system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5: the lack of biped land animals

When dinosaurs roamed the earth there were many species that were bipedal and were strictly land based. Now only some mammals and a handful of birds are strictly biped. Why is this?
gpt
First of all, birds are dinosaurs. Second of all, the quadrupedal mode of movement has advantages over bipedal in terms of stability, agility, and power. In order for bipedal modes of movement to win out, you need to make quadrupedal movement disadvantageous or impossible. One way to do that is to evolve delicate, sensitive, hands and an upright posture. Another way is to evolve the forelimbs into wings that cannot be used for walking as opposed to bats who can crawl with their wings.