The equatorial rainforests are some of the most richly bio-diverse areas of the planet, accounting for an enormous percentage of all known species on earth. They probably have been for the majority of Earth’s history. But due to the abundant foliage characteristic of rainforests, it is also one of the most difficult places to dig for fossils.
A new study published in March in the Journal of Vertebrate Paleontology took on the daunting task of exploring the jungles of Central America. Authors Alexander Hastings, a paleontologist at Georgia Southern University in Statesborough, and Jonathan Bloch, a paleontologist at the Florida Museum of Natural History and their associates reexamined specimens of Crocodilians found in Panama, including crocodiles, alligators and caimans. Some of the specimens they mention were discovered during the contruction of the Panama Canal in the 1890’s but the team also went on their own dig. What they found casts the region of Panama in an even more mysterious light, at least from an evolutionary standpoint.
North America and South America did not touch for millions of years. Separated by the ocean, the animals in each had time to evolve very distinctly. Yet, we know that most the mammals in South America today are descendants of North American creatures. Likewise, ancestors of species like the armadillo and the alligator must have traveled upwards from South America. At some point in history, scientists know, there was a great interchange of mammals, reptiles, and amphibians between North and South America.
Most of this interchange probably happened about 2.6 million years ago during the Pliocene Epoch when the movement of tectonic plates and underwater volcanos formed the Isthmus of Panama. However, the findings of Hastings and Bloch may tell a different story for Crocodilians.
Hastings and Bloch have discovered some of the oldest fossils ever uncovered in Central America: two new species of Crocodilians that lived in Panama when it was still an island during the Miocene Epoch twenty million years ago, long before it was connected to North or South America. They discovered the skulls of two crocodilians, Culebrasuchus mesoamericanus and Centenariosuchus gilmorei; both primitive species of caimans.
Caimans are closely related to alligators but are smaller with longer tails and snouts. There are many species alive today live in the tropical regions of Central and South America; and the two reptilian fossil species probably closely resembled their living relatives. Crocodilians have changed very little in the past fifty million years. Several of the species of fossils cited in the study are still alive today.
Modern caimans can grow between three and thirteen feet long depending on the species. At seven and five feet long respectively, even the newly discovered species fit right in. Another trait Culebrasuchus mesoamericanus and Centenariosuchus gilmorei have in common with their living cousins is their inability to live in saltwater. Unlike crocodiles, alligators and caimans dehydrate quickly when swimming in salt water. So, if they were unable to swim such a long distance in salt water, how did they get from Panama to South America?
These new fossil records may mean that scientists have to rethink at least part of the interchange of animals in the Americas. It is possible that Panama was not as far away from South America as previously thought, allowing the caimans to swim the short distance. Alternatively, there may have been island chains connecting the continent and island that paleontologists are not yet aware of.
There may has been even more interchange of animals between the Americas than current paleontological research predicts. Whatever the answer to the mystery, it is sure to play an important role in helping paleontologists pinpoint which animals traveled from South to Central to North America (and vice versa) as well as exactly how and when.
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Visit the original article at the journal of Vertebrate Paleontology.
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