[揽瓜阁精读] 310.hummingbirds

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If it's hummingbirds you're after, the New World is the only place to be. Of the 300-plus species of the hovering, nectar-sipping birds, almost all live in Central and South America. Experts agree that all species of modern hummingbirds evolved there and later spread to North America, but it appeared they had never set wing in Eurasia.

Now, fragile bones in 30-million-year-old rocks from southern Germany show that hummingbirds were much farther-flung than anyone expected. “The amazing thing about this fossil is that it's essentially a modern hummingbird,” says Margaret Rubega of the University of Connecticut, Storrs. “My mind is a little blown.” The discovery, which ornithologist Gerald Mayr of the Forschungsinstitut Senckenberg in Frankfurt, Germany, describes on page 861, raises questions about where early hummingbirds evolved and why the European ones became extinct.

Hummingbird history has long been shrouded in mystery, chiefly because the delicate-boned creatures have left so few fossils. None at all have been found in the Western Hemisphere. Hints of Old World origins appeared when a possible primitive insect-eating hummingbird, Parargornis messelensis, turned up in 49-million-year-old rocks in Messel, Germany. The only other fossil hummingbirds are the 30-million-year-old Argornis caucasicus and Jungornis tesselatus, both incomplete, from the Caucasus. They appear to have been able to hover, but it's not clear whether they had modern-style beaks. Last year Mayr classified all three as “stem taxa,” extinct relatives that share a common ancestor with modern hummingbirds, but not all experts were convinced.

The new fossil, called Eurotrochilus inexpectatus, is the first fossil of a modern-looking hummingbird and the closest to modern ones. When Mayr came across two partially prepared specimens of the creature in a museum drawer in Stuttgart, “I didn't have a real idea what it was,” he says. But closer inspection revealed evidence that the specimens were hummingbirds. One of them sports a long, slender beak adapted for feeding on nectar. The clincher was the short, stocky humerus with a bony knob that probably allows the wing to rotate during hovering flight. Although the tip of the beak is not preserved, Mayr estimates that the bird measured 4 to 5 cm from head to tail, as big as a medium-sized modern hummingbird.

Not everyone accepts the identification. “The similarities with modern hummingbirds are pretty superficial,” says Joel Cracraft of the American Museum of Natural History in New York City. Other experts, however, say they are convinced.

Eurotrochilus demonstrates that in the Old World, hummingbird ancestors had evolved the main features of living hummingbirds by 30 million years ago, Mayr says. That might explain why a handful of European flowers appear adapted for hovering birds, he adds. It could be that these plants first evolved with hummingbirds and were pollinated by them. This conclusion makes sense to Ethan Temeles, an ecologist at Amherst College in Massachusetts who studies the coevolution of plants and pollinators. Finding a fossil pollinator, as Mayr has done, can help explain the evolutionary history of both the plant and pollinator, he says.

Why did Old World hummingbirds become extinct? One possibility, Mayr says, is that songbirds outcompeted them. Where the whole hovering tribe came from, meanwhile, remains up in the air. The four European fossils could suggest that stem taxa first appeared in the Old World and spread to the Americas across the Bering Strait, but the fossil record is so sparse that it's just speculation. Answering those questions will take more discoveries. For paleontologists scouting for clues to hummingbird history, the Old World may become the new place to be.

Treeeeeevor.zz

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0320zjx

同意！               

yyychenn

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楓羽_

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YannTse1111

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楓羽_

主題背景-提出問題-解釋問題的困難-新發現-回答問題-延伸(只是推測，需要更多的研究)

P1 大部分的生物都居住於美國中部及南部，專家認為現在的蜂鳥在哪裡演化之後散佈到北美，但是都沒有在歐亞出現
P2 現在在德國發現現代蜂鳥的化石，專家提出問題：最早的蜂鳥是在那裡演化和為何歐洲的蜂鳥會滅絕
P3 說明蜂鳥歷史神秘的原因：太少化石了。並說明在三個地方有看到可能的原始化石，M說這三個是來源有連結，來自於相同的祖先，但是沒人相信
P4 新發現的化石(E)是第一個現在長相的蜂鳥和最接近現代的一個。(被做成標本)描述標本的形狀說明其為蜂鳥，包含身體及骨頭等
P5 但不是每個人都接受標本為蜂鳥，不認同的人覺得這個辨別方式太過表象，而其他專家都是接受的
P6 E這個化石說明蜂鳥的祖先差不多3千萬年前在歐洲進化的，也解釋為何歐洲會有適合蜂鳥的花，M推測這些花一開始是和蜂鳥一起進化的，並由蜂鳥來授粉。ET(研究植物及授粉者共同演化)認為這個結論很合理，可以一同解釋植物及授粉者的共同演化歷史。
P7 推測蜂鳥滅絕的原因是鳴鳥戰勝他們。在歐洲的四個化石說明蜂鳥的源頭來自歐洲，接著散佈到美國，但是因為化石太過分散所以這只是個推測。這個答案將需要更多的探索。對於古生物學家而言，想了解更多蜂鳥歷史，歐洲將會是個新的地方。

YannTse1111

P1:背景

-现代hummingbirds大部分生活在中南美洲，并繁衍到了北美，但从来没有去过欧亚。

P2：提出问题

-德国的化石研究发现早期的hummingbirds可以飞得很远，骨骼也和现代hummingbirds差不多。

-科学家raises questions：

1、早期hummingbirds在哪里进化？

2、为什么欧洲的hummingbirds灭绝了？

P3：过去的发现

-hummingbirds的历史一直是个谜团，因为遗留下来的化石太少了，西半球从来都没有发现过化石。

-遗留下来的化石也不完整

-现代hummingbirds和早期hummingbirds是否是同一物种存在争议。

P4：新发现

-新发现的化石E和现代hummingbirds非常类似，beak，clincher这些特征都很像，although tip of the beak有点不一样。

P5：回答第1个问题

-化石E显示hummingbirds在30 million years ago进化出主要特征，当时欧洲的花为了授粉也跟着一起进化，解释了植物和传粉者的进化史。

P6：回答第2个问题

-早期hummingbirds灭绝的原因之一可能是songbirds打败了它们，但还需要更多的证据证明。

gmat_offer

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feijinbufeijin

看一下！