A re-evaluation of aff. Megaloolithidae eggshell fragments from the uppermost Cretaceous of the Pyrenees and implications for crocodylomorph eggshell structure

Abstract

The Upper Cretaceous outcrops of the Pyrenees yield one of the most extensive and continuous records of paleoological remains anywhere in the world. Most of eggs and eggshells have been referred to the oofamily Megaloolithidae. In this study, we present a revision of eggshell fragments from the Blasi 2 locality, lattermost Maastrichtian in age, previously assigned to aff. Megaloolithidae. The presence of a blocky extinction pattern and basal knobs supports a crocodilian affinity of these materials. We classify them as Krokolithidae indet. Three structural layers can be recognised in the Blasi 2 eggshells, a feature that is shared with other recent eggshells (e.g. Crocodylus porosus and Crocodylus niloticus) and fossil crocodylomorph eggshells (Krokolitheswilsoni), which were previously described as single layered. The new proposed affinity of the Blasi 2 eggshells reduces the Megaloolithidae oodiversity of the last few million years of the Cretaceous in the Pyrenees to only two valid ootaxa, Megaloolithusmamillare and Megaloolithusbaghensis. The lack of more complete material precludes the erection of new ootaxa based on the Blasi 2 material.

Keywords::

• Krokolithidae
• Megaloolithidae
• Maastrichtian
• crocodylomorph eggshells
• Tremp Basin
• Arén Formation

Acknowledgements

This paper forms part of the projects CGL2009-07574 and CGL2010-16447, subsidised by the Spanish Ministry of Economy and Competitiveness, the Gobierno de Aragon and the European Social Fund (‘Grupos Consolidados’ and ‘Dirección General de Patrimonio Cultural’). M. M-A was supported by a FPI grant (BES-2008-005538) from the Ministerio de Economía y Competitividad. The authors would like to acknowledge the use of the Servicio General de Apoyo a la Investigación-SAI, Universidad de Zaragoza. The authors specially thank Margarita Diaz Molina, who provided access to the materials studied by Nieves López- Martínez. M. M-A thanks Karen Chin and Tony Culver for their assistance when visiting the Hirsch Eggshell Collection at the Museum of Natural History, Boulder. Mariela Soledad Fernández and Bernat Vila provided Megaloolithidae eggshells used for comparison. R. Glasgow edited the text in English. Mariela S. Fernández and Frankie Jackson reviewed and helped improve the paper substantially. We thank our editor, Gareth Dyke, for his comments and suggestions.