The platypus has small, sharp spurs on its hind limbs that it uses to inject defensive poisons into predators, an unusual feature not found in other mammals. Where did these venoms come from?

The platypus (Ornithorhynchus anatinus) has a puzzling array of features. Not only does it have that iconic duck bill, it lays eggs like a bird or reptile but feeds milk to its young like a mammal.