Thylacosmilus: extinct South American sabre-toothed metatherian (Miocene–Pliocene)

Appearance and feeding adaptations

In overall size it was comparable to a modern jaguar, but its skull bore extremely long, laterally compressed upper canine teeth, giving it a sabre-toothed aspect. Several features indicate a killing technique different from that of most living big predators:

• Very enlarged upper canines set in an elongated skull, which show prolonged growth and wear patterns consistent with repeated stabbing motions.
• A prominent bony flange on the front of the lower jaw that appears to have helped protect the long canines when the mouth was closed.
• Powerful neck musculature inferred from the skull and vertebrae, suggesting bites driven by head and neck strength to inflict deep wounds to soft tissues rather than by crushing with the teeth.

These anatomical traits represent a clear case of functional convergence with placental sabre-toothed cats such as Smilodon, even though the two groups are not closely related.

Paleobiology and extinction

Evidence from wear on the teeth and from associated fauna implies Thylacosmilus was an active predator or specialized scavenger occupying large-mammal niches in South American ecosystems. The genus disappears from the fossil record in the late Pliocene. Saber-toothed felids like Smilodon reached South America only after the Isthmus of Panama formed, during the Pleistocene; consequently, the last known occurrences of Thylacosmilus predate the arrival of those placental sabre-tooths by well over a million years.