Question: In the question; [Hollow-boned Humanoids](https://worldbuilding.stackexchange.com/questions/13619/hollow-boned-humanoids) Nathaniels humanoids were a flying mammal species called soarfolk. But let's say that I want a sapient mammal to have hollow bones but not fly.

These furred, sapient mammals are called Lokk, they evolved in the plains after leaving jungles. They are an average of 5"4 and 50 kg. The length of their arms(3.1 ft) Legs(2.8 ft) and tail(2.7 ft). They will be preferably digitigrade(though not a requirement) and of course they have hollow bones. 

How could a creature like this evolve in an earth like world?

Answer: 
Maybe while living in the jungles they were arboreal and the lighter animals were able to stay higher in the trees, or be able to 'flee' across smaller branches in the trees allowing them to live, as they 'ran' from predators. 

So like flying, staying up higher in the trees would encourage lighter bodies, but having hollow bones turned out to be more advantageous than a smaller frame, (like longer arms to help reach farther to grab the next branch.

The other might be if they were originally a flying species that started living in the treetops of the jungles and lost the ability to fly, but became more monkey like as generations came and went.
Overall, make weight a major concern in some way, while maintaining that there is an advantage in having more upright height on land (*To keep them bi-pedal*).

The easiest way to do so is if gravity were considerably stronger, which may or may not be considered "Earth-*like*". There would be more advantage to have stronger, denser, bones. But the weight might not be worth having *solid* bones, so they might become hollow.

There are probably other ways to make one's weight heavy without simply adapting to lose that weight, but I can't think of them at the moment. Hopefully others will have more ideas if you don't want to mess with gravity.