Octávio Mateus

Two new Late Jurassic (uppermost Late Kimmeridgian) dinosaur eggshell sites are described, Casal da Rola and Porto das Barcas, both near Lourinha˜, central-west Portugal. Casal da Rola yields eggshells with an obliquiprismatic morphotype comparable to those from a nest with the associated fossil embryos from Paimogo, tentatively assigned to the theropod Lourinhanosaurus antunesi. The Porto das Barcas eggshells have a dendrospherulitic morphotype with a prolatocanaliculate pore system. This morphotype was also recognised in eggshells from a clutch with associated Torvosaurus embryos at the Porto das Barcas locality. A preliminary cladistic analysis of eggshell morphology suggests theropod affinities for the Casal da Rola eggs, but is unable to resolve the phylogenetic position of the Porto das Barcas eggs. The eggshells at both sites are preserved in distal flood plain mudstones and siltstones. Carbonate concretions within the deposits indicate paleosol development.

Despite more than a century of collecting, resulting in one of the best-studied vertebrate fossil records anywhere in the world, the Upper Jurassic Morrison Formation has produced surprisingly few examples of dinosaur eggs associated with embryonic remains. Even more puzzling, none of these seem to pertain to the theropod Allosaurus, one of the most common and best-understood dinosaur taxa in the formation. Here we
report on a dinosaur nest site that has produced both abundant prismatoolithid eggshell and embryonic (or perinatal) bones of Allosaurus from Fox Mesa, Wyoming. This represents the first such discovery for any theropod in the Jurassic of North America. The nest is heavily weathered but contains a few ellipsoid eggshell clusters that suggest an egg size of about 8 x 6.5 cm. Study of the eggshell morphology and microstructure confirms that a single egg type is present throughout, which is indistinguishable from Prismatoolithus coloradensis. All of the identifiable embryonic materials pertain to theropods, and two premaxillae specimens show the five alveoli diagnostic for Allosaurus among Morrison theropods. This confirms the theropod origin of Prismatoolithus eggs and implicates Allosaurus as the specific Morrison parent taxon. As a result, it is now possible to assign several previous discoveries of dinosaur eggs and potential nests to Allosaurus, including the isolated egg from the Cleveland-Lloyd Quarry. This discovery
also calls into question prior assignments of Prismatoolithus eggs to ornithopods, and suggests that more detailed study of such sites is warranted. Prismatoolithus eggshells are also associated with the Upper Jurassic theropod Lourinhanosaurus from Portugal, along with larger embryos that exhibit four premaxillary alveoli.

A clutch of several crushed eggs and embryos from the Late Jurassic (near the Kimmeridgian-Tithonian
boundary), Lourinhã Formation, Portugal contains a complete maxilla, erupted and scattered teeth,
and presacral vertebrae. The maxilla bears four teeth separated by individualized interdental plates,
the dorsal process of the maxilla is confluent with the maxillary body, the ventral rim of the antorbital
fossa is parallel to the tooth row, and the anterior border of the maxilla forms a right angle with the
ventral margin. The teeth are conical and recurved distally with carinae on mesial and distal sides. The
vertebrae are amphiplatyan, with a ventral pair of neurovascular foramina and heavily pitted articular
facets. These fossils allow unambiguous association of basal theropod osteology (Megalosauroidea) with
a new eggshell morphotype. Synchrotron micro-computed tomographic scanning (SRμCT), scanning
electron microscopy, and thin-sections under polarized and normal light revealed that the outer
ornamentation of the eggshell is composed of anastomosing ridges and islets, the pores communicate
near the outer region of the eggshells, and in radial section they are irregular canals that ramify towards
the surface. Micro-proto induced x-ray emission (micro-PIXE) analysis of the eggshell (excluding pores)
revealed the presence of Mg, Fe, Mn (0.33%, 0.27% and 0.18%, respectively) and several trace elements,
with a corresponding loss of Ca (39.4% detected but 40.0% expected for calcite), which suggests minimal
eggshell diagenesis. The eggshells do not luminesce, which could imply that no diagenetic alteration
took effect. However, the quenching effect of Fe2+ has to be taken into consideration. Conversely,
luminescence is observed in the pores since they are filled with sediment, composed of phyllosilicates,
as revealed by SRμCT, micro-PIXE and x-ray diffraction analyses.

Four different localities from the Late Jurassic of Lourinhã formation with eggshells and embryos were studied: Paimogo (lower Amoreira-Porto Novo member), Peralta (Praia Azul member), Porto das barcas (Bombarral member) and Casal da Rôla (Amoreira-Porto Novo member). All but Casal da Rôla have embryonic material. Preliminary results show that eggshells from Paimogo correspond to obliquiprismatic morphotype (0.92mm thick), similar to those from Morrison Formation. Within Paimogo site a different type of eggshell was discovered, having a radial section of 153 μm with a mammilary layer measuring 65 μm. Porto das Barcas eggshells represent a discretispherulitic morphotype (1,23 mm thick).
This locality presents a nest 60-cm diameter containing many eggshells but an indeterminate number of eggs. Some embryonic bones were discovered between the eggshells including teeth and skull bones showing that the eggs belong to a saurischian, tentatively a sauropod dinosaur. Peralta nest eggshells are preliminary ascribed to obliquiprismatic morphotype (column: 0,56mm and mammilla: 0,21mm) probably related to Paimogo’s nest taxon (Lourinhanosaurus). Peralta site bears embryonic bones namely small theropod teeth associated with bone fragments, and unidentifiable dinosaur vertebra. Only eggshells have been collected at Casal da Rôla (ML1194). The eggshells (0,78mm thick) are prismatic morphotype and it was impossible to determine the pore system, the outer surface is smooth with no ornamentation.
Lourinhã formation has the oldest sauropod and theropod nest with embryos known so far.