Why do bats sleep upside down?
Probably, most bats sleep and hang upside down, because they descend from quadruped ancestors (shrews and hedgehogs). So, during the course of their evolution, they invested a lot in transforming arms into wings, and legs were left behind with an ancestral quadrupede strucutre. Additionally, there was a twist in the knee joint, and now bat knees fold backwards. Therefore, it is impossible for bats to stand on their feet. Following another evolutionary path, birds descend from biped ancestors (a group of dinosaurs), so their legs were already quadrupede-like and strong and were kept this way.
Bats sleep upside down because they like the sensation when the blood rushes to their heads. But seriously, they sleep upside down because they have trouble flying if they are on the ground, their wings are weak, and it is easier for them to launch into flight when they are already up in the air. Look here for more information: http://www.whyzz.com/why-do-bats-sleep-u…
