A fossilized jawbone from a newly-described species of acrodontan iguana, Gueragama sulamericana, that lived about 80 million years ago has been unearthed in the municipality of Cruzeiro do Oeste in Southern Brazil.

Iguanas are one of the most diverse groups of extant lizards, spanning from acrodontan iguanians (those with teeth fused to the top of their jaws) dominating the Old World to non-acrodontans in the New World, as well as Madagascar and a few Pacific islands.

Gueragama sulamericana is the first acrodontan found in South America, suggesting both groups of ancient iguanas roamed throughout Pangaea before its final breakup.

“The roughly 1,700 species of iguanas are almost without exception restricted to the New World, primarily the southern United States down to the tip of South America,” said Dr Michael Caldwell of the University of Alberta, Canada, a co-author of a paper published in the journal Nature Communications.

“And yet, the iguana’s closest relatives – including chameleons and bearded dragons all hail from the Old World.”

According to Dr Caldwell and his colleagues, the Upper Cretaceous Gueragama sulamericana is a missing link in the sense of the paleobiogeography and possibly the origins of the group.

“It’s pretty good evidence to suggest that back in the lower part of the Cretaceous, the southern part of Pangaea was still a kind of single continental chunk,” Dr Caldwell said.

Distributions of plants and animals from the Upper Cretaceous reflect the ancestry of Pangaea when it was whole.

Dr Caldwell explained: “this Gueragama sulamericana fossil indicates that the group is old, that it’s probably Southern Pangaean in its origin, and that after the breakup, the acrodontans and chameleon group dominated in the Old World, and the iguanid side arose out of this acrodontan lineage that was left alone in South America.”

“South America remained isolated until about 5 million years ago. That’s when it bumps into North America, and we see this exchange of organisms north and south,” he added.

“It was kind of like a floating Noah’s Ark for a very long time, about 100 million years.”

“This is an Old World lizard in the New World at a time when we weren’t expecting to find it. It answers a few questions about iguanid lizards and their origin.”

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Tiago R. Simoes et al. 2015. A stem acrodontan lizard in the Cretaceous of Brazil revises early lizard evolution in Gondwana. Nature Communications 6, article number: 8149; doi: 10.1038/ncomms9149