Fig. 9 in Large onychites (cephalopod hooks) from the Upper Jurassic of the Boreal Realm

Fig. 9. Functional morphology of a hook or claw in a logarithmic spiral shape, penetrating a surface. A, B. Thrusting action, pole proximal. The angle φ at the contact point and the direction of the force vector (arrow) are constant during penetration. C, D. Pulling action, pole distal.