concept

Time-averaging

A thin layer of sediment does not record a moment but bundles anywhere from centuries to hundreds of thousands of years into one bedding plane. The consequence is easy to misread: organisms that never coexisted can lie side by side in the same rock, looking like a community, while short-term fluctuations are flattened out and vanish entirely. So "found together" does not mean "lived together" - and the temporal resolution of any fossil record is coarser than it appears.