Why are sloths so slow? - Kenny Coogan

譯者: Allison Huang 審譯者: Tammy Yuting Chiang

In 1796, Thomas Jefferson received a box of bones he couldn't identify.

1796 年，湯瑪斯·傑佛遜

收到了一隻不明生物的骸骨

A long, sharp claw reminded him of a lion,

又長又尖的爪子讓他想起了獅子

but the arm bones suggested a larger animal,

但牠的手臂骨頭看起來 像是更大隻的動物

one about three meters long.

一個大概三公尺長的生物

Thinking it might be huge unknown species of North American lion,

傑佛遜認為這可能是一種 新發現的巨大美洲擬獅

Jefferson warned explorers Lewis and Clark

他特別警告了探險家路易斯和克拉克

to keep an eye out for this mysterious predator.

一定要特別小心這種神秘的掠食者

But Jefferson's box of bones didn't come from a lion.

但是這些骸骨並不屬於獅子

它們來自於已絕種的巨大地懶

They came from an extinct giant sloth.

Prehistoric ground sloths first appeared around 35 million years ago.

史前地懶最早 是在 3 千 5 百萬年前出現

Dozens of species lived across North, Central and South America,

史前北美、中美及南美 有數十種地懶居住

alongside other ancient creatures like mastodons

與許多古老生物同時期

比如乳齒象

and giant armadillos.

還有大犰狳

Some ground sloths, like the megalonychid, were cat-sized,

一些地懶，像是二趾樹懶

大小和家貓差不多

but many were massive.

但也有許多地懶體型巨大

Jefferson's sloth, Megalonyx, weighed about a ton,

傑佛遜收到的骨頭屬於巨爪地懶

體重約一噸

and that was small compared to megatherium,

而大地懶的體型更加巨大

which could reach six metric tons, as much as an elephant.

可以達到 6 公噸

相當於一頭大象的體重

They ambled through the forests and savannas using their strong arms

牠們漫步於森林及莽原之中

強壯的手臂及尖利的爪子 可以將植物連根拔起

and sharp claws

to uproot plants and climb trees,

或是用來爬樹

grazing on grasses, leaves, and prehistoric avocados.

牠們吃草、樹葉和史前酪梨

In fact, we might not have avocados today if not for the giant sloths.

事實上

我們今天能有酪梨可吃

還得歸功於大地懶

Smaller animals couldn't swallow the avocado's huge seed,

體型較小的動物無法吞下酪梨的種子

but the sloths could,

但是地懶可以

and they spread avocado trees far and wide.

牠們將酪梨的種子散佈地又廣又遠

Ground sloths flourished for millions of years,

地懶繁盛地生存了數百萬年

but around 10,000 years ago, they started disappearing

但是在大約一萬年前

牠們開始漸漸消失

along with the Western Hemisphere's other giant mammals.

其他西半球的巨大生物也是如此

Researchers think that ground sloths could have been pushed out

研究人員認為地懶 可能是因為冰河期而開始滅絕

by an oncoming ice age,

或是因為和其他生物競爭而消失

or competition with other species, maybe humans,

地懶的競爭對手可能是人類

who arrived in the region around the time most of the sloths went extinct.

人類正好是在大部份 地懶消失的時期出現

Some of the smaller sloths did survive and migrated to the treetops.

一些體型較小的樹懶存活了下來

並且遷移到樹梢生活

Today, there are six species left living in the rainforest canopies

時至今日，仍有六種樹懶

生活在中美及南美的 熱帶雨林林冠之中

of Central and South America.

Hanging out in the trees is a good way to avoid predators,

在樹上生活可以避開掠食者

and there are plenty of leaves to eat.

而且還有很多樹葉可吃

But this diet has its drawbacks.

不過這種飲食習慣也有缺點

Animals extract energy from food and use that energy to move around,

動物透過從食物攝取的 能量供自己移動、

maintain their body temperature,

維持體溫、

keep their organs working,

使器官正常運作、

and all the other activities necessary for survival.

以及其他所有生存必須的活動

But leaves don't contain much energy,

但樹葉含有的能量少之又少

and that which they do have is tough to extract.

而樹葉之中僅有的能量 也很難被攝取利用

Most herbivores supplement a leafy diet with higher energy foods

大部分的草食動物除了樹葉以外

還會補充高能量的食物

like fruit and seeds.

像是種子還有水果

But sloths, especially three-toed sloths, rely on leaves almost exclusively.

但是樹懶，尤其三趾樹懶

幾乎完全只吃樹葉而已

They've evolved finely tuned strategies for coping with this restricted diet.

牠們演化出了專門 應付這種飲食的策略

First, they extract as much energy from their food as possible.

首先

牠們盡量從樹葉中攝取足夠的能量

Sloths have a multi-chambered stomach that takes up a third of their body,

樹懶的胃佔了身體的三分之一

而且有許多隔間

and depending on the species,

根據品種的不同

they can spend five to seven days, or even weeks, processing a meal.

樹懶可以花上五至七天

甚至是數週

來消化胃裡的食物

The other piece of the puzzle is to use as little energy as possible.

另一個策略就是減少能量的消耗

One way sloths do this is, of course, by not moving very much.

其中一個達成目標的方法

很明顯地，就是盡量少動

They spend most of their time eating, resting, or sleeping.

樹懶大部分的時間都在 吃飯、休息或者睡覺

They descend from the canopy just once a week for a bathroom break.

牠們一個禮拜只會 從樹冠上下來上一次廁所

When sloths do move, it's not very fast.

當樹懶移動的時候，通常都不是太快

It would take a sloth about five minutes to cross an average neighborhood street.

讓一隻樹懶跨越住宅區的馬路 會花上牠整整五分鐘

This unhurried approach to life means that sloths don't need very much muscle.

這種超緩慢的生活步調

使樹懶不需要太多的肌肉

In fact, they have about 30% less muscle mass than other animals their size.

事實上牠們比其他體型相近的 動物少了 30% 的肌肉量

Sloths also use less energy to keep themselves warm

樹懶們也盡量減少消耗 在保暖方面的能量

because their body temperature can fluctuate by about five degrees Celsius,

牠們的體溫變化範圍 可以達到攝氏五度

體溫變化較冷血動物的爬蟲類小

less than a cold-blooded reptile, but more than most mammals.

但是比大多數的哺乳類動物要大

這些生理上或者行為上的適應策略

These physical and behavioral adaptations minimize the sloth's energy expenditure,

將樹懶消耗的能量 代謝速率降到最低

or metabolic rate.

Three-toed sloths have the slowest metabolism of any mammal.

三趾樹懶的代謝速率 在哺乳類之中是最慢的

The giant panda is second slowest,

大貓熊的代謝是第二慢的

and two-toed sloths come in third.

而二趾樹懶則是第三慢

Moving slowly has allowed sloths to thrive in their treetop habitat.

緩慢的動作讓樹懶 得以在樹冠層棲地中繁衍昌盛

But it's also made the sloths themselves a great habitat for other organisms,

但這也使得樹懶自己 變成了其他有機生物的棲地

including algae, which provides a little extra camouflage, and maybe even a snack.

比如長在樹懶身上的藻類

能幫助樹懶偽裝

還能當零嘴吃

Sloths may not be giant anymore,

儘管樹懶的體型不再巨大

but that doesn't make them any less remarkable.

人們對樹懶的興趣還是絲毫未減