Micromorphology of the titanosaur dinosaur eggshells from the Upper Cretaceous Tama nesting site (La Rioja, Argentina) based on μCT scan: preliminary results

HECHENLEITNER, ESTEBAN MARTÍN; DAVID JARAMILLO-VOGEL; LÉA LEUZINGER; FIORELLI, LUCAS ERNESTO; GERALD GRELLET-TINNER; ANNELEEN FOUBERT

Congreso; 11º Congreso de la Asociación Paleontológica Argentina; 2016

Titanosaur dinosaurs repeatedly came to lay their eggs in nesting colonies. During the Cretaceous, two species selected specific environments to oviposit their eggs in Sanagasta and Tama, La Rioja. These localities expose isolated patches of the Los Llanos Formation, a unit respectively characterized by paleohydrothermal seepage and spring deposits and the accumulation of paleosols. Recently, the extremely thick Sanagasta eggshells have been analyzed with X-ray μCT scanning techniques. The measurements of their pore canal system allowed evaluating the physiological impact of dissolution by acidic pore fluids during incubation in a hydrothermal environment. However, the image resolution used in previous work (20.3 μm) was not sufficient to study the thinner Tama eggshells. Capitalizing on technological advances, we scanned two eggshell samples from Tama (CRILAR-Pv 530/4c) with a multiscale x-ray nano-CT scanner (Bruker Skyscan 2211) at 3 μm voxel resolution. The scans show that the pore canals of the titanosaur eggshells are filled with diagenetic calcite. A second diagenetic phase is evidenced by the partial silicification of the eggshell units. The pore canals show lateral interconnections and dichotomic ramifications across the 1.47 mm thin eggshells. Due to the limitations of the technique, the samples are yet too small to estimate water vapor conductance of the Tama eggs. However the complex pore morphology of their shells suggests an incubation environment with high humidity, typical of burial nesting conditions. Future quantitative measurements will allow analytic and morphological comparisons with Sanagasta and other nesting sites.