Combined with a long and complete sedimentary depositional sequence, these diverse fossil assemblages are an unparalleled paleontologic resource of international importance.

Therefore, stages can be defined as a group of strata containing the same major fossil assemblages.

Of course, many graptoloids also drifted into shallower water, where they are associated with a more normal kind of fossil assemblage.

This behaviour is consistent with fossil finds where adult/juvenile fossil assemblages usually contain only female adult remains.

As a result, the Mazon Creek fossils are one of the world's major Lagerstätten, or concentrated fossil assemblages.

This is supported by fossil assemblages and cave paintings showing groups.

These deposits were once thought to be latest Cretaceous, but it is now clear that they are Paleocene channels with time-averaged fossil assemblages.

At the same time paleontologists define a system of faunal stages, of varying lengths, based on changes in the observed fossil assemblages.

It is important to distinguish the influences of both, as both may introduce particular sets of biases into the fossil assemblage.

Nearby, one of the richest Neogene fossil assemblages in the whole of South America is known.