Diagrams depicting functional postures for the shell instability (A) and hindrance (B) in the spire height and aperture inclination (log₁₀T − Δ) morphospace for W = 10^0.2, D = 0, and Г = 0. Each color in the morphospace shows which posture achieves the lower value of the norm/projected area on each shell shape (yellow for P_aperture, light blue for P_growth). The criterion for including a specimen on the plots is that W = 10^{0.2 ± 0.1}. (C) Theoretical models with log₁₀T = −0.1 and Δ = 0 at P_aperture (left) and P_growth (right). Both the norm and projected area become small at P_growth. (D) Theoretical models with log₁₀T = 0.9 and Δ = 0 at P_aperture (left) and P_growth (right). Both the norm and projected area become small at P_aperture.