The suborder Iguania is the most diverse group of existing lizards with over 1,700 species. The suborder is divided into two groups based on jaw features and teeth placement: acrodontan, with teeth fused to the top of the jaw; and non-acrodontan. The acrodontans, including chameleons and bearded dragons, dominate the Old World: Africa, Europe, and Asia. Meanwhile, non-acrodontans, like iguanas, dominate the New World: the Americas, as well as Madagascar and a few Pacific islands. This divide has been the subject of great speculation, because although restricted the two lizard groups are very much related.
In the municipality of Cruzeiro do Oeste in southern Brazil, paleontologists Tiago Simões and colleagues recovered the remains of an acrodontan dating to the late Cretaceous period, approximately 80 million years old. The date suggests that acrodontans are older than what was previously thought. Although G. sulamericana is the only acrodontan fossil found in South America, its discovery nonetheless suggests that acrodontans once ranged across much of Gondwana before the supercontinent’s breakup. This contradicts previous ideas that proposed acrodontans evolved after the Atlantic formed.
Whether this current domination of lizard species in the New World is a result of acrodontans losing the competition for resources to non-acrodontans and subsequently becoming extinct is yet to be established. G. sulamericana has answered a few questions about the origins of non-acrodontians like iguanas, but it has also raised a number of others. One of the difficulties in providing answers to the questions on lizard evolution is the lack of fossil record, state Simões and colleagues, however new fossil finds in Brazil and Argentina in older rocks may continue to expand our understanding on the subject.