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

MARTÍN HECHENLEITNER; DAVID JARAMILLO-VOGEL; LEA LEUZINGER; LUCAS E. FIORELLI; GERALD GRELLET-TINNER; ANNELEEN FOUBERT

Río Negro

Congreso; XI Congreso de la Asociación Paleontológica Argentina; 2016

Universidad Nacional de Río Negro

Titanosaur dinosaurs repeatedly came to lay their eggs in nesting colonies. During theCretaceous, 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 theaccumulation of paleosols. Recently, the extremely thick Sanagasta eggshells have beenanalyzed with X-ray μCT scanning techniques. The measurements of their pore canal  ystemallowed evaluating the physiological impact of dissolution by acidic pore fluids duringincubation in a hydrothermal environment. However, the image resolution used in previouswork (20.3 μm) was not sufficient to study the thinner Tama eggshells. Capitalizing ontechnological 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 diageneticcalcite. A second diagenetic phase is evidenced by the partial silicification of the eggshellunits. The pore canals show lateral interconnections and dichotomic ramifications across the1.47 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 poremorphology of their shells suggests an incubation environment with high humidity, typical of burial nesting conditions. Future quantitative measurements will allow analytic andmorphological comparisons with Sanagasta and other nesting sites.