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  3. Rare Fossil Record The preservation of embryos and juveniles is a rare occurrence in the fossil record. The tiny, delicate s

Rare Fossil Record The preservation of embryos and juveniles is a rare occurrence in the fossil record. The tiny, delicate s

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问题     Rare Fossil Record
    The preservation of embryos and juveniles is a rare occurrence in the fossil record. The tiny, delicate skeletons are usually scattered by scavengers (食腐动物) weathering before they can be fossilized. Ichthyosaurs (鱼龙) had a higher chance of being preserved than did terrestrial creatures because, as marine animals, they tended to live in environments less subject to erosion. Still, their fossilization required a suite of factors: a slow rate of decay of soft tissues, little scavenging by other animals, a lack of swift currents and waves to jumble and carry away small bones, and fairly rapid burial. Given these factors, some areas have become a treasury of well-preserved ichthyosaur fossils.
    The deposits at Holzmaden, Germany, present an interesting case for analysis. The ichthyosaur remains are found in black, bituminous marine shales(页岩) deposited about 190 million years ago. Over the years, thousands of specimens of marine reptiles, fish and invertebrates have been recovered from these rocks. The quality of preservation is outstanding, but what is even more impressive is the number of ichthyosaur fossils containing preserved embryos.
    Ichthyosaurs with embryos have been reported from 6 different levels of the shale in a small area around Holzmaden, suggesting that a specific site was used by large numbers of ichthyosaurs repeatedly over time. The embryos are quite advanced in their physical development; their paddles, for example, are already well formed. One specimen is even preserved in the birth canal. In addition, the shale contains the remains of many newborns that are between 20 and 30 inches long.
    Why are there so many pregnant females and young at Holzmaden when they are so rare elsewhere? The quality of preservation is almost unmatched and quarry operations have been carried out carefully with an awareness of the value of the fossils. But these factors do not account for the interesting question of how there came to be such a concentration of pregnant ichthyosaurs in a particular place very close to their time of giving birth.
Which of the following is true of the fossil deposits discussed in the passage?
选项 A、They include examples of newly discovered species.
B、They contain large numbers of well-preserved specimens.
C、They are older than fossils found in other places.
D、They have been analyzed more carefully than other fossils.
答案B
解析 由第二、三段可以看出，该地发现的化石的特别之处在于数量之多、保存完好。因此B是最佳选择。其余的选项：并不是发现了新物种，因此排除A；文中未提到其年代比其他地方的久远，因此C不正确；文中没有提及它们比其他的化石更仔细地被研究，D选项也不对。
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