Thylacosmilus

Thylacosmilus is a genus of saber-toothed mammals that once lived in South America during the Late Miocene and Pliocene epochs. Like the saber-toothed cats of North America, this animal had prominent upper canines that grew out of its mouth. Interestingly, it was not related to the saber-toothed cats. In fact, it wasn’t a cat at all. Instead, this predator was more related to marsupials (pouched mammals) such as kangaroos and wombats. 

Description and Size

Thylacosmilus was a genus of saber-toothed mammals that lived in South America from the end of the Miocene epoch into the Pliocene. The generic name Thylacosmilus translates as “pouch knife” in English. Thylacosmilus was a sparassodont and not a felid. This means it was more closely related to the marsupials even though it resembled the saber-toothed cats physically. 

Two main species have been named. They are the Thylacosmilus atrox and Thylacosmilus lentis. The specific name “atrox” translates as “cruel” or “terrible.” Thylacosmilus had a massive head, relatively bigger than other parts of its body. This has made it difficult to estimate the actual size of this mammal. Based on recent studies, scientists think they weighed between 180-260 pounds (80–120 kg). Based on this estimate, this carnivore was probably around the same size as present-day jaguars and is among the largest carnivorous marsupials ever found. It was about 2 feet tall and 4 feet long.

The most prominent feature of their enormous head was the long, slender saber-like canines. The canines were covered with enamel (as thick as 0.25 millimeters). Little information about its incisors and other teeth is available because of poor fossilization. However, we know that animals that tend to develop large saber-like teeth often have some missing or reduced teeth as well. Unlike the North American Smilodon, Thylacosmilus had flanges on its lower jaws which protected the canines when their mouth was closed.

The humerus and femur were very thick, which is expected since the carnivore dealt with bigger prey compared to today’s carnivores. The structure of their limbs suggests that the animal was not adapted for speed but probably caught prey by stalking and ambushing. Unlike felids, Thylascosmilus did not have retractable claws.

Diet—What Did the Thylacosmilus Eat?

The animal has been described as a unique flesh-eating mammal. It fed on grazers (mainly large notoungulates). The size of its head and jaws meant this carnivore had a significant bite force—sufficient to take down big prey. Since it was not a runner, it would immobilize its prey before delivering deep bites into its soft tissues. 

There are also speculations that this animal was not a ferocious predator but a scavenger that only ate the internal organs of dead animals. However, there’s no conclusive evidence to confirm this. 

The more prevalent theory is that this animal was an ambush predator that could deliver a surprise kill by leaping down from trees or hiding in the vegetation. Their canines were long enough to inflict deep injuries and sever arteries, leading to the prey’s death in a matter of minutes. Thylacosmilus is often depicted as a lone hunter. However, like many modern cats, they probably hunted in groups. 

Habitat—When and Where Thylacosmilus Lived

Thylacosmilus lived in South America between the Late Miocene and the Early Pliocene epochs. It most likely preferred savanna and sparsely forested areas where it could capture its prey more easily compared to more open locations. Additionally, the chances of the species facing aggressive competition were higher in the open fields. 

Threats and Predators

The greatest threat to the Thylacosmilus was the phorusrhacids (terror birds). They were vicious and aggressive prey hunters. Although they didn’t prey on the Thylacosmilus, they competed with them for food. Thylacosmilus was at a disadvantage because it was mainly an ambush predator. This forced the animal to stick to areas with trees and vegetation cover, while the terror birds were free to take down prey anywhere.

Discoveries and Fossils – Where It Was Found

The first fossils of Thylacosmilus were found in 1926 by the Marshall Field paleontological expeditions. The discovery was made in the Ituzaingo Formation of Corral Quemado in the Catamarca Province of northern Argentina. Elmer S. Riggs, an American paleontologist, named the fossil in 1933. 

The specimen included cranial bones with the teeth of the right jaws entirely preserved. The left canine and fragments of the mandibles were also preserved, along with a few post-cranial bones. Riggs published a full description of the animal in 1934 based on a comparison with other mammalian carnivores that lived around the same time. 

Fossils of the second species, Thylacosmilus lentis were found shortly afterward and collected by American paleontologist Robert C. Thorne. In 1972, experts concluded that the two fossils belonged to a single genus. 

Other fragmentary fossils have been found in Late Miocene and Early Pliocene formations across Argentina. Some of them include Cerro Azul, Montehermosan Brochero, and Monte Hermoso Formations.

Extinction—When Did the Thylacosmilus Die Out?

In the past, scientists believed Thylacosmilus went extinct during the Pliocene (about 3.6 to 2.58 Million years ago) due to competition with the Smilodon after the Great American Interchange. However, more recent studies show that this is inaccurate. 

While competition probably contributed to the decline of this genus of marsupial carnivores, it didn’t include competition with the saber-tooth cats. Still, this doesn’t rule out the competition with other species as a possible cause of their extinction. Climate change was probably the biggest factor that led to their decline. The Thylacosmilus’ home range became drier, and vegetation began to disappear.‭ ‬This affected the prey population, leaving too little for the marsupial to survive on in the face of growing competition. 

Similar Animals to the Thylacosmilus

Similar animals to the Thylacosmilus include: 

• Smilodon — Popularly known as saber-toothed cats, Smilodon is an extinct genus of giant cats that lived in the Americas during the Pleistocene Epoch. It was robust, with long canines and well-developed forelimbs. Although Smilodon and Thylacosmilus look similar, they’re not related. 
• Borhyaena — This was a large predator with a massive head that lived in South America between 17.5 and 15.5 million years ago. The Borhyaena is very similar to present-day hyenas.
• Thylacine — This is an extinct carnivorous marsupial that lived in Australia until recently. It is also known as the Tasmanian wolf or Tasmanian cat. 

Related Animals 

• Saber-Toothed Tiger
• Machaeroides
• Dinofelis