All mammals have a number of traits in common: they’re all warm blooded, have hair, have seven cervical vertebrae, breathe air, and feed their young milk. Nearly all mammals also give birth to live young, but monotremes are an exception. This order, which contains platypuses and echidnas, are also somewhat peculiar in that they don’t use nipples to give their young milk, they just secrete it out. Monotremes are endemic to Australia and New Guinea.
In 1974, CSIRO released “Comparative Biology of Lactation,” featuring a clip of a baby echidna (called a puggle) hatching from its shell. Echidna mothers deposit the fertilized egg into a specialized pouch on their underside, incubating the egg for about 10 days.
As adults use their tongues to collect and feed on ants and termites, they don’t have much use for teeth as adults. However, at birth they make use of a specialized tooth which allows the puggle to evacuate the soft, leathery egg shell. This tooth makes nursing dangerous for the mother, so milk is secreted out of the skin instead of the baby latching on to a nipple.
The mother carries the puggle around in a pouch for 45-55 days while the baby develops and grows protective spines. After this phase is over, the puggle is brought to a burrow, where it will develop over the next seven months with the mother returning once or twice a week to provide milk. After it has been weaned, the echidna is ready to go out and continue its life cycle.
[Hat tip: Fiona McDonald, ScienceAlert]