Split by the Isthmus of Panama: Species of butterfly fish, sand dollar and cone snail that today live on the Pacific and Caribbean coasts of Central America are very closely related. Genetic sequencing shows that only 4 to 3 million years ago, each pair was a single species, demonstrating that marine connections between the oceans must have existed until that time.
Image courtesy Simon Coppard, Alexander Medvedev, Ross Robertson, Shellnut, Bob Fenner