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THE MAMMALS  ~210 million years


The evolution of mammals within the synapsid lineage (mammal-like-reptiles) was a gradual process that took approximately 70 million years, beginning in the mid-Permian. By the mid-Triassic, there were many species that looked like mammals, and the first true mammals appeared in the early Jurassic. The earliest known marsupial, Sinodelphys, appeared 125 million years ago in the early Cretaceous, around the same time as Eomaia, the first known eutherian (member of placentals' "parent" group); and the earliest known monotreme, Teinolophos, appeared two million years later. After the Cretaceous-Tertiary extinction wiped out the non-avian dinosaurs (birds are generally regarded as the surviving dinosaurs) and several other mammalian groups, placental and marsupial mammals diversified into many new forms and ecological niches throughout the Tertiary, by the end of which all modern orders had appeared. (click to see all the article on Wikipedia)

哺乳動物 ~21千萬年前 

哺乳類歸屬於合弓綱的譜系(類哺乳爬行動物),花了大約7千萬年,始於二疊紀中期,慢慢演化而來。到了三疊紀中期,有許多物種看起來像哺乳動物,而真正的哺乳動物首次出現在侏儸紀早期。已知最早的有袋類,中國袋獸,出現在1250萬年前,即為白堊紀早期。同時間還有始祖獸,已知最早的真下獸綱(胎盤類的上一階的成員之一),以及已知最早的單孔目,Teinolophos,在20萬年前出現。在白堊紀第三紀後,非禽類恐龍 (鳥類被視為殘存下來的恐龍) 和一些其他的哺乳動物群都滅亡了,有袋及胎盤哺乳動物演化出許多新的物種,在整個第三紀時找到了其生態棲位,在其結束時,所有最新的物種都已演化出來。



生態棲位(ecological niches)任何一種生物,都有其最適合生存發展的環境,泛指生存地點,食物來源,活動空間,成長繁殖方式,覓食條件、生態食物鏈網位置,若是錯亂了 niche 違反生存法則,不是適應進化,便注定走向毀滅。


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