Bricks rigs labled map of city1/25/2024 ![]() Hard prey processing has not been extensively surveyed in batoid fishes, but at least two strategies exist ( Figure 1): what we will call “chemical durophagy,” where predators rely on low stomach pH or chinitase to break down prey exoskeletons ( Fänge et al., 1979 Holmgren and Nilsson, 1999 Cortés et al., 2008 Anderson et al., 2010) and “mechanical durophagy,” where predators crush prey before ingestion ( Summers, 2000 Summers et al., 2004 Kolmann et al., 2015b Rutledge et al., 2019 Ajemian et al., 2021). shrimp or even insects) ( Wilga and Motta, 2000 Kolmann et al., 2015b, 2016). Durophagy in batoid fishes takes a variety of forms: diets can involve comparatively thin-shelled crustaceans, thick-shelled molluscs and/or prey with softer, tougher exoskeletons (e.g. We discuss interactions and implications of character states, framing a classification scheme for exploring cartilage structure evolution in the cartilaginous fishes.Īmong cartilaginous fishes (Chondrichthyes), the consumption of hard prey (durophagy) is most common in the clade of skates and rays (Batoidea Elasmobranchii), particularly in the subfamilies Rhinopterinae and Myliobatinae (both Myliobatiformes: Myliobatidae), which contain only durophagous taxa ( Figure 1). Rhynchobatus), or both reinforcing features can be lacking (e.g. Rhina, Aetobatus), whereas cortical thickening is more significant in others (e.g. Comparisons with several other durophagous and non-durophagous species illustrate that batoid skeletal reinforcement architectures are modular: trabeculae can be variously oriented and are dominant in some species (e.g. Trabeculae were previously thought to have arisen twice independently in Batoidea our results show they are more widespread among batoid groups than previously appreciated, albeit apparently absent in the phylogenetically basal Rajiformes. This is particularly striking in Rhina, where the upper/lower occlusal surfaces are mirrored undulations, fitting together like rounded woodworking finger-joints. ![]() Unlike the flattened teeth of durophagous myliobatiform stingrays, both rhinopristiform species have oddly undulating dentitions, comprised of pebble-like teeth interlocked to form compound “meta-teeth” (large spheroidal structures involving multiple teeth). Age series of both species illustrate that tesserae increase in size during growth, with enlarged and irregular tesserae associated with the jaws’ oral surface in larger (older) individuals of both species, perhaps a feature of ageing. Rhina and Rhynchobatus exhibit impressively thickened jaw cortices, often involving >10 tesseral layers, most pronounced in regions where dentition is thickest, particularly in Rhynchobatus. Both species possess trabeculae, more numerous and densely packed in Rhina, albeit simpler structurally than those in stingrays like Aetobatus and Rhinoptera. We perform a quantitative analysis of micro-CT data, describing jaw strengthening mechanisms in Rhina ancylostoma (Bowmouth Guitarfish) and Rhynchobatus australiae (White-spotted Wedgefish), durophagous members of the Rhinopristiformes, the sister taxon to Myliobatiformes. These strategies for skeletal strengthening against durophagy, however, are largely understood only from myliobatiform stingrays, although a hard prey diet has evolved multiple times in batoid fishes (rays, skates, guitarfishes). The cartilage jaws of durophagous stingrays are known to be reinforced relative to non-durophagous relatives, with a thickened external cortex of mineralized blocks (tesserae), reinforcing struts inside the jaw (trabeculae), and pavement-like dentition. Crushing and eating hard prey (durophagy) is mechanically demanding. ![]()
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