Thylacosmilus

*Thylacosmilus atrox*

***Thylacosmilus*** is an extinct genus of saber-toothed sparassodont which was endemic to South America during the Neogene period from the Late Miocene epoch to the Late Pliocene epoch. It is known for looking similar to the machairodonts, an unrelated family of felids, due to it possessing a pair of "saber teeth".

Despite popular belief, *Thylacosmilus* is not related to machairodonts or any other type of felid. Instead, sparassodonts are a sister taxon to the more closely related marsupials. Their similarities were caused by convergent evolution.

## Taxonomy

*Thylacosmilus* was described and named by Elmer S. Riggs in 1933. He named two species, *T. atrox* and *T. lentis*.

Though *Thylacosmilus* is one of several predatory mammal genera typically called "sabre-toothed cats", it was not a felid but a sparassodont, a group closely related to marsupials, and only superficially resembled other sabre-toothed mammals due to convergent evolution.

## Description

   The most notable feature of *Thylacosmilus* is its canines, which are saber-like and whose roots grew throughout the animal’s life, growing in an arc up the maxilla and even above the orbits. Its cervical vertebrae were very strong and to some extent resembled the vertebrae of machairodonts. Recent comparative biomechanical analysis have estimated the bite force of *T. atrox* starting at maximum gape at 38 newtons (8.5 lbf), much weaker than that of a leopard, suggesting its jaw muscles had an insignificant role on the dispatch of prey. Its skull was similar to that of *Smilodon* in that it was much better adapted to withstand loads applied by the neck musculature, which, along with evidence for powerful and flexible forelimb musculature and other skeleton adaptations for stability, support the hypothesis that its killing method consisted on immobilization of its prey followed by precisely directed, deep bites into the soft tissue driven by powerful neck muscles.

Body mass estimates suggest that *Thylacosmilus* weighed between 80 to 120 kilograms, which is similar to the weight of a modern jaguar or leopard. This would make it one of the largest carnivorous metatherians.

## Decline and extinction

Old and outdated sources suggested that the extinction of *Thylacosmilus* was caused by competition with machairodonts such as *Smilodon*. However, recent studies suggest that that is not the case. *Thylacosmilus* became extinct during the late Pliocene whereas the earliest South American *Smilodon* fossils date back to the middle Pleistocene epoch; the two genera were separated by 1.5 million years. There's another theory stating it went extinct during the Great American Interchange, where the two fauna from North America and South America met eachother. It may have been that during this time, carnivores that entered South America which was where Thylacosmilus lived, may have had very similar roles and outcompeted the metatherian to extinction, possibly due to packs or possessing more effective weaponry suited to predatory roles.

## JPInstitute.com Description

Thylacosmilus atrox is a very interesting creature. It looked like the famous saber-toothed cats, but it was actually a marsupial, which means it is a close relative of kangaroos. This ferocious-looking animal probably had a pouch in which it carried its young.

Thylacosmilus lived in South America about eight million years ago when it was still separated from North America by water. There were no members of the cat family in South America, so it is interesting that nature found a way to recreate a very successful design using the types of animals that already existed in that area. Once the land bridge between North and South America formed, many of the marsupials gave way to placental mammals that filled the same ecological niche.

## Appearance in other media

### *Jurassic Park*

* *Thylacosmilus* appeared in the video game Jurassic Park Builder.
* *Thylacosmilus* appeared in the video game Jurassic World: The Game.