- UID
- 800800
- 在线时间
- 小时
- 注册时间
- 2012-8-30
- 最后登录
- 1970-1-1
- 主题
- 帖子
- 性别
- 保密
|
想带着大家每天坚持读英语，就拿来Source为WSY的文章（有500多篇），每天带着大家读，希望大家能坚持每天学习+阅读打卡；
大家可以在有限时间内阅读，本帖回复文章结构。
看不懂英语的，可以来微信群要我要中文
每日的中文大意在揽瓜阁阅读群更新
考试群：
GMAT入群／揽瓜阁入群方式：https://forum.chasedream.com/thread-1382779-1-1.html
公众号：1.考什么试
2.商校百科
申请群
1. ChaseDream 2023 MBA 申请／校友答疑／面试群： https://forum.chasedream.com/thread-863011-1-1.html
2.英国，新加坡，美国，香港，德国商科申请群：
请加小白斩鸡进群（killgmat）
3. 行业分享交流／职业规划群：
https://forum.chasedream.com/thread-1388171-1-1.html
小红书：
1.留学+考试 最新消息 关注妥妥妥了 （小红书号：323014154）
2.求职+MBA 最新消息 关注元（小红书号：895404330）
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.
|
|
[复制链接]
京公网安备11010202008513号 京ICP证101109号 京ICP备12012021号
发表于 2023-6-1 09:48:36
收藏
收藏
