Many species of iguanas dig shelters for protection against predators, fires and extreme weather. Most also make underground nests. Anthony J. Martin, CC BY-SA
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.
In December 2013, while exploring a roadcut on San Salvador Island in the Bahamas with 19 undergraduate geology students from Emory University, one of us (Anthony) noticed this unusual structure in the rock. It turns out the road excavators had unwittingly exposed a section of ancient sand dune, containing this iguana burrow from long ago. Read more >>