Creature of the Week #20: Thylacosmilus

marco_polo

Thylacosmilus (meaning 'Pouch Sabre') was a relatively large saber-toothed predator that lived and hunted on the plains of prehistoric South America during the Miocene period until about 2 million years ago . About the size and build of a modern jaguar it was approximately 1.5 meters in length and weighed an estimated 100 kilos.






Despite the striking resemblance to eutherian saber-toothed cats like Smilodon, this is entirely due to Thylacosmilus being an outstanding example of convergent evolution, as it was not closely related to cats at all, but was rather a highly specialized genus of pouched marsupial. Of all known saber-toothed puncture killers, the canine teeth of Thylacosmilus appear to have been the longest and most specialized of them all


Thylacosmilus and other unusual marsupial predators are believed to have evolved from primitive marsupial insectivores that became isolated as South America became separated from the rest of the world. This isolation allowed them to evolve to fill ecological niches as top predators.The doglike borhyaenids and saber-toothed thylacosmilids are placed into separate families, the Borhyaenidae and Thylacosmilidae respectively, within the superfamily Borhyaenoidea.


Its huge sabre teeth began deep in the skull giving an unusual convex shape to the skull. At 15 cm long its sabres were even larger than those of Smilodon, and were tapered to a sharp edge on both the front and the back cusps. When the jaws were closed, its distinctive large flat flanges protruding downwards from the base of the jaw provided excellent protection for the sabers. The premolars and molars were narrow lineal blades, also specialised for slicing. Unusually, its teeth continued to grow continuously throughout its life, much like rodents teeth today. It is speculated that this may have been to counter damage sustained while attacking the often well armoured herbivorous South American fauna of the time.





All the indications are that unlike like the more slender and agile eutherian cats, Thylacosmilus was poorly suited for fast running, with proportionately shorter stouter limbs than true cats as well as a lacking retractable claws. Instead it appears to have been well powerful predator that thrived on ambushing prey after a short dash. A number of adaptations suggest was it well suited for such a lifestyle. Tremendous forelimb strength and a semi-opposable thumbs meant that Thylacosmilus was capable of pinning down and restraining prey with ease. A long and powerful neck allowed for both great power and fine control to be exerted over the head. Combined with a fairly weak bite force this suggest that like the eutherian saber tooths, Thylacosmilus had perfected a neck driven biting motion, designed for precision slashing of vunerable areas, rather than brute biting force to make a kill.


Thylacosmilus was amongst the last of the Borhyaenoide line and died out shortly after North and South America became connected via the Panama land bridge about 3 million years ago. The most common extinction theory is that Thylacosmilus and other native carnivores were simply out-competed by better adapted placental carnivores such as Smilodon arriving into South America after the new American continent formed, eventually leading to their ultimate extinction.

Galvasean

Not only does Thylacosmilus atrox look like a sabertooth cat, but to ad to the confusion it shares a species name with another large prehistoric cat, the 'American lion' (Panthera atrox).