Question

Thylacosmilus is a marsupial, and Smilodon is a mammal. Thylacosmilus and Smilodon both have saber teeth, but they do not share an ancestor that had saber teeth. What are saber teeth for these organisms?

Answer 1

A saber-toothed cat is any member of various extinct groups of predatory mammals that were characterized by long, curved saber-shaped canine teeth. The large maxillary canine teeth extended from the mouth even when it was closed.
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Answer 2

Answer :

The saber teeth's for Thylacosmilus and Smilodon are analogous structures.

Analogous structure's are those structure's whose functions are same or similar but they do not have some morphology.

These structures are a result of convergent evolution.

As in the question although Thylacosmilus and Smilodon do not have any common ancestor but still they both have saber teeth's. These are the example's of convergent evolution leading to the formation of analogous structures.