海洋化學成分改變後骨骼才發展出來

原文網址：www.sciencedaily.com/releases/2017/04/170404104738.htm

海洋化學成分改變後骨骼才發展出來

研究提出在5.5億年前，當海水化學組成改變後才首度出現骨骼和甲殼。

研究人員表示可能是隨著史前海洋的氧濃度提高，以及鎂和鈣的含量發生變化，古代的海洋動物才開始從體態柔軟的動物演化成身上具有硬殼的生物。

團隊表示直到現在，還不太瞭解由碳酸鈣組成的骨骼和甲殼如何首度演化出來。

過往的理論認為體態柔軟的生物經歷了一場大滅絕之後，才讓擁有骨骸和甲殼的生物得以繁盛生長。

然而，愛丁堡大學的研究人員卻發現最早擁有硬殼的生命型式，跟牠們親緣密切的體態柔軟物種曾經共同生存過。

團隊檢視了從西伯利亞的石灰岩中挖掘出來的一系列化石。此岩層生成於數億年前具有高濃度碳酸鈣的海水。

他們總結出只有在具有高濃度碳酸鈣的環境，才能讓生物發展出原始的堅硬部位而首度形成具有堅硬外型的生命型式。

大約1000萬年之後，地球生命多樣性開始劇烈增加—這段時期稱作寒武紀大爆發—同時身體具有堅硬部位的生命也開始大量生長。團隊表示掠食者給予的威脅增加，迫使在碳酸鈣含量較少的環境中生活的生物，也開始發展出更新且更複雜的堅硬部位。

團隊表示經由稱作「生物礦化(biomineralisation)」的作用，堅硬身體部位的出現代表了演化史上的一次重大革新，脫離了過往由體態柔軟的生物組成的世界。

這項研究刊登於期刊《英國皇家學會學報B》(Proceedings of the Royal Society B)，並由羅蒙諾索夫莫斯科國立大學協助完成。

領導此研究的愛丁堡大學地質科學院的Rachel Wood教授表示：「動物開始產生甲殼和骨骼是生命演化史上最為重大的事件之一。而我們現在才剛開始瞭解這道革新背後的發展過程。」

Skeletons developed as chemistry of oceans changed

Skeletons and shells first came into being 550 million years ago as the chemical make-up of seawater changed, a study suggests.

Ancient marine life may have developed from soft-bodied animals into creatures with hard body parts as oxygen levels rose and calcium and magnesium levels in prehistoric oceans changed, researchers say.

Until now, little was known about how skeletons and shells -- which are made of calcium carbonate -- first evolved, the team says.

Previous theories suggested that soft-bodied organisms had undergone a mass extinction, which allowed organisms with skeletons and shells to flourish.

However, researchers at the University of Edinburgh have found that the earliest lifeforms with hard body parts co-existed with closely related soft-bodied species.

The team examined a range of fossils unearthed from limestone rocks in Siberia, which formed millions of years ago from seawater with high levels of calcium carbonate.

They concluded that hard-bodied lifeforms were first present only in such environments where high levels of calcium carbonate allowed organisms to develop primitive hard parts.

Around 10m years later, the diversity of life of Earth increased rapidly -- a period known as the Cambrian explosion -- and hard-bodied life began to thrive. An increased threat from predators led lifeforms to develop new, more complex hard parts in environments that were less carbonate-rich, the team says.

The development of hard body parts -- through a process called biomineralisation -- marked a significant evolutionary advance from the previous world of soft-bodied life, the team says.

The study is published in the journal Proceedings of the Royal Society B. The research was carried out in collaboration with Lomonosov Moscow State University.

Professor Rachel Wood, of the University of Edinburgh's School of GeoSciences, who led the study, said: "How animals produced shells and skeletons is one of the major events in the evolution of life. We are only now starting to understand the processes underlying this revolution."

原始論文：Rachel Wood, Andrey Yu Ivantsov, Andrey Yu Zhuravlev. First macrobiota biomineralization was environmentally triggered. Proceedings of the Royal Society B: Biological Sciences, 2017; 284 (1851): 20170059 DOI: 10.1098/rspb.2017.0059

引用自：University of Edinburgh. "Skeletons developed as chemistry of oceans changed." ScienceDaily. ScienceDaily, 4 April 2017.