Crocodylomorph eggs and eggshells from the Adamantina Formation (Bauru Group), Upper Cretaceous of Brazil

Abstract

Compared with crocodylomorph body fossils, the record of fossil crocodiloid eggs is scarce and poorly understood, a gap partially attributed to their typically thin eggshell, which is not conducive to preservation. A remarkable new association of well-preserved eggs and eggshells from the Adamantina Formation (Bauru Group, Upper Cretaceous) is described and compared to other known materials, while the significance of their unique oological features is discussed. These eggs constitute a new ootaxon, Bauruoolithus fragilis oogen. et oosp. nov., diagnosed by the following characteristics: elongate and elliptical egg with blunt ends; length-to-diameter ratio of 1:0.55; outer surface slightly undulating; shell thickness ranging from 0.15 to 0.25 mm; pore openings elliptical or teardrop-shaped, ranging from 30 to 80 lm in diameter; and shell units wider than higher, with the interstices forming an obtuse triangle. Specimens of Bauruoolithus also show only slight signs of extrinsic degradation that, coupled with the evidence that some of them constitute hatched eggs, suggests that the egg-laying taxon had a different pattern of egg incubation, in which the hatchling could break through the rather thin eggshell relatively easily and that the extrinsic degradation of the eggshell was not necessary. This contrasts with the pattern of incubation for all other known crocodylomorphs and crocodiloid eggs, where extrinsic degradation is a key component of the hatching process.

Oldest known dinosaurian nesting site and reproductive biology of the Early Jurassic sauropodomorphMassospondylus

“…This analysis highlights the fact that well-studied egg occurrences remain unavailable for most nonavian dinosaurian taxa, and their Mesozoic archosaurian relatives, including crocodylians and pterosaurs (23)(24)(25). Evidence for avian nesting is also unknown from Mesozoic deposits.…”

“…This illustration underscores the rarity of nest information in Dinosauria, and their temporal distribution. Although eggs of pterosaurs and crocodylomorphs have been recently reported, little useful nest information is available for these archosaurian outgroups to dinosaurs (24,25) and is not included here. Square boxes to the Left of the major clade names indicate presence (solid box), absence (diagonally divided box), or unknown condition (empty box) for the following characters (listed above the boxes): 1, evidence of nesting-site fidelity; 2, evidence of gregarious nesting; 3, nests organization consisting of a single layer of tightly clustered eggs; 4, elongate egg shape (absence denotes spherical eggs); 5, evidence of brooding.…”

RAREIN SITUPRESERVATION OF ADULT CROCODYLIAN WITH EGGS FROM THE MIDDLE EOCENE OF GEISELTAL, GERMANY

“…The fossils were interpreted as representing adults near excavated nesting sites. Later exploration of Upper Cretaceous units of Brazil revealed adults within 2 m of eggshells they believed to belong to the crocodyliform Baurusuchus, based on lack of any other crocodylomorph taxon preserved at the site (Oliveira et al 2011). These fossil discoveries are compelling, but not quite as close an association as was found in the theropods.…”

“…Even though crocodylian eggs have been discovered from many fossil sites ranging from the Upper Jurassic through Miocene (Kohring 1992(Kohring , 1995Kohring and Hirsch 1996;Antunes et al 1998;Rogers 2001;Novas et al 2009;Oliveira et al 2011) they have not been found in close association with the parent (within centimeters) as in the above theropod specimens. The closest crocodyliform discovery reported thus far was that of the Late Cretaceous Yacarerani boliviensis from Bolivia, which included two partially disarticulated skeletons and two complete eggs found together ''in a small area'' (Novas et al 2009).…”

Fossil egg and eggshells from the Upper Cretaceous Hell Creek Formation, Montana

“…In addition, the shell units in Bauruoolithus are broader than they are tall, which is typical of some turtle eggshells (Lawver and Jackson, 2014) but differ from most crocodilian eggshell (Kohring, 1999). Most importantly, Oliveira et al (2011) fail to describe or provide evidence of compact, book-like tabular structure, a characteristic of crocodilian eggshells (Ferguson, 1982;Moreno-Azanza et al, 2014: fig. 3A, B).…”