By Kelly Delancy, AMMC Abaco
A thousand years ago, the islands of The Bahamas were home to land-dwelling crocodiles and large tortoises. They were the island’s top predators and prey species before humans arrived in the archipelago. An abrupt change in the island’s animal populations occurred around the same time people migrated into the Bahamian Archipelago.
The large reptiles, as well as many species of birds, bats and a large rodent have since disappeared. They can no longer be found in the islands, except through their skeletons which remain as evidence that these animals once lived here.
Research into the past environments of the Bahamas continues with a recently published landmark study in the Proceedings of the Royal Society B on January 11, 2017. The study titled “Tropical ancient DNA reveals relationships of the extinct Bahamian giant tortoise Chelonoidis alburyorum” was completed by an international team of researchers and scientists from Germany, the United States, and The Bahamas. The fossil remains of the 1000-year-old tortoise in the study were recovered from Sawmill Sink Blue Hole on the island of Abaco, Bahamas.
“In recent decades, the skeletal remains found in the Bahamas blue holes prompted us to reconsider our understanding of the Bahamian natural environment, both in the past and also how our activities today may be affecting our natural world,” said Nancy Albury, co-author in the study and curator of the Bahamian fossils for the National Museum of The Bahamas.
“The exceptional preservation of fossils from blue holes has allowed us to better understand how the pre-human ecology functioned in the Bahamas by identifying species that were abundant long ago and their patterns of migration through time,” continued Albury. “The opportunity to extract and study the ancient DNA (aDNA) of tropical species presents itself within certain blue holes where hydrogen sulfide layers in the oxygen-free water of some blue holes enhance preservation of DNA in tissues. Because this species is extinct today, we were not necessarily hopeful that the DNA would be preserved”.
DNA from extinct tropical species is rare because the warm climate causes rapid decomposition of the collagen in the bones. For this reason, large animals from colder climates have been widely studied, while little is known of the ecology, evolution, biogeography and causes of extinction among species from tropical and subtropical regions.
“This study shows that the tortoise from Abaco is most closely related to the tortoise in the Galapagos Islands in the Pacific Ocean and the Chaco Tortoise of South America,” said Albury. “What’s interesting here is that the tortoise from Abaco in the northern Bahamas did not share its genetic ancestry with tortoises that are regionally closer in North America. Rather, its closest relatives are tortoises that today inhabit an island group in a different ocean system. Further, both of these island tortoises share their direct ancestry with tortoises from the southern regions of the South American continent, not the northern areas of South America. The study provides evidence of the recurrent movement of this land-dwelling tortoise group overseas and highlights their ability to successfully colonize islands systems.”
The complete study can be accessed here: http://rspb.royalsocietypublishing.org/content/royprsb/284/1846/20162235.full.pdf?ijkey=LG3fymRbx8vpRBi&keytype=ref