Great American Interchange
Sparassodonts shared the ecological niches for large predators with fearsome flightless "terror birds" (phorusrhacids), whose closest extant (living) relatives are the seriemas.  Terrestrial ziphodont crocodilians were also present at least through the middle Miocene.  Some of South America's aquatic crocodilians reached monstrous sizes, with lengths up to 12 m.