Lizards are remarkable amongst amniotes, for they display a unique mosaic of reproduction modes ranging from egg-laying to live-bearing. Within this patchwork, geckoes are believed to represent the only group to ever have produced fully calcified rigid-shelled eggs, contrasting with the ubiquitous parchment shelled-eggs observed in other lineages. However, this hypothesis relies only on observations of modern taxa and fossilised gecko-like eggshells which have never been found in association with any embryonic or parental remains. We report here the first attested fossil eggs of lizards from the Early Cretaceous of Thailand, combining hard eggshells with exquisitely preserved embryos of anguimoph (e.g. Komodo dragons, mosasaurs). These fossils shed light on an apparently rare reproduction strategy of squamates, demonstrate that the evolution of rigid-shelled eggs are not an exclusive specialization of geckoes, and suggest a high plasticity in the reproductive organs mineralizing eggshells.

CNRS 8538 Laboratoire de Géologie de l'Ecole Normale Supérieure 24 Rue Lhomond 75231 Paris France

European Synchrotron Radiation Facility 71 rue des Martyrs 38043 Grenoble France

European Synchrotron Radiation Facility 71 rue des Martyrs 38043 Grenoble France; Evolutionary Studies Institute University of the Witwatersrand Wits 2050 Johannesburg South Africa

Palaeontological Research and Education Centre Mahasarakham University Khamrieng Sub district Kantharawichai District Maha Sarakham Province 44150 Thailand

Sorbonne Universités CR2P MNHN CNRS UPMC Paris6 Muséum national d'Histoire Naturelle 57 rue Buffon CP 38 75005 Paris France

Subdepartment of Development and Evolution Department of Organismal Biology Evolutionary Biology Centre Uppsala University Norbyvägen 18A 752 36 Uppsala Sweden; Department of Biomathematics Institute of Physiology Academy of Sciences of the Czech Republic Vídeňská 1083 142 20 Praha Czech Republic

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