A series of underwater caves off the southern coast of Sicily holds clues about Ice Age-era human migration. A team of ‘citizen scientists’ — including a tugboat captain and both recreational and Italian navy divers — helped discover them.

The findings, reported in PLOS ONE, describe 25 caves and rock shelters that show signs of human occupation from about 17,000 years ago. Many scholars consider Sicily to be among the first islands humans settled in the Mediterranean.