Campanian and Maastrichtian hippuritid rudists (Hippuritida, Bivalvia) of the Chiapas Central Depression (southern Mexico) and implications for American multiple-fold hippuritid taxonomy

Hippuritids, particularly those with multiple-folds, are one of the most characteristic components in uppermost Cretaceous rudist-bearing strata of the Caribbean Province. The hippuritid rudist fauna of the Chiapas Central Depression includes the following taxa:Vaccinites vermuntiMac Gillavry, 1937 andBarrettiacf.B. ruseaeChubb, 1967 from the early Campanian Suchiapa Formation;B. moniliferaWoodward, 1862,B. gigasChubb, 1955, andParastroma trechmanniChubb, 1967 from the mid Campanian Suchiapa Formation; andPraebarrettia sparcilirata(Whitfield, 1897) from the early Maastrichtian Ocozocoautla Formation. These six species are described herein in detail. New observations on the outer shell layer structure of the right valve and the pore-canal system of the left valve led to amending the diagnoses of the g|eneraBarrettiaWoodward, 1862,ParastromaDouvillé, 1926, andPraebarrettiaTrechmann, 1924. Also, the revision of Chiapas’ and other American species of multiple-fold hippuritids led to proposed changes in their generic adscription.

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

The Cretaceous Sanagasta neosauropod nesting site (La Rioja, Argentina) was the first confirmed instance of extinct dinosaurs using geothermal-generated heat to incubate their eggs. The nesting strategy and hydrothermal activities at this site led to the conclusion that the surprisingly 7 mm thick-shelled 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.

Ultrastructure of the eggshell of selected Palaeognathae species – a comparative analysis

The study aimed at comparative analysis of the eggshell ultrastructure, indicating differences and similarities in its structure depending on the bird species. The study was carried out in ostrich, emu and rhea breeding flocks. The birds were kept under open system. The ostrich flock comprised 6 females and 3 males, the emu flock included 22 birds with equal sex ratio, while the rhea flock consisted of 16 females and 4 males. Emus and rheas were 5 years old and in their 3rd laying year, whereas ostriches were 4 years old and in their 2nd laying year. The analysis of eggshell ultrastructure and porosity was performed on the post-hatching eggshells being obtained after the incubation of eggs from around peak laying period of these birds. In total, 27 eggshells were evaluated, 9 of each species. Analysis of the ultrastructure of ostrich, emu and rhea eggshells showed their different architecture being dependent on the bird species. The cuticle in ostrich eggs adhered firmly to the vertical crystal layer, it mainly occurred around pore canal orifices in rhea eggs, while only its residual presence was observed in emu eggs. The percentage of the vertical crystal layer was similar in the ostrich and rhea eggshells (2-3%) but significantly higher in the emu eggshells (9%). The largest number of mammillae per unit of inner eggshell surface area was recorded in emus, while the broadest palisades in rheas. The ostrich eggshells were shown to be characterised by the least number of pores per unit of surface area, with significantly narrower pore canals.