It is animals and plants which lived in or near water whose remains are most likely to be preserved， for one of the necessary conditions of preservation is quick burial， and it is only in the seas and rivers， and sometimes lakes， where mud and sit have been continuously deposited， that bodies and the can be rapidly covered over and preserved.

    But even in the most favourable circumstances only a small fraction of the creatures that die are preserved in this way before decay sets in or， even more likely， before scavengers eat them. After all， all living creatures live by feeding on something else， whether it be plant or animal， dead or alive， and it is only by chance that such a fate is avoided. The remains of plants and animals that lived on land are much more rarely preserved， for there is seldom anything to cover them over. When you think of the innumerable birds that one sees flying bout， not to mention the equally numerous small animals like field mice and voles which you do not see， it is very rarely that one comes across a dead body， except， of course， on the roads. They decompose and are quickly destroyed by the weather or eaten by some other creature.

    It is almost always due to some very special circumstances that traces of land animals survive， as by falling into inaccessible caves， or into an ice crevasse， like the Siberian mammoths， when the whole animal is sometimes preserved， as in a refrigerator. This is what happened to the famous Beresovka mammoth which was found preserved and in good condition. In his mouth were the remains of fir trees —— the last meal that he had before he fell into the crevasse and broke his back. The mammoth has now just a suburb of Los Angeles. Apparently what happened was that water collected on these tar pits， and the bigger animals like the elephants ventured out on to the apparently firm surface to drink， and were promptly bogged in the tar. And then， when they were dead， the carnivores， like the sabre-toothed cats and the giant wolves， came out to feed and suffered exactly the same fate. There are also endless numbers of birds in the tar as well.

    preservationn.  保存

    siltn.  淤泥

    scavengern.  食腐动物

    volen.  野鼠，鼹鼠

    decomposev.  腐烂

    inaccessibleadj. 不能到达的

    crevassen.   缝隙
    
    Siberianadj.西伯利亚的

    palaeontologicaladj. 古生物学的

    St. Petersburgn.  圣彼得堡

    sabre-toothedadj. 长着锐利的长牙

    venturev.  冒险

    boggedadj. 陷入泥沼的，陷入要困境的

    只有生活在水中或水边的动植物尸体最有可能被保存下来，因为保存的必要条件之一是迅速掩埋，所以只有在泥沙不停淤积的海洋和江河里，有时在湖泊里，尸体之类的东西才能被迅速地覆盖而保存下来。

    即使是在最有利的环境中，死去的生物中也只有一小部分能在开始腐烂前，或更可能在被食腐动物吃掉之前，被这样保存下来。因为一切生物都是靠吃别的东西来活命的，不管这种东西是植物还是动物，死的还是活的，因此，生物偶尔才能避免被吃掉的命运。曾在陆地上生活过的动植物的遗体被保存下来的更为罕见，因为陆地上几乎没有什么东西覆盖它们。你可以想象出天上有看得见的飞来飞去、数不清的鸟，地上有不显眼的无数的老鼠和田鼠之类的小动物，但是，除非在路上，很少有人遇到这些动物的尸体，因为它们腐败之后很快就被风化掉，或被别的动物吃掉了。

    几乎总是由于某些特殊的条件，陆地动物的遗体才被存下来，如掉进难以到达的洞穴，或掉进冰河裂缝里，或者像西伯利亚长毛象那样掉进冰窟中，有时整个动物像被放在冰箱里一样被保存下来，著名的那林索夫卡长毛象就是这样被保存下来的，而且保存得很好。它嘴里还留着冷杉 —— 它掉进冰河裂隙折断脊椎柱之前的最后一顿饭。这头长毛象已被修复，现存于圣彼得堡古生物学博物馆。有的动物掉进天然沥清坑里被保存下来，如在兰桥。拉。布里 —— 现在是洛杉矶的郊区发现的大象、剑齿虎和许多其他动物。显然，事情的经过是这样：沥青坑里积存了水，大象那样的大动物冒险到似乎坚固的水面上去饮水，立即掉进了沥青坑。大象死后，一些食肉动物，如剑齿虎和大灰狼就来吃大象，结果遭到了同样的命运。沥青坑里还有无数只鸟的尸体。