Living fossil

Living fossil is a term for any living species (or clade) of organism which closely resembles 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 reason for this is that 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.

Related Topics:
Species - Clade - Fossil - Extinction events - Genetic bottleneck

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There is a subtle difference between a "living fossil" and a "lazarus taxon". A lazarus taxon is a taxon (either one species or a group of species) that suddenly reappears, either in the fossil record or in nature (i.e., as if the fossil had "come to life again"), while a living fossil is a species that (seemingly) hasn't changed during its very long lifetime (i.e., as if the fossil has always lived). The mean species turnover time (the time a species lasts before it is replaced) varies widely among the phyla, but is about 2-3 million years. So, a living species that was thought to be extinct (the coelacanth fish for instance) is not a living fossil by strict definition, it is a lazarus species. Coelacanths disappeared from the fossil record some 80 million years ago (upper Cretaceous). If, however, Cenozoic Latimeria (thus belonging to the Latimeria genus) fossils were to be found, Latimeria chalumnae would be considered a true living fossil, as that would fill in the gap where the species is "dead". Of course, species do not just appear out of thin air, so all living lazarus species (excluding disappearing and reappearing red list species) are nonetheless considered living fossils, if it can be shown they are not Elvis taxa.

Related Topics:
Lazarus taxon - Taxon - Group of species - Phyla - Coelacanth - Cretaceous - Cenozoic - Genus - Red list species - Elvis taxa

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Some living fossils are species that were known from fossils before living representatives were discovered. The most famous examples of this are the coelacanth fishes, Latimeria chalumnae and Latimeria menadoensis and the Dawn Redwood, Metasequoia, discovered in a remote Chinese valley. Others are a single living species with no close living relatives, but which is the survivor of a large and widespread group in the fossil record (a well-known example of this is the ginkgo tree, Ginkgo biloba).

Related Topics:
Dawn Redwood - Ginkgo

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Note the similarity between the 170 million year old fossil Ginkgo sp. leaves on the left, and the living plant on the right.

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