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.  食腐動物

    volen.  野鼠，鼴鼠

    decomposev.  腐爛

    inaccessibleadj. 不能到達(dá)的

    crevassen.   縫隙
    
    Siberianadj.西伯利亞的

    palaeontologicaladj. 古生物學(xué)的

    St. Petersburgn.  圣彼得堡

    sabre-toothedadj. 長著銳利的長牙

    venturev.  冒險

    boggedadj. 陷入泥沼的，陷入要困境的

    只有生活在水中或水邊的動植物尸體最有可能被保存下來，因為保存的必要條件之一是迅速掩埋，所以只有在泥沙不停淤積的海洋和江河里，有時在湖泊里，尸體之類的東西才能被迅速地覆蓋而保存下來。

    即使是在最有利的環(huán)境中，死去的生物中也只有一小部分能在開始腐爛前，或更可能在被食腐動物吃掉之前，被這樣保存下來。因為一切生物都是靠吃別的東西來活命的，不管這種東西是植物還是動物，死的還是活的，因此，生物偶爾才能避免被吃掉的命運。曾在陸地上生活過的動植物的遺體被保存下來的更為罕見，因為陸地上幾乎沒有什么東西覆蓋它們。你可以想象出天上有看得見的飛來飛去、數(shù)不清的鳥，地上有不顯眼的無數(shù)的老鼠和田鼠之類的小動物，但是，除非在路上，很少有人遇到這些動物的尸體，因為它們腐敗之后很快就被風(fēng)化掉，或被別的動物吃掉了。

    幾乎總是由于某些特殊的條件，陸地動物的遺體才被存下來，如掉進(jìn)難以到達(dá)的洞穴，或掉進(jìn)冰河裂縫里，或者像西伯利亞長毛象那樣掉進(jìn)冰窟中，有時整個動物像被放在冰箱里一樣被保存下來，著名的那林索夫卡長毛象就是這樣被保存下來的，而且保存得很好。它嘴里還留著冷杉 —— 它掉進(jìn)冰河裂隙折斷脊椎柱之前的最后一頓飯。這頭長毛象已被修復(fù)，現(xiàn)存于圣彼得堡古生物學(xué)博物館。有的動物掉進(jìn)天然瀝清坑里被保存下來，如在蘭橋。拉。布里 —— 現(xiàn)在是洛杉磯的郊區(qū)發(fā)現(xiàn)的大象、劍齒虎和許多其他動物。顯然，事情的經(jīng)過是這樣：瀝青坑里積存了水，大象那樣的大動物冒險到似乎堅固的水面上去飲水，立即掉進(jìn)了瀝青坑。大象死后，一些食肉動物，如劍齒虎和大灰狼就來吃大象，結(jié)果遭到了同樣的命運。瀝青坑里還有無數(shù)只鳥的尸體。