象的演化
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後設資料
- 資料識別：
- 系統識別碼:0b00000180ab8d91
- 資料類型：
- 型式:合集
- 紀錄類別:脊椎動物化石知識單元
- 主題與關鍵字：
- 學域-大分類:地質-化石類
- 分類:脊椎動物化石
- 拉丁界名:Animalia
- 中文界名:動物界
- 拉丁門名:Chordata
- 中文門名:脊索動物門
- 拉丁亞門名:Vertebrata
- 描述：
- 簡介:大象堪稱是當今世界上體型最大的陸生哺乳動物，它擁有壯碩的身軀、傲視群倫的長鼻與威武的大門牙。然而，卻在人類貪婪的獵捕與無情地破壞環境之下，它已逐漸沒落與凋零；儘管古生物學家從化石遺跡中，瞭解到大象家族曾經在地質年代中的新生代時期盛極一時，種類超過了400多種，足跡幾乎遍佈全世界；但是，令人感到無奈的是現今僅存亞洲象和非洲象二種，而它們也正面臨著滅絕的危機。
- 在分類地位上，象屬於哺乳綱長鼻目。象的祖先可以追溯至5500萬年前，在非洲北部埃及莫里斯湖附近的始祖象，體型僅有如現代的豬一般大小。始祖象尚未具備發達的門齒與長鼻，但是，其頭骨較長，眼眶位置靠前，下顎壯大，已經呈現長鼻目動物高度特化的頭骨的雛形；此外，亦可從臼齒齒冠磨蝕型態、門齒琺瑯質紋路與骨骼關節等特徵，進一步推斷始祖象與大象家族的親緣關係。
- 長象目動物經歷了複雜的演化歷程，除了始祖象亞目以外，尚有恐象亞目、乳齒象亞目、真象亞目等。各支系的象類發展趨勢各有不同，變化也大。而且，隨著遷徙到不同的棲息環境，經由輻射適應而演化出各種奇異的型式。例如：下門齒銳利且向內彎曲的恐象（恐象亞目），上下門齒皆發達且相互交錯的嵌齒象（乳齒象亞目），下門齒發展成平鏟狀的鏟齒象（乳齒象亞目），門齒像一把短利刃的劍齒象（真象亞目），還有最為我們熟知身披長毛且門齒劇烈彎曲的猛象（真象亞目）。
- 大約在更新世晚期（距今約4萬年至2萬年前），真象科中的一支—古菱齒象，由華北地區經長途跋涉來到了台灣。這類大象具有既長且直的大門牙，高聳的背部脊椎神經棘，臼齒齒板磨蝕略呈菱形。在台灣的澎湖海溝發現了成千上萬的古菱齒象化石，顯示它們曾經在此地度過一段繁盛的歲月。而今，繁華的景象早已不復在，古菱齒象所遺留既珍貴且豐富的化石遺骸，正是我們研究其演化史、探索古地理與古氣候環境變化、解開古菱齒象滅絕之謎的重要線索與證據。
- Mammals Evolution of Elephants
- 哺乳動物化石概論
- The elephant is the largest terrestrial mammal in the world today. It has a strongly built body, a long trunk and powerful incisors. These noble animals are, however, gradually being driven to extinction by greedy poachers and environmental destruction. Fossil evidence suggests that the elephant family reached its peak during the Cenozoic Era with over 400 different species spread throughout the world. Unfortunately, only the Asian and African elephants are left, and these two species are faced with the threat of extinction as well.
- Elephants belong to the Order Proboscidea in the Mammalia class. Elephants trace their ancestry back to the Moeritherium that appeared 55 million years ago in northern Africa around Egypt and Lake Moeris and was about the size of a modern pig. The Moeritherium lacked the well-developed incisors and trunk, but its longer skull, forward eye sockets and powerful lower jaw were the prototype for the highly-specialized skulls of later Proboscidean . The wear pattern on the molar crows, the texture of the incisor enamel as well as the shape of the skeletal joints all suggested a relationship between the Moeritherium and the elephant family.
- The proboscidean animal underwent a complex evolutionary process. Apart from the Moeritherium , there were also the Deinotheriidae , the Mammutidae and Elphantidae . Each family evolved and changed in very different ways as well. As they moved into different habitats, all kinds of strange forms evolved due to radiative adaptation. For example, the Hoe Tusker ( Deinotheriidae ) evolved sharp lower incisors that curved inwards, the Gomphotheres ( Mammutidae ) well-developed intersecting upper and lower incisors, the Mastodon ( Mammutidae ) shovel-like lower incisors, the Stegodon incisors like short knives ( Elephantidae ) and the woolly Mammoth long curved tusks ( Elphantidae ) that we know so well.
- During the late Pleistocene Epoch (around 40,000 to 20,000 years ago), the Palaeoloxodon , a branch of the Elephantidae family, migrated through Northern China and arrived in Taiwan. This elephant species had long and straight incisors, a distinctive humped neural spine and molar tooth-plates that wear into a rough rhombus-shape. Tens of thousand of Paleoloxodon fossils were found in the Taiwan 's Penghu Channel, so they flourished in this area for some time. Though they have now died out, the rich variety of precious fossils they left behind offer important clues and evidence that we can use to study their evolutionary history and climate and weather changes in the past, and also use to solve the mystery of their extinction.
- 出版者：
- 數位化執行單位:國立自然科學博物館：地質學組脊椎動物化石學
- 管理權：
- 典藏單位:國立自然科學博物館
- 使用聲明:館內公開瀏覽
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- 鍾舜丞
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chungnmns@nmns.edu.tw
