An Ultimate Guide to Thylacosmilus: The Pouch Knife

Leave a comment / / Updated on: 24th September 2023

NameThylacosmilusDietCarnivorous
Name Meaning“Pouch knife”Height0.5 meters (1.6 feet)
PronunciationFy-lak-o-smy-lussLength1.2–1.3 meters (3.9–4.2 feet)
EraCenozoic– Neogene PeriodWeight80–120 kilograms (176–265 pounds)
ClassificationMammalia, Sparassodonta & ThylacosmilidaeLocationArgentina, South America

Thylacosmilus Pictures

Thylacosmilus
Thylacosmilus | Heraldo Mussolini via GettyImages

The Thylacosmilus

Gage Beasley Prehistoric's Thylacosmilus Concept
Gage Beasley Prehistoric’s Thylacosmilus Concept

The Thylacosmilus was often called the marsupial version of a saber-toothed cat.

In reality, there’s so much more to this creature, proving its importance in our world’s evolutionary history!

This mammalian form inhabited prehistoric Argentina roughly 9–3 million years ago.

Although widely considered a ferocious predator, scientists suspect it may have been a scavenger.

Also, large birds of prey may have preyed on it.

Besides its unique saber-like teeth, the Thylacosmilus is renowned for having a strong neck that supports its remarkably large head.

Have we aroused your curiosity?

Keep reading, as you’re about to discover more jaw-dropping details about the famous pouch knife!

Gage Beasley's Prehistoric Shirt Collection
Gage Beasley’s Prehistoric Shirt Collection
Gage Beasley's Prehistoric Plush Collection
Gage Beasley’s Prehistoric Plush Collection

Physical Characteristics

Restoration of the head of Thylacosmilus
Restoration of the head of Thylacosmilus | Dmitry Bogdanov via Wikipedia Public Domain

The Thylacosmilus was a mammal that resembled the extinct saber-toothed cats, although the two are part of different animal groups.

While the saber-toothed cat was a felid, Thylacosmilus were sparassodonts closely related to marsupials.

These creatures are known for having unusually large heads, leading to inaccurate body mass calculations.

Some scientists argued that they weighed 80–120 kilograms (176-265 pounds) on average but could reach 150 kilograms (330 pounds) at the maximum.

Gage Beasley Prehistoric's Thylacosmilus Size Comparison Chart
Gage Beasley Prehistoric’s Thylacosmilus Size Comparison Chart

The length was estimated at 1.2–1.3 meters (3.9–4.2 feet), while the height was 0.5 meters (1.6 feet).

Unfortunately, but not unusually, since many details of our world’s prehistoric wildlife remain only speculation, scientists cannot confirm these numbers.

The Thylacosmilus had remarkably robust limbs and likely well-developed pectoral and deltoid muscles that may have been used to capture and hold prey.

The physiological characteristics of the hind limbs indicate that Thylacosmilus were not adapted for fast running.

The large, saber-like canines represent another distinctive characteristic of the genus.

They are relatively longer and more slender than the canines of other similar carnivorans.

Despite their size and uniqueness, not all scientists agree that the canines were used to dispatch prey, as a study shows.

Habitat and Distribution

Thylacosmilus fossils were discovered in the following Argentinian formations:

  • Ituzaingo Formation, also known as Entre Rios
  • Cerro Azul Formation, also known as Epecuen Formation
  • Possibly Monte Hermoso Formation

During the Late Miocene, when the Thylacosmilus was alive, our planet’s climate started becoming more and more similar to the climate we experience today.

However, between 7 and 5.3 million years ago, the Late Miocene Cooling (LMC) event occurred, during which temperatures dropped significantly.

By the end of the period, however, the temperatures rose again, resulting in a remarkable increase in global temperature at the beginning of the Pliocene.

By the Middle Pliocene, when Thylacosmilus went extinct, the temperatures were approximately 2–3 degrees Celsius higher compared to today.

As such, we can conclude that over the six million years these mammals were inhabitants of Earth, they experienced several climatic changes and learned to adapt to various environments.

Savannah Landscape
Savannah Landscape | Arte Index via iStock

At that time, Argentina was a savanna-like habitat, possibly featuring sparsely forested areas.

It is believed that the Thylacosmilus avoided hunting in totally open areas where it would have had to compete with other animals for food and may have fallen prey to other prehistoric predators.

Behavior and Diet

Considering its robust build, you’d expect the Thylacosmilus to be a ferocious and agile predator.

While we cannot argue about it being ferocious, we must tell you that this mammal was likely a slow-moving predator that did not pursue its prey.

Scientists suspect it relied on stalking the prey, immobilizing it, and then delivering deep bites into its soft tissue.

Life restoration  of Thylacosmilus
Life restoration of Thylacosmilus | Jose manuel canete via Wikipedia CC BY-SA 4.0

Contrary to what you may think when imagining its large canines, the Thylacosmilus had a weak bite force of only 38 Newtons.

Its canines were, in fact, controlled and supported by the unusually powerful neck muscles, not by the masticatory muscles.

Additionally, the Thylacosmilus could flex its head enough to be able to deliver the required bites.

Some studies also show that its hip was quite mobile, thus allowing it to stand up on its hindlimbs, which may have been useful while immobilizing prey.

As such, while it’s not a fast runner, the Thylacosmilus was undoubtedly a fearful predator capable of killing whatever prey it laid its eyes on!

Was that truly the case?

Scifi Tylacosmilus
Scifi Tylacosmilus | Image via IdeasFandom

Other studies show that the Thylacosmilus did not, in fact, use its canines to dispatch prey and was not even a predator.

Instead, the authors argue it was a scavenger, and the canines helped it open carcasses rather than kill live prey.

The Thylacosmilus probably didn’t have keen eyesight and relied primarily on its hearing sense.

This is one of the reasons why habitat assumptions are oriented toward relatively dry environments; in humid areas, the sound absorption is higher, and the hearing sense wouldn’t compensate for poor eyesight.

But what stands behind this poor eyesight?

Experts say that its bony orbits were divergent and differed from those of other mammalian predators.

They were similar to those of horses or cows.

According to a study published on the subject, the rootless canines were responsible for this unusual skull shape, including the orbital displacement.

Thylacosmilus skull
Thylacosmilus skull | Jonathan Chen via Wikipedia CC BY-SA 4.0

However, this did not completely limit the vision, and it could see enough to catch prey (if it was indeed a predator).

Another behavioral trait worth mentioning is that the Thylacosmilus may have engaged in cooperative behavior.

Scientists concluded this after suggesting that young individuals could not deliver efficient bites and grasp prey well enough.

As such, they argue that adults may have taught their young how to hunt.

Nevertheless, this behavior hasn’t been observed in other marsupials, so it remains only a theory.

Life Cycle

Thylacosmilus vertebra
Thylacosmilus vertebra | Carl F. Gronemann via Wikipedia Public Domain

Although some fossils are thought to have belonged to a young adult, no research papers have focused particularly on the ontogenesis, reproductive behavior, or life cycle of the Thylacosmilus.

In this regard, we must turn to what is known about marsupial reproduction, hoping to outline the possible behavior of its prehistoric relatives.

The reproductive organs of marsupials are different from those of other mammals.

More precisely, females had two lateral vaginas, each leading to separate uteri.

They also have a third canal called the median vagina, which is used for giving birth.

The males, in turn, have a bifurcated penis with two ends, one for each of the two female vaginas.

When not erect, the penis is retracted into the body.

Thylacosmilus in Jurassic World
Thylacosmilus in Jurassic World | Xenephos via Jurassic World Game

The pregnancy period is quite short.

The red kangaroo, for example, gives birth after 33 days of pregnancy.

The baby, called a neonate, is highly underdeveloped; it’s blind, hairless, and tiny.

Upon being born, the babies crawl up into their mother’s pouches.

Obviously, while the above details may at least partly be valid for the Thylacosmilus, the pouch part is unlikely, as there’s no fossilized evidence of it having a pouch.

While the genus’ name translates to pouch knife, and many sources mention that this mammal carried its babies in its pouch, evidence shows things may have happened differently.

Or, even if it had a pouch, we still don’t know if it was used in the same way. 

Thylacosmilus skeletal reconstruction
Thylacosmilus skeletal reconstruction | Ivan Iofrida via Wikipedia CC BY-SA 4.0

Studies confirm that sparassodonts had highly reduced epipubic bones, meaning bones that supported the pouch.

As such, they may not have possessed a pouch altogether, or if they did, it may have been underdeveloped.

Based on this, we may assume that the babies were not as underdeveloped as marsupial babies.

Still, there’s no paleontological evidence to confirm that either theory is valid for the Thylacosmilus precisely.

Marsupial babies require approximately 190 days to grow large and develop enough to stick their heads out of the pouch.

A few weeks later, they get out and venture into the outside world.

When they’re approximately 235 days old, they’re ready to leave the pouch altogether.

In the wild, marsupials are known to live up to six years, while some captive individuals reach an extraordinary lifespan of 20 years.

We must stress again that none of these details have been confirmed as valid for the Thylacosmilus.

Thylacosmilus recreation
Thylacosmilus recreation | Baperookamo via Wikipedia

Things are even more complicated because sparassodonts, including the Thylacosmilus, are not considered true marsupials anymore but are excellent examples of convergent evolution.

This adds further uncertainties regarding the Thylacosmilus reproductive behavior and life cycle.

One thing is certain, though: its saber-like teeth grew continuously throughout its life.

Evolution and History

As already mentioned, Thylacosmilus is a sparassodont.

The earliest well-known sparassodont is Callistoe vincei, which dates from the middle Eocene.

While the earliest Paleocene members are known, they have been poorly studied due to the fragmentary nature of their fossils.

Recreation of a sparassodont
Recreation of a sparassodont |  Apokryltaros via Wikipedia CC BY 2.5

Sparassodonts were initially thought to be closely related to creodonts, carnivorous placental mammals.

Supposedly, they formed a transitional group that linked carnivorous placentals and metatherians.

This theory was subsequently disapproved of by other scientists, who argued that these mammals were close relatives of daryurids (marsupials) and thylacines (carnivorous marsupials known as Tasmanian tigers).

Other theories implied that opossums, deltatheroidans (basal metatherians), and paucituberculatans (South American marsupials) were close relatives of sparassodonts.

Today, the Sparassodonta group is often placed just outside of Marsupialia, under the Marsupialiformes subgroup.

Thylacosmilus hunting
Thylacosmilus hunting | Image via Wikimedia Commons

The Thylacosmilus is classified in the Thylacosmilidae family under the Sparassodonta order alongside the Anachlysctis, Eomakhaira, and Patagosmilus.

When its fossils were first discovered, scientists regarded them as marsupial material closely related to borhyaenids, which are now also part of the Sparassodonta order.

A few years following the discovery, Elmer S. Riggs named the genus Thylacosmilus and assigned two species: T. atrox and T. lentils, but only T. atrox is recognized today.

Based on the assumption that Thylacosmilidae were specialized borhyaenids, the Thylacosmilinae subfamily was placed within the Borhyaenidae family.

More recent discoveries confirmed that the group deserves the same rank as the Borhyaenidae family.

While the Thylacosmilus resembles saber-tooth cats in appearance, it is not related to these extinct felids.

Scientists suspect they exhibited saber-tooth mammal characteristics due to convergent evolution but remained closely related to marsupials.

Interactions with Other Species

Restoration of Thylacosmilus
Restoration of Thylacosmilus | Olllga via Wikipedia CC BY 3.0

A fascinating prehistoric creature that the Thylacosmilus may have shared its habitat with is the Macrauchenia.

It was a large, long-necked ungulate closely related to odd-toed ungulates.

It was an herbivore and may have fallen prey to the ferocious Thylacosmilus.

Considering that it was almost three times as large and ten times as heavy as the Thylacosmilus, we can safely assume that, if this sparassodont mammal was an active predator, it was quite an efficient one!

Argentavis
Argentavis | Radomil via Wikipedia CC BY-SA 3.0

Another worth-mentioning creature that lived in the same habitat is the Argentavis, a bird of prey known as a giant teratorn.

It is the largest flying bird known, having a wingspan of more than seven meters.

As such, it may have been a predator of the Thylacosmilus.

Terror birds were also quite common in South American habitats.

They are members of the Phorusrhacidae family, which consists of large, carnivorous, flightless birds.

They were so powerful that they served as the main rivals for the ferocious Argentavis mentioned above, as well as for thylacosmilids.

Other creatures found in prehistoric Argentina included various sparassodonts and ungulates, rodents, xenarthrans, lizards, turtles, crocodiles, amphibians, and fish.

Cultural Significance

Thylacosmilus with fur
Thylacosmilus with fur | Dinosaurs20 via Jurassic Park Fandom

Since it’s an excellent example of convergent evolution, no wonder the Thylacosmilus aroused the curiosity of scientists, who focused on studying this mammal’s physical and predatory traits.

The way it used its canines and hunted prey was of particular interest, and many researchers admit that, unfortunately, some details may never be fully confirmed.

The popular media was not as concerned with Thylacosmilus as scientists were.

It appears only in the Life After Dinosaurs documentary.

Additionally, it is a character in the Jurassic Park Builder and Jurassic World: The Game video games.

We can only hope that future media productions will feature this fascinating yet mysterious creature.

Conclusion

The Thylacosmilus was a sparassodont mammal featuring distinctive saber-like canines that grew continuously as the animal aged, sometimes curving above the orbits.

Contrary to popular belief, this mammal was closely related to marsupials, not to saber-tooth cats, and may represent an example of convergent evolution.

It lived in Argentina from the Late Miocene until the Middle Pliocene and may have been active predators or scavengers; scientists aren’t entirely sure of its dietary preferences yet.

The Thylacosmilus carnivores were quite small, had short yet robust limbs, and an unusually strong neck that supported the large head.

FAQs

Why did Thylacosmilus go extinct?

The Thylacosmilus likely went extinct due to environmental changes that resulted in a lack of prey.

What is the difference between a Smilodon and a Thylacosmilus?

The most important difference between a Smilodon and a Thylacosmilus is that the former was a felid, while the latter was a sparassodont closely related to marsupials.

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