Alligator Relative Traveled Across Ancient Land Bridge
March 5, 2013

Ancient Caiman Traveled Across The Isthmus Of Panama

April Flowers for - Your Universe Online

The Isthmus of Panama uplifted 2.6 million years ago to form a land bridge connecting North and South America. This bridge has long been thought to be the crucial step in the interchange of animals between the Americas. Armadillos and giant sloths moved up into North America and ancient relatives of modern horses, rabbits, foxes, pigs, cats, dogs and elephants moved down into South America.

A new study from the University of Florida and the Smithsonian Tropical Research Institute describes fossil crocodilians that shed surprising new light on the interchange and animal distributions between North and South America.

Partial skulls of two new species of caiman, which are relatives of alligators that only live in South America today, were discovered in rocks dated from 19.83 to 19.12 million years old. Excavations associated with the expansion of the Panama Canal exposed the fossils.

"These are the first fossil crocodilian skulls recovered from all of Central America. They fill a gap in evolution between the alligators of North America and the caimans of South America. It's quite incredible." states Dr. Alex Hastings, a fossil crocodilian specialist at Georgia Southern University. Hastings conducted the research while finishing his PhD work at the University of Florida.

The fossils in Panama indicate the caiman species dispersed north from South America by the early Miocene. This is over ten million years before the spread of mammals. Another exciting aspect of this discovery is caimans are unable to excrete excess salt from their bodies, restricting them to freshwater environments. This means the ancient caimans could have only dispersed a short distance across seawater. This supports a recently constructed hypothesis Central and South America were much closer to each other over 19 million years ago then scientists previously believed, painting a new picture of the histories of American animals.

Jonathan Bloch, a vertebrate paleontologist at the Florida Museum of Natural History, said, "We are starting to understand that while the mammals in Panama 19-21 million years ago were very similar to those found in Mexico, Texas, and Florida at that time, the reptiles tell a different story. Somehow, they were able to cross over from South America when it was completely isolated by seaways–this is one of the mysteries that will drive future inquiry and research in this region."

This study is part of the Panama Canal Program, a multinational research collaboration funded by the National Science Foundation in partnership with the Panama Canal Authority. The Program studies the geological and biological evolution of the Neotropics based on new discoveries in Panama.

The results of this study were recently published in the Journal of Vertebrate Paleontology.