Answer: An Endling

Given enough time eventually, the family tree of every species and subspecies must reach a termination point where there exists a single surviving member. Historically, there was no word to describe that creature, the final member of its long and winding genetic lineage.

In the April 4, 1996 issue of Nature, commentators writing into the publication proposed the adoption of a new word to describe such a creature: an endling, the last of its species. It was a suitably weighty and grave word for such a state of affairs and it has since appeared in various publications to describe the last surviving member of a species.