獺形狸尾獸
Castorocauda

context: zh_tw: 在柱齒獸目中，獺形狸尾獸似乎與歐洲的卡路沙齒獸及辛氏柱齒獸接近。這顯示歐洲及亞洲在侏羅紀中期出現了一次動物遷徙。這兩個大洲可能日後會被圖爾蓋海峽所分隔。
en: Among docodonts, Castorocauda appears to have been related to Krusatodon and Simpsonodon, both European animals. This may be evidence that Europe and Asia underwent a faunal interchange in the Middle Jurassic. The two continents would later be separated by the Turgai Strait.
qas: question: zh_tw: 獺形狸尾獸與那兩個齒獸有關係？
en: Castorocauda was related to which two docodants?
answers: zh_tw: text: 卡路沙齒獸及辛氏柱齒獸
en: text: Krusatodon and Simpsonodon

context: zh_tw: 柱齒獸目一般都有獨特的牙齒，而獺形狸尾獸的牙齒卻有可分辨的特徵。獺形狸尾獸的牙齒在很多方面都與其他柱齒獸目的不同，主要原因是牠們的食性不同。大部份的柱齒獸目都是雜食性的，但獺形狸尾獸的牙齒顯示牠們是魚食性的，以魚類及細小的脊椎動物為食物。牠的首兩顆臼齒有直排的月角，可見不是用來磨食物，而是用來咬住食物。這種特徵可以在其哺乳動物親屬的三錐齒獸目見到，但卻明顯是從獺形狸尾獸處衍生而來。這些臼齒亦是彎曲的，可以幫助咬緊光滑的獵物，非常像中爪獸目及海豹的牙齒。
en: Docodonts in general have distinctive teeth, and the teeth of Castorocauda have the distinguishing features of the group. The teeth of Castorocauda are different in many ways from all other docodonts, presumably due to a difference in diet (though see below). Most docodonts had teeth specialized for an omnivorous diet. The teeth of Castorocauda suggest that the animal was a piscivore, feeding on fish and small invertebrates. The first two molars had cusps in a straight row, eliminating the grinding function suggesting that they were strictly for gripping and not for chewing. This feature of three cusps in a row is similar to the ancestral condition in mammal relatives (as seen in triconodonts), but is almost certainly a derived character in Castorocauda. These first molars were also recurved in a manner adapted to hold slippery prey once grasped. These teeth are very similar to the teeth seen in mesonychids, an extinct group of semi-aquatic carnivorous ungulates, and resemble, to a lesser degree, the teeth of seals.
qas: question: zh_tw: 什麼導致了獺形狸尾獸的牙齒牙齒的不同
en: What is the likely cause for the difference in Castorocauda teeth?
answers: zh_tw: text: 食性不同
en: text: a difference in diet

context: zh_tw: 獺形狸尾獸的發現顯示了恐龍在 6 千 5 百萬年前消失前，哺乳動物的近親已經適應在水中生活。哺乳動物親屬在半水中的生活模式亦被推前了 1 億 1 千萬年。基於現時已知的化石，哺乳動物直至始新世才演化出半水中形態。由於只有少量的化石被發現，過往認為直至白堊紀－古近紀界線，所有哺乳動物都是細小、陸地生活的夜行性動物，是鼩鼱科、刺蝟、樹鼩目或馬島蝟科的族類。這個觀念已被像犰狳的 Fruitafossor、吃恐龍的爬獸、像鼯鼠的古翔獸及這種像水獺的獺形狸尾獸所推翻。
en: The discovery of Castorocauda lutrasimilis is the first sign that a close relative of mammals adapted to water before dinosaurs lost dominance 66 million years ago, pushing back the estimated date for mammal relatives adapted to a semi-aquatic lifestyle by 110 million years. Based on fossils known at present, the mammal line would not see another semi-aquatic form evolve until the Eocene. Because few fossilized remains had been found, it was previously thought that, until the Cretaceous–Paleogene boundary (K–Pg boundary), all mammals were tiny, ground-dwelling or tree-dwelling, nocturnal animals akin to shrews, hedgehogs, treeshrews, or tenrecs. This notion has now been falsified by the armadillo-like Fruitafossor, the dinosaur-eating Repenomamus, the flying squirrel-like Volaticotherium, the small and spiny tenrec-like creature called Spinolestes and now the beaver-like Castorocauda.
qas: question: zh_tw: 為什麼人們曾經認為哺乳動物原本是微小的陸地動物或樹棲動物？
en: Why was it once thought that mammals were originally tiny ground dwelling or tree dwelling animals?
answers: zh_tw: text: 少量的化石被發現
en: text: few fossilized remains had been found

question: zh_tw: 何時會發生另一次演變？
en: When is another evolution expected to occur?
answers: zh_tw: text: 始新世
en: text: the Eocene