….air!
Two young Barbary Macaques (Macaca sylvanus) in the Berlin Tierpark Friedrichsfelde. These two were climbing and jumping around together, and I couldn’t help but feel each was daring the other to copy dangerous jumps. Previously, I showed a picture of one climbing, now I’ll add some more photos to emphasize what the ability to pronate a hand is really good for. Just to drive home what theropods never could do….
I goes there, I comes back.
Jumping to and fro is all fine, but how do you get UP to a point to jump down FROM? Here’s how:
OK, I guess I have made my point by now: climbing is a lot easier with pronatable hands. You can grasp a trunk with medially facing palms, but you need a lot of strength to pull yourself up that way, because your center of mass is further away from the tree than when you do a pull-up.
EDIT: two great posts to check out about the uselessness of theropod arms.
The enclosure for the Macaques in the Tierpark is made up from ruined buildings – they selected sandstone columns and other stonemason’s work with decorative elements. german cities had a lot of such stones to get rid off after the Second World War, and turning them into a playground for monkeys is a pretty nice idea 
Pingback: Mammal Monday 45: more mammals from the cold | dinosaurpalaeo