The puzzles:   How do stunning functional innovations -- like the spectacular snapping claws in some shrimp -- evolve from unspecialized ancestors? Does the evolution of dramatic novel functions depend on dramatic morphological change?

What we did:   We used advanced imaging methods (microCT and confocal), high-speed video, and kinematic experiments with select 3D-printed models to reconstruct the evolutionary changes in form and function that yielded spectacular snapping claws from simple pinching claws in two shrimp families.

What we found:   We discovered two novel claw-joint types in shrimp claws: slipjoint and cocking slipjoint (torque-reversal joint). Each joint type allowed claws to close more quickly. Cocking slipjoints facilitate ultra-fast closing, and eventually the ability to ÔsnapÕ (break water by creating a cavitation bubble), because energy can be stored before the claw starts to close.

The news:   Key functional transitions between ancestral (simple pinching) and derived, ultra-fast (snapping) claws were achieved by minute differences in joint structure. Therefore, subtle changes in form appear to have facilitated the evolution of wholly novel functional change in a saltational or stepwise manner.