The Long-Beaked Echidna
The echidna is similar to the platypus, in that it is a mammal that lays eggs. That makes them an outlier from the characteristics of what mammals actually are. Despite laying eggs, they also lactate like other mammals so that their young can feed. They kind of look like a cross between a duck and a porcupine, but it’s not really clear what kind of food they eat. It’s unknown what those spines are used for, but the males have spurs on their hind legs that they use for fighting each other over mates and territory.