What is a Monotreme? Monotremes Explained

Written by Em Casalena
Published: April 13, 2023
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Have you ever heard of monotremes? Maybe not, but you’ve probably heard of the platypus and the echidna. These two animals are considered monotremes. Monotremes are species of mammals that lay eggs, rather than give birth to live young. They are also known for producing milk despite not giving birth to live young. Pretty crazy, right?

In this guide, we’ll break down everything you need to know about these exceptionally unique mammals. We’ll also explore all five of the current living monotremes, their behavior, their habitat, and more. Let’s start with a solid definition of what a monotreme actually is.

What is a Monotreme?

Monotremes are members of the Monotremata suborder of prototherian mammals. Along with placentals and marsupials, they are one of the three subgroups of today’s living mammals. In addition to laying eggs, monotremes differ from other mammals in that they lack teats. Numerous pores on the female’s belly release milk, which is given to the young to lap up from their fur. Five main species make up the unusual order of mammals known as monotremes: the duck-billed platypus, the short-billed echidna, Sir David’s long-beaked echidna, the eastern long-beaked echidna, and the western long-billed echidna. However, there are a number of different subspecies of the echidnas.

Although they have split from all other mammals in evolutionary history by up to 115 million years and hold a special place in the evolution of mammalian brains, monotremes shouldn’t be seen as evolutionary relics or representations of the extinct mammalian brain. The monotreme brain is as far from the ancestral mammal brain as any other contemporary mammal. The neural systems of surviving monotremes show specializations that make them uniquely extraordinary.

In contrast to the more prevalent mammalian orders, monotremes differ structurally in their brains, jaws, digestive tracts, reproductive tracts, and other body components. Additionally, the female monotremes suckle their young with milk, much like all mammals, even though they lay eggs rather than give birth to live offspring.

Although they were also prevalent in South America throughout the Late Cretaceous and Paleocene periods, monotremes are only seen in the wild from Australia and New Guinea today. The platypus and four echidna species are the only monotreme species still living today. Unfortunately, several of these monotreme species are on the endangered species list, with one labelled as critically endangered.

The echidna (pictured) is the most common monotreme alive today, outside of the duck-billed platypus.

The History of Monotremes

Millions of years ago, the earliest animals started to emerge. All of the earliest animals laid eggs. There were two primary branches to this group. Mammals that lay eggs still existed on one branch. The capacity to reproduce and produce young was evolved by the other group, known as Theria.

The descendants of the group that continued to lay eggs are the monotremes. The platypus and four different species of echidna are the only monotremes that are still living today.

Steropodon galmani, a Cenomanian monotreme found in New South Wales, is the first Mesozoic monotreme to have been uncovered. The monotremes separated from the mammalian lineage before marsupials and placental mammals appeared, according to biochemical and anatomical data. One theory is that monotremes originated in Australia in the Late Jurassic or Early Cretaceous since a platypus tooth has been discovered in the Palaeocene of Argentina. Some have even been hypothesized to have crossed Antarctica on their way to South America, which at the time was still connected to Australia. However, a number of genetic studies point to a Triassic origin.

So, to summarize:

  • Monotremes are mammals that lay eggs but also provide milk to their young.
  • There are only five main species of monotremes alive today.
  • They nurse by dispelling milk from their mammary glands for their young to drink from their skin.
  • Today’s living monotremes are only found in the wild in Australia and New Guinea.

Different Types of Monotremes

As mentioned earlier, there are currently only five species of monotremes alive today.

Duck-Billed Platypus

Scientific Name: Ornithorhynchus anatinus

Small and reserved, duck-billed platypuses are fascinating little creatures. To help them float in the water, they can flatten down their head and bodies. Their thick, water-repellent fur keeps them warm and dry even after swimming for a long period of time. Their fur is dark brown on top and tan underneath. The head, body, and tail of the duck-billed platypus all reach a maximum length of around 15 inches. Their incredible snout is their most striking characteristic. Although it resembles a duck’s beak, the platypus’s bill is really quite soft and covered in millions of sensors that aid in the detection of prey.

Platypuses have a lengthy lifespan, living up to 12 years in the wild and at least 20 years in captivity. These amazing species are theorized by some to be the ancestors of all contemporary mammals, though researchers have struggled to find ample evidence of this animal in fossil records. Recent research indicates that they began to develop more than 112 million years ago, long before the dinosaurs became extinct.

The platypus has even more distinct qualities. This species’ males are actually venomous! They can utilize the stinging stingers on the heels of their back feet to deal any opponent a powerful venomous blow.

The majority of this animal’s time is spent alone, usually napping or eating. They are bottom feeders that consume worms, shellfish, and insect larvae. They also collect pebbles and dirt from the bottom of their bill. All of this material is kept in their cheek pouches and crushed when they reach the surface. Because platypuses lack teeth, this gravel helps them chew their food.

There are no sub-species of platypus.

Weirdest Animals: Platypus

The platypus (pictured) is known for its large beak, which is actually a snout made of soft tissue.

©John Carnemolla/Shutterstock.com

Short-Beaked Echidna

Scientific Name: Tachyglossus aculeatus

One of the four echidna species still in existence and the sole representative of the genus Tachyglossus is the short-beaked echidna. It has a peculiar snout and a specialized tongue, and is coated in fur and spines. It employs these features to rapidly grab insects to eat. The short-beaked echidna lays eggs, much like the other living monotremes.

The front limbs and claws of the short-beaked echidna are incredibly strong, enabling it to burrow fast and powerfully. It has a strong tolerance to high amounts of carbon dioxide and low levels of oxygen since it must be able to thrive underground. 

This unusual creature has no weapons or fighting skills, but instead wards off predators by balling up and scaring them off with its spines. Due to its inability to sweat and poor heat tolerance, it prefers to avoid outdoor activities throughout the day while it’s hot outside. If necessary, it can swim. Mechanoreceptors and electroreceptors on the snout enable the echidna to sense its environment. This animal enters a profound state of torpor and hibernation during the Australian winter, slowing its metabolism to conserve energy. 

A baby echidna is about the size of a grape when it is born, but it develops quickly on its mother’s milk since it is so nutrient-rich. Around seven weeks after hatching, baby echidnas are ejected from the pouch into the mother’s burrow because they eventually become too big and spiky to stay in the pouch.

Where are Short-Beaked Echidna Found?

This species can be found in coastal and highland areas of eastern New Guinea, as well as across Australia, where it is the most common native animal. It is not currently in danger of going extinct. However, its range in Australia has been affected by human activities including hunting, habitat degradation, and the introduction of exotic parasites and predatory animals.

There are several sub-species of short-beaked echidna. These include the common short-beaked echidna, the northern short-beaked echidna, the New Guinea short-beaked echidna, the Kangaroo Island short-beaked echidna, and the Tasmanian short-beaked echidna.

The short-beaked echidna (pictured) is found around the coast of New Guinea and Australia, where it feeds on insects.

Sir David’s Long-Beaked Echidna

Scientific Name: Zaglossus attenboroughi

One of the three Zaglossus species that can be found in New Guinea is Sir David’s long-beaked echidna. It is named in honor of renowned naturalist Sir David Attenborough.

The woods of the Cyclops Mountains, which are close to the Indonesian state of Papua cities of Sentani and Jayapura, are home to Sir David’s long-beaked echidnas. These echidnas are not sociable animals and only associate with other members of their own species during the mating season. At night, they are the most active. When threatened by a predator, these animals curl up into a spiky ball, resembling a hedgehog.

Very little is known about this species’ mating habits and reproductive activities. However, it is well known that mating occurs in July. The eggs are laid by females after approximately eight days, and the young remain in the mother’s pouch for around eight weeks, or until the development of their spines is completed.

Being smaller than other Zaglossus species and resembling a short-beaked echidna, Sir David’s long-beaked echidna is the smallest member of the genus. The spurs on its hind legs help to distinguish the male from the female, which tends to be larger than the male. Earthworms, termites, larvae, and ants are the principal food sources for Sir David’s long-beaked echidnas.

Sadly, this species of echidna is classified as severely endangered. Hunting and habitat degradation have historically posed threats to Sir David’s long-beaked echidnas. In fact, until several specimens were discovered in the mountains of New Guinea, this species of monotreme was believed to be extinct. These creatures are so severely threatened that villagers are now being taught about them and encouraged to give up their long-standing practice of hunting and killing them.

There are no know sub-species of this type of echidna.

Eastern Long-Beaked Echidna

Scientific Name: Zaglossus bartoni

Another one of three Zaglossus species to exist in New Guinea is the eastern long-beaked echidna. It is also commonly known as Barton’s long-beaked echidna. It is mostly located in the eastern range of New Guinea at altitudes of 6,600 to 9,800 feet.

Eastern long-beaked echidnas are only native to New Guinea. They live in scrub, highland meadows, and subalpine to tropical hill forests. This species also occupies subterranean burrows or areas of thick vegetation. They live as insectivores, or insect and worm eaters.

White spines and long, thick black to dark brown hair are features of the eastern long-beaked echidna. The whole dorsal surface of their bodies is covered with spines. They also lack teeth, as all monotremes do. At the rear of their mouth is a horny plate that is used to aid in food grinding or chewing. The forefeet of eastern long-beaked echidnas have five claws, whereas the rear feet have four. Even though these echidnas lack a tail, they can roll into a spiny ball to defend themselves.

The eastern long-beaked echidna tends to steer clear of other echidnas and live a solitary life. Researchers find it challenging to examine their behavior since they have such an enigmatic existence. However, we do know that eastern long-beaked echidnas are nocturnal animals. Using their claws to rip through logs, they hunt at night in search of grubs and other invertebrates. These echidnas dig sparsely vegetated underground tunnels that they live in, especially during winter. 

Are Eastern Long-Beaked Echidna Endangered?

Currently, this species is classified as vulnerable. Eastern long-beaked echidna populations are declining mostly due to humans. Locals often hunt them for food. Wild dogs will also occasionally eat eastern long-beaked echidna. Another significant issue contributing to the eastern long-beaked echidnas’ decrease in population is deforestation.

There are several sub-species of this echidna. These include Z. b. bartoni, Z. b. blunius, Z. b. diamondi, and Z. b. smeenki.

New Guinea (pictured) is the only native habitat of the eastern long-beaked echidna.


Western Long-Beaked Echidna

Scientific Name: Zaglossus bruijnii

Three different Zaglossus species can be found in New Guinea, the last of the three being the western long-beaked echidna. The type species of the Zaglossus genus was formerly named Tachyglossus bruijnii. The Bird’s Head Peninsula and the Foja Mountains in the Indonesian provinces of West Papua and Papua are home to western long-beaked echidnas. The southern lowlands and the north coast do not seem to be home to any of this species. These animals favor wet montane forests and alpine meadows as their habitats.

The western long-beaked echidna’s nose is long and curves downward, and it is bigger than the short-beaked species. The lengthy hair and spines of this species resemble its short-beaked cousin almost exactly. The amount of claws on the forefoot and hindfoot helps to identify it from other long-beaked echidna species. Instead of four claws, they only have three.

Western Long-Beaked Echidna Behavior

Western long-beaked echidnas are notoriously elusive and exceedingly reclusive. They tend to live solitary lives away from other echidnas. They normally spend the day sleeping in their burrows and emerge at night to hunt earthworms on the forest floor. The heads of western long-beaked echidnas stay low to the ground as they travel slowly. If a stone or a log is in their way, they would rather climb over it than go around it. Long-beaked echidnas will stoop or hide when they feel threatened in order to expose their spikes to the outside by bending their beak under their bodies. Western long-beaked echidnas are insectivores that mostly eat earthworms for food.

There are no know sub-species of the western long-beaked echidna.

How cool are monotremes? These are arguably the most unique mammals in existence. While some species are facing endangerment and extinction, many humanitarian efforts have been made to boost their populations. We won’t be seeing the end of monotremes anytime soon!

The photo featured at the top of this post is © Wayne Butterworth/Shutterstock.com

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About the Author

Em Casalena is a writer at A-Z Animals where their primary focus is on plants, gardening, and sustainability. Em has been writing and researching about plants for nearly a decade and is a proud Southwest Institute of Healing Arts graduate and certified Urban Farming instructor. Em is a resident of Arizona and enjoys learning about eco-conscious living, thrifting at local shops, and caring for their Siamese cat Vladimir.

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