Iguanas and their close relatives (Iguanians) represent one of the most diverse groups of lizards in the world, with more than 1,700 species.

Of those still living, species characterised by teeth connected to the rim of the jaw bone (acrodontan) have an Old World distribution (Africa, Europe and Asia), like chameleons and bearded dragons.

While those with teeth that are attached to the lingual wall of the jaws (pleurodont) dominate the New World (North and South America), as well as Madagascar and a few Pacific islands, these include iguanas.

But the origins of these two groups, and their distinctive distribution, continues to be debated.

A poor fossil record globally during the evolutionary period of their parent order Squamata, which comprises all snakes and lizards, has made answering these questions difficult.

Now a new species of extinct lizard discovered in southern Brazil suggests that both groups of ancient lizards were found throughout the world.

Palaeontologists from the University of Alberta found the lizard fossil, named Gueragama sulamericana, in the rocky outcrops of a Late Cretaceous desert, which is said to date back around 80 million years.

It is the first acrodontan lizard to be found in South America and shows that this group of lizards were more widely distributed on the supercontinent Pangaea, which formed about 270 million years ago and broke apart about 200 million years ago, than previously thought. 

It’s a missing link in the sense of the palaeobiogeography

“This fossil is an 80 million year old specimen of an acrodontan in the New World,” explains Dr Caldwell.

“It’s a missing link in the sense of the palaeobiogeography and possibly the origins of the group, so 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.”

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

This is an Old World lizard in the New World at a time when we weren’t expecting to find it

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

“South America remained isolated until about five million years ago. That’s when it bumps into North America, and we see this exchange of organisms north and south. It was kind of like a floating Noah’s Arc 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.”

But lead author Tiago Simoes says the discovery also poses some questions that have yet to be considered.

“This finding raises a number of biogeographic and faunal turnover questions of great interest to both palaeontologists and herpetologists that we hope to answer in the future.”

Dr Caldwell says, having established that the group evolved much earlier than previously thought, they now need to look for even older rock formations to uncover further details of the evolutionary process.

The findings are published in the journal Nature Communications.

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