A number of these mammalian predators closely resemble placental predators that evolved separately in Eurasia. They were first described by Florentino Ameghino, from fossils found in the Santa Cruz beds of Patagonia.
For example, sparassodont molars were similar to the meat slicing teeth of modern cats. The canines were also lengthened, and in some cases, such as Thylacosmilus, resemble those of saber-toothed cats like Smilodon. Their body size varied, ranging from 80 cm (2 ft 8 in) long to the size of today's modern big cats.
Another family of large predators wrere the borhyaenids, which were more like wolves or dogs.
- Naish, Darren (2008). "Invasion of the marsupial weasels, dogs, cats and bears... or is it?". Tetrapod zoology. Retrieved 2008-12-07.