A New Galapagos Tortoise Species May Have Just Been Discovered

The island in the Galapagos upon which Charles Darwin first landed in 1835 was once thought to be home to a single lineage of giant tortoise. But a team of researchers from across the world has identified a second, genetically distinct lineage there—one they believe has long been extinct.

The finding is laid out in a new paper published last month in the peer-reviewed journal Hereditary, the work of a group of 12 scientists from Newcastle University, Yale, MIT, the non-profit Galapagos Conservancy, and more. If the findings are confirmed to represent a new species, the living tortoises on the island may need a new name, the researchers say. 

The Galapagos Islands is an archipelago comprising 13 major islands, six smaller islands, and a few hundred islets and rocks. Its rich biodiversity comes in part from the habitats scattered across these islands, their isolation from one another and the movement of species between them—it’s a researcher’s paradise, one with ample room to track evolutionary patterns between land bodies. 

Tortoises, in particular, are well-studied on the island, and to date, fifteen species have been identified—three have gone extinct, and several others are in danger of extinction. It was thought that there was one tortoise species per island, but lead author Evelyn Jensen, told Motherboard via video call that, prior to her study, she had heard rumors (via “stories from old ships, logbooks and things”) that the island of San Cristóbal was actually home to two. 

“There are people that for more than 20 years have been trying to determine the evolutionary relationships,” Jensen, who is a lecturer in molecular ecology at Newcastle University, said. “We feel like we know them really well. But there's some questions that we just haven't been able to answer.” 

After locating a number of old, damaged tortoise bones that were found in 1906 in a cave in the central part of the island, currently held by the California Academy of Sciences, the researchers sequenced a small section of each bone’s genome. They compared this to the genome of the dominant living species of Tortoise on San Cristóbal (currently known as Chelonoidis chathamensis, characterized by their rounded, saddle-shaped shells, that primarily occupy the northern part of the island), and found the two to be different. It’s evidence that the island had indeed once been home to two different species of tortoise, and also that, for reasons yet unknown, they didn’t interbreed.

“One of them has just vanished. And the only traces are these bones from a cave,” Jensen said. “We looked very closely at the population that's still on the island today—that's what a lot of the part of the study is about—and we just find no trace of it.” 

Historical records show that tortoises that once resided on the south and central parts of San Cristóbal were “heavily harvested” in the mid-1800s, the paper notes. This has left only those in the northern section, and could explain the genetic distinction between the species. The authors also posit that San Cristóbal has, at some point in history, split into two, or that one or both of the species came over from a neighboring island.

The new species Jensen and her team discovered is almost certainly extinct, but until today, has been formally attached to the name C. Chathamensis, which is also used to describe the living population of around 8,000 tortoises on San Cristóbal Because the genome of the living turtle population fits a different section of the genetic tree from the cave tortoises entirely, the living population could end up in need of a rename.

“We thought the cave specimens and the living population were the same species, which is why we have been calling the living population chathamensis,” Jensen said. “But this new study shows that they are from different lineages. If the additional data can confirm that they are not just different lineages, but actually different species, then the living population will need a new name.” 

Their discovery was recognized by the Ministry of Environment, Water and Ecological Transition of Ecuador, which tweeted the revelation around the need for a species rename last week. 

Jensen says her team has a ways to go before it can confidently rename San Cristóbal’s living giant tortoise population. First, she’d like to sequence a longer stretch of DNA of the extinct cave species; and, to do that, she needs more bones. A number of Galapagos tortoise bones live in museums across the world today, she said, and many look like they might match the genetic profile of the bones found in the San Cristóbal cave in 1906. This could open new doors for research. 

“It's a treasure hunt, basically. These bones in the backs of warehouses, museums,” Jensen said. “Those museum specimens are completely changing how we're conserving the species, and the insights we can get for that.”

“Just when we thought we knew everything about the Galapagos tortoises,” she continued, “Surprise! There's more things. We have to rework our entire understanding.”