What male mammal has a venomous spur on its hind leg?

The male platypus is the mammal with a venomous spur on its hind leg. Each adult male has a hollow spur on the hind ankle connected to a venom-producing crural gland.

Platypuses are monotremes, a rare group of egg-laying mammals that also includes echidnas. Both sexes are born with spur buds, but females lose theirs during development and do not retain functional venom glands. In males, venom production increases during the breeding season.

The spur is not a detachable horn or an ordinary claw. It can inject venom when the animal kicks, causing intense pain, swelling, and prolonged sensitivity in humans. The venom is generally not lethal to people, but an injury can be seriously incapacitating.

Solenodons are venomous mammals too, but they deliver venom through modified saliva grooves in their teeth. Male echidnas have non-venomous spurs, making the platypus the canonical answer to this question.