8,000 Giant Galápagos Tortoises May Belong to New Species

A giant Galapagos tortoise
The tortoise formerly known as Chelonoidis chathamensis on San Cristóbal Island in the Galápagos. mtkopone / CC BY-SA 2.0

The giant tortoises of the Galápagos Islands are some of the most famous reptiles in the world, but there is still much more to learn about them. 

It turns out that the 8,000 or so giant tortoises that live on the island of San Cristóbal do not belong to the species scientists thought they did. 

“The species of giant tortoise that inhabits San Cristóbal Island, until now known scientifically as Chelonoidis chathamensis, genetically matches a different species,” Ecuador‘s environment ministry announced on Twitter Thursday. 

The Galápagos Islands were made famous by naturalist Charles Darwin, who developed his theory of evolution while observing the archipelago’s unique animals, ScienceAlert explained. One of those animals is the giant tortoise. There were once 15 different species of giant tortoise on the islands, but at least three are believed to be extinct. 

In 1906, a research team from the California Academy of Sciences found bones and shells in a cave in the southwestern highlands of San Cristóbal, the Galápagos Conservancy explained. Based on these findings, they named the species C. chathamensis, and it was assumed that all of the tortoises on San Cristóbal belonged to this species. 

However, the tortoises now live on the lowlands of San Cristóbal, where the 1906 expedition never visited. Researchers from University of Newcastle, Yale University, Galápagos Conservancy and other groups compared the DNA from the current tortoises with the 1906 bones and found that they did not in fact match. They published their findings in the journal Heredity in late February.

The discovery has three main implications, according to the Galápagos Conservancy:

  1. The tortoises living on San Cristóbal may not belong to the species C. chathamensis because they represent a different taxon, or lineage. 
  2. C. chathamensis itself is “almost certainly extinct.” 
  3. Until its extinction in the mid-20th century, there were two taxons of tortoise living on San Cristóbal, one in the highlands and one in the lowlands

“The authors are currently working to recover more DNA from the extinct taxon to clarify the taxonomic status of the San Cristóbal tortoises and better understand how the current living species is related to the extinct one,” the Galápagos Conservancy wrote. “It seems likely that there were two species on San Cristóbal, not one, and if this is the case, the name of C. chathamensis should be assigned to the extinct species, and the extant taxa should be given a new name.”

It is possible that two different species developed because San Cristóbal may have been split into two islands millions of years ago because of higher sea levels. The highland tortoises were killed off by whalers and settlers in the early 20th century. 

Scientists began a genetic analysis of all living Galápagos tortoises in 1995 and moved on to extinct species in 1999, according to the Ecuadorian government. The researchers underscored the importance of preserved museum samples in understanding past and present tortoise species. 

“Without the museum samples, this important discovery of an additional lineage of Galápagos giant tortoise would not have been possible, underscoring the value of such collections and providing insights into the early evolution of this iconic radiation,” the study authors wrote in Heredity. 

The Galápagos Islands are now part of a protected reserve that the Ecuadorian government expanded recently by 23,166 square miles, Reuters reported. 

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