Searching for a Clue to Characterize a Crystalline Dinosaur's Eggshell of Baja California, Mexico

This work presents a detailed structural and morphological analysis of different dinosaur eggshells such as Spheroolithus (sample 1, 2), lambeosaurinae, Prismatoolithus, and one unidentified ootaxon performed by high-resolution scanning electron microscopy (HRSEM). These ancient eggshells of Late Cretaceous dinosaurs were collected in the coastal area of El Rosario, Baja California in Mexico. Additionally, a thorough study was performed on the elements present in the samples by different techniques such as energy-dispersive spectroscopy (EDS), X-ray fluorescence (XRF), and X-ray photoelectron spectroscopy (XPS). The XPS technique was performed to make an accurate identification of the compounds of two different types of eggshells (Spheroolithus sample 1 and Prismatoolithus). This contribution compares the surface of five different dinosaur eggshells of 74 Ma and their inner section to determine the morphology, distribution of the chemical elements present, as well as their relationship. The observed morphology of the ornithopod eggshells of the herbivorous species shows that the mammillary cones are in the form of columns with microaggregates and irregular pores. In contrast, in the theropod eggshells, the mammillary cones are observed in different forms with wider pores. Finally, the chemical components present in the structures of each of the samples were estimated using the information obtained from SEM-EDS, evidencing the presence of calcite, quartz, and albite in each of the samples. The composition reveals that eggshells contain Si, P, S, K, Ca, Mn, Fe, and Sr and trace elements such as Cr, Cu, and Zn. The presence of heavy metals may be an indication that the eggshells presented diagenetic alterations.