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托福阅读背景知识:恐龙的繁衍

2014-08-25 16:19

来源:新东方网

作者:富亦聪

  在2014年8月23日的托福阅读考试中有这样一道题:Reproductive biology 恐龙的繁衍。针对这道托福考题,新东方富亦聪老师来为大家普及一下关于恐龙的繁衍的背景知识,这样有助于考生在面对这类题目时方便作答

  Reproductive biology生物繁殖

  托福阅读真题再现:

  版本一:

  恐龙有两种hatch的方式,一个是在nest里下蛋,总之不好确定,因为fossil。。后来两个实验,都证明了是在nest里。又讨论了可以和其他动物对比,和bird,发现是一个祖先,所以发展特征也差不多。

  版本二:

  有一篇讲恐龙的两种保护宝宝行为。一种是生前行为如筑巢,另一种是生后的如喂养。M恐龙巢里有小宝宝,故推断有第一种,但后面一种就不好说了,后一种m的巢距离一定,所以可能孵蛋,小龙牙上有痕迹可能喂养。

  相关背景:

  Reproductive biology

  Three eggs, bluish with black speckling, sit atop a layer of white mollusk shells pieces, surrounded by sandy ground and small bits of bluish stone.

  Nest of a plover (Charadrius).

  All dinosaurs lay amniotic eggs with hard shells made mostly of calcium carbonate. Eggs are usually laid in a nest. Most species create somewhat elaborate nests, which can be cups, domes, plates, beds scrapes, mounds, or burrows. Some species of modern bird have no nests; the cliff-nesting Common Guillemot lays its eggs on bare rock, and male Emperor Penguins keep eggs between their body and feet. Primitive birds and many non-avialan dinosaurs often lay eggs in communal nests, with males primarily incubating the eggs. While modern birds have only one functional oviduct and lay one egg at a time, more primitive birds and dinosaurs had two oviducts, like crocodiles. Some non-avialan dinosaurs, such as Troodon, exhibited iterative laying, where the adult might lay a pair of eggs every one or two days, and then ensured simultaneous hatching by delaying brooding until all eggs were laid.

  When laying eggs, females grow a special type of bone between the hard outer bone and the marrow of their limbs. This medullary bone, which is rich in calcium, is used to make eggshells. A discovery of features in a Tyrannosaurus rex skeleton provided evidence of medullary bone in extinct dinosaurs and, for the first time, allowed paleontologists to establish the sex of a fossil dinosaur specimen. Further research has found medullary bone in the carnosaur Allosaurus and the ornithopod Tenontosaurus. Because the line of dinosaurs that includes Allosaurus and Tyrannosaurus diverged from the line that led to Tenontosaurus very early in the evolution of dinosaurs, this suggests that the production of medullary tissue is a general characteristic of all dinosaurs.

  Fossilized egg of the oviraptorid Citipati, American Museum of Natural History

  Another widespread trait among modern birds is parental care for young after hatching. Jack Horner's 1978 discovery of a Maiasaura ("good mother lizard") nesting ground in Montana demonstrated that parental care continued long after birth among ornithopods, suggesting this behavior might also have been common to all dinosaurs. There is evidence that other non-theropod dinosaurs, like Patagonian titanosaurian sauropods (1997 discovery), also nested in large groups. A specimen of the Mongolian oviraptorid Citipati osmolskae was discovered in a chicken-like brooding position in 1993, which indicates that they had begun using an insulating layer of feathers to keep the eggs warm. Parental care being a trait common to all dinosaurs is supported by other finds. For example, a dinosaur embryo (pertaining to the prosauropod Massospondylus) was found without teeth, indicating that some parental care was required to feed the young dinosaurs. Trackways have also confirmed parental behavior among ornithopods from the Isle of Skye in northwestern Scotland. Nests and eggs have been found for most major groups of dinosaurs, and it appears likely that all dinosaurs cared for their young to some extent either before or shortly after hatching.

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