Two skulls found in the Panama Canal Zone shed new light on the migration history of caimans, southern relatives of the alligator – and also hint that North and South America were much closer together earlier than previously thought.
The new study released Monday by the Journal of Vertebrate Paleontology finds that some creatures may have made the leap more than 19 million years ago, 10 million years earlier than mammals did and well before Panama finally filled the continental gap.
The formation of the Isthmus of Panama around 3 million years ago had profound effects on global climate and on the continents' biodiversity. That slim strip of newly formed land separated the Pacific and Atlantic oceans, rerouted major currents and allowed for an animal exchange of sorts: For example, relatives of armadillos and porcupines in South America headed north, and the relatives of modern horses and elephants in North America went south, making Panama a sort of melting pot of immigrant species.
The two partial skulls in question, set in rocks that were 19.83 and 19.12 million years old, were dug up around the time the Panama Canal was being expanded. According to researchers from the University of Florida and the Smithsonian Tropical Research Institute, they appear to belong to two new species of caiman – relatives of North American alligators that live in South and Central America.
Because these caiman skulls cropped up in Panama before it connected to the southern continent, it’s possible the animals swam over. But because caimans and alligators are part of a family of crocodilian reptiles that can’t properly process saltwater, the freshwater beasts would not have survived an excessively long swim through the sea. Perhaps the two continents were closer together than researchers had previously thought.