Simplify the following text for a Grade 13 native English-speaking person.
Original: 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 ) .
Simplified: 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 ) .