Why is the Tasmanian tiger a mammal?

The Tasmanian tiger, or Thylacine, was not a tiger, but a carnivorous marsupial. It was not related to the tiger in any way, being a marsupial, but it had a vague resemblance to a small tiger by its colouring. Its fur was grey-brown (not orange, as sometimes depicted), and it had up to 16 black or brown stripes on its back, predominantly at the tail end.

The name of "tiger" was first suggested by Dutch crewman Jacobszoon who was aboard Abel Tasman's ship when he discovered Tasmania in 1642, naming it Van Diemen's Land. As several crew explored the island, Jacobszoon described seeing "footprints not ill-resembling the claws of a [tyger]". Once convicts arrived in Tasmania after 1804, they referred to the "native tiger", and the name grew from there, even though early free settlers referred to the "marsupial wolf".