100 things challenge - 27: Monotremes

There are some very weird animals in the world.... A few of these belong to the family of the Monotremes, an order of mammals which is singular for the fact that it lays eggs in stead of giving birth to life young. The most famous of these is no doubt the platypus, but also four species of echidnas or spiny ant eaters belong to the Monotremes. While the platypus is only found in Australia, the spiny ant eaters are endemic to New Guinea, with one species also occuring in Australia. From fossile evidence it is known there used to be a much larger number of Monotreme species and they used to occur over a larger part of the world.

As mentioned, Monotremes lay eggs. However, the egg is retained for a while within the mother and actively supplied with nutrients. After birth, the baby animals drink milk from their mothers. However, as the Monotremes have no nipples, the milk is suckled from pores in the skin. 

Next to this difference, Monotremes have other anatomical differences from other mammals. They have a so-called cloaca (also found in birds and reptiles): one single opening for the urinary, genital and gastrointestinal tract. Monotremes have a reptile-like gait, as their legs are on the sides in stead of underneath their bodies. They all have a spur in the ankle region, in echnidas, this has not apparent function, but it contains a powerful venom in the male platypus.


Short-billed echnida