Strange Planet by Nathan W. Pyle

Opposable thumbs and ability to vocalize a wide range of sounds also helped. Though with the brains, we probably would have figured out a way to communicate with more complexity than other animals regardless of the 2nd one.

And the mechanism for that infinite stamina also enabled our hands to be even more useful (and if I had to guess, bipedalism probably arose as a result of our ancestors wanting to hold things while they moved instead of that being an extra bonus).