Sun, Jun 03, 2018 - Page 9 News List

Birds had to relearn flight after meteor wiped out dinosaurs
流星造成恐龍滅絕後 鳥禽重新學飛

Artist’s impression of a 1000km-diameter planetoid hitting a young Earth. Don Davis (work commissioned by NASA)
直徑一千公里的小行星擊中早期地球之想像圖。唐‧戴維斯繪圖(美國太空總署委託)。

Photo: Wikimedia Commons
照片:維基共享資源

Fossil records suggest only flightless birds survived when T-rex was wiped off the Earth. Birds had to rediscover flight after the meteor strike that killed off the dinosaurs, scientists say.

The cataclysm 66 million years ago not only wiped out Tyrannosaurus rex and ground-dwelling dinosaur species, but also flying birds, a detailed survey of the fossil record suggests. As forests burned around the world, the only birds to survive were flightless emu-like species that lived on the ground.

“Looking at the fossil record, at plants and birds, there are multiple lines of evidence suggesting that the forest canopies collapsed,” said Regan Dunn, a member of the team from the Field Museum in Chicago, US. “Perching birds went extinct because there were no more perches.”

The six to nine-mile-wide meteor struck the Earth off the coast of Mexico, releasing a million times more energy than the largest atomic bomb. Hot debris raining from the sky is thought to have triggered global wildfires immediately after the impact. It took hundreds or even thousands of years for the world’s forests of palms and pines to recover.

Fossil records from New Zealand, Japan, Europe and North America, all show evidence of mass deforestation. They also reveal that birds surviving the end of the Cretaceous period had long sturdy legs made for living on the ground. They resembled emus and kiwis, said the researchers.

“The ancestors of modern tree-dwelling birds did not move into the trees until the forests had recovered from the extinction-causing asteroid,” said Daniel Field, from the University of Bath and a co-author of the paper published in Current Biology. “Today, birds are the most diverse and globally widespread group of terrestrial vertebrate animals — there are nearly 11,000 living species,” he added. “Only a handful of ancestral bird lineages succeeded in surviving the mass extinction event 66 million years ago, and all of today’s amazing living bird diversity can be traced to these ancient survivors.”

TODAY’S WORDS
今日單字

1. meteor n.

流星 (liu2 xing1)

2. wipe out phr.

抹除 (mo3 chu2);抹殺 (mo3 sha4)

3. dwell v.

居住 (ju1 zhu4);棲息 (qi xi1)

4. forest canopy phr.

林冠 (lin2 guan4)

5. extinct adj.

絕種 (jue2 zhong3)

6. ecological niche phr.

生態棲位 (sheng1 tai4 qi1 wei4)


The team are now focused on reconstructing the recovery of bird populations and how new species emerged and thrived in the ecological niche left by the extinction of dinosaurs.

(The Guardian)

科學家指出,化石紀錄顯示,當暴龍從地球上滅絕後,只有不會飛的鳥禽存活下來。在造成恐龍滅絕的流星撞擊後,鳥禽必須重新學習飛行。

一份詳細的化石紀錄調查報告指出,六千六百萬年前發生的這場大災變,不僅徹底造成暴龍和其他陸棲恐龍滅絕,也造成飛行的鳥類滅亡。隨著世界各地的森林都起火燃燒,唯一存活下來的鳥禽是像鴯鶓;這類不會飛行、生存在地面上的物種。

美國芝加哥菲爾德博物館研究團隊的成員雷根‧鄧恩表示:「仔細觀察植物與鳥類的化石紀錄,許多證據顯示當時的林冠紛紛倒塌。」他指出:「需要棲木停歇的雀形目也因此絕種,因為那時已經沒有棲木了。」

當時,一顆直徑達六到九英里的流星在墨西哥沿外處撞上地球,釋出超過最大原子彈威力一百萬倍的能量。從天而降的炙熱灰燼,被認為在撞擊後旋即在全球各地引燃多處野火。世界各地的棕櫚樹林和松樹林直到數百年,甚至是數千年後,才漸趨復原。

從紐西蘭、日本、歐洲,以及北美洲等地蒐集的化石紀錄,全都呈現出大規模森林破壞的痕跡。這些化石紀錄也顯示,從白堊紀末期存活下來的鳥禽,具有適合在陸地上生活、修長而健的腿骨。研究人員表示,這些鳥類相近於今日的鴯鶓;與鷸鴕。

這篇論文發表於學術期刊《當代生物學》,共同作者之一丹尼爾‧菲爾德表示:「一直到森林從滅絕性的小行星災難中恢復過來後,現代樹棲鳥類的祖先才又棲息到樹上去。」來自巴斯大學的菲爾德補充說:「今天,鳥禽類是種類最多且全球分布最廣的陸棲脊椎動物群體──近乎一萬一千種。」不過,「在六千六百萬年前的大滅亡中,只有少數幾種古代鳥禽類的後裔成功存活下來,今日讓人驚艷的鳥禽類多樣性全部都能追溯到這些古老的倖存者。」

這組團隊現在的研究焦點在重建當初鳥禽類群體恢復數量的過程,以及後來新物種如何從恐龍滅絕留下的生態棲位中浮現,並繁衍增長。

(台北時報章厚明譯)

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