從澳洲的化石裡找到所有動物的祖先

原文網址：https://news.ucr.edu/articles/2020/03/23/ancestor-all-animals-identified-australian-fossils

從澳洲的化石裡找到所有動物的祖先

最早的兩側對稱動物是一種生活在5.5億年前、像是蠕蟲的生物

By Holly Ober

由加州大學河濱分校的地質學家領導的團隊，發現了一類動物家族樹上最初的祖先。這株家族樹不僅包括了大部分我們所熟知的動物，也包含了人類在內。

藝術家繪製的Ikaria wariootia復原圖。圖片來源：Sohail Wasif/UCR

科學家發現形成於5.5億年前，迄今最古老的消化道化石

原文網址：https://news.missouri.edu/2020/a-gutsy-proposition/

科學家發現形成於5.5億年前，迄今最古老的消化道化石

在美國內華達州沙漠發現年代為5.5億年的消化道化石，或許是瞭解地球動物早期歷史的關鍵。

這兩幅立體圖顯示了5.5億年前形成的管狀化石(左圖紅色部分)以及內部的消化道(兩圖的橘色部分)。圖片來源：密蘇里大學

5.5億年前的化石顯示了動物留下的最早足跡

原文網址：https://vtnews.vt.edu/articles/2019/09/Science-  Shuhai_Xiao_half_billion_animal_trail.html

5.5億年前的化石顯示了動物留下的最早足跡

由維吉尼亞理工大學的地球科學家共同領導的科學團隊，做出了一項關於演化的重大發現：他們找到了大約五億年前，可能是動物在地球表面留下的第一道痕跡。

這道由夷陵帶刺蟲(Yilingia spiciformis)留下的痕跡化石年代為5.5億年。包括維吉尼亞理工大學的肖樹華在內的科學團隊，於中國發現了這道足跡。圖片來源：維吉尼亞理工大學

研究人員找到古生物學的聖杯：5.58億年前的脂質揭露出已知最古老的動物身分

原文網址：https://anu.prezly.com/researchers-find-holy-grail-of-palaeontology-558-million-year-old-fat-reveals-earliest-known-animal

研究人員找到古生物學的聖杯：5.58億年前的脂質揭露出已知最古老的動物身分

澳洲國立大學和其他國家的科學家在一具年代久遠的化石中發現脂質分子，從而得出地質紀錄中有證據顯示其為動物的化石最早存活於5.58億年前。

一具狄更遜水母的化石。圖片來源：澳洲國立大學

地球最古老的動物組成了複雜的生態群集

原文網址：https://news.vanderbilt.edu/2018/09/17/earths-oldest-animals-formed-complex-ecological-communities/

地球最古老的動物組成了複雜的生態群集

Heidi Hall

謎樣的埃迪卡拉生物群(Ediacara biota)生活在5.7億至5.4億年前，是地球第一批肉眼可見的動物。一項新的分析結果使我們對牠們有了更深的理解。

Darroch最近於納米比亞進行研究時發現了這些埃迪卡拉生物群的化石。圖片來源：Simon A.F. Darroch

地球上的生物體型首次變大的原因為何？

原文網址：http://www.cam.ac.uk/research/news/why-life-on-earth-first-got-big

地球上的生物體型首次變大的原因為何？

地球上某些最早期的複雜生物――同時可能也是最早出現的動物――體型增加的原因並非是為了競爭食物，而是想要盡可能地把後代散佈到遠方。

太初時代的巨大變形動物

原文網址：http://www.cam.ac.uk/research/news/big-shape-shifting-animals-from-the-dawn-of-time

太初時代的巨大變形動物

在五億年以前，海洋化學成分的重大改變使得第一批大型生物――或許也是某些最早的動物得以出現並繁榮生長，此時間點同時也標記出地球環境的改變讓動物接管了這個世界。

為什麼地球上的動物體型會在某個時刻由小變大？劍橋大學和東京工業大學的研究人員找出了某些最初的大型生物，稱作「脈形類」(rangeomorph)，藉由從周圍環境吸收養分時能改變體型和形狀的能力而可以長到兩公尺高。

刊登在期刊《自然―生態學和演化》(Nature Ecology and Evolution)的研究結果也有助於解釋地球上的生命如何從成員一度僅有微生物，最後變成能演化出恐龍和藍鯨之類的巨大生物。

脈形類是地球上最初的大型生物之一，牠們出現的時候其他大多數生命形式的體型得用顯微鏡才能看見。某些脈形類的高度僅有數公分，但有些最多可以長到兩公尺高。

這些居住在海中的生物生存於6億3500萬年至5億4100萬年前的埃迪卡拉紀(Ediacaran period)。牠們柔軟的身體是由許多分枝組成，而每根分枝又分岔出許多更小的旁枝，使牠們的外型呈現出幾何學中的碎形，就像我們今天所看到的肺部血管、蕨類或雪花一樣。

由於沒有任何一種跟脈形類相似的現存生物，使得科學家難以瞭解牠們如何攝食、生長或者繁殖，更別說是牠們跟其他現存動物族群之間可能的關係為何。然而，雖然牠們某種程度上看起來很像植物，科學家相信牠們或許是存活在地球的最早動物之一。

論文第一作者，劍橋大學生命科學系與東京工業大學地球生命研究所的Jennifer Hoyal Cuthill博士表示：「我們想要知道為什麼這些大型生物會在此特定時間點出現在地球歷史上。牠們以相當巨大的體型突如其來地出現在化石紀錄中，我們猜測牠們跟海洋化學的改變只是剛好在同一時刻發生，或者是有直接因果關係？」

研究人員利用微電腦斷層攝影、攝影測量法以及數學和電腦模型來觀察從加拿大紐芬蘭西南方、英國和澳洲出土的脈形類化石。

化石證據的分析結果首次證明了牠們的體型增長跟養分有關。所有生物都需要養分才能存活並成長，但養分多寡同時也決定了生物的體型大小和外型，此概念稱為「生態表型可塑性」(ecophenotypic plasticity)。Hoyal Cuthill和共同作者Simon Conway Morris教授提出脈形類不僅表現出高度的生態表型可塑性，此能力也讓牠們在劇烈變化的世界中取得大量優勢。舉例來說，如果上方海水氧濃度提高，底下的脈形類可以迅速「變形」成修長的錐狀外形。

Hoyal Cuthill表示：「在埃迪卡拉紀時，地球海洋似乎出現了重大變化。這可能刺激了生物生長，使地球上的生物體型突然之間開始變大許多。埃迪卡拉紀的海中出現了什麼樣的重大地球化學變化使得生物體型開始變大，要下確切的結論恐怕還言之過早，但我們認為有幾個強力的候選因素，特別是氧濃度的提高，因為動物需要氧氣來進行呼吸作用。」

海洋化學的重大變化接續在稱作Gaskiers冰期的大規模冰河期之後。當海洋的的養分濃度低落時，生物顯然會讓牠們的體型維持在比較嬌小的狀態。但氧氣或是其他種養分突然(地質上來說)增加時，生物就有機會長到比原本大上許多，即使牠們是基因組成完全一樣的生物。這意味著巨大脈形類的突然出現可能是氣候和海洋化學發生的重大變化造成的直接後果。

然而，雖然脈形類對埃迪卡拉紀的環境適應相當良好，海洋化學仍持續變化。到了5億4100萬年前的「寒武紀大爆發」――在這段演化疾速進行的時期中，大多數主要動物類群首次在化石紀錄中登場――環境已經劇烈改變，使得脈形類走向滅亡，之後再也沒有出現跟牠們十分類似的物種了。

Big, shape-shifting animals from the dawn of time

Major changes in the chemical composition of the world’s oceans enabled the first large organisms – possibly some of the earliest animals – to exist and thrive more than half a billion years ago, marking the point when conditions on Earth changed and animals began to take over the world. 

Why did life on Earth change from small to large when it did? Researchers from the University of Cambridge and the Tokyo Institute of Technology have determined how some of the first large organisms, known as rangeomorphs, were able to grow up to two metres in height, by changing their body size and shape as they extracted nutrients from their surrounding environment.

The results, reported in the journal Nature Ecology and Evolution, could also help explain how life on Earth, which once consisted only of microscopic organisms, changed so that huge organisms like dinosaurs and blue whales could ultimately evolve.

Rangeomorphs were some of the earliest large organisms on Earth, existing during a time when most other forms of life were microscopic in size. Some rangeomorphs were only a few centimetres in height, while others were up to two metres tall.

These organisms were ocean dwellers that lived during the Ediacaran period, between 635 and 541 million years ago. Their soft bodies were made up of branches, each with many smaller side branches, forming a geometric shape known as a fractal, which can be seen today in things like lungs, ferns and snowflakes.

Since rangeomorphs don’t resemble any modern organism, it’s difficult to understand how they fed, grew or reproduced, let alone how they might link with any modern group. However, although they look somewhat like plants, scientists believe that they may have been some of the earliest animals to live on Earth.

“What we wanted to know is why these large organisms appeared at this particular point in Earth’s history,” said Dr Jennifer Hoyal Cuthill of Cambridge’s Department of Earth Sciences and Tokyo Tech’s Earth-Life Science Institute, the paper’s first author. “They show up in the fossil record with a bang, at very large size. We wondered, was this simply a coincidence or a direct result of changes in ocean chemistry?”

The researchers used micro-CT scanning, photographic measurements and mathematical and computer models to examine rangeomorph fossils from south-eastern Newfoundland, Canada, the UK and Australia.

Their analysis shows the earliest evidence for nutrient-dependent growth in the fossil record. All organisms need nutrients to survive and grow, but nutrients can also dictate body size and shape. This is known as ‘ecophenotypic plasticity.’ Hoyal Cuthill and her co-author Professor Simon Conway Morris suggest that rangeomorphs not only show a strong degree of ecophenotypic plasticity, but that this provided a crucial advantage in a dramatically changing world. For example, rangeomorphs could rapidly “shape-shift”, growing into a long, tapered shape if the seawater above them happened to have elevated levels of oxygen.

“During the Ediacaran, there seem to have been major changes in the Earth’s oceans, which may have triggered growth, so that life on Earth suddenly starts getting much bigger,” said Hoyal Cuthill. “It’s probably too early to conclude exactly which geochemical changes in the Ediacaran oceans were responsible for the shift to large body sizes, but there are strong contenders, especially increased oxygen, which animals need for respiration.”

This change in ocean chemistry followed a large-scale ice age known as the Gaskiers glaciation. When nutrient levels in the ocean were low, they appear to have kept body sizes small. But with a geologically sudden increase in oxygen or other nutrients, much larger body sizes become possible, even in organisms with the same genetic makeup. This means that the sudden appearance of rangeomorphs at large size could have been a direct result of major changes in climate and ocean chemistry.

However, while rangeomorphs were highly suited to their Ediacaran environment, conditions in the oceans continued to change and from about 541 million years ago the ‘Cambrian Explosion’ began – a period of rapid evolutionary development when most major animal groups first appeared in the fossil record. When the conditions changed, the rangeomorphs were doomed and nothing quite like them has been seen since.

原始論文：Jennifer F. Hoyal Cuthill, Simon Conway Morris. Nutrient-dependent growth underpinned the Ediacaran transition to large body size. Nature Ecology & Evolution, 2017; DOI: 10.1038/s41559-017-0222-7

引用自：University of Cambridge. "Big, shape-shifting animals from the dawn of time." 

前寒武紀的生命也許比之前認為得還要更加活躍

原文網址：www.sciencedaily.com/releases/2017/05/170519084411.htm

前寒武紀的生命也許比之前認為得還要更加活躍

在地球遙遠的過去曾有一段時期，淺海充斥著許多不知該如何分類的謎樣軟體生物，稱為「埃迪卡拉花園」(Garden of the Ediacaran)。科學家將這段從6.35億年至5.4億年前的時期想像成演化史上一片寧靜，近乎與世無爭的插曲。但是新的跨領域研究提出，生活在此時的生物也許比專家之前認為得還要更有活力。

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.