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By Anthony J. Martin and Melissa Hage 15 Dec 2020, 12:00
A pregnant iguana dug into a vegetated sand dune about 115,000 years ago on a small island in a chain of islands that one day would be called the Bahamas. Once she buried herself and was surrounded by loose sand, she scraped out a chamber and laid her eggs in it. On her way out of this underground nursery, she packed sand behind her, forming distinctive layers that marked her progress to the surface.
Once back in the sunshine, she tamped down the top to conceal the nest. Over many centuries, a thin layer of soil developed over the former nesting burrow, and minerals from that soil formed between the sand grains, turning the dune into limestone, which preserved the structure of the nesting burrow.
A trace fossil preserved in the Grotto Beach Formation on San Salvador Island, the Bahamas, is the first known fossil example of an iguana nesting burrow.
Illustration shows a cross section of the prehistoric iguana burrow, and how the surrounding landscape may have looked during the Late Pleistocene epoch. Image credit: Anthony Martin.
Iguanas are relatively large terrestrial lizards that are primarily native to Central America, South America, the Caribbean, and the Bahamas.
They can grow up to 1.8 m (6 feet) in length, including their tails. Despite their large size, formidable claws and fierce-looking spikes arrayed on their backs, iguanas are mostly herbivores.
The study in
PLOS ONE also uncovers new clues to the geologic and natural history of the Bahamas, where the burrow was found.
The fossilized burrow dates back to the Late Pleistocene Epoch, about 115,000 years ago, and is located on the island of San Salvador best known as the likely spot where Christopher Columbus made his first landfall in his 1492 voyage.
“San Salvador is one of the outer-most islands in the Bahamas chain and really isolated,” says Anthony Martin, a professor in Emory University’s environmental sciences department and senior author of the paper. “It’s a mystery how and when the modern-day San Salvadoran rock iguanas arrived there. Today, they are among the rarest lizards in the world, with only a few hundred of them left.”