Australia has considerably fewer species of carnivorous mammals than any other continent does but about as many carnivorous reptile species as other continents do  This is probably a consequence of the unusual sparseness of Australia' s ecosystems
To survive, carnivorous mammals must eat much more than carnivorous reptiles need to; thus carnivorous mammals are at a disadvantage in ecosystems in which there is relatively little food
Because Australia's ecosystems are unusually sparse, carnivorous mammals there are at a disadvantage relative to carnivorous reptiles.