Living fossil

living organism of which the most closely related organisms have been extinct and exist only in fossil form

Living fossil is an informal term for any living species (or clade) of organism which seems to be the same as a species otherwise only known from fossils and has no close living relatives. These species have all survived major extinction events, and generally retain low taxonomic diversities. A species which successfully radiates (forming many new species after a possible genetic bottleneck) has become too successful to be considered a "living fossil". The term is frequently misinterpreted, however.
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An extant species which is morphologically very similar to a species from the ancient past. Despite apparent lack of change, they seem to have escaped extinction. Coelacanth (a 350 million-years-old lobe-finned fish), Horseshoe Crab (a 510 million-years-old marine arthropod), Amazon River Dolphin, Gingko (maidenhair tree, a gymnosperm), and Metasequoia (Metasequoia glyptostrobodes, a conifer) are examples.