Why did Megalodon go extinct? - Jack Cooper and Catalina Pimiento

譯者: 穎君 紀 審譯者: Helen Chang

In 1667, a Danish scientist finally concluded that certain mysterious stones

1667 年，丹麥科學家 判定一顆神秘的石頭

prized for their supposed medicinal powers,

—據說可以治病，因而受到重視—

hadn’t fallen from the sky during lunar eclipses

不是月蝕期間從天上掉下來的，

and weren’t serpent tongues.

也不是蛇的舌頭，

In fact, they were fossilized teeth—

而是牙齒的化石—

many belonging to a prehistoric species that would come to be called megalodon,

屬於生存在史前時代的巨齒鯊，

the biggest shark to ever live.

有史以來最大隻的鯊魚。

So what was it like when megalodon ruled the seas?

那麼，巨齒鯊稱霸海洋時， 水面下的生活是什麼樣子呢？

And what brought this formidable predator to extinction?

巨齒鯊為什麼滅絕了呢？

Because their skeletons were cartilaginous,

因為巨齒鯊的骨骼是軟骨，

what remains of megalodons are mostly scattered clues,

所以巨齒鯊死後留下的化石相當零碎，

like some isolated vertebrae and lots of their enamel-protected teeth.

像是一塊塊的脊椎骨， 和許多被琺瑯質保護的牙齒。

Like many sharks, megalodons could shed and replace thousands of teeth

和其他鯊魚一樣，

巨齒鯊在牠們的一生中 換下數以千計的牙齒。

over the course of their lives.

Interestingly, some fossil sites harbor especially high numbers

有趣的是，有些化石挖掘地

藏有特別多小顆的巨齒鯊牙齒。

of small megalodon teeth.

Experts believe these were nurseries that supported countless generations

專家認為這些地方是巨齒鯊的育嬰場所，

養育無數幼小的巨齒鯊們成長茁壯。

of budding megalodons.

They grew up in sheltered and food-packed shallow waters

牠們在糧食充足、環境安全 的淺水區域長大，

before becoming unrivaled adult marine hunters.

之後長大成為所向無敵的 成年水生狩獵者。

Looking at the similarities with great white shark teeth,

觀察巨齒鯊牙齒 和大白鯊牙齒的相似處後，

scientists estimate that megalodons might have stretched up to 20 meters—

科學家估計巨齒鯊身長 可能長達 20 公尺，

three times longer than great whites.

整整是大白鯊的三倍。

And during their reign, which began around 20 million years ago,

距今兩千萬年前是巨齒鯊的全盛時期，

megalodons lived just about everywhere,

那時隨處可見牠們的蹤影，

with individuals also potentially undertaking transoceanic migrations.

有些個體可能正在跨洋遷徙的半路上。

The world was warmer and the ocean was brimming with life.

那時全球氣溫較溫暖， 海洋裡的生命欣欣向榮，

Otters and dugongs thrived in newly formed kelp forests,

水獺和儒艮在新形成的 巨藻林裡繁衍生息，

and baleen whales were at their most diverse.

鬚鯨在當時則擁有最多樣化的基因。

Megalodons had no shortage of high-energy, edible options.

巨齒鯊不缺高營養價值的可食獵物，

And it seems they were ambitious eaters.

而且似乎牠們的食慾相當旺盛。

Generally, as carnivores consume protein-rich meat,

食肉動物吃下富含蛋白質的獵物時，

certain nitrogen isotopes accumulate in their tissues—

有幾種氮同位素會累積在體內組織裡，

including the enamel of their teeth.

包括牙齒琺瑯質裡。

Analyzing megalodon teeth, scientists confirmed they were apex predators

分析完巨齒鯊的牙齒後，科學家確認 巨齒鯊是當時的頂級掠食者，

that not only ate large prey species—

牠們不僅只吃大型獵物，

but also other predators, perhaps even each other.

還可能吃下其他掠食者，甚至彼此。

In addition to megalodon’s teeth,

除了牙齒之外，

researchers have access to one exceptionally well-preserved spinal column

科學家還經手研究了一條 保存狀態極好的脊椎骨，

that comprises 141 vertebrae of a 46-year-old megalodon.

有 141 節椎骨， 主人是 46 歲的巨齒鯊。

A 3D model of the megalodon’s body suggests that its stomach

巨齒鯊身體的 3D 模型表明

巨齒鯊的胃容量高達接近一萬公升，

could reach volumes of almost 10,000 liters—

big enough to fit an entire orca.

裝得下一整隻虎鯨。

Reconstructing their jaws, researchers think megalodons could eat

重建巨齒鯊的上下顎之後，學者認為

牠們或許可以只用四口就吃下 已滅絕的 7 公尺長抹香鯨。

a now-extinct 7-meter sperm whale in as few as four bites.

And the fossilized bones of ancient cetaceans do indeed show evidence

古老鯨豚類動物的化石上

也看得到巨齒鯊的咬痕， 有些咬痕已經癒合，

of megalodon bite marks— including some that healed over,

confirming that megalodons pursued live prey.

因此證實巨齒鯊會獵食活的獵物。

But if megalodons were so powerful, why did they go extinct?

既然巨齒鯊那麼強悍， 那到底為什麼會滅絕？

It seems there were a few contributing factors.

有幾個因素。

By the time they disappeared around 3.5 million years ago,

牠們滅絕時，也就是 距今 350 萬年前，

the global climate had cooled,

全球氣溫下降，

causing more glaciers to form and the sea level to drop.

冰河擴大，導致海平面下降，

This dried up many coastal habitats,

讓許多淺灘生態區乾涸，

meaning some of the world’s most resource-rich marine sites were lost.

也就代表牠們失去許多 提供牠們豐富營養來源的地點。

About a third of all marine megafauna eventually went extinct,

約三分之一的巨型水生生物走向滅絕，

so fewer prey species were available.

所以能捕食的獵物數量銳減。

And megalodons already faced high energetic demands because of their size

巨齒鯊本身又需要大量能量， 因為牠們體型龐大，

and the mechanism they likely used to regulate their body temperature,

控制體溫的機制也消耗許多熱量，

which allowed them to navigate cold waters

牠們才能在低溫水體中活動自如，

and attack prey with bursts of speed.

在轉眼間捕捉到獵物。

Environmental changes may have made megalodons vulnerable

環境條件變化可能威脅到巨齒鯊的生存，

and increasingly put them in competition with other predators,

讓巨齒鯊跟其他掠食者的競爭更加激烈，

including the great white shark, a relative newcomer.

其中包括大白鯊，相對較晚出現的對手。

Because megalodons were highly mobile predators,

巨齒鯊掠食範圍廣大，

their extinction had global consequences.

所以牠們的滅絕會影響到全世界。

The end of their long-distance travels probably disrupted nutrient transport

沒了巨齒鯊長距離的移動，

很可能讓不同生態系統間的 營養傳輸鏈斷裂，

between different ecosystems.

And many animals were suddenly released

使得許多動物突然從 被巨齒鯊咬噬的壓力中解放。

from the immense predatory pressure of their bite.

Interestingly, some marine mammals dramatically increased in size afterwards,

有趣的是，有些水生哺乳類的 身體尺寸在巨齒鯊滅絕後變大，

which was perhaps partially afforded

部分原因可能是

because they were no longer dealing with such a mega-existential threat.

牠們再也不用面對 如此重大的存亡危機。

Knowing that the decline of apex predators can destabilize entire ecosystems,

因知頂級掠食者的稀缺 會撼動整個生態系統，

conservationists are working to prevent today’s sharks from facing a similar fate—

所以現在環境保育家們著手保護 海裡的鯊魚，以免重蹈覆徹，

this time, because of humans.

這次是從人類手中保護牠們。

And meanwhile, the megalodon remains a colossal testament

巨齒鯊成為生態系統內 生物互相依附而生存的鐵證，

to ecological interdependence

and millions of years of bones well-bitten and waters well-wandered.

以及百萬年來攪亂水流、 咬食獵物的風雲動物。