Here's why:
* Monotremes are a distinct group of mammals: They lay eggs, have a pouch for raising their young, and possess some reptilian features like a cloaca (a single opening for waste and reproduction).
* Platypuses evolved millions of years ago: They are one of the most ancient mammal lineages, and their evolutionary path is distinct from other mammals.
* Rat and duck are not closely related to platypuses: Rats are rodents and ducks are birds, both belonging to entirely different evolutionary branches.
While the platypus's unusual features might seem like a combination of different animals, its unique characteristics are the result of its own evolutionary history.