What you can do with an extra jaw - Darien Satterfield

翻译人员: David Shi 校对人员: Helen Chang

After stalking an unsuspecting cuttlefish across the seafloor,

在海底跟踪了一条毫不知觉的 墨鱼一段时间后，

this moray eel is finally ready to pounce.

这条海鳗终于准备进攻了。

As the eel snags the mollusk in its long teeth,

当海鳗长长的牙齿咬住 这个软体动物后，

its prey struggles to escape.

它的猎物拼命地试图挣脱。

But before it can wriggle away,

但在它能成功逃脱前，

a second set of teeth lunge from the eel's throat,

海鳗喉咙里的第二套 牙齿咬了上来，

making short work of the captive cuttlefish.

让猎物无法逃脱。

This adaptation is called a pharyngeal jaw.

这个进化被称为咽颚。

And while it might seem more fitting for an alien parasite than a fish,

虽然它更像来自外星的寄生虫， 而不是一条鱼，

it's actually one of the most common adaptations under the sea.

而事实上它是海底 最常见的进化之一。

At some point millions of years ago,

在数百万年前的某个时间点，

early fish evolved a jointed oral jaw from one of the bony arches

早期鱼类从一个嘴弓进化出了 一个连接在一起的口腔颌骨，

that supported their frontal gills.

它可以支撑它们前面的鱼鳃。

This exterior, oral jaw was perfect for capturing or chewing prey,

这个外部的口腔颌骨非常适合 抓捕或咀嚼猎物，

but these early fish had a problem.

但这些早期鱼类有一个难题。

They had no limbs to manipulate food while eating,

它们没有肢体来操弄食物，

making it easy for their mobile prey to escape

在它们咬第一口之前，

before they took the first bite.

它们灵活的食物会很容易逃脱。

Essentially, it was impossible for fish to capture and chew their prey

简而言之，要鱼用 一套牙齿在同一时间

at the same time with just one set of jaws.

既抓捕又咀嚼是不太可能的。

So to hold their food and eat it too,

所以为了既抓住又食用它们的食物，

an even deeper gill arch evolved into a secondary set of jaws.

一个更深的鳃弓 就进化成了第二套牙齿。

Unlike oral jaws connected by a bone joint,

和由骨关节连接的口腔牙齿不同，

these pharyngeal jaws were suspended in muscle,

这些咽颚长在肌肉上，

offering them a wide range of motion to turn, tug, and tear on food.

使得它们能够对食物进行扭转、 拖拉和撕扯等一系列的动作。

Some pharyngeal jaws actively chew,

有的咽颚可以咀嚼食物，

while others retract to pull chunks of food down the throat.

而同时其它咽颚可以收缩 把食物块拖下喉咙。

Of course, the teeth a jaw has also factor in here.

当然，颚上所长的牙齿 也是一个重要因素。

For example, an oral jaw with fangs is exceptional for catching and holding

例如，长着尖牙的口腔颌骨 非常容易捕获并抓牢

on to fast-moving prey.

快速游动的食物。

But depending on what that prey is,

但由于食物的不同，

a fish might want sharp pharyngeal teeth to tear through tissue,

有的鱼可能需要锋利的咽齿 以便撕扯软组织，

flat pharyngeal molars to grind plant matter,

需要平的咽磨牙 以便研磨植物食物，

or a powerful pharyngeal bite to crush shelled prey.

或一个有力的咽牙 来咬碎带壳的猎物。

Fortunately some fishes can change their secondary teeth

幸运的是，有些鱼能够花几年时间 更换它们的第二套牙齿，

to match a new diet over several years.

以适应不同的食物。

This flexibility allows fish to adapt

这种灵活性使得它们能够适应

and find food in a huge variety of aquatic environments.

非常广泛的海洋环境并获取食物。

Some pharyngeal jaws have formed to eat food too hard for most fishes.

有的咽颚演化到可以吃 对大部分鱼都太硬的食物。

California Sheephead use pointed teeth from their oral jaws

加州羊头鱼使用嘴巴上的尖牙

to pry urchins off rocks before crushing their spiny exteriors

将海胆从岩石上撬开，

用强壮的已经和头骨融合的咽颚

in strong pharyngeal jaws that have fused with the bones of their skulls.

把海胆长满刺的身体压碎。

Other fish prioritize eating huge quantities of food.

有的鱼则偏重吃大量的食物。

The pharyngeal jaws of grass carp have two bone components

草鱼的咽颚有两个骨骼组件，

that move in unison to pull plant life into their stomachs,

它们一致行动以便 把植物拖进它们的胃，

consuming over 18 kilograms of seaweed a day.

这样它们可以一天吃掉 超过18公斤的海藻。

Other pharyngeal jaws are adapted to suit incredibly specific circumstances.

其它咽颚演化到能适应 令人难以置信的特定环境。

Consider this species of pearlfish that lives inside sea cucumbers

比如这种珍珠鱼， 它们生活在海参身体里面

and feeds on their guts.

并以它们的内脏为食。

Fish are the most diverse group of vertebrates

鱼类是最多样化的脊椎动物群体，

with over 30,000 unique species,

它们拥有超过 30,000 种独特的物种，

and much of that diversity is due to the hundreds of unique jaws

而大部分的多样性是 由于数百个独特的颌骨，

separating otherwise identical species.

使得它们和其它相同 的物种不一样。

Perhaps the best example of this dental diversity can be seen in cichlids.

也许慈鲷是多样性牙齿的最好例子。

This family of fish is primarily found in select African and South American lakes.

该鱼科主要分布于 非洲和南美的某些湖泊。

Typically, large lakes like these would be occupied

通常像这样的大湖

会被少数远亲物种占用，

by a handful of distantly related species,

each adapted to consume one of the lake's limited food sources.

而每种物种演化成食用 湖泊有限的食物中的一种。

But here, almost every corner of the ecosystem

但在这里，几乎生态系统的每个角落

is occupied by a different species of cichlid.

都被不同的慈鲷物种占据。

There are over 1,700 cichlid species,

有 1,700 多种的慈鲷，

many almost identical save for their uniquely adapted jaws

许多都有独特的 几乎完全相同的下颚，

which have evolved to eat crustaceans, mollusks, worms, algae, plankton,

这些演化使得它们可以吃甲壳类动物、 软体动物、蠕虫、藻类、浮游生物，

and even the scales of other fish.

甚至其他鱼的鳞片。

These oral adaptations are so essential for survival,

这些嘴的进化 对它们的繁衍至关重要，

that different species use their pharyngeal jaws

使得不同的物种可以使用咽颚

to make unique mating sounds

来发出独特的交配声音，

that allow female cichlids to identify males of their own species.

这样雌性慈鲷得以识别 属于自己物种的雄性。

This technique limits interspecies breeding,

这个技能限制了 不同种类间的交配，

and ensures the parent fish will pass on their specialized jaws.

从而确保父母能遗传 它们独特的嘴巴。

Scientists are still discovering all the ways

科学家们仍在不断发现

this incredible skeletal mechanism functions.

这种令人难以置信的 骨骼机制的所有职能。

But given what we know already, it's fair to say that for most fish,

但鉴于我们已经知道的， 可以公平地说，对于大多数鱼来说，

two jaws are better than one.

两个嘴巴比一个好。