A giant crane that has been counted as extinct for about 150 years was not a separate species at all, according to a study that sequenced ancient DNA from 18 crane bones.
Grus primigenia was named in the nineteenth century by the French biologist Alphonse Milne-Edwards, working from bone fragments recovered in caves in southern France. The bones date to the end of the last ice age, more than 20,000 years ago, and they were large.
The new work, led by Bournemouth University and announced by the university in a release carried by Phys.org, finds that they came from unusually large individuals of the common crane, which is still very much alive.
The study was led by Dr John Stewart, professor of evolutionary palaeoecology at Bournemouth, with the Centre for Palaeogenetics in Stockholm, and appears in Royal Society Open Science.
The team extracted ancient DNA from 18 crane bones found in England, Wales, France, Germany and the Balearic Islands. Earlier studies had relied on the size and shape of bones alone.
Stewart suggested that the difference between large males and smaller females may have helped fuel the idea that two species were present.
The open question is now the reverse of the original one. Rather than asking what killed the giant crane, the team wants to know why cranes became smaller. Wetland drainage and changes in human land use are suspected, but more work is needed.
The authors note a broader implication: other extinct birds identified only by their size may need the same DNA check, and the number of past extinctions may have been overestimated.
That last point deserves stating in its strongest form, because the study has done something unusual. It has reduced the extinction total.
Grus primigenia has not been rediscovered. It has been withdrawn. The animal whose bones were measured in the nineteenth century is now a living species that used to be larger, which means the extinction consisted entirely of a change in dimensions.
The Department of Unnecessary Research considers this the most forgiving definition of survival yet put forward. Under it, nothing that shrinks can die out, and nothing that has died out can be shown to have done so until somebody sequences it.
The rule generalises cleanly in the other direction as well. Any sufficiently large member of a living species is an undescribed extinct species, pending a laboratory result.
Our analysts accept that the method is sound, that the correction is welcome and that the common crane is not pretending to be two things. They note only that the bones have not changed since the nineteenth century and the species count has.
The team's next question is why the cranes got smaller. The previous question, which was what became of them, has been answered. They are outside, and they are shorter.