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.