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Guegoolithus, new oogenus from the Lower Cretaceous of Spain

Available online today:

Moreno-Azanza, M., J.I. Canudo & J.M. Gasca. 2014. Spheroolithid
eggshells in the Lower Cretaceous of Europe. Implications for eggshell
evolution in ornithischian dinosaurs. Cretaceous Research, 51: 75-87.

Early Cretaceous spheroolithid eggshells have always been extremely
scarce, unlike their putative egg layers, ornithopod dinosaurs, which
are ubiquitous in Early Cretaceous ecosystems. In this paper, we
re-evaluate eggshells previously assigned to the oofamily
Elongatoolithidae, an oofamily related to derived theropod dinosaurs
(including maniraptorans and oviraptorids), and reassign them to the
oofamily Spheroolithidae, on the basis of the lack of a squamatic
ultrastructure, and the presence of a prolatocanaliculate pore system
and undulating extinction, typical of spheroolithid eggshells. We
erect a new oogenus, Guegoolithus to include material previously
reported as Macroolithus turolensis Amo-Sanjuan, Canudo and
Cuenca-Bescos 2000, and new material from several lower Barremian
localities of the Maestrazgo Basin in Spain. Guegoolithus eggshells
exhibit an acicular radial ultrastructure in the lower part of the
shell units, which develops into a tabular radial ultrastructure in
the upper part, giving an appearance of a two-layered eggshell in thin
sections that is not seen in SEM pictures. These features fill the gap
between the two-layered prismatic eggshell of ceratopsians and the
prolatospherulitic ornithopod eggshell of derived hadrosaurs.

Ornithopod, Macroolithus, Elongatoolithidae, Parataxonomy, Spain,
Maestrazgo Basin

Jose Ignacio Ruiz-Omenaca
Museo del Jurasico de Asturias (MUJA)
E-33328 Colunga, Spain