The saber-toothed predator that was not a cat, but a marsupial relative

Nature · Published 3 October 2026 Swipe more like this →

In short: Thylacosmilus looked like a classic saber-toothed cat, but it was actually a sparassodont, a group closely related to marsupials. This South American predator evolved its iconic, constantly growing fangs through convergent evolution, proving that nature often arrives at the same lethal design through entirely different biological paths.

Inhabiting South America from the Late Miocene to the Late Pliocene, Thylacosmilus was a large, specialized predator. While its appearance—complete with long, blade-like canines—mimicked placental saber-toothed cats like Smilodon, it belonged to the Sparassodonta. These animals were not felids, but metatherians, sharing a closer evolutionary history with modern marsupials. First named by paleontologist Elmer S. Riggs in 1933, the genus name translates to 'pouch knife,' reflecting its unique dental anatomy.

The animal's most striking feature was its teeth. Unlike the fixed fangs of cats, the canines of Thylacosmilus grew continuously throughout its life, with roots extending deep into the skull above the braincase. These teeth were protected by a large symphyseal flange on the lower jaw. Because their bite force was relatively low, researchers believe Thylacosmilus did not use its jaw muscles to dispatch prey. Instead, it likely relied on powerful neck musculature to drive precise, deep stabs into soft tissue after immobilizing prey with its robust forelimbs.

Debate persists regarding its exact lifestyle. Some studies suggest it was an ambush predator in open, arid environments, potentially hunting notoungulates. Others have proposed it might have been an intestine-specialist scavenger, though this is contested by evidence of its physical adaptations for killing. Regardless, its existence highlights the power of convergent evolution, where distinct lineages independently develop similar tools to master the same ecological niche, even when their underlying biology—from brain structure to reproductive constraints—remains fundamentally different.

The physical remains of Thylacosmilus, primarily found in Argentina, reveal a creature that was not built for running, but for stalking. Its robust limbs and non-retractable claws suggest a life of ambush. While its brain was gyrencephalic and globular, its sensory adaptations, such as limited stereoscopic vision, were likely compensated for by acute hearing, allowing it to thrive in the changing, increasingly arid landscapes of the Southern Plains.

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