tpo1-18综合写作阅读听力文本共23页

tpo1-18综合写作阅读听力文本共23页内容摘要：

ersian canals. These canals house nerves and blood vessels that allow the living animal to grow quickly, and rapid body growth is in fact a characteristic of endothermy. The presence of Haversian canals in bone is a strong indicator that the animal is an endotherm, and fossilized bones of dinosaurs are usually dense with Haversian canals. Listening Professor: Many scientists have problems with the arguments you read in the passage. They don39。 t think those arguments prove that dinosaurs were endotherms. Take the polar dinosaur argument. When dinosaurs lived, even the polar regions, where dinosaur fossils have been found, were much warmer than today, warm enough during part of the year for animals that were not endotherms to live. And during the months when the polar regions were cold, the socalled polar dinosaurs could have migrated to warmer areas or hibernated like many modern reptiles do. So the presence of dinosaur fossils in polar regions doesn39。 t prove the dinosaurs were endotherms. Well, what about the fact that dinosaurs have their legs placed under their bodies, not out to the side like crocodiles. That doesn39。 t necessarily mean dinosaurs were highenergy endotherms built for running. There is another explanation for having legs under the body. This body structure supports more weight, so with the legs under their bodies, dinosaurs can grow to a very large size. Being large had advantages for dinosaurs, so we don39。 t need the idea of endothermy and running to explain why dinosaurs evolved to have their legs under their bodies. Ok, so how about bone structure? Many dinosaur bones do have Haversian canals, that39。 s true. The dinosaur bones also have growth rings. Growth rings are thickening of the bone that indicates periods of time when the dinosaurs weren39。 t rapidly growing. These growth rings are evidence that dinosaurs stopped growing or grew more slowly during cooler periods. This pattern of periodic growth, you know, rapid growth followed by no growth or slow growth, and then rapid growth again, is characteristic of animals that are not endotherms. Animals that maintain a constant body temperature yearround as true endotherms do grow rapidly even when the environment bees cool. TPO5 Reading As early as the twelfth century ., the settlements of Chaco Canyon in New Mexico in the American Southwest were notable for their great houses, massive stone buildings that contain hundreds of rooms and often stand three or four stories high. Archaeologists have been trying to determine how the buildings were used. While there is still no universally agreed upon explanation, there are three peting theories. One theory holds that the Chaco structures were purely residential, with each housing hundreds of people. Supporters of this theory have interpreted Chaco great houses as earlier versions of the architecture seen in more recent Southwest societies. In particular, the Chaco houses appear strikingly similar to the large, wellknown apartment buildings at Taos, New Mexico, in which many people have been living for centuries. A second theory contends that the Chaco structures were used to store food supplies. One of the main crops of the Chaco people was grain maize, which could be stored for long periods of time without spoiling and could serve as a longlasting supply of food. The supplies of maize had to be stored somewhere, and the size of the great houses would make them very suitable for the purpose. A third theory proposes that houses were used as ceremonial centers. Close to one house, called Pueblo Alto, archaeologists identified an enormous mound formed by a pile of old material. Excavations of the mound revealed deposits containing a surprisingly large number of broken pots. This finding has been interpreted as evidence that people gathered at Pueblo Alto for special ceremonies. At the ceremonies, they ate festive meals and then discarded the pots in which the meals had been prepared or served. Such ceremonies have been documented for other Native American cultures. Listening Professor: Unfortunately none of the arguments about what the Chaco great houses were used for is c First, sure, from the outside, the great houses look like later and native American apartment ^ ut the inside of the great houses casts serious doubt on the idea that many people lived there. I39。 ll explain. If hundreds of people were living in the great houses, then there would have to be many fireplaces, where each family did its daily cooking, but there are very few fireplaces. In one of the largest great houses, there were fireplaces for only around ten families. Yet there were enough rooms in the great house for more than a hundred families, so the primary function of the houses couldn39。 t have been residential. Second, the idea that the great houses were used to store grain m163。 unsupported by evidence. It may sound plausible that large empty rooms were used for storage, but excavations of the great houses have not uncovered many traces of maize or maize containers. If the great houses were used for storage, why isn39。 t there more spilled maize on the floor? Why aren39。 t there more remains of big containers? Third, the idea that the great houses were ceremonial centers isn39。 t well supported either. You know that mound at Pueblo Alto? It contains lots of other materials besides broken pots, stuff you wouldn39。 t expect from ceremonies. For example, there are large quantities of building materials, sands, stones, even construction tools. This suggests that the mound is just a trash heap of construction material, stuff that was thrown away or not used up when a house was being built. The pots in the pile could be regular trash too, leftover from the meals of the construction workers. So the Pueblo Alto mound is not go。