Giant beaver

Castoroides, or giant beaver, is an extinct genus of enormous beavers that lived in North America during the Pleistocene. C. leiseyorum and its northern sister species C. ohioensis, were the largest beavers to ever exist.

Giant beaver in A Different Flesh
Beavers near big as bears, imported from America, were on display in the London zoo when Samuel Pepys visited there on 13 May 1661.