Life After Extinction
by Sid
Perkins 胡德良 译
| Mass extinctions have a silver lining, providing
opportunities for marginalized creatures to rise to power. While
that notion seems obvious, it hadn't been demonstrated for the
end-Permian extinctions, which occurred about 252 million years ago
and wiped out about 90% of life on Earth. So, researchers took a
detailed look at the numbers and distribution of land-dwelling
species at five sites scattered across the southern part of
Pangaea, the supercontinent that existed at the time of the
die-offs. (Previous analyses had looked at only trends in marine
species or for limited regions on land, the team notes.) Of the 62
species found at the sites about 5 million years before the
die-offs, 21 (or about 34%) were found in two or more of the sites,
suggesting a wide distribution of those creatures. But 10
million years after the end-Permian extinctions, only five species
out of 68—none of which matched the 62 that lived before the
die-offs—were
found at more than one site. The analysis also reveals that after the mass
extinctions, species typically had smaller, less-connected
geographical ranges than did the species living before the
die-offs, the researchers report online today in the Proceedings
of the National Academy of Sciences. Altogether, the
trends suggest that when widely prevalent creatures such as the
pig-sizedDicynodon (left)
were removed from the scene, species such as the
3-meter-long Asilisaurus (right)—a
member of the archosaurs, which included dinosaurs and many groups
alive today, such as crocodilians and birds—could diversify and
thrive. |
大灭绝存在一线希望：为边缘化生物强大起来提供机会。尽管这个观点是显而易见的，但二叠纪末期的灭绝事件并没有证实这一点。二叠纪末期的那次大灭绝发生在大约2.52亿年之前，消灭了地球上大约90%的生命。因此，研究人员仔细观察了分散在泛大陆南部五个地点的陆栖物种数量及分布。泛大陆是存在于那次大灭绝时期的超大陆。（研究小组指出：先前的分析只观察了海洋物种的趋势，或陆地上有限范围之内物种的趋势。）在那次大灭绝之前大约500万年时，在五个地点发现的62个物种中，有21个物种（大约占34%）存在于两个或更多的地点，这表明那些物种分布广泛。但是，在二叠纪末期大灭绝之后1000万年之后， 68个物种中只有5个物种存在于不止一个地点之上，其中没有任何一个物种跟生活于大灭绝之前那62个物种相匹配。今天，研究人员在《美国国家科学院院刊》在线版上报道说：这项分析还显示，跟大灭绝之前的物种相比，大灭绝之后的物种通常生活于较狭小的、不大相连的地理范围之上。总而言之，这种趋势表明：当分布广泛的动物（如跟猪一般大小的二齿兽，左图）从地球上消失之后，像体长三米的阿希利龙（右图）这样的物种才会变得多样化并兴旺起来。阿希利龙是祖龙家族中的一个成员，而祖龙包括恐龙以及当今仍然存活的许多生物群，如鳄鱼及鸟类。 |
译自：美国《科学》杂志网站（29 April 2013, 3:05 PM）
原著：Sid Perkins
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