Monotreme Animals What is a Monotreme?

Photo: Short-beaked echidna walking

Monotremes are a unique group of animals. They possess characteristics of mammals, reptiles, birds, and marsupials—all in one animal. These fascinating creatures lay eggs like reptiles, but feed their young with milk like mammals. They have a beak like birds and a single opening, called a cloaca, for excretion and reproduction like marsupials, reptiles and birds. Monotremes are some of the oldest mammals on Earth. There are only three species of monotremes: the amphibious platypus , and two species of terrestrial echidna. Monotremes are found only in Australia and New Guinea.

The term ' monotreme' is derived from the scientific animal classification Monotremata which means "one hole" ( mono=one and  treme=hole). This is because these mammals have only one rear opening, called a  cloaca, for their anus, urinary and reproductive tracts. Monotreme is pronounced mo-no-tree-m.

Monotremes Characteristics Is it a Mammal, Reptile, Marsupial or Bird?

Photo: Platypus swimming underwater

Monotremes are mammals because, like all mammals, they produce milk (lactate) to feed their young. But unlike other mammals, monotremes don’t have teats or nipples from which the milk is delivered. Instead, milk seeps out of special pads on the surface of the mother's abdomen from which the young animals lap it up. Monotremes are also warm-blooded like all mammals, but with a body temperature of 30°C, they have the lowest body temperature among mammals. That is 8°C lower than a placental mammals.

Monotremes share several characteristics with reptiles. These include a single opening, called a cloaca, for reproductive, digestive, and urinary systems; a reptilian gait with the legs positioned on the side of their body rather than beneath them; egg laying in an external environment; semi-cold blooded body temperatures with limited temperature tolerances; and the lack of a corpus callosum to connect the brain's two hemispheres.

Monotremes are like marsupials and share many similarities. The most significant being certain features of their brains, giving birth prematurely and the presence of a pouch or depression on their abdomen for their young and a a single opening, called a cloaca, for reproductive, digestive, and urinary systems.

Monotremes also have bird-like features. These include a bird-like skull,  a leathery beak—called a bill, no teeth, a single opening for reproductive, digestive, and urinary systems, and a spur on each ankle, similar to turkeys, pheasants and peacocks.

Difference Between Marsupials, Placentals and Monotremes

Monotreme Habitat Where do Monotremes Live?

Photo: Platypus distribution map

Monotremes live in forests, grasslands, and wetlands in Australia and New Guinea.

The platypus lives in heavily wooded areas along eastern Australia, ranging from Queensland to South Australia. They inhabit ponds, lagoons and rivers with gravelly or pebbled riverbeds and prefer tropical, semi-tropical, or temperate climates. Platypuses establish home ranges on these waterways and feed on the aquatic animals found there.

Photo: Echidna distribution map

Echidnas live in many different habitats across Australia and the island of New Guinea. They typically inhabit areas with rocks, logs and hollows among tree roots. They often choose sites that offer protection from extreme temperatures or adverse weather conditions. Echidnas are solitary animals who roam over large territories but will usually remain in one place if there is an adequate food supply.

Monotreme Diet What do Monotremes Eat?

Monotremes are carnivorous animals that typically forage for food in the mornings and evenings. They use electro-receptors at the tip of their beak to detect their prey.

Photo: Platypus foraging for food underwater

The platypus's diet consists of invertebrate prey such as water beetles, water-bugs, snails, shrimp, mussels, seed shrimp, water-mites, worms, and small crayfish. It searches out its prey underwater by using the super-sensitive electro-receptors in its bill to detect its food. As the adult platypus does not have teeth, it grinds its food between two bony plates on its upper and lower jaws and swallows this mashed food.

Echidna Feeding Video

Video: Echidna feeding

The echidna's diet is predominantly termites and ants. It uses its nostrils and the electro-receptors at the tip of its beak to detect its food, usually hidden inside termite mounds, anthills, rotting logs, or under leaf litter. The echidna uses its powerful claws to rip open the hiding place of its victims and flicks its sticky 15-centimetre-long tongue in and out to lap up its prey. The echidna has no teeth and uses hard pads at the base of its tongue to push food up against the roof of its mouth and grinds it into a paste before swallowing.

Monotreme Reproduction

Photo: Platypus egg

Rather than giving birth to live young like most mammals do, monotremes lay one to three relatively small leathery eggs. The female echidna will place her eggs in the backwards-facing pouch on her body and incubate them for up to two weeks. The platypus, on the other hand, doesn't have a pouch. Instead, it incubates its eggs by placing them in a shallow depression on its belly and holds them in place with its tail until they hatch. Once the eggs hatch, the monotreme's young lick milk seeping out of pores in their mother's abdomen.

Baby platypuses remain in the burrow for about 3-4 months feeding on milk and then on solids brought to them by their mother. After this time, the mother abandons them, and they must fend for themselves. An echidna baby stays in its mother's pouch for about three months. Then, at about six months old, the mother will abandon the young puggle to fend for itself.

Monotreme Threats & Predators What Treats Do Monotremes Face?

The only native predators of adult echidnas are the Tasmanian devil and dingo. Platypuses fall prey to dingoes, large birds of prey and crocodiles. Baby echidnas fall victim to native monitor lizards and snakes that venture into their nursery burrow and capture spineless little puggles. Several introduced animals such as dingoes, foxes, feral cats, , and dogs, are known to attack monotremes. Fortunately, the echidna’s spiky defences offer it good protection, and these attacks are rarely successful. As for the platypus: its watery environment and venomous spurs offer it sufficient protection from predators.

Human impact on monotreme survival has been minimal. Aborigines have hunted echidnas and platypuses since they arrived in Australia about 50,000 years ago. They have, however, had little impact on the overall survival of the monotreme population. Since the arrival of European settlers in 1778, humans have had a more significant effect due to land clearing and forest felling. Monotremes, however, are versatile and adaptable animals and don't seem to have been seriously affected by these activities either.

Australian bushfires are the most significant single threat to an echidna as they are too slow to run away. The drying out of waterways can seriously affect the viability of platypuses.

Monotreme Conservation Status Is the echidna Endangered?

Monotremes are relatively common and not considered threatened. They are protected by Australian law. It is illegal to capture, kill or keep these animals as pets.

Prehistoric Monotreme Monotremes Were The Dominate Animals in Australia Once

Monotremes dominated the Australian landmass until marsupials arrived 71—54 million years ago and swept them away. In the end, only two types of these animals survived because they took to the water. These were the echidna which now lives only on land, and the platypus which still lives in the water. Genetic analysis shows that these two species of monotremes only diverged about 25-20 million years ago when the present land-dwelling echidna evolved.