Rodentia

The order Rodentia is the most numerous of all the branches on the mammal family tree.  Currently there are between 2000 and 3000 species of rodent.  This represents roughly half of all mammal species.

Kingdom: Animalia (kingdom comprising all living or extinct animals)
Phylum: Chordata (comprises true vertebrates and animals having a notochord)
Class: Mammalia warm-blooded vertebrates characterized by mammary glands in the female)
Order: Rodentia (small gnawing animals: porcupines; rats (Norway Rat, Roof Rat😉 Nutria, mice; squirrels; ground squirrels; grey squirrel; red squirrel; flying squirrels; chipmunks; marmots; beavers; gophers; voles; woodchucks; hamsters; guinea pigs; agoutis)

Rodents are found in vast numbers on all continents except Antarctica.  Rodentia is the only placental order (other than bats) to reach Australia without the aid of human introduction.