When Archaeopteryx, a feathered skeleton that was seemingly half dinosaur and half bird, turned up in 1862—three years after the publication of “The Origin of Species”—the origin of birds became a subject of raging debate among palaeontologists. Suggestions that they were the direct descendants of theropod dinosaurs (a group of bipedal meat-eaters that include Allosaurus, Velociraptor and Tyrannosaurus) caused quite a flap. Today, most researchers agree that birds are, indeed, a branch of the Dinosauria. How they made the transition from the land to the sky, though, has yet to be agreed. But a paper in this week's Current Biology, by Christopher Glen and Michael Bennett of the University of Queensland, makes a strong case that they did it by jumping.

　　Considering the diversity of life on Earth, flight is surprisingly rare. It has evolved only four times: among the insects about 300m years ago, the pterosaurs (230m), the birds (150m) and the bats (50m). That suggests it is a hard trick to pull off. For birds, there is general agreement that feathers came before flight. Fossils from north-eastern China show animals that had feathers but clearly could not have flown, as well as ones that look like proper birds. The best guesses are that feathers evolved either for insulation (as fur did in mammals) or for display, and that natural selection took advantage by turning them into a means of transport.

　　There are two broad schools of thought about what happened next. One argues that birds' immediate ancestors lived in trees. Members of this school think that powered flight developed as a natural extension of gliding (such controlled falling is used as a way of travelling from tree to tree by several arboreal species today). Gliding itself developed because of the lift provided by feathered forearms.

　　The alternative is that flight evolved on the ground. Some researchers who belong to this school of thought suggest that the power provided by flapping protowings may have given their owners an edge in the pursuit of prey. Others hypothesise that feathery forearms helped animals steer and stabilise themselves.

　　Unfortunately, behaviour does not fossilise, so it looked as though the question might never be answered. But Dr Glen, a palaeobiologist, and Dr Bennett, a biomechanic, think they have worked out how to do so. Their crucial observation is that in modern birds the curvature of the third toe (which carries a lot of weight during walking and climbing) varies with species' lifestyles. Birds that spend lots of time climbing around on the trunks of trees have dramatically curved third toes. Those that hop around on branches have mildly curved ones. Those that forage mainly on the ground have the least curved of all.

　　The two researchers compared these observations with their findings for the bird-like dinosaurs and dinosaur-like birds of China. They noticed that the toes of both feathered dinosaurs and of the earliest flying birds were similar to those of modern birds that spend most of their time on the ground. Flight, in other words, came before birds took to the trees. They are not fallen angels, but risen reptiles.

　　1. Which one of the following statements is NOT true of the current debate on the origin of birds?

　　[A] The opinion that birds were the direct descendants of dinosaurs gives the world a shock.

　　[B] Palaeontologists have get consensus on the specie’s transition from the land to the sky.

　　[C] Palaeontologists have different opinions on the process of the transition.

　　[D] The paper in this week's Current Biology demostrate that the specie moved by hopping before they flied.

　　2. The reason why flight is surprisingly rare is that _____

　　[A] life on earth is diversified.

　　[B] many species of this kind were eliminated during evolution.

　　[C] feathers evolved not for a means of transport.

　　[D] it is very hard to have such evolution.

　　3.The two schools of thought have different opinions on _____

　　[A] the functions of feathered forearams in transition from ground to sky.

　　[B] the location of living place before the animals’ evolution to birds.

　　[C] the development of powered flight.

　　[D] the power provided by either gliding or flapping.

　　4. The conclusion of the study carried out by Dr. Glen and Dr. Bennet is that_____

　　[A] powered flight developed as feathered forearms provided lift.

　　[B] flight evolved on the ground before they descend on the trees.

　　[C] earliest birds share similar toes with their modern counterparts.

　　[D] earliest flying birds evovled from feathered dinosaurs.

　　5.Which one of the following statements is NOT true of opinions of Dr. Glen and Dr. Bennet?

　　[A]Birds realized the transition from reptile to flight by jumping.

　　[B] Dinasaurs are, as a matter of fact, the direct ancester of birds.

　　[C]Feathers evolves not for the purpose of flight.

　　[D] Bird’s behaviors is indeed fossilised by their various shape of the third toe.

　　參考答案：DDCBB

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