Fishes of the Desert?

I must admit to being surprised that what is now the Sahara desert once had a seaway and that fossils of giant fish and enormous sea snakes were found around Mali (https://www.theguardian.com/science/2019/jul/12/sahara-was-home-to-some-of-largest-sea-creatures-study-finds). It just reinforces that geographical areas can show impressive (and unexpected?) changes.