Evidence of Egg Diversity in Squamate Evolution from Cretaceous Anguimorph Embryos

PLoS One. 2015 Jul 15;10(7):e0128610. doi: 10.1371/journal.pone.0128610. eCollection 2015.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Biodiversity
  • Bone and Bones / diagnostic imaging
  • Ecological and Environmental Phenomena*
  • Egg Shell
  • Embryo, Nonmammalian*
  • Evolution, Molecular*
  • Lizards / embryology*
  • Lizards / physiology
  • Ovum* / diagnostic imaging
  • Ovum* / physiology
  • Radiography
  • Reproduction

Grants and funding

This project was funded by the European Synchrotron Radiation Facility (ESRF, France), the ECLIPSE 2 programme of the Centre National de la Recherche Scientifique (CNRS, France), the CNRS–Thailand Research Fund joint project, the Biodiversity Research and Training Program (BRT, Thailand), the Department of Mineral Resources (Bangkok, Thailand), the Linnaeus Framework Grant “The Genomics of Phenotypic Diversity in Natural Populations” (the Swedish Research Council), and the Czech Science Foundation (P302/12/1207).