Natural History Magazine | Featured Story

Partner Highlight

May 2008

Fossils from Bahamian Blue Hole May Give Clues to Early Life By Aaron Hoover and Cathy Keen
Scientists uncovered 25 species of birds, including the Caracara, from the Sawmill Sink. Photo by Nancy Albury, The Antiquities,Monuments and Museums Corporation

The following story is contributed by The Florida Museum of Natural History, one of Natural History magazine’s Museum Partners. Members of any of our partner organizations receive Natural History as a benefit of their museum membership. To see a list of the participating institutions and links to their Web sites, click here.

At the Florida Museum of Natural History, visitors may enjoy hundreds of exotic butterflies in a rainforest setting, witness a South Florida Calusa Indian welcoming ceremony, experience a life-sized limestone cave, and see a mammoth and mastodon from the last Ice Age. Permanent exhibits include Northwest Florida: Waterways & Wildlife; South Florida People & Environments; Florida Fossils: Evolution of Life & Land; and the McGuire Center for Lepidoptera and Biodiversity, which features the screened, outdoor Butterfly Rainforest exhibit with hundreds of live butterflies.

Located at the University of Florida, in Gainesville, this is Florida’s state museum of natural history, dedicated to understanding, preserving and interpreting biological diversity and cultural heritage. For further information, visit the Museum’s Web site, www.flmnh.ufl.edu.

Hold mouse over photo to pause slide change.

Long before tourists arrived in the Bahamas, ancient visitors took up residence in this archipelago off Florida’s coast and left remains offering stark evidence that the arrival of humans can permanently change—and eliminate—life on what had been isolated islands.

The unusual discovery of well-preserved fossils in a water-filled sinkhole called a blue hole revealed the bones of landlubbing crocodiles and tortoises that did not survive human encroachment, said David Steadman, a paleo-ornithologist at the Florida Museum of Natural History and the lead author of a paper published by the Proceedings of the National Academy of Sciences in December 2007.

“The climate and environmental conditions back then weren’t much different from those of today,” said Steadman. “The big difference is us. When people got to the island, there was probably nothing easier to hunt than tortoises so they cooked and ate them. And they got rid of the crocodiles because it’s tough to have kids playing at the edge of the village where there are terrestrial crocodiles running around.”

The first entire fossilized skeletons of a tortoise and a crocodile found anywhere in the West Indies were uncovered from Sawmill Sink on Great Abaco Island in the Bahamas, along with bones of a lizard, snakes, bats and 25 species of birds, as well as abundant plant fossils.

Radiocarbon analyses date the bones at between 1,000 and 4,200 years old with the youngest fossil being that of a human tibia, he said. The fossils are the best preserved of any ever found in the Bahamas because of their unusual location in the deep saltwater layer of the sinkhole that contains no oxygen, which normally would feed the bacteria and fungi that cause bones to decay, Steadman said. Expert diver Brian Kakuk and other skilled scuba divers retrieved the fossils from various places along the floor and walls of the blue hole, which contains salt water covered by a layer of freshwater.

“The fossils from Sawmill Sink open up unparalleled opportunities for doing much more sophisticated work than ever before in reconstructing the ancient plant and animal communities of the Bahamas,” Steadman said. “It helps us to understand not only how individual species evolve on islands, but how these communities changed with the arrival of people because we know that changes in the ecosystem are much more dramatic on islands than they are on continents.”

The skull of the land-roaming Cuban crocodile is one of many preserved fossils found in the Sawmill Sink on Great Abaco Island. This crocodile lived in the Bahamas until humans arrived.

Photo by Nancy Albury, The Antiquities, Monuments and Museums Corporation

There are many blue holes on Abaco and other Bahamian islands, but this is the first to be the site of a sophisticated fossil excavation, Steadman said. Although the Bahamian government has gone to great lengths to protect its coastline, blue holes with their submerged cave passages have received little attention as a marine resource, he said.

The fossil site is especially valuable because of the presence of fossilized plants—leaves, twigs, flowers, fruits and seeds—pollen and spores, and vertebrates, giving evidence of both the island’s flora and fauna, Steadman said.

“In a typical vertebrate fossil site, you identify the species of vertebrates—reptiles, birds or mammals—and based on that identification you speculate what the habitat might have been,” he said. “For the first time here in the West Indies, we have here on Abaco plant fossils right in with the vertebrates, so we can reconstruct the habitats in a much more sophisticated way.”

For instance, because bracken ferns are one of the first plants to recolonize after a fire, the presence of their spores would indicate regular burning in prehistoric times and indicate that an area was grassland. Evidence for this also comes from the numerous fossils of burrowing owls or meadow larks, which prefer open habitats, he said.

Among the excavation’s findings are that the land-roaming Cuban crocodile lived in the Bahamas until humans arrived, Steadman said. “People tend to think of crocodiles as aquatic and certainly most of them are, but in the Bahamas where there is no fresh water, the crocodile became a terrestrial predator,” he said.

The collaborative project includes Bahamian scientists Nancy Albury, Keith Tinker and Michael Pateman, as well as paleontologist Gary Morgan of the New Mexico Museum of Natural History.