Cracking the egg: the use of modern and fossil eggs for ecological, environmental and biological interpretation

Microstructural and crystallographic evolution of palaeognath (Aves) eggshells

The avian palaeognath phylogeny has been recently revised significantly due to the advancement of genome-wide comparative analyses and provides the opportunity to trace the evolution of the microstructure and crystallography of modern dinosaur eggshells. Here, eggshells of all major clades of Palaeognathae (including extinct taxa) and selected eggshells of Neognathae and non-avian dinosaurs are analysed with electron backscatter diffraction. Our results show the detailed microstructures and crystallographies of (previously) loosely categorized ostrich-, rhea-, and tinamou-style morphotypes of palaeognath eggshells. All rhea-style eggshell appears homologous, while respective ostrich-style and tinamou-style morphotypes are best interpreted as homoplastic morphologies (independently acquired). Ancestral state reconstruction and parsimony analysis additionally show that rhea-style eggshell represents the ancestral state of palaeognath eggshells both in microstructure and crystallography. The ornithological and palaeontological implications of the current study are not only helpful for the understanding of evolution of modern and extinct dinosaur eggshells, but also aid other disciplines where palaeognath eggshells provide useful archive for comparative contrasts (e.g. palaeoenvironmental reconstructions, geochronology, and zooarchaeology).

Raman Spectra and Ancient Life: Vibrational ID Profiles of Fossilized (Bone) Tissues

Raman micro-spectroscopy is a non-destructive and non-contact analytical technique that combines microscopy and spectroscopy, thus providing a potential for non-invasive and in situ molecular identification, even over heterogeneous and rare samples such as fossilized tissues. Recently, chemical imaging techniques have become an increasingly popular tool for characterizing trace elements, isotopic information, and organic markers in fossils. Raman spectroscopy also shows a growing potential in understanding bone microstructure, chemical composition, and mineral assemblance affected by diagenetic processes. In our lab, we have investigated a wide range of different fossil tissues, mainly of Mesozoic vertebrates (from Jurassic through Cretaceous). Besides standard spectra of sedimentary rocks, including pigment contamination, our Raman spectra also exhibit interesting spectral features in the 1200-1800 cm-1 spectral range, where Raman bands of proteins, nucleic acids, and other organic molecules can be identified. In the present study, we discuss both a possible origin of the observed bands of ancient organic residues and difficulties with definition of the specific spectral markers in fossilized soft and hard tissues.

The diverse terminology of reptile eggshell microstructure and its effect on phylogenetic comparative analyses

Reptile eggshell ensures water and gas exchange during incubation and plays a key role in reproductive success. The diversity of reptilian incubation and life history strategies has led to many clade-specific structural adaptations of their eggshell, which have been studied in extant taxa (i.e. birds, crocodilians, turtles, and lepidosaurs). Most studies on non-avian eggshells were performed over 30 years ago and categorized reptile eggshells into two main types: "hard" and "soft" - sometimes with a third intermediate category, "semi-rigid." In recent years, however, debate over the evolution of eggshell structure of major reptile clades has revealed how definitions of hard and soft eggshells influence inferred deep-time evolutionary patterns. Here, we review the diversity of extant and fossil eggshell with a focus on major reptile clades, and the criteria that have been used to define hard, soft, and semi-rigid eggshells. We show that all scoring approaches that retain these categories discretize continuous quantitative traits (e.g. eggshell thickness) and do not consider independent variation of other functionally important microstructural traits (e.g. degree of calcification, shell unit inner structure). We demonstrate the effect of three published approaches to discretizing eggshell type into hard, semi-rigid, and soft on ancestral state reconstructions using 200+ species representing all major extant and extinct reptile clades. These approaches result in different ancestral states for all major clades including Archosauria and Dinosauria, despite a difference in scoring for only 1-4% of the sample. Proposed scenarios of reptile eggshell evolution are highly conditioned by sampling, tree calibration, and lack of congruence between definitions of eggshell type. We conclude that the traditional "soft/hard/semi-rigid" classification of reptilian eggshells should be abandoned and provide guidelines for future descriptions focusing on specific functionally relevant characteristics (e.g. inner structures of shell units, pores, and membrane elements), analyses of these traits in a phylogenetic context, and sampling of previously undescribed taxa, including fossil eggs.

Trace elements and stable isotopes in penguin chicks and eggs: A baseline for monitoring the Ross Sea MPA and trophic transfer studies

Multi-tissue trace elements (TEs), C, N concentrations and stable isotopes (δ¹³C, δ¹⁵N) of chick carcasses and eggs of Adélie and Emperor penguins were studied to i) provide reference data before the recent institution of the Ross Sea Marine Protected Area (Antarctica), and ii) provide conversion factors that allow estimating C, N, δ¹³C and δ¹⁵N in edible tissues from non-edible ones, thus improving the use of stable isotopes in contamination and trophic transfer studies. Higher concentrations of As, Cd, Cr, Cu, Hg, Mn and Pb were found in chick carcasses than in eggs, suggesting increasing contamination in recent decades and high toxicity risks for penguin consumers. Isotopic conversion factors highlighted small differences among body tissues and conspecifics. These values suggest that chick carcasses are reliable indicators of the energy pathways underlying the two penguin species, their trophic position in the food web and their exposure to TEs.

Eggshell geochemistry reveals ancestral metabolic thermoregulation in Dinosauria

Studying the origin of avian thermoregulation is complicated by a lack of reliable methods for measuring body temperatures in extinct dinosaurs. Evidence from bone histology and stableisotopes often relies on uncertain assumptions about the relationship between growth rate and body temperature, or the isotopic composition (δ¹⁸O) of body water. Clumped isotope (Δ₄₇) paleothermometry, based on binding of ¹³C to ¹⁸O, provides a more robust tool, but has yet to be applied across a broad phylogenetic range of dinosaurs while accounting for paleoenvironmental conditions. Applying this method to well-preserved fossil eggshells demonstrates that the three major clades of dinosaurs, Ornithischia, Sauropodomorpha, and Theropoda, were characterized by warm body temperatures. Dwarf titanosaurs may have exhibited similar body temperatures to larger sauropods, although this conclusion isprovisional, given current uncertainties in taxonomic assignment of dwarf titanosaur eggshell. Our results nevertheless reveal that metabolically controlled thermoregulation was the ancestral condition for Dinosauria.