A new faveoloolithid oogenus from the Wido Volcanics (Upper Cretaceous), South Korea and a new insight into the oofamily Faveoloolithidae

Abstract

The Cretaceous oofamily Faveoloolithidae has a unique shell unit and pore canal system that clearly differs from most of the extant and fossil eggshells. Despite its distinctiveness, morphological (micro- and ultrastructural) and crystallographic features of the Faveoloolithidae are poorly known. Here we report a new faveoloolithid nesting ground from the Upper Cretaceous siltstones within the Daeri Andesite of the Wido Volcanics (Coniacian–Santonian), South Korea. Forty-one of the same kind of dinosaur eggs distributed in at least eight clutches occur in seven different stratigraphic horizons, suggesting a colonial nesting ground and paleontological site fidelity (reuse of a site over geological time scale). These eggs were assigned to a new ootaxon, Propagoolithus widoensis oogen. et oosp. nov., based on a unique shell unit morphology which is branching towards the external part of eggshell, unlike other faveoloolithid eggs. New morphological and crystallographic features of P. widoensis provide a new insight into the oofamily Faveoloolithidae: (1) superimposed shell units, which are widely used as diagnoses of the Faveoloolithidae and Dictyoolithidae, are in fact taphonomic artifacts and (2) round and crystallographically upright shell units partially connected by inclined crystals (bridges) at the inner portion in the tangential section is proposed as an additional synapomorphy of the oofamily Faveoloolithidae. Furthermore, elemental analysis combined with light microscopy, EBSD, and CL analyses provide a successful reconstruction of the complex pore canal infilling process, and suggest that magnesium concentration can be used as a proxy for calcite overgrowth.