長按/掃描二維碼 |
長按/掃描二維碼 |
恐龍遺址
The partial skeletons of more than 20 dinosaurs and scattered bones of about 300 more have been discovered in Utah and Colorado at what is now the dinosaur natural monument. Menu of the best specimens may be seen today at museums of natural history in the largest cities in the United States and Canada. This dinosaur pit is the largest and best-preserved deposit of dinosaurs known today. Many people get the idea from the massive bones in the pit wall that some disaster such as a volcanic explosion or a sudden flood killed a whole herd of dinosaurs in this area. This could have happened but it probably did not. The main reasons for thinking otherwise are the scattered bones and the thickness of the deposit. In other deposits where the animals were thought to have died together, the skeletons were usually complete and often all the bones were in the proper places, rounded pieces of fossil bone have been found here. These fragments got their smooth round shape by rolling along the stream bottom. In a mass killing, the bones would have been left on the stream or lake bottom together at the same level. But in this deposit, the bones occur throughout a zone of sand stone about 12 feet thick. The mixture of swamp dwellers and dryland types also seems to indicate that the deposit is a mixture from different places. The pit area is a large dinosaur graveyard, not a place where they died. Most of the remains probably floated down on eastward flowing river until they were left on a shallow sandbar. Some of them may have come from far away dryland areas to the west, perhaps they drowned trying to cross the small stream or were washed away during floods. Some of the swamp dwellers may have got stuck in the very sandbar that became their grave, others may have floated for miles before being stranded, even today similar events take place. When floods come in the spring, sheep, cattle and deer are often trapped by rising waters and often drown. Their dead bodies float down-stream until the flood recedes and leaves them stranded on the bar or shore where they lie, half buried in sand until they decay. Early travelers on the Missouri river reported that shores and bars often lined with the decaying bodies of buffalo that have died during spring floods /X
Question 19: Where can many of the best dinosaur s specimens be found in North America?
Question 20: What occurs to many people when they see the massive bones in the pit wall?
Question 21: What does the speaker suggest about the large number of dinosaur bones in the pit?
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