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舊 2006-10-30, 10:36 PM   #1
野人
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科學家在南非發現有3.6億年曆史的七鰓鰻化石

新華網

  新華網北京10月29日專電 南非金山大學和美國芝加哥大學的科學家們日前在南非發現了一塊有3.6億年曆史的七鰓鰻化石。這是迄今發現的最古老的魚類化石。  

  根據最新一期《自然》雜誌刊登的研究報告,這塊化石是在南非東開普省格雷厄姆斯敦附近的沃特山岩石群發現的,它證實了現代七鰓鰻是意義不同尋常的活化石。

  報告說,古代海洋中最先出現無頜類脊椎魚形動物,後演變為有頜類魚類,包括人類在內的所有脊椎動物都是由有頜類魚類演變而來的。而七鰓鰻是目前僅存的無頜類脊椎動物,所以引起了科學家們的濃厚興趣。

  七鰓鰻是高度特化的寄生生物,用圓形漏斗狀吸盤吸附在活魚身上,在銼舌的幫助下靠吸食活魚的血和組織維持生存。知道七鰓鰻何時獲得這種特化器官將間接表明它們在多大程度上真正代表了古代魚類。然而,七鰓鰻的骨骼幾乎沒有留下任何化石記錄——早先只有3種化石標本的相關描述,但無一可見吸盤。

  這塊新發現的化石保存完好,是迄今發現的年代最久遠的七鰓鰻化石。化石長僅42毫米,但鰭和最重要的嘴部形態特徵都清晰可見。這塊化石證實了七鰓鰻是存活了3.6億多年且幾乎沒有多大變化的活化石。

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Scientists from South Africa discover world's oldest fish fossil

PRAVDA.Ru

Scientists from the University of the Witwatersrand and the University of Chicago have discovered a 360 million-year-old lamprey.

The discovery was made at Witteberg Group rocks near Grahamstown, in the Eastern Cape.

According to the scientists, this demonstrated that modern lampreys are remarkable living fossils.

The report is published in Nature today.

This jawless fish fossil was discovered by Robert Gess, a PhD student at the Bernard Price Institute for Palaeontological Research at Wits, under the supervision of Professor Bruce Rubidge of Wits and Dr Mike Coates of the University of Chicago.

Scientists from around the world are currently engaged in reconstructing the evolutionary tree of life, combining data from the structure of living organisms, the fossil record and the analysis of DNA, reports AllAfrica.

According to Spotlighting News, the lamprey and the hagfish appear to be the only survivors of what is believed to be the first family of vertebrates, which according to some paleontology experts developed into jawed, bony fish.

The jawed fish, most likely descending from the jawless lamprey and other fish-like creatures of that time, appeared half a billion years ago, taking another evolutionary path.

Current lampreys have big eyes, a nostril, and a total of 14 gills. Their first 5-7 years are spent in the form of burrowing freshwater larvae, then metamorphose into predatory/parasitic creatures which cling onto fish with their mouths, and feed on its blood and tissues.

Lampreys reproduce in fresh water by creating a nest, then spawn and die.

When the fossilized lamprey lived, there were probably many types of jawless vertebrates. Except for the lamprey and hagfish, all of them seem to have died out.

"This fossil shows that the lampreys are the closest living representatives of backboned animals of that era,'' Coates said, reports National Geographic.
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舊 2013-04-19, 10:08 AM   #2
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thanks for the information
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