Material Before Morphology: Substrate‐Dependent Mechanical Tuning of Radular Teeth

ABSTRACT Biological systems often adapt to mechanical demands through localized tuning of material properties rather than morphological redesign. Here, we identify a natural strategy for functional optimization in gastropod radular teeth—microscale scraping tools subjected to substrate‐dependent loading. Using scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, and nanoindentation, we quantify structure–composition–property relationships across closely related taxa occupying soft to hard feeding substrates. Tooth morphology remains largely conserved across taxa. In contrast, material composition and mechanical performance vary systematically with ecological demand. Soft‐substrate feeders exhibit predominantly organic teeth with low stiffness and hardness (Young's modulus ≈3–4 GPa; hardness ≈0.30–0.40 GPa). Mixed feeders show moderate calcium enrichment and intermediate properties. Rock‐scraping specialists display pronounced calcium and silicon incorporation, reaching stiffness and hardness values up to ≈10.8 and ≈1.1 GPa, respectively. Across all taxa, mechanical properties peak in the central radular region and decrease toward the margins, forming functional gradients that are most pronounced under high abrasion. These results demonstrate that localized mineral reinforcement of an organic matrix enables substrate‐specific mechanical optimization while maintaining conserved morphology. The radula thus represents a natural model of a functionally graded composite, illustrating how compositional modulation can precede structural change and providing design inspiration for abrasion‐resistant synthetic materials.