Whenever I see a number like that it gets my attention. Where does it come from?
My rough calculations suggest that mice and voles, in the USA, account for about 1/6 as much as human biomass. I suppose I could do frogs and salamanders and such, but maybe you don't allow them as "land-based."
I wonder about lizards. And deer, moose, raccoons, porcupines, bears, coyotes, wolves, foxes, snakes, prarie dogs, gophers, chipmonks...
There are about 300 million rabbits in Australia. At 5 pounds each, that's 1.5e9 pounds of rabbits, about 0.2% of the mass of all the humans on Earth.
Numbers are fun. Anybody want to do kangaroos?
John