哺乳動物化石異型齒
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後設資料
- 資料識別：
- 系統識別碼:0b000001807cd945
- 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:同型齒異型齒 在多采多姿的生物世界中，哺乳動物可說是最為我們所熟知的一群，因為我們自己就是哺乳動物的成員之一。一般而言，哺乳動物具備了會分泌乳汁的乳腺、毛髮、胎盤、紅血球無細胞核…等多樣特徵。然而，這些特徵卻會隨著動物的死亡而消失地無影無蹤。
- 哺乳動物的牙齒和骨骼遺骸所形成的化石，正是古生物學家追尋哺乳動物，研究與探索哺乳動物演化歷程的重要線索。哺乳動物乃屬於異型齒，即牙齒可區分為門齒、犬齒、前臼齒與臼齒，型態與功能皆有所不同，而有別於爬行動物的同型齒—及所有牙齒的型態與功能皆相似。
- 不同種類的哺乳動物，也會因著食性的差異或行為上的發展，牙齒特化成各種形式。古生物學家正可利用這些特徵，將哺乳動物-不論是現生種或已滅絕的化石種，一一分門別類，再進一步深入研究其演化親緣關係。例如現今全世界的大象僅存亞洲象和非洲象，但是從世界各地所找到的各式各樣大象化石中，顯示大象在5千萬年前起源於北非，曾經在新生代盛極一時，種類超過了400種，足跡幾乎遍佈全世界。當然也曾經遷徙至台灣，在此地繁殖、演化，而留下了許多珍貴的化石證據。
- 一般而言，食肉動物（獅子、老虎）犬齒發達，前臼齒與臼齒齒尖峰利並形成裂齒，以利撕裂、切割食物；草食動物（牛、羊）則是上門齒及犬齒退化，前臼齒與臼齒扁平且齒尖形成半月型，作為研磨食物之用；還有些哺乳動物（例如豬、猴子）以發達的犬齒作為嚇阻敵人及競爭交配的利器。
- 唯一的例外，就是在哺乳動物中最為奇特的鯨家族，牠們退化成同型齒（齒鯨亞目），甚至無齒（鬚鯨亞目）。這可能反映了牠們在重返海洋，適應完全水中生活的過程中，牙齒不再需要如此複雜與特化的形式；而這也顯示了哺乳動物在生態適應與演化歷程中的多樣化。
- Mammals Heterodonts
- Mammals are probably the group we are most familiar with in the colorful world of biology. We are after all mammals ourselves. Generally speaking, mammals are characterized by the possession of mammary glands, hair, placenta and red blood cells with no nucleus. When an animal dies, however, these features eventually disappear without a trace.
- For paleontologists, the fossils formed by the teeth and skeletons of mammals provide them with important clues for studying how mammals evolved. Mammals have heterodont dentition, meaning their teeth are divided into different types such as incisors, canines, premolars and molars. Each type has its own purpose as well, unlike reptiles with their homodont dentition – i.e. all the teeth have the same shape and similar functions.
- The teeth of mammals have gradually evolved into more specialized forms due to differences in diet and behavior. Paleontologists can use these features to classify each mammal and study how they relate to each other on the evolutionary adaptation. These can be living species or extinct fossils. For example, only the Asian and African elephants now survive on the planet. Elephant fossils from around the world, however, show that elephants originated 50 million years ago in North Africa. They were extremely successful during the Cenozoic Era with more than 400 species spread throughout the world. At one point, they migrated to Taiwan where they reproduced and evolved, leaving behind many precious fossils.
- Generally speaking, carnivores (such as lions and tigers) have very well developed canines while the premolars and molars have sharp points, forming carnassials (scissor teeth) for ripping and cutting food. In herbivores (such as cattle and sheep) the upper incisors and canines are reduced or absent while the premolars and molars have become flattened. The points also form a half-moon shape for grinding up food. Some mammals (such as pigs and monkeys) have very well developed canines for intimidating their enemies and competing for mating.
- The only exception is the whale group. They are an unusual branch of the Mammalian Family that devolved back to homodonts (Odontoceti) or even no teeth (Mysticeti). This may reflect how their complete adaptation to an aquatic existence after returning to the seas meant there was no need for complicated or specialized teeth. It also demonstrated the diversity in mammals when it came to adaptation and evolution.
- 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
授權聯絡窗口
- 鍾舜丞
04-23226940*762
chungnmns@nmns.edu.tw
