A species of giant Galapagos tortoise previously thought to be extinct may still be alive, scientists have revealed.
The species, known as chelonoidis elephantopus, inhabited the island of Floreana and was heavily hunted by whalers who visited the area to refresh their supplies. It was thought that the species had subsequently gone extinct in the 1840s.
However, the discovery of so-called hybrid tortoises on another island by a Yale University team has provided fresh hope that the species is still alive because the hybrid tortoises, some of whom are only 15 years old, appear to have chelonoidis elephantopus as a parent.
Now researchers have found DNA evidence that purebred Floreana tortoises must be living on Isabela Island among a population of its native Chelonoidis becki species. The researchers think there could potentially be 38 or more of the Floreana among an estimated 8,000 or so Isabela tortoises. Their paper is in Monday’s edition of the journal Current Biology.
The discovery dates back to 1994 when the same researchers took 60 blood samples from tortoises living on the sides of rocky and forbidding Wolf volcano on Isabela. But what lay locked in the DNA of some of the samples was surprising.
A further expedition to Volcano Wolf found 84 tortoises that appear, from genetic samples, to have a pure-bred C. elephantopus as a parent.
Thirty of these are less than 15 years old; so the chances of the pure-blood parents still being alive are high, given that they can live to over 100 years old.
“Around Volcano Wolf, it was a mystery – you could find domed shells, you could find saddlebacks, and anything in between,” recounted Gisella Caccone, senior scientist on the new study.
“And basically by looking at the genetic fingerprint of the hybrids, if you do some calculations you realise that there have to be a few elephantopus around to father these animals.
“To justify the amount of genetic diversity in the hybrids, there should be something like 38.”
The leading theory on how the tortoises came to be on the island is that whaling ships took the alive chelonoidis elephantopus species on board because the tortoises can survive without food for months and thus make a convenient supply of fresh meat. Some of the tortoises, the theory goes, made it to Isabela and somehow managed to establish a presence.
Given how large the tortoises are, weighing nearly half a tonne, the question of why they haven’t been spotted before is salient. The reason scientists point to is that the densely covered terrain of the Wolf makes tracking even the largest of species extremely difficult.
Scientists must now decide whether to attempt further exploratory expeditions.
Image used under the Creative Commons Attribution License with thanks to Joachim S. Müller. Image used for illustration purposes only and is in fact not the giant Galapagos tortoise chelonoidis elephantopus.