Threat-protection mechanics of an armored fish.

It has been hypothesized that predatory threats are a critical factor in the protective functional design of biological exoskeletons or "natural armor", having arisen through evolutionary processes. Here, the mechanical interaction between the ganoid armor of the predatory fish Polypterus senegalus and one of its current most aggressive threats, a toothed biting attack by a member of its own species (conspecific), is simulated and studied. Finite element analysis models of the quad-layered mineralized scale and representative teeth are constructed and virtual penetrating biting events simulated. Parametric studies reveal the effects of tooth geometry, microstructure and mechanical properties on its ability to effectively penetrate into the scale or to be defeated by the scale, in particular the deformation of the tooth versus that of the scale during a biting attack. Simultaneously, the role of the microstructure of the scale in defeating threats as well as providing avenues of energy dissipation to withstand biting attacks is identified. Microstructural length scale and material property length scale matching between the threat and armor is observed. Based on these results, a summary of advantageous and disadvantageous design strategies for the offensive threat and defensive protection is formulated. Studies of predator-prey threat-protection interactions may lead to insights into adaptive phenotypic plasticity of the tooth and scale microstructure and geometry, "adaptive stalemates" and the so-called evolutionary "arms race".