An important paleontological concept that denotes temporal mixing (or age mixing) of fossils. Unlike live-collected organisms, fossils found together within a single stratum need not be contemporaneous with one another, but may represent mixed remains of organisms that lived at different times and never interacted with one another. Fossilized shells, bones, and other skeletal remains collected from the same sediment layer or the same bedding plane may represent individuals that lived centuries or even millennia apart.