Sparassodonts were the only South American mammals to specialize as carnivores . Their relative inefficiency created openings for nonmammalian predators to play more prominent roles than usual ( similar to the situation in Australia ) . Metatherians were the only South American mammals to specialize as carnivores ; their relative inefficiency created openings for nonmammalian predators to play more prominent roles than usual ( similar to the situation in Australia ) .