<P> In biology , extinction is the termination of an organism or of a group of organisms ( taxon ) , normally a species . The moment of extinction is generally considered to be the death of the last individual of the species , although the capacity to breed and recover may have been lost before this point . 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 Lazarus taxa , where a species presumed extinct abruptly `` reappears '' ( typically in the fossil record ) after a period of apparent absence . </P>
when is a species presumed to be extinct
generally considered to be the death of the last individual of the species