Why do the u. s. and australia have different animals? ?

Australia and the US have different climates that are best for specific animals. Australia has warmer climates in some parts that are perfect for kangaroos while parts of US has tropical regions that are good for parrots, lizards etc.

There are different animals that adapt to different regions. U.S animals not only travel but have special "mechanisms" to adapt continuously to their changing environment and habitat. Australian animals are built to handle the heat and hot sand. All of these "mechanisms" that the animals have help them with hunting and hiding, for prey, and from becoming prey

Dcalifornia they have the most people with 200+ people per square mile