新的化石證據支持了首次大滅絕是由早期動物一手鑄成的理論

原始網址：www.sciencedaily.com/releases/2016/07/160729132912.htm

New fossil evidence supports theory that first mass extinction engineered by early animals

新的化石證據支持了首次大滅絕是由早期動物一手鑄成的理論

Newly discovered fossil evidence from Namibia strengthens the proposition that the world's first mass extinction was caused by "ecosystem engineers" -- newly evolved biological organisms that altered the environment so radically it drove older species to extinction.

從納米比亞新發現的化石證據鞏固了世上首度大滅絕是由「生態工程師」造成的論點。也就是新演化出來的生物劇烈改變環境而驅使原有生物走向滅絕。

The event, known as the end-Ediacaran extinction, took place 540 million years ago. The earliest life on Earth consisted of microbes -- various types of single-celled organisms. These held sway for more than 3 billion years, when the first multicellular organisms evolved. The most successful of these were the Ediacarans, which spread around the globe about 600 million years ago. They were a largely immobile form of marine life shaped like discs and tubes, fronds and quilted mattresses.

這起稱作「埃迪卡拉紀末期滅絕事件」(end-Ediacaran extinction)的大滅絕發生於5.4億年前。地球最早的生命是由微生物組成，包含了各式各樣的單細胞生物。直到第一群多細胞生物演化出來以前，它們支配了地球超過30億年。這些多細胞生物中最成功的一群為埃迪卡拉生物(Ediacarans)，在6億年前牠們已經散佈至全球各地。埃迪卡拉生物大多是無法移動的海洋生物，外表呈現盤狀、管狀、葉狀或是像厚重的床墊一樣。

After 60 million years, evolution gave birth to another major innovation: metazoans, the first animals. Metazoans could move spontaneously and independently at least during some point in their life cycle and sustain themselves by eating other organisms or what other organisms produce. Animals burst onto the scene in a frenzy of diversification that paleontologists have labeled the Cambrian explosion, a 25 million-year period when most of the modern animal families -- vertebrates, mollusks, arthropods, annelids, sponges and jellyfish -- came into being.

在6千萬年之後，出現了另一個演化史上的重大變革：第一群後生動物(metazoan)，也就是一般所稱的動物出現了。後生動物在牠們的生命週期中至少有一個階段可以自發且獨立地移動，並以攝食其他生物或是其他生物的產物維生。很快地動物便進入古生物學家稱作寒武紀大爆發的時期，在這段2500萬年的時光中，動物的多樣性爆炸性地增長。大多數現今可見的動物種類，像是脊索動物、軟體動物、節肢動物、環節動物、海綿和水母，便是在這段期間開始現身。

"These new species were 'ecological engineers' who changed the environment in ways that made it more and more difficult for the Ediacarans to survive," said Simon Darroch, assistant professor of earth and environmental sciences at Vanderbilt University, who directed the new study described in the paper titled "A mixed Ediacaran-metazoan assemblage from the Zaris Sub-basin, Namibia," published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.

「這些新物種為『生態工程師』(ecological engineer)，牠們改變了環境而使得埃迪卡拉生物越來越難以生存。」 Simon Darroch說。這位范德比大學地球與環境科學的助理教授於發表在期刊《古地理學、古氣候學、古生態學》(Palaeogeography, Palaeoclimatology, Palaeoecology)，題名為「A mixed Ediacaran-metazoan assemblage from the Zaris Sub-basin, Namibia」的論文中描述了他所進行的新研究。

Darroch and his colleagues report that they have found one of the best-preserved examples of a mixed community of Ediacarans and animals, which provides the best evidence of a close ecological association between the two groups.

Darroch和他的同僚發表說他們於這處場址發現的埃迪卡拉生物和動物混居而成的群集為保存情況最良好的一例，這給他們相當有力的證據可以證實這兩群生物之間有相當緊密的生態關係。

"Until this, the evidence for an overlapping ecological association between metazoans and soft-bodied Ediacaran organisms was limited," Darroch said. "Here, we describe new fossil localities from southern Namibia that preserve soft-bodied Ediacara biota, enigmatic tubular organisms thought to represent metazoans and vertically oriented metazoan trace fossils. Although the precise identity of the tracemakers remains elusive, the structures bear several striking similarities with a cone-shaped organism called Conichnus that has been found in the Cambrian period."

「在這項發現之前，很少有證據顯示後生動物以及體態柔軟的埃迪卡拉生物混居而成的生態群落。」 Darroch說。「我們在這裡記述的化石地點位於納米比亞南部，這裡保存了構造柔軟的埃迪卡拉生物相、被認為是後生動物的謎樣管狀生物，以及垂直方向的後生動物生痕化石(trace fossil)。雖然留下這些生痕的動物確切身分仍不明朗，但其構造跟寒武紀發現的錐狀生物化石Conichnus之間有著驚人的相似性。」

In a previous paper that Darroch and his collaborators published last September, they reported on a fossil record that showed stressed-looking communities of Ediacara associated with a suite of animal burrows.

在 Darroch和他的同僚於去年九月發表的前一份研究中，他們發表的化石紀錄顯示跟動物挖出來的連串洞穴一起出現的埃迪卡拉生物群有受到壓迫的跡象。

"With this paper we're narrowing in on causation; we've discovered some new fossil sites that preserve both Ediacara biota and animal fossils (both animal burrows -- 'trace fossils' -- and the remains of animals themselves) sharing the same communities, which lets us speculate about how these two very different groups of organisms interacted," he said.

「連同跟這篇論文我們能做出更確實的推論。我們新發現的化石場址保存了處於同一群集的埃迪卡拉生物群和動物化石(包括動物挖出來的洞穴，即『生痕化石』，以及動物本體的遺骸)，這讓我們可以推測兩群截然不同的生物之間會有怎麼樣的互動。」他說。

"Some of the burrow fossils we've found are usually interpreted as being formed by sea anemones, which are passive predators that may have preyed upon Ediacaran larvae. We've also found stands of Ediacaran frondose organisms, with animal fossils preserved in place coiled around their bases. In general, these new fossil sites reveal a snapshot of a very unusual 'transitional' ecosystem existing right before the Cambrian explosion, with the last of the Ediacara biota clinging on for grim death, just as modern-looking animals are diversifying and starting to realize their potential."

「我們發現的一些洞穴化石通常會被解讀為由海葵形成，這種被動掠食者可能會攝食埃迪卡拉生物的幼苗。我們也發現某些聚集成叢的埃迪卡拉葉狀生物會有動物化石盤繞在牠們的基部。總歸來說，這些新化石場址顯現了寒武紀大爆發即將到來前，生態系正處於十分特殊的『過渡期』的那一瞬間。當跟現代動物相似的動物趨向多樣化並開始了解到牠們擁有的無窮潛能時，最後的埃迪卡拉生物群正在做最後一絲掙扎。」

Although Darroch is studying events that took place 540 million years ago, he believes there is a message relevant for today. "There is a powerful analogy between Earth's first mass extinction and what is happening today," he said. "The end-Ediacaran extinction shows that the evolution of new behaviors can fundamentally change the entire planet, and today we humans are the most powerful 'ecosystems engineers' ever known."

雖然Darroch探討的事件發生於5.4億年前，他認為這些研究傳遞出來的訊息跟現在的世界有密切關係。「地球的第一次大滅絕跟當下正在發生的生物滅絕可說是非常相似。」他說。「埃迪卡拉紀末期滅絕事件告訴我們生物新演化出來的行為模式可以從根本上改變整個星球，而現今我們這些人類即是有史以來出現過影響力最強的『生態工程師』。」

引用自：Vanderbilt University. "New fossil evidence supports theory that first mass extinction engineered by early animals." ScienceDaily. ScienceDaily, 29 July 2016.