Sparassodonts

Sparassodonta Temporal range: Paleocene-Pliocene, 65–3 Ma PreЄ Є O S D C P T J K Pg N
Thylacosmilus
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Infraclass:	Metatheria
Order:	†Sparassodonta Ameghino, 1894
Families
†Hathliacynidae †Borhyaenidae †Proborhyaenidae †Thylacosmilidae

†Hathliacynidae
†Borhyaenidae
†Proborhyaenidae
†Thylacosmilidae

Sparassodonta is an extinct order of carnivorous metatherian mammals native to South America. They were once considered to be true marsupials, but are now thought to be either a sister taxon to them, or considerably distantly related, part of a separate clade of Gondwanan metatherians. A number of these mammalian predators closely resemble placental predators that evolved separately on other continents, and are cited frequently as examples of convergent evolution. They were first described by Florentino Ameghino, from fossils found in the Santa Cruz beds of Patagonia. Sparassodonts were present throughout South America's long period of "splendid isolation" during the Cenozoic; during this time they shared the niches for large warm-blooded predators with the flightless terror birds. Previously, it was thought that these mammals died out in the face of competition from "more competitive" placental carnivorans during the Pliocene Great American Interchange, but more recent research has showed that sparassodonts died out long before eutherian carnivores arrived in South America (aside from procyonids).

Although members of the order Sparassodonta showed many similarities with placental carnivores, they were not closely related and are a very good example of convergent evolution. For example, sparassodonts' molars were very similar to the sharp teeth of placental carnivores. The canines were also lengthened, and in some cases resemble those of saber-toothed cats. Sparassodonts spanned a wide range of body sizes, from 2.2 pound (1 kg) weasel or civet-like forms to Thylacosmilus, which was the size of a leopard. Along with the Australian thylacoleonids, sparassodonts include some of the largest metatherian carnivores.