Study suggests Americas connected 20 million years earlier than previously thought
A recent study examining salamander DNA that was co-authored by researchers from UC Berkeley and the University of Glasgow claims that North and South America joined more than 20 million years earlier than previously thought.
Salamanders in South America have genes that are significantly different from their Central American cousins, according to the study, which was published March 4 in the journal BMC Evolutionary Biology.
“What we are finding is that the salamanders are far more deeply differentiated than we thought,” said David Wake, a co-author of the study and a professor in the campus integrative biology department.
This difference implies that salamanders crossed from North America to South America much earlier than 3 million years ago, the date that most researchers currently believe, Wake said.
“When we first did these analyses … we found this old colonization (of salamanders) from South America, but it just didn’t make any sense,” said Kathryn Elmer, a co-author of the study and a lecturer at the University of Glasgow. “There’s no way that salamanders would cross that distance through salt water. We were trying to figure out how it could be that there were these deep divergences.”
These findings support the controversial claim that an isthmus of land connected the American continents as far back as 23.6 million years ago. Carlos Jaramillo, a scientist at the Smithsonian Tropical Research Institute, asserted this hypothesis in a study published last year.
“We are taking information from many different point of views,” Jaramillo said. “We need to do more research because we are gathering more information to really pin down the difference in age.”
Jaramillo’s study, which is independent of the recently published paper on salamanders, examined the age of the isthmus between North and South America. Jaramillo found evidence that the continents connected much earlier than previously believed, similar to Wake and Elmer’s recent findings.
“I thought, wow!” Wake said. “Here’s some geological evidence that’s in accord with what we think has been happening.”
However, many researchers still believe that the continents did not connect any earlier than 3 million years ago.
“I personally think that these people are full of nonsense, and that there is overwhelming evidence against what they say,” said Jeremy Jackson, professor emeritus of oceanography at the Scripps Institute at UC San Diego.
Jackson said that different studies on mammals, fish and fossils show no evidence of major migration by these animals 20 million years into the past.
“Sure, a few things got across, but most things didn’t until (3 million years ago),” Jackson said. “Overwhelming evidence for a mass migration north and south (supports the hypothesis that) the continents were connected by dry land.”
Despite the controversy surrounding Wake and Elmer’s claim that the continents connected 23.6 million years ago, Wake said they will continue their study of the salamanders in South America.
“The geological evidence is supporting us (and) gives us new confidence,” Wake said. “The kinds of evidence we have provided will spur on others to take looks at their data.”
Contact Tara Hurley at thurley@dailycal.org.