Micro-CT scan reveals an unexpected high-volume and interconnected pore network in a Cretaceous Sanagasta dinosaur eggshell

Abstract

The Cretaceous Sanagasta neosauropod nesting site (La Rioja, Argentina) was the first confirmed instance of extinct dinosaurs using geothermalgenerated heat to incubate their eggs. The nesting strategy and hydrothermal activities at this site led to the conclusion that the surprisingly 7 mm thickshelled eggs were adapted to harsh hydrothermal microenvironments. We used micro-CT scans in this study to obtain the first three-dimensional microcharacterization of these eggshells. Micro-CT-based analyses provide a robust assessment of gas conductance in fossil dinosaur eggshells with complex pore canal systems, allowing calculation, for the first time, of the shell conductance through its thickness. This novel approach suggests that the shell conductance could have risen during incubation to seven times more than previously estimated as the eggshell erodes. In addition, micro-CT observations reveal that the constant widening and branching of pore canals form a complex funnel-like pore canal system. Furthermore, the high density of pore canals and the presence of a lateral canal network in the shell reduce the risks of pore obstruction during the extended incubation of these eggs in a relatively highly humid and muddy nesting environment.

The biomechanical, chemical and physiological adaptations of the eggs of two Australian megapodes to their nesting strategies and their implications for extinct titanosaur dinosaurs

“…Hence, eggs can be located all over the place in large mounds but not just in the central core as in malleefowl mounds (Booth, personal communication). The same egg grouping and dispersed variation have been observed in several titanosaur nesting sites (Hechenleitner et al ., ). Nest temperatures average 34°C, but egg temperatures can range from 24.5°C to 40.7°C (Eiby and Booth, ), exposing the eggs to wide temperature fluctuations during incubation, without compromising incubation success (Eiby & Booth, , ).…”

“…This greater thickness, coupled with a large number of nodes in A. lathami , is here hypothesized as an adaptation to an environment rich in organic acids by avoiding any outer shell chemical thinning at the early stage of embryonic development. Similar compensation for potential chemical erosion has also been reported for neosauropod dinosaurs (Grellet‐Tinner and Fiorelli, ; Hechenleitner et al ., , ). The nodes are initially the only shell structures in direct contact with the nesting material, hence they could be eroded by chemical leaching leaving the eggshell thickness intact, thus allowing for diffusion of respiratory gases during the extended incubation time.…”

“…The nodes are initially the only shell structures in direct contact with the nesting material, hence they could be eroded by chemical leaching leaving the eggshell thickness intact, thus allowing for diffusion of respiratory gases during the extended incubation time. This hypothesis is supported by the reported thinning of the external surfaces of eggshells in titanosaur nesting sites (Grellet‐Tinner and Fiorelli, ; Hechenleitner et al ., , ). Moreover, we suggest the internodal spaces act as funnels which, together with the accessory layer, concentrates condensed water vapour where, for the megapodes, the greater thickness of calcium phosphate nanospheres is located (above the pore apertures located between the nodes).…”

The biomechanical, chemical, and physiological adaptations of the eggs of two Australian megapodes to their nesting strategies and their implications for extinct titanosaur dinosaurs

“…communication). The same egg grouping and dispersed variation have been observed in several titanosaur nesting sites (Hechenleitner et al, 2016). Nest temperatures average 34 °C, but egg temperatures can range from 24.5 to 40.7 °C (Eiby and Booth, 2008), exposing the eggs to wide temperature fluctuations during incubation, without compromising incubation success (Eiby and Booth, 2008;2009).…”

Dinosaurios saurópodos de la Formación Los Llanos (Cretácico, La Rioja, Argentina): ocurrencia, caracterización sistemática y tafonómica, bioestratigrafía, análisis paleoambientales y sus implicancias geológico-regionales

“…Así, permite avanzar sobre varios interrogantes que aún quedan por resolver tales como la asignación taxonómica precisa del material y los aspectos biomecánicos y fisiológicos involucrados en la compleja adaptación de esta especie de dinosaurios saurópodos a incubar sus huevos en un ambiente hidrotermal (Grellet-Tinner y Fiorelli, 2010). Por su parte, el reciente descubrimiento de restos esqueletales de saurópodos y de un nuevo sitio de nidificación en la localidad de Tama (Hechenleitner et al, 2014a;2016a), brinda la posibilidad excepcional de realizar un estudio comparativo en sitios de nidificación cercanos entre sí (c.200 km) y que se presumen contemporáneos.…”