Ice-age animals in the Bahamas

Flooded sinkhole reveals ice age island ecology

A paper published in Proceedings of the National Academy of Sciences, USA, on 19 October 2015 (preprint can be found here) reporting the richest set of late Pleistocene (ice age) vertebrates found on any Caribbean island to date.

A tortoise shell in remarkable condition recovered from Sawmill Sink, with PI David Steaman and collaborator Nancy Albury of The National Museum of the Bahamas
A tortoise shell in remarkable condition recovered from Sawmill Sink, with co-PI David Steadman and collaborator Nancy Albury of The National Museum of the Bahamas 

   Almost 100 species of fish, reptiles, birds and mammals were identified from fossils found in Sawmill Sink, a flooded sinkhole cave or "blue hole" on Abaco Island in The Bahamas, allowing changes in the animal community to be tracked through time. The warmer, wetter climate and rising sea levels that occurred from 15,000 to 9000 years ago during the Pleistocene (ice age) to Holocene Transition (PHT) coincided with the disappearance on Abaco of at least 17 species of birds. These 17 species are characteristic of the open habitats (pine woodlands and grasslands) found on cooler, drier, larger ice age Bahamian islands (shown by co-author Janet Franklin using geospatial modeling). A diverse group of 22 species of reptiles, birds, and mammals persisted through those environmental changes, however, but did not survive the last 1000 years of human presence. Thus the late Holocene arrival of people probably depleted more animal populations than the dramatic physical and biological changes associated with the PHT. For the species that remain, direct human activity threatens their immediate future more than climate change.

Writing about this study for the Florida Museum of Natural History, where first-author David Steadman is the Curator of Ornithology, journalist Stephanie Livingston noted that “Exploring why some species were more flexible than others in the face of climate and human-driven changes could alter the way we think about biodiversity conservation and restoration of species today” For island species that have persisted to the present day through dramatic changes in climate and island area, activities like habitat alteration and the introduction of invasive species could pose the greatest immediate threats to their future.

The Bahama or Rose-throated Parrot (Amazona leucocephala), iconic Bahamian bird now found on only two island there, has been indentified from fossils as occuring on Abaco at least since the last ice age

Sawmill Sink is a rich source of well-preserved fossils owing to its unique water chemistry. While this study encompassed the entire vertebrate community, the most well known fossils, recovered from Sawmill Sink by coauthors Brian Kakuk, Nancy Albury and other scientific divers, are spectacular specimens of crocodile and tortoise, species no longer found in The Bahamas. The scientific value of the fossils found in the caves has contributed directly to the recent establishment of a new protected area, South Abaco Blue Holes National Park, protecting the system of flooded caves including Sawmill Sink.

Nancy Albury of The National Museum of the Bahamas, vertebrate paleontologist and cave diver.

This project was sponsored by the National Science Foundation (1118340).


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