託福聽力裡面有很多讓人覺得難以理解的內容，其實回顧內容的時候會發現並不難，只是聽的時候由於缺乏相關背景知識，讓我們的推導能力受到了限制。所以，我們推出了【託福奇葩背景知識系列】，不僅漲分數，還漲姿勢哦！
#託福奇葩背景知識系列#
提到大長腿你們不要只想到維密天使好吧
很多可愛的小動物也是有大長腿（或者大粗腿）的
比如說，鯨魚
你腦中的畫面是不是很詭異哈哈哈哈像這樣
咳咳，圖是杜撰的，不過事兒是真的。
這也是被稱為「生物學知識不夠的人肯定不會相信的奇葩事實」之一。
我們都知道鯨魚是哺乳動物，它的祖先是來自陸地的。根據化石特徵的判斷，鯨魚應該由某種陸地食肉動物，而且是蹄類食肉動物進化而來。
那麼，鯨魚為什麼要從陸地走向海洋，我們是怎麼發現這個進化過程的呢？
一起來看看吧。
Ambulocetus
The Ambulocetus was a genus of animals represented by a single species that inhabited our planet a short time ago in comparison with the dinosaurs.
Its name literally means 「walking whale」 and it is a huge prehistoric semi-aquatic animal that inhabited shallow water areas where it could walk and swim. It has been classified among the cetacean mammals.
They inhabited during what we know as the Cenozoic Era, which appears after the Mesozoic Era (that of the dinosaurs). The Cenozoic Era is quite wide and is divided into several stages, the Ambulocetus inhabited in the Paleogene period.
This genus is said to be the ancestors of today’s whales and to have a physical appearance very similar to today’s crocodiles. It is also speculated that it would have attacked like the crocodiles, waiting for its prey on the shores.
History of the discovery
The first remains of this creature were found in 1994, in Asia, more precisely in the Sulaiman mountain range, located in Pakistan. In a rocky terrain where the ancient Tethys Sea used to be.
Searchers of prehistoric vestiges from Michigan carried out an excavation in which they found very complete fossil remains that would correspond to the hind limbs, vertebrae, ribs and a whole skull of a prehistoric mammal.
This discovery was somewhat disconcerting for its discoverer Johannes GM Thewissen, since this animal had legs similar to those of a land animal but these were webbed, which made swimming easier.
In addition, Thewissen discovered in the fossil remains that the bones of the ear were very similar to those of today’s whales, so he was quick to relate this creature to whales.
Thewissen called this animal Ambulocetus natans.
Later on, it has been proven that the Ambulocetus was a whale with legs, so it was considered one of the links in the evolution of the whale that started with the Pakicetus.
Since this discovery and until now, no more fossils have been found. However, skeletons of Rodhocetus and Basilosaurus have been found, which are species that evolved from the Ambulocetus.
摁頭看中文
現在小學生都知道鯨魚是哺乳動物，不過這一常識直到18世紀才開始被人類所了解。到了19世紀，進化論的奠基者們需要思考的問題是：鯨魚是如何產生的。
查爾斯·達爾文認為，鯨魚的近祖可以是某種熊。依據是黑熊也能在水裡遊很久。雖然他的本意是表達進化所具有的各種可能性：理論上講只要環境合適，熊完全可能進化成鯨魚的樣子。但是當時的人們把這曲解為「熊就是鯨魚的直系祖先」，並大肆加以嘲笑。最後他不得不在《物種起源》再版時把這段話刪去。託馬斯·赫胥黎為達爾文辯護：根據龍王鯨（Basilosaurus，4000萬到3500萬年前）化石的牙齒，鯨魚的確應該由某種陸地食肉動物進化而來。
博物學家和解剖學家威廉·弗勞爾不同意這種看法。他注意到龍王鯨的頭骨和一種古代有蹄類動物（Entelodontidae）相似，進而推測：鯨魚的陸地祖先應該是某種有蹄類雜食動物。因為紅皇后假說而聞名的凡瓦倫（Leigh Van Valen），在二十世紀六十年代提出中爪獸（mesonychid）這種早已滅絕的有蹄類食肉動物才是鯨魚的祖先。可惜到那時為止，人們發現的早期鯨魚（龍王鯨Basilosaurus、矛齒鯨Dorudon、原鯨Protocetus）都是完全的海洋生物，在缺乏過渡形態化石證據的情況下，這些理論更多來自推測。鯨魚、海豚一直只能作為一個單獨的種類被劃分為鯨目。
（G. G. Simpson 1945年的《分類學原理和哺乳動物的分類》The Principles of Classification and a Classification of Mammals裡就說：There is no proper place for them in a scala naturae.）
七十年代，人們在印度和巴基斯坦發現了一些四足動物的化石，菲利普·金格裡奇（Philip D.Gingerich）對化石的聽骨研究後發現，這種動物和鯨魚有親緣關係，因而命名為巴基鯨（Pakicetus）。
九十年代，又在巴基斯坦發現另一種更加過渡形態的鯨魚化石：走鯨（Ambulocetus）。
再加上其他化石的發現，從陸地鯨魚到海洋鯨魚，一個完整的鏈條終於建立起來。人們還發現，巴基鯨和偶蹄目動物的腳踝一樣，有一個明顯的雙滑輪形狀。這說明鯨魚的祖先很可能是偶蹄類動物。再後來，通過對基因序列的研究也證明，現存動物中鯨魚與河馬親緣關係最近，它們在5000多萬年前擁有共同的祖先；與反芻類動物、豬、駱駝等其他偶蹄目動物的關係次之。生物分類必須考慮系統發生，不同的科目要有不同的祖先，同時，一個科目最好包括共同祖先的所有後代。把鯨目單獨劃分在外的方式，破壞了偶蹄目的完整。因而，雖然聽起來很奇怪，鯨魚和海豚最後還是變成了偶蹄目動物。
資料來源：混亂博物館
打開TPO，看ETS給你講晚安故事
TPO2 Passage2 The Origin of Cetaceans
重點詞彙：
cetacean鯨類
gill鰓
fluke扇形尾部
affinity密切關係
in honor of向……致敬
archaeocyte原始細胞
jawbone下頜骨
mesonychids中爪獸
vestigial退化的，殘留的