The tropical conditions of the Caribbean are not ideal for the preservation of DNA, as the molecules degrade quickly in the warm humid environment, leaving little behind. But a team of scientists has managed to extract and sequence the genome of an extinct species of tortoise that once roamed the Bahamas, making it the very first sample of ancient DNA extracted from an extinct tropical species.
“This is the first time anyone has been able to put [an extinct] tropical species into an evolutionary context with molecular data,” explains David Steadman, co-author of the study discussing the finding in the Proceedings of the Royal Society B, in a statement. “And being able to fit together the tortoise’s evolutionary history together will help us better understand today’s tropical species, many of which are endangered.”
The tortoise to which the bones once belonged is thought to have gone extinct around 1,000 years ago, within centuries of the arrival of humans, who probably island hopped from Hispaniola. Evidence for people living in the Bahamas before then is none existent, and in the time after they made landfall, a number of species vanished from the ecosystem, including the tortoises.
The shell from one of the extinct tortoises. Nancy Albury
The fossil was found in the murky depths of a sinkhole on the island of Abaco, which has been found to be littered with the remains of a whole host of creatures that once lived on the island, many of which are now extinct. Researchers have identified an impressive 95 different vertebrate species, giving them an incredible snapshot of what the ecosystem once looked like, and also providing evidence of the fate that befell them.
The unique environment of the Sawmill sinkhole in which the bones that have been found have incredible levels of preservation. The water in the sinkhole has been stratified, and the lower reaches are starved of oxygen preventing the heavy decay typical of tropical regions. For DNA to be preserved, it usually requires a cold, dry environment, the exact opposite of what you tend to find in the wet humid tropics.
This level of preservation of the tortoise, which drifted to the bottom of the flooded cave after it died, means that the researchers didn’t just have sections of the creatures, but the entire skeleton. “That’s really unheard of in the fossil record, especially in the West Indies,” said Steadman. It meant that the researchers were able to describe in intimate detail the anatomy of the creature as if it were still walking the planet today.
To retrieve the fossils, the researchers have to dive to the depths. Brian Kakuk
