The ability of evolution to shape organic form involves the interactions of multiple systems of constraints, including fabrication, phylogeny and function. The tendency to place function above everything else has characterized some of the historical biological literature as a series of ‘Just-So’ stories that provided untested explanations for individual features of an organism. A similar tendency occurs in biomaterials research, where features for which a mechanical function can be postulated are treated as an adaptation. Moreover, functional adaptation of an entire structure is often discussed based on the local characterization of specimens kept in conditions that are far from those in which they evolved. In this work, environmental- and frequency-dependent mechanical characterization of the shells of two cephalopods, Nautilus pompilius and Argonauta argo , is used to demonstrate the importance of multi-scale environmentally controlled characterization of biogenic materials. We uncover two mechanistically independent strategies to achieve deformable, stiff, strong and tough highly mineralized structures. These results are then used to critique interpretations of adaptation in the literature. By integrating the hierarchical nature of biological structures and the environment in which they exist, biomaterials testing can be a powerful tool for generating functional hypotheses that should be informed by how these structures are fabricated and their evolutionary history.

Blue structural colors, produced by diverse tissue nanostructures, are known from all major vertebrate clades except cartilaginous fishes (e.g. sharks, rays). We describe a bright angle-independent structural blue from ribbontail stingray skin, arising from a novel cell type with unique quasi-ordered arrays of nano-vesicles enclosing guanine nanoplatelets. This natural architecture —an intracellular photonic glass— coherently scatters blue, while broadband absorption from closely-associated melanophores obviates the low color-saturation typical for photonic glasses. This first demonstration of structural color in elasmobranchs (the oldest extant clade of jawed vertebrates) illustrates that the capacity for guanine-based colors likely arose extremely early in vertebrate evolution. The structure-function mechanisms underlying ribbontail stingray coloration point to selective pressures driving elasmobranch visual ecology and communication, but also strategies for biomimetic color production.

Blue structural colors, produced by diverse tissue nanostructures, are known from all major vertebrate clades except cartilaginous fishes (e.g. sharks, rays). We describe a bright angle-independent structural blue from ribbontail stingray skin, arising from a novel cell type with unique quasi-ordered arrays of nano-vesicles enclosing guanine nanoplatelets. This natural architecture —an intracellular photonic glass— coherently scatters blue, while broadband absorption from closely-associated melanophores obviates the low color-saturation typical for photonic glasses. This first demonstration of structural color in elasmobranchs (the oldest extant clade of jawed vertebrates) illustrates that the capacity for guanine-based colors likely arose extremely early in vertebrate evolution. The structure-function mechanisms underlying ribbontail stingray coloration point to selective pressures driving elasmobranch visual ecology and communication, but also strategies for biomimetic color production.

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Nanoindentation is one of the most widespread methods to measure the mechanical performance of complex materials systems. As it allows for local characterization of composite architectures with sub‐micron spatial features and a large range of properties, nanoindentation is commonly used to measure the properties of biological materials. In situ nanoindentation, a further development of the approach, is a powerful tool for the analysis of plastic deformation and failure of materials. Here, samples can be mechanically manipulated using the indenter, while their behavior is monitored with the resolution of a scanning electron microscope (SEM). Indeed, numerous studies demonstrate the potential of this approach for studying the most fundamental material characteristics. However, so far, these measurements are performed in high‐vacuum conditions inherent to the conventional electron microscopy method, which are irrelevant when studying biological structures that evolved to perform in hydrated conditions. In this work, the ability to conduct nanoindentation experiments under controlled humidity and temperature inside an environmental SEM is developed. This technique has the potential to become crucial for materials design and characterization in many domains where humidity has a significant impact on performance. These include organic/polymer systems, microelectronic and optoelectronic devices, materials for catalysis, batteries, and many more.