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

Abstract

A myriad of extant and extinct vertebrates produce eggs. Eggs and eggshells provide a useful substrate for reconstructing environment, ecology and biology over a range of time scales from deep time to the present. In this review, methods for analysing and understanding records of diet, climate, environment and biology preserved in eggshells are presented. Topics covered include eggshell structure, assessing diagenesis, stable isotope geochemistry and morphological investigations of eggshell characteristics. This review emphasizes the use of eggshells in the modern and fossil record, as they allow for interpretation of characteristics of a wide variety of amniotes across geological history, uniquely informing environmental and ecological investigations.

Eggshell geochemistry reveals ancestral metabolic thermoregulation in Dinosauria

“…All fossil eggshells were imaged using a scanning electron microscope and a petrographic microscope to assess preservation of primary eggshell microstructure. Biogenic carbonates that retain fine microstructure are more likely to preserve the original mineral and therefore their original geochemical signatures, as recrystallized calcite often loses the preferential orientation of biosynthesized crystals (28). Next, we analyzed fossil carbonate for evidence of recrystallization using trace element concentrations and cathodoluminescence (CL) microscopy.…”

“…Trace elements, such as Fe and Mn, are not common in eggshells of living taxa but are typically present in anoxic pore fluids in which calcite eggshell may recrystallize during diagenesis (28). Bulk concentrations of trace metals were measured in eggshell and mollusk carbonates as indicators of recrystallization and therefore likely alteration of  47 values.…”

“…This technique was used to characterize fossil eggshell preservation by identifying the extent of diagenetic calcite overgrowth, infilling, and replacement of the original mineral. CL microscopy identifies areas within the shell that are enriched in Mn and Fe: regions enriched in Mn luminesce, and when subsequently enriched in Fe, these areas become dimmer (28).…”

The Expanding Role of Natural History Collections

“…In addition to the curation of data and other information related to specimens, the type of material that is curated has also diversified. For example, fish otoliths (e.g., Maslenikov, 2021, this volume), turtle eggs (Montanari, 2018), histological slides (Williston, 2016), and other non-traditional specimen preparations have become recognized as important for accessioning into natural history collections. The physical object is, of course, the root of the specimen, but the associated data also are part of the specimen, and require curation and preservation in their own right.…”

Zooarchaeology and Ancient DNA, part 2: new substrates and perspectives

“…Even at high temperatures, the intracrystalline nature of the latter provides the eggshell with a relatively 'closed-system' when compared to bones and molluscs. This prevents the migration of organic content in or out, and the entry of microbes (Montanari, 2018;Oskam et al, 2010). Such unique characteristics make eggshells good endogenous DNA reservoirs in environments usually considered unfavourable to long-term DNA preservation, as demonstrated by Oskam et al (2010) who successfully recovered both mitochondrial and nuclear DNA from archaeological ratite eggshells dating up to 19,000 years ago and originating from New Zealand, Australia and Madagascar.…”