A Sensory Boundary Interpretation of Spicomellus afer: Skeletal-Level Mechanosensory Integration in a Middle Jurassic Thyreophoran

This work proposes a boundary-first interpretation of the unusual osteological structures observed in Spicomellus afer, a Middle Jurassic thyreophoran from North Africa. Departing from conventional armour-based explanations, the study argues that the rib-fused spikes and circumferential collar-like arrangements are more coherently explained as a distributed mechanosensory boundary system rather than as impact-resistant defensive armour. The hypothesis is grounded in comparative anatomy, mechanical coupling principles, and geometric analysis. Direct fusion of spikes to the ribs minimizes soft-tissue damping and enables efficient transmission of low-amplitude mechanical perturbations into the axial skeleton. Radial spike geometry is interpreted as providing directional resolution of external stimuli, allowing early detection of approaching organisms, environmental disturbances, or close-range contact within dense Jurassic ecosystems. Testable predictions are articulated across bone microstructure, articulation stiffness, wear patterns, spatial distribution, and mechanical modeling outcomes, rendering the hypothesis explicitly falsifiable. By reframing defence as a secondary consequence of perception, this work situates Spicomellus afer as a potential early example of skeletal-level sensory integration in vertebrate evolution and contributes to broader discussions on boundary-first design principles in biological systems. Keywords Spicomellus afer thyreophoran dinosaurs dinosaur sensory systems osteoderms mechanosensation boundary-first biology skeletal sensory integration Jurassic ecosystems functional morphology evolutionary biomechanics