What's wrong with bunny hands on dinosaurs? (2018)
3 days ago
- #forelimb-evolution
- #dinosaur-anatomy
- #paleobiology
- Dinosaur forelimbs, including theropods and sauropods, lacked the ability to fully pronate their hands (rotate palms downward).
- Mammals, due to their evolutionary history (small, arboreal, or burrowing ancestors), developed the ability to pronate their forearms, which dinosaurs never did.
- Elephants have permanently pronated forelimbs, meaning their radius and ulna are twisted into a fixed position, unlike humans who can rotate their forearms.
- Theropod dinosaurs (like raptors) had limited wrist mobility, preventing 'bunny hands' (palms down) as often depicted in media like Jurassic Park.
- Sauropods had massive forelimbs with limited pronation, leading to outward-pointing toes in trackways rather than forward-facing hands.
- Maniraptoran dinosaurs (including birds) evolved specialized wrist bones (semilunate carpals) for side-to-side motion but not rotation, aiding wing-folding but not pronation.
- The evolution of forearm rotation in mammals is linked to their small size, arboreal lifestyle, and need for versatile forelimbs, unlike dinosaurs, which evolved from bipedal ancestors.
- WAIR (Wing-Assisted Inclined Running) is a behavior seen in birds, but its applicability to non-avian theropods is debated due to differences in shoulder anatomy.
- Arboreality in dinosaurs (e.g., birds) likely followed flight rather than preceded it, as their limb anatomy lacks clear climbing adaptations.