Official 48 Passage 2

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Determining Dinosaur Diet

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The word "Traditionally" in the passage is closest in meaning to

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  • A
    typically
  • B
    naturally
  • C
    originally
  • D
    partly
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正确答案: A

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  • 原文
  • 译文
  • Determining what extinct dinosaurs ate is difficult, but we can infer some aspects of their dietary preferences. Traditionally, this information has been derived from direct evidence, such as stomach contents, and indirect evidence, such as establishing a correlation between particular body characteristics and diets of living animals and then inferring habits for dinosaurs.



    Animals such as house cats and dogs have large, stabbing canine teeth at the front of the mouth and smaller, equally sharp teeth farther back in their jaws. Many of these animals are also armed with sharp claws. The advantage of teeth and claws as predatory tools is obvious. Now consider animals like cows, horses, rabbits, and mice. These animals have flat teeth at the back of the jaw that are analogous to and have the same function as grindstones. Unlike the meat-slicing and stabbing teeth of carnivores, the teeth of these animals grind and shred plant material before digestion.



    More clues exist in other parts of the skull. The jaw joint of carnivores such as dogs and cats has the mechanical advantage of being at the same level as the tooth row, allowing the jaws to close with tremendous speed and forcing the upper teeth to occlude against the lower teeth with great precision. In herbivorous animals, rapid jaw closure is less important. Because the flat teeth of herbivores work like grindstones, however, the jaws must move both side to side and front to back. The jaw joints of many advanced herbivores, such as cows, lie at a different level than the tooth row, allowing transverse tearing, shredding, and compression of plant material. If we extend such observations to extinct dinosaurs, we can infer dietary preferences (such as carnivory and herbivory), even though we cannot determine the exact diet. The duck-billed dinosaurs known as hadrosaurs are a good example of a group whose jaw joint is below the level of the tooth row, which probably helped them grind up tough, fibrous vegetation.



    Paleontologists would like to be much more specific about a dinosaur's diet than simply differentiating carnivore from herbivore. This finer level of resolution requires direct fossil evidence of dinosaur meals. Stomach contents are only rarely preserved, but when present, allow us to determine exactly what these animals were eating.



    In the stomach contents of specimens of Coelophysis (a small, long-necked dinosaur) are bones from juvenile animals of the same species. At one time, these were thought to represent embryonic animals, suggesting that this small dinosaur gave birth to live young rather than laying eggs. Further research indicated that the small dinosaurs were too large and too well developed to be prehatchling young. In addition, the juveniles inside the body cavity were of different sizes. All the evidence points to the conclusion that these are the remains of prey items and that, as an adult, Coelophysis was at least in part a cannibal.



    Fossilized stomach contents are not restricted to carnivorous dinosaurs. In a few rare cases, most of them "mummies" (unusually well preserved specimens), fossilized plant remains have been found inside the body cavity of hadrosaurs. Some paleontologists have argued that these represent stream accumulations rather than final meals. The best known of these cases is the second Edmontosaurus mummy collected by the Sternbergs. In the chest cavity of this specimen, which is housed in the Senckenberg Museum in Germany, are the fossil remains of conifer needles, twigs, seeds, and fruits. Similar finds in Corythosaurus specimens from Alberta, Canada, have also been reported, indicating that at least two kinds of Late Cretaceous hadrosaurs fed on the sorts of tress that are common in today's boreal woodlands.



    A second form of direct evidence comes from coprolites (fossilized bodily waste). Several dinosaur fossil localities preserve coprolites. Coprolites yield unequivocal evidence about the dietary habits of dinosaurs. Many parts of plants and animals are extremely resistant to the digestive systems of animals and pass completely through the body with little or no alteration. Study of coprolites has indicated that the diets of some herbivorous dinosaurs were relatively diverse, while other dinosaurs appear to have been specialists, feeding on particular types of plants. The problem with inferring diets from coprolites is the difficulty in accurately associating a particular coprolite with a specific dinosaur.


  • 确定灭绝的恐龙吃什么是困难的,但我们可以推断出他们的饮食偏好的某些方面。传统上,这些信息来自直接的证据(如胃含物)和间接证据(如建立动物特定体征和饮食之间的关系,然后推断恐龙的生活习惯)。

    像猫和狗这样的动物,在嘴巴前方有着又大、又尖利的牙齿,在下巴后面也有着同样锋利的牙齿。这些动物中也有许多都装备有锋利的爪子。牙齿和爪子作为捕食工具的优势是明显的。现在细想一下像牛、马、兔子和老鼠这样的动物。这些动物下巴后面有平齿,形似磨石并且功能也相同。不像食肉动物切肉的、尖锐的牙齿,这些动物在消化植物体之前,用牙齿将它们磨粉碎。

    在头骨的其他部分有更多的线索。像狗和猫这样的食肉动物的下颌关节有着机械优势,下颌关节和牙排在同一水平上,让下颌高速闭合,迫使上牙紧密地晈合下牙。在草食动物中,下颚快速闭合是不重要的。由于食草动物的牙齿像磨刀石一样工作,而下巴必须前后左右移动。许多先进的草食动物的颌关节和牙排排列在不同的水平面上(如牛),这样可以横向撕裂、切碎、压缩植物材料。如果我们将这样的观察延伸到灭绝的恐龙上,我们可以推断出饮食偏好(如食肉的和食草的),虽然我们无法确定准确的饮食。鸭嘴形的恐龙,也就是鸭嘴龙是一组已知的颌关节低于齿列水平的一个很好的例子,这可能帮助他们把坚韧的纤维植物磨碎。

    古生物学家希望更明确恐龙的饮食,而不是简单的区分食草动物和食肉动物。这一更高层次的决心需要直接的恐龙食物的化石证据。胃内容物很少被保存下来,但如果存在,就可以让我们来确定这些动物吃什么。

    腔骨龙标本的胃内容物(小的长颈恐龙的骨头)是同一物种的幼年动物的骨头。他们一度被认为是胚胎动物的代表,这表明这个小恐龙是怀孕生下的而不是产卵生下的。进一步的研究表明,小恐龙太大,成长地太好,他们是不可能是孵化出来的幼体。此外,在体腔内的幼崽大小各有不同。所有的证据都指向这个结论,这些都是猎物遗骸,作为一个成年恐龙,腔骨龙至少是某种程度上的食人族。

    化石胃内容物不局限于食肉恐龙。在一些罕见的情况下,他们中的大多数“木乃伊”(罕见的保存完好的化石标本),实话的植物遗已经在鸭嘴龙体腔内发现。一些古生物学家认为,这些代表食物链的累积,而不是最后的晚餐。这些案例中最著名的是施特恩伯格氏收集的第二个埃德蒙顿木乃伊。在这个标本胸腔内,现在被置于德国沙根堡博物馆,有针叶、小枝、种子和果实的化石。阿尔伯塔和加拿大冠的龙标本也有类似报道,这表明至少有两种晚白垩纪的鸭嘴龙以各种各样的枝条为食,这些种枝条在今天的北方针叶林很常见。

    直接的证据第二种形式来自粪化石(身体废物化石)。几个恐龙化石的地点保存粪化石。粪化石为恐龙的饮食习惯的提供了明确证据。植物和动物的许多部分对动物的消化系统有着极强的抵抗力,并完整地通过身体,几乎没有任何变化。研究表明,一些粪化石显示,食草恐龙的饮食比较多样化,而其他恐龙似乎已吃的比较专一,取食特定种类的植物。从粪化石推断饮食的问题是:准确地将特定的粪化石与一个特定的恐龙联系起来的很困难。
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    解析

    题型分类:词汇题

    原文定位:词汇所在句Traditionally this information has been derived from direct evidence, such as stomach contents, and indirect evidence”即“传统上,这些信息来自直接证据,如胃内食物,以及间接证据”traditionally:传统上地,一般地。

    选项分析:typically:代表性地,一般地;naturally:自然地;originally:最初,起初;partly:部分地。因此,选项A符合题干词意。

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