Why do scientists think that some environments are missing from the fossil record?

Photo of a distant mountain, an erosional environment, with a lake, where silty sediments are accumulating, in the foreground.

Organisms that die and fall to the bottom of this lake are much more likely to be buried and fossilize than those that die in the distant mountains. Click to zoom. Photo by K. Lee. From Wikipedia.

Scientists expect that the plants and animals living in some environments will be underrepresented in the fossil record, or even completely absent from it. This is because the places where they live are not well suited for the deposition of sediments that bury plant and animal remains, or to the long term preservation of fossils. In mountainous areas, for example, most eroding sediments are carried away by wind or by water that rushes down steep slopes. Few remains are buried, and those that are will be uncovered again as erosion continues to wear away at the mountains. The result is that we have very few fossils of animals and plants from mountain ecosystems. Organisms that live in and around lowland lakes and streams, on the other hand, have a much higher chance of being buried in accumulating sediments - and of staying buried for long periods of time.