A comparison between the Fusioolithus baghensis titanosaur eggs of Auca Mahuevo (Neuquén, Argentina) and Poyos (Guadalajara, Spain)

Resumen

Fusioolithus baghensis is a widespread ootaxon recorded from the lower Campanian of SouthAmerica up to the uppermost Maastrichtian of Europe and India. This ootaxon exhibits highvariability in its ornamentation and histostructure, with some parameters (e.g., eggshell thickness)a priori exceeding the range expected for a single parent species. Some of the best Fusioolithusbaghensis specimens have been found at the mid Campanian Auca Mahuevo site from Neuquén(Argentina), where numerous eggs and clutches, sometimes bearing titanosaur embryos, havebeen recovered. The late Campanian–early Maastrichtian site of Poyos from Guadalajara (Spain)has also yielded partial eggs and clutches attributable to Fusioolithus baghensis but, while somespecimens from Poyos resemble those from Auca Mahuevo, most of them seem to represent theopposing extreme of the variability range of the oospecies in several characters. The eggshellthickness and egg size of the Auca Mahuevo specimens resemble those reported from otherGondwanan sites of India, whereas those from Poyos present the thinnest eggshells and largesteggs reported so far for this ootaxon. The histostructure, as seen in thin section preparations, ofthe Auca Mahuevo specimens tends to be composed of wider spheroliths with a lower height/width ratio. Spheroliths with this proportion are uncommon in the Poyos eggshells, and mostspheroliths present a higher ratio, akin to samples from other European and Indian localities.Specimens from both sites present the typical compactituberculated ornamentation withridges connecting some nodes of this ootaxon, although the Auca Mahuevo eggshells presentslightly wider nodes and the Poyos eggshells have more marked, often wider internodal spaces.Given the extensive geographical and chronological distribution of Fusioolithus baghensis, theaforementioned differences could be related to the oospecies being laid by several, closely relatedproductor titanosaur taxa across Gondwana and Europe at the end of the Cretaceous