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At last, it’s the episode about the platypus, a monotreme! Only two kinds of monotremes remain: the platypus and the echidna. Monotremes are mammals that lay eggs! Not even making that up. The echidna: Do not eat: A platypus and another platypus: Show transcript: Welcome to Strange Animals Podcast. I’m your host, Kate Shaw. This week we’re finally, finally going to look at the platypus and its relations, called monotremes. I’ve been promising a platypus episode for months and now, it is time. There is so much weird about the platypus, it’s hard to know where to start. So let’s pull back for a second and look at the bigger picture. Hopefully most of my listeners are familiar with what traits make an animal a mammal instead of a bird or a fish or what have you. At some point in elementary school, you either had to memorize a list of mammalian traits or you will have to memorize one. The list will be something like this: mammals are warm-blooded, grow hair, and feed their babies with milk. Boom, that’s a mammal. There are more differences than that, and some minor exceptions in the growing hair category, but those are the big differences. But even a little tiny baby who doesn’t know anything knows the difference between a bird and, say, a cat or dog. Birds have feathers, mammals never do. Birds lay eggs, mammals never do. But wait. That’s wrong. Not the feather thing, but the egg-laying. Some mammals lay eggs. Specifically, the monotremes. There are three main types of mammals. The biggest is the placental mammal group, which includes humans, dogs, cats, mice, bats, horses, whales, giraffes, and so on. A female placental mammal grows her babies inside her body in the uterus, each baby wrapped in a fluid-filled sac called a placenta. During birth, the placenta tears open and the baby is born first, followed by the placenta, which is frequently called the afterbirth. Placental mammals are pretty well developed when they’re born, with considerable variation. Baby deer and horses, for instance, can stand and run within a few hours of birth, while kittens and puppies don’t even have their eyes open yet. But they’re all mostly done cooking, so to speak. The second type is the marsupial mammal group, which includes possums, kangaroos, koalas, wombats, sugar gliders, and so on. A female marsupial has two uteruses, and while her babies initially grow inside her, they’re born very early. A baby marsupial, called a joey, is just a tiny little pink squidge about the size of a bean that’s not anywhere near done growing, but it’s not completely helpless. It has relatively well developed forelegs so it can crawl up its mother’s fur and find a teat. Some species of marsupial have a pouch around the teats, like possums and kangaroos, but other species don’t. Either way, once the baby finds a teat, it clamps on and stays there for weeks or months while it continues to grow. The third and rarest type of mammal is the monotreme group, and monotremes lay eggs. But their eggs aren’t like bird eggs. They’re more like reptile eggs, with a soft, leathery shell. The female monotreme keeps her eggs inside her body until it’s almost time for them to hatch. The babies are small squidge beans like marsupial newborns, and I’m delighted to report that they’re called puggles. Echidnas have pouches and after a mother echidna lays her single egg, she tucks it in the pouch. The platypus doesn’t have a pouch, so after she lays her one to three eggs, a mother platypus holds them against her belly with her flat tail to keep them warm. Monotremes show a number of physical traits that are considered primitive. Some of the traits, like the bones that make up their shoulders and the placement of their legs, are shared with reptiles but not found in most modern mammals. Other traits are shared with birds. The word monotreme means “one opening,” and that opening, called a cloaca,