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  • Meet Odontochelys semitestacea.

    譯者: Lilian Chiu 審譯者: Carol Wang

  • This little creature spends its days splashing in Late Triassic swamps

    來見見半甲齒龜。

  • with a host of other reptiles.

    這小生物會整天在 晚三叠世的沼澤中玩水,

  • Under the surface lies its best defense against attack:

    和其他爬蟲類一起玩。

  • a hard shell on its belly.

    在水面之下,有著 抵禦攻擊的最佳防護:

  • Odontochelys is an early ancestor of the turtle.

    腹部的硬殼。

  • Its half-shelled body illustrates an important point about the modern turtle:

    半甲齒龜是烏龜的早期祖先。

  • it actually has two shells that develop totally separately

    牠的身體上有半甲,可以說明 現代烏龜的一個重要特點:

  • while the turtle is still an embryo.

    烏龜其實有兩個殼,

  • Both are extensions of the animal's skeleton,

    在胚胎就是完全分開發展的。

  • and together they are made of almost 60 bones.

    兩個殼都是從該動物的 骨骼延伸出來的,

  • Like other embryos,

    加起來,它們一共由 近六十塊骨頭組成。

  • turtle embryos are made of undifferentiated cells

    和其他胚胎一樣,

  • that become specific cell types,

    烏龜胚胎是由未分化的細胞構成,

  • and then organs and tissues,

    它們會變成特定的細胞類型,

  • through gene activity and communication between cells.

    接著透過基因活動 以及細胞之間的溝通,

  • At first, turtle embryos look very similar to those of other reptiles,

    變成器官和組織。

  • birds, and mammals,

    一開始,烏龜胚胎 看起來和其他爬蟲類、

  • except for a bulge of cells called the carapacial ridge.

    鳥類、哺乳類的胚胎很相似,

  • The ridge expands around the body between the neck and lower back,

    差別只有一塊細胞 凸起,稱為背甲脊。

  • creating a disc shape.

    背甲脊沿著身體擴張, 從脖子一直延伸到下背,

  • It guides the formation of the upper part of the turtle's shell,

    創造出一個圓盤型。

  • called the carapace, likely by attracting the cells that will become ribs.

    它引導了龜殼上半部的形成,

  • Instead of curving downwards to make a regular rib cage,

    上半部稱為背甲,形成方式 可能是吸引會變成肋骨的細胞。

  • the ribs move outwards towards the carapacial ridge.

    這些肋骨並沒有向下彎曲 形成一般的胸廓,

  • They then secrete a signaling protein

    反而朝背甲脊的方向向外移動。

  • that converts surrounding cells into bone-forming cells.

    它們能夠分泌一種訊號蛋白質,

  • These fifty bones grow until they meet and connect with sutures.

    將周圍的細胞轉換為 形成骨頭的細胞。

  • A ring of bone solidifies the carapace's edges.

    這五十塊骨頭不斷成長, 直到相碰、相接,形成縫合線。

  • The outer layer of skin cells produces the scales, known as scutes,

    一圈骨頭讓背甲的邊緣 變得更堅固。

  • that cover the carapace.

    皮膚細胞的外層會產生鱗片, 即一般所知的鱗甲,

  • The development of the bottom half of the shell, the plastron,

    將背甲覆蓋住。

  • is driven by neural crest cells,

    龜殼的下半部的發展, 也就是胸甲的發育,

  • which can produce a variety of different cell types including neurons,

    是由神經脊細胞所驅動,

  • cartilage and bone.

    這些細胞能產生各種細胞類型,

  • A thick shield of these cells spreads across the belly,

    包括神經元、軟骨,和骨頭。

  • coming together in regions that produce nine plate-like bones.

    這些細胞所形成的厚盾 散佈在整個腹部上,

  • Eventually, these connect to the carapace by sutures.

    集結起來,在一些部位 產生出九塊板狀的骨頭。

  • A turtle's shell has obvious advantages for guarding against predators,

    最後,透過縫合線, 它們會和背甲連結起來。

  • but the rigid casing also presents some challenges.

    龜殼很明顯有利於 抵抗捕食性動物,

  • As the turtle grows,

    但堅硬的外殼也造成了一些困難。

  • the sutures between the bones of the carapace and plastron spread.

    隨著烏龜長大,

  • Most mammals and reptiles rely on a flexible rib cage

    背甲和胸甲的骨頭 之間的縫合線會伸展開。

  • that expands to allow them to breathe,

    大部分的哺乳類和爬蟲類

  • but turtles use abdominal muscles attached to the shell instead:

    仰賴擴張有彈性的胸廓, 讓牠們能夠呼吸,

  • one to breathe in, and one to breathe out.

    但烏龜卻是用連結在 龜殼上的腹部肌肉:

  • So how did the shell evolve?

    一組肌肉拉動肺部吸氣, 另一組肌肉擠壓肺部吐氣。

  • Though there are still gaps in the fossil record,

    所以,龜殼怎麼演進?

  • the first step seems to have been a thickening of the ribs.

    雖然在化石記錄中 還有些空白未知之處,

  • The oldest known turtle ancestor,

    第一步似乎是肋骨變粗。

  • a creature called Eunotosaurus africanus,

    我們所知最古老的烏龜祖先

  • lived 260 million years ago and looked almost nothing like a modern turtle,

    是一種叫做正南龜的生物,

  • but it had a set of broad, flat ribs

    牠們生活在兩億六千萬年前,

  • that anchored the muscles of its powerful forearms.

    看起來一點也不像現代的烏龜,

  • Eunotosaurus was likely a burrowing creature,

    但牠們有一組寬廣、平坦的肋骨,

  • digging homes for itself in what's now southern Africa.

    用來固定其強壯前臂的肌肉。

  • Odontochelys semitestacea illustrates another, later step in turtle evolution,

    正南龜很可能是會挖地洞的生物,

  • with thick ribs like Eunotosaurus plus a belly plate for protection.

    在現今的南非,自己挖洞造窩。

  • Our first fossil evidence of the full shell characteristic of modern turtles

    半甲齒龜則代表了烏龜 演化過程中較後段的另一步,

  • is about 210 million years old,

    牠們有正南龜的粗肋骨, 再加上腹部的保護板塊。

  • and belongs to a species called Proganochelys quenstedti,

    我們所能找到具有現代龜殼 所有特性的化石證據當中,

  • whose ribs had fused.

    最早的來自大約兩億一千萬年前,

  • Proganochelys could move between water and land.

    隸屬於一種叫做原顎龜的物種,

  • Unlike modern turtles, it couldn't retract its head into its shell,

    牠們的肋骨是接在一起的。

  • but had defensive spines on its neck.

    原顎龜可以在水中及陸地上移動。

  • Modern turtle shells are almost as diverse as the turtles themselves.

    和現代烏龜不同, 牠們無法把頭縮到龜殼中,

  • Sea turtles have flatter, lighter shells for streamlined gliding through the water.

    但在脖子上有防禦用的刺。

  • Land-dwelling tortoises, meanwhile,

    現代烏龜的殼,幾乎 和烏龜本身一樣多樣化。

  • have domed shells that can slip free of predators' jaws

    海龜的殼比較平、比較輕, 流線造型讓牠們能在水中滑行。

  • and help them turn right-side up if they fall on their backs.

    至於生活在陸地上的陸龜,

  • Leatherback and softshell turtles

    則有半球形的殼,被捕食性 動物咬住時還可以滑出來,

  • have shells without the ring of bone around the edge of the carapace

    且如果翻過來的時候, 可以協助牠們翻身回來。

  • or the tough scutes covering it,

    稜龜和軟殼龜

  • making it easier for them to squeeze into tight spaces.

    背甲的邊緣沒有一圈骨頭,

Meet Odontochelys semitestacea.

譯者: Lilian Chiu 審譯者: Carol Wang

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B2 中高級 中文 美國腔 TED-Ed 烏龜 細胞 骨頭 肋骨 腹部

龜殼是如何進化的......兩次--朱迪-塞布拉-托馬斯。 (How turtle shells evolved... twice - Judy Cebra Thomas)

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    Sophie 發佈於 2021 年 01 月 14 日
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