巨大的奧陶紀“殺手蝦”（右）看起來就像它的寒武紀表親Laggania（左）
這個發(fā)現(xiàn)肯定讓全世界癡迷怪獸的孩子們感到心滿意足：大約5.05億年前,，巨大的“殺手蝦”——或者說像蝦一樣的生物anomalocaridid——潛伏在海洋中,，并貪婪地吞噬著那些不小心在它們面前經(jīng)過的軟體獵物。如今,，新發(fā)現(xiàn)的化石表明這些奇異的無脊椎動物要大得多——體長甚至超過1米,，并且比之前的推測“多活”了幾千萬年。這一發(fā)現(xiàn)迫使古生物學家重新思考發(fā)生在生命進化史上最大的一次生物滅絕事件,。
新發(fā)現(xiàn)的食肉動物是在5.05億年前名為寒武紀大爆發(fā)的一次突然生物擴增中進化出的一種新的生命形式,，當時所有的生物都被禁閉在海洋中。分節(jié)且生有柄眼的anomalocaridid位于食物鏈的頂端,，統(tǒng)治著寒武紀的珊瑚礁,。科學家曾認為,，在寒武紀末期發(fā)生的一次生物大滅絕中,，這種生物與其他許多奇形怪狀的生物一道在距今4.88億年前從地球上被統(tǒng)統(tǒng)抹去。隨后在下一個地質年代奧陶紀中,，新的生物又重新在海洋中進化形成,。
然而如今，美國耶魯大學的古生物學家Peter Van Roy和Derek Briggs發(fā)現(xiàn)了一個巨大的anomalocaridid化石，其生存年代可以回溯到距今4.88億至4.72億年前——這正是早奧陶紀的時期,。在摩洛哥東南部發(fā)現(xiàn)的這一巨大無脊椎食肉動物是生態(tài)系統(tǒng)的的一部分,，而后者似乎是從較早的地質年代直接轉移過來的。研究表明,，這種怪異的寒武紀生物的生存時間比科學家之前的預計增加了3000萬年,。
這一發(fā)現(xiàn)表明，anomalocaridid可能在海洋生物的進化中一直扮演了一個重要的角色,，其時間要比之前的預測長得多,。Briggs指出：“很顯然，anomalocaridid在奧陶紀早期也是一種重要的食肉動物,。”他說：“它們在海洋生態(tài)系統(tǒng)變得更為復雜的過程中產(chǎn)生了作用,。”在距今4.88億年前發(fā)生的奧陶紀生物多樣性事件中，海洋中的動物屬種數(shù)量幾乎增加了4倍,。相關論文發(fā)表在《自然》雜志上,。（生物谷Bioon.com）
生物谷推薦原文出處：
Nature DOI:10.1038/nature09920
A giant Ordovician anomalocaridid
Peter Van Roy; Derek E. G. Briggs
Anomalocaridids, giant lightly sclerotized invertebrate predators, occur in a number of exceptionally preserved early and middle Cambrian (542–501?million years ago) biotas and have come to symbolize the unfamiliar morphologies displayed by stem organisms in faunas of the Burgess Shale type. They are characterized by a pair of anterior, segmented appendages, a circlet of plates around the mouth, and an elongate segmented trunk lacking true tergites with a pair of flexible lateral lobes per segment1, 2. Disarticulated body parts, such as the anterior appendages and oral circlet, had been assigned to a range of taxonomic groups—but the discovery of complete specimens from the middle Cambrian Burgess Shale showed that these disparate elements all belong to a single kind of animal3. Phylogenetic analyses support a position of anomalocaridids in the arthropod stem, as a sister group to the euarthropods4, 5, 6. The anomalocaridids were the largest animals in Cambrian communities. The youngest unequivocal examples occur in the middle Cambrian Marjum Formation of Utah7 but an arthropod retaining some anomalocaridid characteristics is present in the Devonian of Germany5. Here we report the post-Cambrian occurrence of anomalocaridids, from the Early Ordovician (488–472?million years ago) Fezouata Biota8 in southeastern Morocco, including specimens larger than any in Cambrian biotas. These giant animals were an important element of some marine communities for about 30?million years longer than previously realized. The Moroccan specimens confirm the presence of a dorsal array of flexible blades attached to a transverse rachis on the trunk segments; these blades probably functioned as gills.
