Type Species: Thylacoleo carnifexAge: Pliocene to Pleistocene, 4 million to 30,000 years ago
Thylacoleo, or the marsupial lion, is the biggest known example of the thylacoleonids, reaching almost the size of a modern lion. When it was first discovered in the 19th century, debated ensued whether or not it was an herbivore or carnivore. Its tooth pattern seems similar to modern herbivorous Australian marsupials like kangaroos and koalas. But other lines of evidence support carnivorous lifestyle. These include gnawed bones matching the animal's back teeth, large slashing and retractable claws, and an enlarged olfactory sensor for smelling food. However unlike a big cat, it is not very fast and likely gripped its prey or slashed it after ambushing it. Thylacoleo also shows chevrons, which protect the blood vessels in the tails of kangaroos. Since its body plan shows strange specializations, it could be that the thylacoleonids diverged from other diprotodont marsupials long ago.