Guegoolithus turolensis from the El Horcajo site (La Rioja). Scanning electron microscope microphotographs (a-d), petrographic microscope photograph in parallel nicols (e), and petrographic microscope photograph in cross nicols.
Moreno-Azanza et al. (2016) described the new fossil site of El Horcajo in the vicinity of Trevijano (La Rioja, Spain). It is located in the palustrine facies of the Enciso Group (Cameros Basin). This new locality has provided dozens of eggshell fragments, together with other vertebrate remains and charophyte fructifications, which allow dating of the locality as Valanginian-Hauterivian. Five ootaxa have being recognized: 1) the Spheroolithidae Guegoolithus turolensis; 2) a surprisingly thick Prismatoolithidae indet., with certain affinities to the oogenus Sankofa, that may represent a new oogenus and oospecies for this oofamily; 3) the Krokolithidae Krokolithes sp.; 4) recrystallized Testudoolithidae? eggshells; and 5) ?Geckoolithidae eggshells of uncertain affinity.
This oodiversity is similar to that of other eggshell microsites. The ootaxonomic list differs from the other Iberian locality of the same age, Pochancalo 1 (Villanueva de Huerva Formation, Zaragoza) in lacking sauropod and megalosauroid theropod eggshells, but shares the presence the ornithopod and coelurosaurian theropod eggshells with other younger microsites found in similar facies. The age of the new locality has immediate consequences for the tectono-sedimentary framework of the Cameros Basin, and the new data will need to be considered in future stratigraphical works. Furthermore, the reliability of eggshells as biostratigraphic markers is questioned, and the viability of Guegoolithus as a guide fossil for the lower Barremian is rejected.
Eggshells of Guegoolithus have been recovered in many localities of the neighboring Iberian Basin, but its presence was restricted to the lower Barremian. If the Hauterivian-Valanginian age of El Horcajo is confirmed, it would imply that these eggs where laid in the Iberian Peninsula up to seven million years before than previously thought. Guegoolithus has been tentatively related to iguanodontoid dinosaurs on the basis of their resemblance to eggshells assigned to derived ornithopods from the Upper Cretaceous of North America and, more recently, from the Lower Cretaceous of Asia.
Moreno-Azanza, M., Gasca, J.M., Díaz-Martínez, I., Bauluz Lázaro, B., Canudo Sanagustín, J.I., Fernández, A. Pérez-Lorente, F. 2016. A multi-ootaxic assemblage from the Lower Cretaceous of the Cameros Basin (La Rioja; Northern Spain). Spanish Journal of Palaeontology, 31 (2), 305-320. DOWNLOAD HERE