What Is a Monotreme?

A monotreme is a type of mammal that lays eggs. There are only two kinds of monotremes that exist, the platypus and the echidna, which are only found in Australia, New Guinea or Tasmania. A monotreme is a unique and unusual mammal, not only because it lays eggs, but also because some of its skeletal structure resembles birds and reptiles. These characteristics make the monotreme a more primitive type of animal.

The platypus is considered a strange-looking mammal, with a bill, a tail and webbed feet, in addition to its fur. It uses its bill to hunt along the bottom of the water, gathering food such as insects, shellfish and worms into its cheek pouches, then bringing the food up to the surface to eat. Since the platypus does not have any teeth, it also gathers gravel and mud to help it chew the food. A platypus can stay underwater for a few minutes, but will have to come back to the surface for air.

The male platypus has a poisonous spur on the heel of its back legs that, while not particularly dangerous to humans, can be deadly to other animals. The webs on a platypus’ feet retract to reveal individual nails, which enables it to dig burrows along the bank of the water where the female lays her eggs. Usually, a female platypus will lay one or two eggs, which hatch in about 10 days. The mother stays in the burrow to warm the eggs and then to take care of the babies when they hatch. She will nurse them until they are about three- to four-months-old, in which time they can swim.

The echidna, also called the spiny anteater, is a monotreme that lives on scrubland. It has small eyes and a long beak on a tiny face and short legs with claws used for digging. The short-beaked echidna has dark fur and spines located on its back and sides. In comparison, the long-beaked echidna has less fur and more visible spines. The echidna protects itself by curling up into a ball, or by digging a hole, to expose only its spines and to protect its face and belly.

Like the platypus, the echidna does not have teeth. The echidna uses its long, sticky tongue to catch and eat its food, which consists of ants, earthworms and termites. When digging for ants or other food, the echidna will also often eat a lot of dirt. To crush the food into paste so that it can swallow it, the echidna uses its tongue and the roof of its mouth.

Also like the platypus, a female echidna will lay one or two eggs that hatch in about 10 days. The echidna has a pouch, though, where she holds these eggs and the babies when they hatch. A baby echidna stays in the pouch, holding onto its mother’s hair with its front legs and lapping up milk secreted into the pouch by its mother, until it grows its spines. Then, the mother keeps the baby in a burrow where she will return to feed it periodically.

Monotremes are a unique group of egg-laying mammals, distinct from the more common live-bearing placental mammals and marsupials. They possess a single opening for excretion and reproduction, known as a cloaca, which is a trait shared with reptiles and birds. Monotremes are represented by only five species: the platypus and four species of echidnas.

Monotremes are indigenous to Australia and New Guinea. The platypus is native to eastern Australia and Tasmania, thriving in freshwater environments. Echidnas, on the other hand, have a wider distribution, with four species found in both Australia and New Guinea, inhabiting forests, grasslands, and arid regions.

Monotremes lay eggs, which is an unusual characteristic among mammals. Female monotremes have a specialized pouch or a burrow where they incubate their eggs. After hatching, the young are fed with milk secreted from the mother's mammary glands, although monotremes lack nipples, so the milk is absorbed through the skin or fur.

The platypus is carnivorous, feeding on aquatic invertebrates, and it locates prey using electroreception, a unique ability to detect electric fields generated by muscle contractions. Echidnas are insectivores, primarily eating ants and termites, and they use their keen sense of smell and long, sticky tongues to capture their food.

Some monotreme species are considered vulnerable or near threatened, such as the platypus, mainly due to habitat destruction, water pollution, and climate change. Conservation efforts are in place to protect their habitats and monitor populations. Echidnas are not currently endangered but are protected by law and also face habitat loss as a threat.

Monotremes boast several unique features: they lay eggs, have a cloaca, and possess spurs on their hind limbs (in males). The platypus is particularly distinctive with its duck-like bill, which contains electroreceptors, and its ability to produce venom, which is rare among mammals. These adaptations make monotremes a fascinating study in evolutionary biology.