same time, the lower jaw¹ pushes down, widening the gape¹⁷. Next, special muscles in grooves¹⁸ in the skull push the upper jaw forward, exposing gums and teeth. The lower jaw rises, latching¹⁹ onto the prey, and the snout slams down, hammering the upper jaw with almost 700 pounds of force.

These extraordinary teeth are clearly designed to kill, but they may also serve another purpose: delivering a message to other great whites.

"She actually has some scarring out here. You can see where this scar's coming down, turn around underneath the eye. The ones on the side of a pectoral fin⁷, they appear to be shark bites. This one is likely to be a tooth mark, possibly another shark. These guys are not necessarily one big happy family when they get together."

Great whites can be covered in battle scars. It's believed they bite one another to assert dominance, compete for a meal and even to mate.

"How these guys get together, of course, and don't kill each other is an, it's a really interesting question."

braincase: The part of the skull that encloses the brain; the cranium. Also called brainpan

snout: The projecting nose, jaws, or anterior facial part of an animal's head

pectoral fin: Either of the anterior pair of fins attached to the pectoral girdle of fishes, corresponding to the forelimbs of higher vertebrates