A stem acrodontan lizard in the Cretaceous of Brazil revises early lizard evolution in Gondwana

ARTICLE Received 5 Apr 2015 | Accepted 23 Jul 2015 | Published 26 Aug 2015 DOI: 10.1038/ncomms9149 OPEN A stem acrodontan lizard in the Cretaceous of Brazil revises early lizard evolution in Gondwana Tiago R. Simões1, Everton Wilner2, Michael W. Caldwell1,3, Luiz C. Weinschütz2 & Alexander W.A. Kellner4 Iguanians are one of the most diverse groups of extant lizards (41,700 species) with acrodontan iguanians dominating in the Old World, and non-acrodontans in the New World. A new lizard species presented herein is the first acrodontan from South America, indicating acrodontans radiated throughout Gondwana much earlier than previously thought, and that some of the first South American lizards were more closely related to their counterparts in Africa and Asia than to the modern fauna of South America. This suggests both groups of iguanians achieved a worldwide distribution before the final breakup of Pangaea. At some point, non-acrodontans replaced acrodontans and became the only iguanians in the Americas, contrary to what happened on most of the Old World. This discovery also expands the diversity of Cretaceous lizards in South America, which with recent findings, suggests sphenodontians were not the dominant lepidosaurs in that continent as previously hypothesized. 1 Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G2E9. 2 Centro Paleontológico da UnC (CENPALEO), Universidade do Contestado, Mafra, Santa Catarina, Brazil CEP 89300-000. 3 Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada T6G2E9. 4 Laboratory of Systematics and Taphonomy of Fossil Vertebrates, Departamento de Geologia e Paleontologia, Museu Nacional/ Universidade Federal do Rio de Janeiro, Quinta da Boa Vista s/n, São Cristóvão, Rio de Janeiro, Brazil CEP 20940-040. Correspondence and requests for materials should be addressed to T.R.S. (email: ). NATURE COMMUNICATIONS | 6:8149 | DOI: 10.1038/ncomms9149 | www.nature.com/naturecommunications & 2015 Macmillan Publishers Limited. All rights reserved. 1 ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/ncomms9149 S quamates (lizards, snakes and amphisbaenians) are the most speciose extant group of reptiles, represented by more than 9,000 living species, and iguanians are one of the most diverse group of lizards globally, with more than 1,700 species1. Acrodontan iguanians are characterized by unique jaw features among lizards, as well as an evolutionary trend towards tooth placement at the apex of the jaws and fusion to it (acrodonty and pleuroacrodonty), whereas non-acrodontans (iguanids, tropidurids, among others) are pleurodont, with teeth attached to the lingual wall of the jaws. Among extant taxa, while acrodontans have an Old World distribution, non-acrodontan iguanians dominate the New World, as well as Madagascar and a few Pacific islands2. The origins of these two groups, with their almost disjunct distributions, and the dominance of non-acrodontans in the Americas have been the subject of great conjectures and debate3–8. The difficulty in providing answers to these questions is due to a poor fossil record worldwide during the time of origin of squamates (Early-Mid Mesozoic), and during the entire Mesozoic of Gondwana—nine valid species of lizards9, versus B150 species in Laurasia (data compiled from7 and several subsequent publications). Here we report on the first known acrodontan iguanian lizard from South America, the New World component of ancient Gondwana, recovered from a new locality in Brazil dated as Late Cretaceous. This discovery overturns long held hypotheses of the evolution and palaeobiogeography of modern iguanian lizards and provides important insights into the early evolution of lizards in South America. Results Systematic palaeontology. Description. The preserved dentary has a convex ventral border that is partially broken in its midsection, and bears six mental foramina laterally. The coronoid process would have covered the coronoid eminence laterally, probably reaching to or beyond its posterior margin. In medial view, the anterior tip of the dentary has a horizontally elongate symphysial flat surface that would have butted against its right counterpart, and is barely indented ventrally by the Meckelian canal. The subdental shelf has a medial ridge that diminishes in height posteriorly and which delimits a dental sulcus anteriorly that is not filled with cementum (as opposed to teiids) and is mostly empty. Despite the ventral border of the dentary being broken in its midsection, the ventral crest of the dentary is preserved and visible in medial view ventral to the subdental shelf, anteriorly and posteriorly. It does not extend medially, and does not contact the subdental ridge, even in its deepest part on the anteriormost section of the dentary. This indicates that the Meckelian canal was fully open medially, even in the region where the subdental shelf was deepest. Posterior to the last tooth position there is a large facet for the coronoid anteriomedial process, and posterior and laterally to this, facets for the surangular and angular bones (Fig. 1). Inside the Meckelian canal, the intramandibular septum is not seen posteriorly. There is an excavation on the dorsolateral surface of the dentary, which creates a posterodorsal crest that extends onto the coronoid process, as observed in the extant agamid Uromastyx. There is no facet for the splenial medially on the subdental shelf. There are 18 tooth positions, with most teeth preserved in situ and displaying moderate heterodonty. The anteriormost five teeth display no obvious ankylosis to the labial wall. However, there is a C.Pr. Squamata Oppel, 1811 Acrodonta Cope, 1864 Gueragama sulamericana gen. et sp. nov. San.fr. Etymology. ‘Guera’, meaning ‘ancient’ (native Brazilian TupiGuarani); ‘agama’(gender feminine) in reference to agamid lizards; ‘sulamericana’, meaning ‘from South America’ (Portuguese). Holotype. CP.V 2187, partial lower jaw (Fig. 1), CENPALEO—Universidade do Contestado, Santa Catarina, Brazil. Additional material. CP.V 2188 (unprepared fragments of possible maxillary and teeth). Type locality and horizon. Cruzeiro do Oeste, Paraná State, Brazil; Goio-Erê Formation, Caiuá Group, Bauru Basin; Turonian-Campanian, Late Cretaceous10. Diagnosis. Stem acrodontan species separated from all other squamates by the following combination of characters: coronoid process of dentary with dorsal and posteriorly elongate component; posterior process of dentary undivided and extending well beyond level of coronoid process; presence of subdental shelf; dental sulcus present anteriorly; no splenial articulatory facet on dentary (splenial either small or absent); large facet for anteromedial process of coronoid on dentary; angular extending anterior to posteriormost tooth; anterior teeth pleurodont, peg-like, with pointed and laterally compressed apices; posterior marginal teeth: pleuroac (...truncated)