Monotremes are the only mammals that lay eggs. An egg-laying mammal is unique because all other mammals give birth to live babies. But once a Monotreme’s eggs hatch, the mother feeds its babies milk like all other mammals. For this reason, a monotreme is classified as a mammal. There are only two examples of monotremes; the amphibious platypus and the terrestrial echidna. While echidnas and platypuses look quite different, they are very similar anatomically.
The definition '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.
Monotreme Characteristics The Oddball Mammal
A monotreme is a mishmash of an animal. It has characteristics of mammals, reptiles and marsupials—all in one animal.
How is a Monotreme Like a Mammal?
Monotremes are classified as 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 milk pads on the surface of the mother's abdomen from which the young animals lap it up. Monotremes are warm-blooded (endothermic) but have the lowest body temperature amongst mammals at 30°C. This is 8°C lower than a placental mammal and 5°C lower than a marsupial. Monotremes have basal metabolic rates (BMRs) 25-30% lower than most placental mammals. For this reason, they are incapable of maintaining their internal body temperatures through extreme weather conditions.
How is a Monotreme Like a Marsupial
Monotremes have more in common with marsupials than with reptiles or placental mammals. For example, certain brain features and the act of “premature” birthing are similar between monotremes and marsupials. Additionally, like marsupials, monotremes too have a pouch or a depression on their abdomen for their young.
How is a Monotreme Like a Reptile?
Like reptiles, monotremes have a single opening, called a cloaca, for their digestive, urinary and reproductive tracts. Monotremes have a reptilian gait with their legs on the sides of their body rather than underneath it. Monotreme females lay eggs that hatch into an external environment like reptiles. Monotremes are semi-cold-blooded. That is to say that they are warm-blooded, but can only control the temperature of their bodies over a narrow range of outside environmental temperatures. Like reptiles, monotremes lack a corpus callosum, the connective structure in placental mammals that allows the brain’s right and left hemispheres to communicate. (Monotremes do have some connection between the hemispheres formed by white matter.) And finally, the male penis of a monotreme has four heads, similar to the bifurcated penis of reptiles.
Characteristics Unique to Monotremes
Monotremes have bird-like skulls. They have leathery electro-sensory bills, which help them detect their prey hidden away within a termite mound, anthill, a rotting log or under leaf litter in the case of the echidna, and under pebbles underwater in the case of the platypus.
They have no teeth. They use hard pads at the base of their tongues to push food up against the roof of their mouths and grind the food into a paste before swallowing. Male monotremes have a spur on their ankles. The spurs of the platypus contain venom.
Monotreme Habitat Where do Monotremes Live?
The platypus lives in heavily wooded areas along the eastern coast of Australia, where there are freshwater creeks and streams with steep stable riverbanks. Their range extends from Queensland to South Australia. The climatic range covers tropical, semi-tropical and temperate zones of eastern Australia. It prefers waterways with riverbeds that are gravelly or pebbled, because this is where its food is found. The platypus establishes a home range and forages in that range.
Echidnas are mainly found in Australia. They are also found on the island of New Guinea close by. They are found throughout Australia in almost all habitats, from snow-covered mountains to deserts and even urban areas. They are usually found among rocks, in hollow logs, and in holes among tree roots or rummaging through leaf litter. They are solitary, territorial animals roaming over a large territory. While there is an adequate food supply, echidnas will generally remain in a fixed location. Echidnas tend to avoid temperature extremes.
Monotreme Diet What do Monotremes Eat?
The platypus and echidna are carnivorous mammals that typically forage for food in the mornings and evening. They both use electro-receptors at the tip of their beak to detect their prey.
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 duck-like bill to detect its food. These receptors pick up even the slightest electrical pulses that all animals make when they move. It moves its head from side to side, as it swims underwater picking up the tell-tale electrical signals given off by its prey, quickly homing in on them, unearthing them with its bill when required, and pouncing on them. 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 up food.
The echidna's diet is predominantly termites and ants. They will also eat the larvae of other invertebrates. Like the platypus, it uses its nostrils and the electro-receptors at the tip of its beak to detect its food, usually hidden away inside termite mounds, anthills, rotting logs, or under leaf litter. Once it has identified its prey, the echidna uses its powerful claws to rip open the hiding place of its victims and flicks its long sticky 15-centimeter tongue in and out to lap up its prey. The echidna has no teeth. So it uses hard pads at the base of its tongue to push food up against the roof of its mouth and grinds its meal into a paste before swallowing.
Until other mammals, monotremes lay one to three eggs relatively small leathery eggs. The echidna places its eggs in a backward-facing pouch and incubates them for a week to two weeks. The platypus, which does not have a pouch, incubates its eggs by placing them in a shallow depression on its belly and holding them in place with its tail until they hatch in about ten days. The babies lick milk that seeps out of pores in their mother's abdomen.
Monotreme Threats & Predators What Treats Do Monotremes Face?
The only native predators of adult monotremes are the Tasmanian devil and dingo. Baby echidnas sometimes fall victim to goannas — native monitor lizards that tear open their nursery burrow and capture spineless little puggles. Snakes too venture into nursery burrows and attack the young puggles. Platypuses fall prey to dingoes, large birds of prey and crocodiles.
Aborigines have been hunting 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 larger impact due to land clearing and forest felling. Monotremes, however, are very versatile and adaptable animals and don't seem to have been seriously affected by these activities either.
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.
Australian bushfires are the largest single threat to an echidna. The echidna is too slow to run away. So instead of fleeing, it stays put and adapts a rather bizarre survival tactic. The drying out of waterways can seriously affect the viability of platypuses.
25 Monotreme Facts
- Monotremes are mammals that lay eggs.
- But they feed their babies milk like mammals.
- They are called monotremes because they have only one rear opening for peeing, pooping and reproduction.
- There are only two types of monotremes; echidnas and platypuses.
- The echidna lives in Australia and New Guinea.
- The platypus only lives in Australia.
- Monotremes have a reptilian gait with their legs splayed out from their sides.
- Other mammals have their legs under their bodies.
- Monotremes have bird-like skulls.
- Males have a spur on their ankles.
- Adult monotremes don’t have teeth.
- They use electro-location, which works like a radar, to find their prey.
- They are carnivorous mammals.
- They search for food in the mornings and evenings.
- Monotremes have a metabolic rate 25-30% lower than other mammals.
- They are warm-blooded but can only control their body temperature in a narrow range of outside temperatures.
- The male penis of a monotreme has four heads.
- They have more in common with marsupials.
- Monotremes lay eggs, hatch them and then feed their babies milk.
- But they don't have nipples.
- Instead, milk oozes from the mother's abdomen, and the babies lick it up.
- Monotremes are relatively common and not considered threatened.
- Monotremes once dominated the Australian landmass.
- That was until marsupials arrived 71—54 million years ago.
- They live for about ten years.
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 managed to survive 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.
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