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Skulls of alligator kin shed new light on reptiles' murky history

March 04, 2013|By Amina Khan
  • This image shows a life reconstruction of Culebrasuchus mesoamericanus in its ancient near-coastal environment during the early Miocene of Panama. Researchers have found skull fragments from two caimans that show the reptiles may have crossed continents earlier than thought.
This image shows a life reconstruction of Culebrasuchus mesoamericanus… (Danielle Byerley / Florida…)

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.  

The two caimans' surprise appearance may help tweak the geological narrative, researchers say: The finds could support a recent theory that only about 120 miles of water separated Panama (at the tip of Central America) from the South American mainland.

The skull fragments also help fill in a significant gap in the understanding of the Alligatorid family history. Until now, the researchers write, “Most of what should arguably be a rich history of Central American crocodylians has been poorly or completely unknown from the fossil record.”

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