Thylacosmilus – Extinct Animals of South America

Full Grown Art Depiction ThylacosmilusThylacosmilus lived in South America 9 million years ago and was a saber-toothed metatherian. What is a metatherian? Metatherians largely comprise of marsupials but also include extinct relatives of marsupials, such as Thylacosmilus. They looked similar to saber-toothed tigers of North America (Smilodon) but they weren’t cats. Thylacosmilus were sparassodonts, a group of marsupial or near-marsupial carnivores who evolved in South America. Similarities to Smilodon may be because they filled similar ecological niches in their respective habitats.

 

Fossil remains of Thylacosmilus come largely from Argentina. The first was discovered in 1926 by the expedition led by Marshall Field for the Field Museum of Natural History in Chicago. The specimen was identified as a marsupial at that point but it wasn’t until 1933 when the species would be named by Elmer Riggs.

Skull of ThylacosmilusWe can see from skull specimens that the saber teeth of Thylacosmilus were more advanced than those of Smilodon or other sparassodonts. Their teeth were more firmly anchored in their skulls. They wouldn’t be likely to break while attacking prey. They also replaced the incisors. Smilodon still had incisors, even though they might not have been used as much as other animals would. Thylacosmilus eliminated them altogether, along with the grinding molar teeth. The smaller lower canines made the saber teeth self-sharpening, as the two sets of teeth grate against one another. They further had very strong neck muscles and vertebrae, which meant that they would be able to put more force behind any attacks with the saber teeth than others.

 

 

Thylacosmilus Full Fossil Skeleton
Thylacosmilus
Museo de Miramar

But we know more about this animal than just their teeth. Thylacosmilus had a short tibia and plantigrade feet (meaning that like us, they walked on the whole of their foot rather than their toes, which is digigrade). This all tells us that they were not runners and so probably relied on stalking rather than chasing. Based on the alignment of the hips, scientists believe that they might have been able to stand on their hind legs to attack. They did not have retractable claws.

From weighing bones such as the tibia and ulna, scientists have proportionally estimated the weight of Thylacosmilus to be about 200 to 250 pounds, with one outlying estimate being a little over 300 pounds. This could mean that they were roughly the size of a modern-day jaguar, making them one of the largest known metatherians.

 

The climate of Argentina during the lifetime of Thylacosmilus was a savanna-like grassland with sparse wooded areas. Many think that they were likely to have stuck to the trees to avoid competition with larger carnivores. Competition may also be why they went extinct. It has long been thought that competition from North America was the reason for their extinction, although recently it has been more commonly suggested that competition endemic to South America was the reason.

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