The skulls belong to two new species of ancient crocodilians (a group that today contains alligators, crocodiles, caimans and gharials) that lived about 20 million years ago during the Miocene epoch. These new findings, detailed in the March issue of the Journal of Vertebrate Paleontology, suggest these alligator brethren slinked between the continents using ancient seaways much earlier than once thought.

"The tropics hold some of the greatest diversity on the planet. Yet there's still so little that we know about them," study co-author Jonathan Bloch, a paleontologist at the Florida Museum of Natural History, told LiveScience. The fossil record in Central America is limited, because rocks there tend to be covered by forest, Bloch said, so the Panama excavation provides "a new window back into the past that's very difficult to get at in the tropics."