concept

Ghost lineage

The span during which a lineage existed but left no fossils - a real stretch of history about which the rock is entirely silent. It arises necessarily because a clade's first fossil gives only a *minimum age*: the lineage must have existed before it happened to be preserved for the first time. So when a molecular clock puts two lineages' divergence earlier than the oldest fossil, that is usually not a contradiction to be resolved but the width of the ghost lineage itself.