A review of the Cenozoic fossil record of avian eggs, eggshells, and nests

Modern avian lineages evolved and radiated during the Cenozoic Era (66 Ma–present) following the end-Cretaceous extinction. Despite a wealth of isolated eggshells and nest structures, the global oological record remains unevenly studied. This review integrates the scattered literature on Cenozoic oological remains to produce the first comprehensive synthesis of their distribution, structure, palaeobiogeography, and palaeobiological significance. This record reconstructs temporal patterns in eggshell microstructure, nesting ecology, and biogeography. Methodological advances in microscopy, electron backscatter diffraction, isotopic geochemistry, and biomolecular preservation have enabled and refined taxonomic attributions and ecological interpretations of oological material. This synthesis highlights key gaps—particularly in Africa, Antarctica, and Oceania—and outlines research priorities aimed at linking palaeontology, molecular biology, conservation, de-extinction, and Earth-system sciences to better understand the evolutionary trajectory of avian reproduction. Furthermore, this evolving avian fossil record offers a critical foundation for reconstructing past ecosystems and informing efforts to conserve biodiversity into the future