It is animals and plants which lived in or near water whose remains（遗迹） are most likely to be preserved（保护）, for one of the necessary conditions of preservation（保存） is quick burial（ 埋葬）, and it is only in the seas and rivers and sometimes lakes where mud and silt（淤泥） have been continuously deposited（使沉淀） that bodies and the like can be rapidly（快） covered over and preserved（保护）. But even in the most favorable circumstances（情况） only a small fraction（小部分） of the creatures（生物） that die are preserved（保护） 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（命运） is avoided. The remains of plants and animals that lived on land are much more rarely preserved, for there is seldom（ 很少） anything to cover them over.