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本帖最后由 sunsong7 于 2012-3-9 14:40 编辑
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古老岩石中现海绵生物体 或为人类最早祖先(图)http://www.kexue.com 2012-02-13 09:18:37 腾讯科学 * F5 F4 s: q2 t. T
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这种名为Otavia antiqua的微小生物体发现于一块7.6亿年前的岩石中
据国外媒体报道，我们最早的进化祖先或许是显微镜下的海绵状生物体，这种生物体最近发现于极其古老的非洲岩石内部。如果结果是真的，它将取代之前已知的最早动物生命祖先（另外一种平凡的海绵状多细胞动物），它在日期上早了约一亿年。
8 }, v; A/ l! j1 E" N7 v( \- _ 研究人员声称这种名为Otavia antiqua的微小生物体发现于纳米比亚的一块7.6亿年前的岩石中，它很可能是出现在地球上的第一种多细胞动物。这就意味着，包括了从前体细胞到恐龙再到现代人类的所有动物生命，能够直接追溯到生物体Otavia。这就同样意味着动物生命很可能比我们之前推断的早出现了数千万年。+ n% r+ C$ E( ~' i& _/ n; I
Otavia被圣安德鲁斯大学的研究人员发现，并被认为存活于平静的浅水中，以水中非常丰富的细菌和藻类为食。简单的设想一下：它以一个管状身体通过气孔把食物吞进身体中心，并且在那里基本上直接吸收进生物体细胞中。. W7 Y& I; U0 ~% A1 d: n% h. P
Otavia没有进化太多，但是或许是它并不需要。这个记录显示如果研究人员是正确的，那么Otavia经历了至少两个“雪球地球”时期，当时全球温度剧降而且几乎全球都被冰雪覆盖。通过最佳推算这种生物体至少存活了两亿年，这表明这个所有动物的潜在祖先自从出现之后就比许多更大的多细胞物种更加的耐寒。（过客/编译）
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The oldest animal ever found is 760 million years old # \* B2 C+ t! C
: m; Z! M) ?6 z0 U" z a: Y+ bThe origins of life is one of the biggest mysteries scientists have been trying to unravel for a very long time. While a lot of effort is being directed to finding alien life, it’s crucial, at least in my opinion, for us to understand how the first signs of life spurred on our own planet. There are a number of more or less accepted theories, that range from the primordial soup to alien bacteria brought to earth via asteroids and so on. Maybe we’ll never learn how life first flourished on this paradise surrounded by the infinite darkness of space we like to call Earth, since such an event might have forever been lost, leaving no trace., E& S0 ?3 ~3 H. x) O0 i' q
It’s amazing, however, the kind of things we can trace back though. Scientists for instance have recently discovered, what they claim is, the oldest animal on Earth, uncovered so far. Dubbed, Otavia antiqua, this primitive life form was found in a 760-million-year-old rock in Namibia, Africa. There, scientists discovered hundreds of such fossils, the size of a grain of sand, and with sponge-like appearance., |4 p8 o# `2 q8 S9 ]6 M
These microscopic creatures are now considered the oldest animals in the world, since the previous holder, another primitive sponge, was dated to about 650 million years ago. It’s important to understand that any organism with cells differentiated into tissues and organs, such as the Otavia a., are considered animals. Actually, Otavia a. might actually be the ancestors to all modern animals on Earth today .5 V A9 e5 I& c) O; G# z
The researchers who discovered the ancient animal also made a small background description of it. It most likely lived in calm waters, including lagoons and other shallow environments and most likely fed on algae and bacteria, which the animal drew through pores on its tubelike body into a central space. The digestion occurred directly into the animal’s cells.
% m+ P) t$ Y/ IFossil records indicate that Octavia remarkably went through several snowball Earth events, times when the planet was almost entirely covered in ice. Analyzing fossil samples from the oldest to the earliest, the researchers observed that roughly for 200 million years the Octavia didn’t evolve one bit, all sharing the same quasi-ovid form, with large openings leading from the exterior.! Q& D! D) o# f4 h
The findings were reported in the South African Journal of Science.
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http://www.zmescience.com/research/studies/the-oldest-animal-ever-found-is-760-million-years-old/
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Oldest Animal Discovered—Earliest Ancestor of Us All?.
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# `1 M1 {$ y" p% m" r; L* z, ?/ }A scanning electron microscope view of Otavia antiqua. H" y- [4 ]$ Z3 _* `
Image courtesy Anthony Prave, University of St. Andrews
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for National Geographic News. w8 t* l1 P- V# T% ?4 V
3 o4 d5 s0 A3 O7 E* Z) U# m! J2 MPublished February 7, 2012
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Microscopic, sponge-like African fossils could be the earliest known animals—and possibly our earliest evolutionary ancestors, scientists say.
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9 b* l. P- E* f$ B(Related: "Earliest Animals Were Sea Sponges, Fossils Hint.")' v& G% b7 b) P1 B& z
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The creature, Otavia antiqua, was found in 760-million-year-old rock in Namibia and was as tiny as it may be important.2 h; r# g% |( B0 F
/ I5 i! T1 q7 @0 \- ^1 Y& k3 H"The fossils are small, about the size of a grain of sand, and we have found many hundreds of them," said study leader Anthony Prave, a geologist at the University of St. Andrews in the U.K. f7 }+ t$ k6 U3 W
) _. w/ C5 z+ _ D. j! i3 H"In fact, when we look at thin sections of the rocks, certain samples would likely yield thousands of specimens. Thus, it is possible that the organisms were very abundant."
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, V& h+ j: f4 j+ aFrom these tiny "sponges" sprang very big things, the authors suggest. As possibly the first muticellular animals, Otavia could well be the forerunner of dinosaurs, humans-basically everything we think of as "animal."
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- m6 T7 U. J: ~" h+ g! f+ L# P(Related: "405-Year-Old Clam Called Longest-Lived Animal.")
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Oldest Animal Built to Last?
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Prior to the new discovery, the previous earliest known "metazoan"—animals with cells differentiated into tissues and organs—was another primitive sponge, dated to about 650 million years ago.
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$ ^% v7 G5 U) |& NBased on where the new fossils were found, Prave and his colleagues think Otavia lived in calm waters, including lagoons and other shallow environments.0 c3 |$ {0 S5 c# J0 {
3 i% p8 {$ R6 H% D* `1 K0 sThe team thinks Otavia fed on algae and bacteria, which the animal drew through pores on its tubelike body into a central space. There the food was digested and absorbed directly into Otavia's cells.
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(Also see "Was The Humble Sponge Earth's First Animal?")9 i: b+ {0 `3 s }& \2 u) i1 b
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The simple setup seems to have worked.
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The fossil record indicates Otavia survived at least two long-term, severe cold snaps known as "snowball Earth" events, when the planet was almost completely covered in ice.+ R7 M- B$ L7 _4 Y2 d& z: ]
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Despite such wild environmental swings, "the oldest and youngest Otavia fossils all have the same quasi-ovid form, with large openings leading from the exterior," Prave said in an email.
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% o' H: [$ F: q2 a) {: H& Q+ dIn short, the animals didn't evolve much, he said—suggesting that, at least for its roughly 200 million years of existence, Otavia was built to last.
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" |8 x# v5 S- r4 Q# J4 [/ hThe new oldest-animal study is detailed in the current issue of the South African Journal of Science.
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发表于 2012-3-9 14:38
