Identification and comparison of modern and fossil crocodilian eggs and eggshell structures

Abstract

Eggshells from the three extant crocodilian species Crocodylus mindorensis (Philippine Crocodile), Paleosuchus palpebrosus (Cuvier's Smooth-fronted Caiman or Musky Caiman) and Alligator mississippiensis (American Alligator or Common Alligator) were prepared for thin section and scanning electron microscope analyses and are described in order to improve the knowledge on crocodilian eggs anatomy and microstructure, and to find new apomorphies that can be used for identification. Both extant and fossil crocodilian eggs present an ornamentation that vary as anastomo-, ramo- or the here newly described rugosocavate type. The angusticaniculate pore system is a shared character for Crocodylomorpha eggshells and some dinosaurian and avian groups. Previously reported signs of incubated crocodilian eggs were found also on our only fertilised and hatched egg. Paleosuchus palpebrosus presents unique organization and morphology of the three eggshell layers, with a relatively thin middle layer characterised by dense and compact tabular microstructure.

Keywords::

• Extant and fossil crocodyliform eggshells
• Crocodylus mindorensis
• Paleosuchus palpebrosus
• Alligator mississippiensis
• eggshell structures
• rugosocavate pore canals type

Acknowledgements

We thank the technicians of the GEAL – Museu da Lourinhã and the Faculdade de Ciências e Tecnologia da Universidade de Lisboa (Portugal) where this research was conducted. We also thank Rene Hedegaard (Krokodile Zoo, Denmark) and Jesper Mílan (Geomuseum Faxe, Denmark) for kindly providing the extant crocodilian eggs. Our thanks also go to Carlos Galhano and Nuno Leal (FCT–UNL, Portugal) for making the SEM sessions possible, to Joaquim Simão (FCT–UNL) for allowing us the use of the petrographic microscope and to Simão Mateus (GEAL – Museu da Lourinhã) for the illustrations. We are grateful to two former DinoEggs fellows and colleagues of our: Vasco Ribeiro, for the given support during the preparation of samples and SEM sessions, and Femke Holwerda (BayerischeStaatssammlung fur Paläontologie und Geologie/LMU, Germany), for preliminary sample selection and preparation. Finally, we thank Daniel Barta and an anonymous referee for the revision of the manuscript.

Additional information

Funding

Funding

This research is part of Project Dinoeggs – dinosaur eggs and embryos in Portugal: paleobiological implications and paleoenvironmental settings (PTDC/BIA–EVF/113222/2009) funded by the FCT, Portugal.