is the cessation of existence of a species
or group of taxa
, reducing biodiversity
. The moment of extinction is generally considered to be the death of the last individual of that species (although the capacity to breed and recover may have been lost before this point; see population bottleneck
). Because a species' potential range
may be very large, determining this moment is difficult, and is usually done retrospectively. This difficulty leads to phenomena such as a Lazarus taxon
, where a species presumed extinct abruptly "re-appears" (typically in the fossil record
) after a period of apparent absence.