Dr. Pyron also found that dispersal during the Cenozoic Era (66 million years ago to the present), likely across land bridges or short distances across oceans, also contributed to their distribution.
Given their ancient origin, it is unsurprising that the history of amphibians is a mixture of both vicariance and dispersal. But the third and final distribution pattern that Dr. Pyron notes in his study was an unexpected finding.
Past studies have assumed that long-distance over water dispersal was essentially impossible for amphibians due to salt intolerance. However, when Dr. Pyron began completing his analysis, he noticed a number of cases of distribution that could not be explained by old age.
For instance, one group of frogs found in Australia and New Guinea (pelodryadine hylids) that originated around 61 to 52 million years ago is deeply nested within a group of amphibians that exist only in South America. By the time pelodryadines originated, all major continental landmasses occupied their present-day positions, with South America and Australia long separated from Antarctica.
"They're 120 million years too late to have walked to Australia," Dr. Pyron said.
So how could this group of South American amphibians be related to frogs on the other side of the world?
"You wouldn't think that frogs would be able to swim all the way there, but that seems like one of the more likely explanations for how you could have such a young group nested within South America and have it somehow get to this other continent," Dr. Pyron said.
In his study, Dr. Pyron points two other instances of long-distance oceanic dispersal.
"What you have is this mixture of processes. You have vicariance, which over 300 million years has put certain groups in Africa, some in Australia and others in South America," Dr. Pyr
|Contact: Kurtis Hiatt|
George Washington University