Fossil Eggs

Abstract
Since the beginning of the 20th Century the Upper Cretaceous continental and transitional marine deposits of the southern Pyrenees have produced more than 220 dinosaur fossil localities. New discoveries and advances in magnestostratigraphy and biostratigraphy provide a
robust biostratigraphical framework for the latest Cretaceous dinosaur faunas in the region, although the age of some localities has remained uncertain. Here, we re-evaluate the age of some classic and new dinosaur fossil localities on the basis of the potential dating of megaloolithid oospecies and provide parataxonomic and age data for twenty-three localities with new megaloolithid egg fossils. Further, we review the nomenclature and probable synonymies of several of the most historically significant localities in the southern Pyrenees. With the new age assignments proposed for some significant localities (Basturs, Orcau-1, Els Nerets, Figuerola-2, Suterranya-1), we claim that in the southern Pyrenees a) the ankylosaurian dinosaurs survived beyond the early Maastrichtian-late Maastrichtian boundary and coexisted with
hadrosauroids; b) the theropod record is scarce in the early Maastrichtian and the taxonomic diversity (richness) of theropods is notably higher in the late Maastrichtian; and c) the megaloolithid egg record assigned to sauropods is continuous through the entire Maaastrichtian but is scarce in the Upper Campanian.

The Late Jurassic Lourinhã Formation is known for its abundant remains of dinosaurs, cro-codylomorphs and other vertebrates. Among this record are nine localities that have produced either dinosaur embryos, eggs or eggshell fragments. Herein, we describe and identify the first crocodiloid morphotype eggs and eggshells from the Lourinhã Formation, from five occurrences. One clutch from Cambelas, composed of 13 eggs, eggshell fragments from Casal da Rola and Peralta, one crushed egg and eggshells from Paimogo North, and four crushed eggs as well as eggshell fragments from Paimogo South. We observed and confirmed diagnostic morphological characters for crocodiloid eggshells and which are consistent with a crocodylomorph affinity, such as the ellipsoidal shape, wedge-shaped shell units, triangular extinction under cross-polarized light, and tabular ultrastruc-ture. This material is distinctive enough to propose two new ootaxa within the oofamily Krokolithidae, Suchoolithus portucalensis, oogen. and oosp. nov., for the material from Cambelas, the most complete clutch known for crocodiloid eggs, and Krokolithes dinophilus, oosp. nov., for the remaining material. These are the oldest crocodylomorph eggs known, extending the fossil record for this group to the Late Jurassic. Furthermore, except for the clutch from Cambelas, the material was found with theropod eggs and nests, in the other four occurrences, which seem to suggest some form of biological relationship, still unclear at this point.

In 1991, Sabath described “larger avian eggs” from the Upper Cretaceous Barun Goyot and Djadokhta Formations of Mongolia. These were later included in the ootaxon Gobioolithus major. Here we recognize the larger avian eggs of Sa- bath as a distinct ootaxon, Styloolithus sabathi, oogen. et oosp. nov. These eggs differ from those of Gobioolithus in being larger (70 by 32 mm) and more elongate. Microscopically, the shell bears a third layer (possible external zone) thicker than the mammillary layer and nearly as thick as the second layer (possible squamatic zone); the continuous layer (in- cluding layers two and three) to mammillary layer thickness ratio is 3.1:1. Within the clutch, the tightly spaced eggs stand with their long axes steeply inclined. Adult remains are associated with two clutches, suggesting an incubation mode similar to that of troodontid maniraptorans, where adults sat atop largely buried eggs. S. sabathi provides evidence that relative egg size in Mesozoic non-ornithuromorph birds had increased markedly from the non-avian theropod condition in oviraptorids and troodontids, but had not yet reached the modern egg-adult proportions of Neornithes. Sediment-bound upright eggs appear common to Enantiornithes and more basal avians, suggesting that like non-avian theropods, these birds lacked chalazae, the chords of albumen allowing egg rotation in modern birds. Absence of this simple structure may have restricted these basal birds to ground nesting in areas with appropriate substrates and not permitted the type of nesting diversity found in Neornithes. Neornithes are the only Mesozoic clade of Dinosauria to nest completely free of sediment; this may have played a crucial role in their surviving the K-Pg mass extinction event.