Western Long-Beaked Echidna - Zaglossus bruijnii
Like all monotremes, the echindas are egg-laying mammals. Unlike their relatives, the platypodes, echidnas lay just a single egg per year, and the female carries the egg in an abdominal egg-pouch, rather than laying multiple eggs in a burrow. The female raises the offspring on her own, so cannot afford to spend her entire time curled around a nest.
The egg incubates 21 days internally, and 10 days externally. When the puggle hatches, it’s nearly as undeveloped as a marsupial infant. For the next 45-55 days, the puggle develops within the pouch, lapping milk from the mother’s milk patches - the modified sebaceous glands that excrete milk aren’t organized into a “nipple” in monotremes, but are simply gathered in patches on the skin.
When the puggle begins to develop spines, the mother deposits it into a nursery burrow, and leaves it there for 4-5 days at a time, while she forages. Around seven months of age, she comes back less and less frequently, until the puggle (now fully-developed) leaves the burrow on its own. Its food-finding and “hunting” skills are all instinctual, and don’t require teaching by the mother to develop, unlike in most mammals.
Genera Mammalium: Monotremata - Marsupalia. Angel Cabrera, por Museo Nacional de Ciencias Naturales, 1919.