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5 Mammals That Lay Eggs — What Are Monotremes? 

Egg-laying mammals may sound like mythical creatures. Out of over 6,000 mammalians, only five species actually lay eggs instead of giving birth to live young. This post will discuss the unique characteristics of these living mammals that lay eggs and how they compare to other animals.

Get ready to learn about some fascinating egg-laying mammals!

Monotremes: Mammals That Lay Eggs

The egg-laying mammals are called monotremes. Under this mammalian order are five creatures — platypus and four species of echidna. The other two types of mammals are marsupials and placentals. The former further develops their young in their pouches, while the latter have independent newborns.

1. Duck-Billed Platypus (Ornithorhynchus anatinus)

duck billed platypus
Photo: iStock

The first monotreme is the Duck-Billed Platypus, which is interestingly the only species for its genus, just like lions and humans. This fascinating creature boasts an intriguing mix of characteristics, like its distinctive duck bill and webbed feet, beaver tail, and body of an otter.

Unlike placental mammals, the platypus does not give birth to live young; they lay eggs. The female lays one to three leathery eggs in a shallow nest before incubating them for about two weeks until they hatch.

Once hatched, the newborn platypuses stay with their mother for several months while she feeds them until they are ready to hunt independently. Aside from laying eggs, the monotreme has more unique adaptations that can impress us. First, platypuses have electroreceptors that allow them to locate food underwater. Second, these monotremes are one of the few venomous mammals1. Such fascinating creatures!

Related Read: Platypus Facts

2. Western Long-Beaked Echidna (Zaglossus bruijni)

western long beaked echidna
Photo by Gunnar Creutz on Wikimedia Commons licensed under CC BY-SA 4.0 (Cropped from Original)

The Western Long-Beaked Echidna is another mammal that lays eggs living in the Indonesian province of Papua. This remarkable creature has strong back legs with sharp claws for digging burrows and finding food on land or water. Along with its short, pointy snout full of sharp teeth, the Western Long-Beaked Echidna resembles a reptile with its reptilian-like gait but is definitely not one!

When fully grown, an adult Western Long-Beaked Echidna measures up to 23 in (60 cm) long from head to rump. These nocturnal creatures feed mainly on worms and small invertebrates in stony soils. It plays a crucial role in nature by maintaining balance within its ecosystem. Notably, it is referred to as an ecosystem engineer.

Its diet assists in tendering these ecosystems. After its egg-hatching season, care for its babies becomes paramount. This typically happens yearly, generally between late winter and early spring.

Interestingly, the female Western Long-Beaked Echidna can produce milk from its mammary glands. This nurtures its offspring once the eggs hatch. The hatching coincides with the time when temperatures start warming up.

Related Read: Echidna  Facts

3. Eastern Long-Beaked Echidna (Zaglossus bartoni)

eastern long beaked echidna
Photo by Matteo De Stefano/MUSE on Wikimedia Commons licensed under CC BY-SA 3.0 (Cropped from Original)

The next echidna species is the Eastern Long-Beaked Echidna, found in eastern Australia and New Guinea. This small mammal has a tall conical snout up to 6 in (15 cm) long.

Although it looks like a spiny anteater, the Eastern Long-Beaked Echidna feeds mainly on earthworms, larvae, spiders, and small aquatic animals. During the summer breeding season, female Western Long-Beaked Echidnas lay a single egg at a time. This egg is not incubated within the body as in many animals. Instead, it rests in a shallow nest with leaves or grass blades, nestled within the mother's fur. After about ten days, the egg hatches into a tiny, developing echidna, fondly known as a 'puggle.'

The newborn puggle lives in its mother's pouch until it matures into an adult around seven months later. These species have spines covering their backs. Like porcupines, these serve as their main line of defense against predators. They can also curl up on the ground to further their protection when attacked. Moreover, camouflaged against rocks and logs, they seamlessly blend with their environment.

Related Read: Anteater Facts

4. Short-Beaked Echidna (Tachyglossus aculeatus)

Photo by Enguerrand Blanchy on Unsplash

The Short Beaked Echidna is another echidna species found in both mainland Australia and New Guinea. Physically, Short-Beaked Echidnas have short spines covering their body with long hind legs for digging and powerful claws perfect for burrowing through the dirt.

Diet-wise, the Short-Beaked Echidnas are carnivores who feed on small invertebrates like worms, centipedes, termites, and larvae which they find by digging using their long snouts and sticky tongues.

Because their ears and nostrils are not external, the Short-Beaked Echidna can dive underwater better than most mammals.

5. Sir David's Long-Beaked Echidna (Zaglossus attenboroughi)

Sir David's Long-Beaked Echidna is a unique species of egg-laying mammal native to New Guinea. It has a long snout like its other echidna relatives and can measure up to 28 inches in length due to its spiny coat.

Sir David’s Echidnas have large, sharp claws, which they use for digging for earthworms, termites, and other tiny invertebrates. They move around in a reptile-like gait, using their strong but short limbs.

The females lay one to three eggs at once into the mother’s fur pouch before burying them under hillsides or logs. Once laid, the female echidna guards the egg during the incubation period. About ten days pass before the egg hatches. The mother then nurtures her young, preparing it for independence. Roughly at six months, the offspring is ready to venture independently.

Reproduction and Raising Young When Mammals Lay Eggs

During mating season, male echidnas form trains and follow the females. When the female echidna is ready to mate, she chooses the biggest and most aggressive male in her train of suitors. 

Laying eggs

nesting mammal that lay eggs
Photo by Steve Franklin on Unsplash

These eggs are first placed inside a pouch. This protective pouch forms from skin folds. They usually incubate for ten days. After hatching, the furless hatchlings resemble reptiles more than any other mammals.

The female Western Long Beaked Echinida, Platypuses, and other monotremes keep these eggs within their body until ready to hatch after incubation. 

Incubation

Incubation is essential for the growth and development of eggs laid by egg-laying mammals. These animals have developed unique methods to protect their developing embryos to ensure adequate temperature regulation.

Duck-billed platypuses, for example, wrap themselves around their eggs to provide warmth. At the same time, they are submerged in water or sprawled out on land. Similarly, when incubating, echidnas build burrows during the breeding season and curve their bodies around the eggs.

Incubation times can vary greatly, influenced by species and environmental factors like temperature. A Platypus, for instance, takes around six to ten days. An Eastern Long-Beaked Echidna typically takes up to ten days.

Hatching

baby echidna puggle
Photo by Ian R McCann on Museums Victoria licensed under CC BY 4.0 (Cropped from Original)

Hatching marks the beginning of a new life for egg-laying mammals. During the incubation period (one to two weeks long, depending on the species), neural pathways and other organs form inside an egg that will develop into a baby mammal upon hatching.

Monotremes often use body heat from their mothers or environment to aid the development of their young before hatching. After the process completes, monotreme embryos hatch on their own. They exit their protective eggs with minimal adult assistance. Some species do provide post-hatching care. This includes protection and warmth until the newborns develop further.

Feeding

Egg-laying mammals have some unique adaptations when it comes to feeding that makes them quite fascinating. Firstly, the duck-billed platypuses are equipped with special electroreceptors to detect minute electric fields generated by their prey.

These specialized receptors help them identify and capture small aquatic animals like shrimp and amphipods in murky water since they are usually hidden beneath the surface from sight.

Echidnas, known as spiny anteaters, feed on ants and other tiny invertebrates on land using their strong claws and sticky tongues. They can be active both during day and night time, depending on species or seasonality pattern.

Maternal care

Mammals that lay eggs, or Monotremes, exhibit maternal care behaviors to ensure their offspring's successful growth and development. The Female western long-beaked Echidna will form a nest where she can incubate her egg before hatching to protect her precious young from harm and predators.

Duck-billed Platypuses are also known to construct nesting burrows near bodies of water where eggs can hatch safely with minimal disturbance. Females will then return to the nest after the mating season, during which she will produce milk from their mammary glands to feed their baby echidnas.

During this period, mother Echidna possessively guards her baby against intruders and pushes away those who get too close using her back legs and claws on their front limbs.

The egg-laying mammals are an amazingly unique group of animals and a key part of the mammalian evolutionary story. These creatures have an extraordinary array of adaptations for surviving in their environment, from producing milk to laying eggs; these species still exist today as living fossils that bridge the gap between reptiles and other mammals.

Evolutionary Significance of Monotremes

swimming mammal that lays eggs
Photo by Julien Renoult on iNaturalist licensed under CC BY 4.0 (Cropped from Original)

Monotremes have played a significant role in shaping our understanding of mammalian evolution, giving us an insight into the first stages of its development. Their egg-laying abilities provide intriguing evidence about mammalian reproduction during prehistoric times2.

Fossil evidence shows us that early monotremes were small animals that mainly ate insects. They passed down some of their distinct traits to their present-day relatives. They include laying leathery eggs having a single opening, or cloaca, for both waste and reproduction. Fossil records also show that they used electroreception to find their prey.

Conclusion: Mammals That Lay Eggs

With five extant species of monotremes from Australia to New Guinea, ensuring their conservation through proper research and protection efforts is crucial. These critters give us clues about our history and remind us how fragile yet complex life on Earth really is.

1

Torres, A. M., Menz, I., Alewood, P. F., Bansal, P., Lahnstein, J., Gallagher, C. H., & Kuchel, P. W. (2002). D-amino acid residue in the C-type natriuretic peptide from the venom of the mammal, Ornithorhynchus anatinus, the Australian platypus. FEBS letters, 524(1-3), 172-176.

2

Musser, A. M. (2013). Review of the monotreme fossil record and comparison of palaeontological and molecular data. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 136(4), 927-942.

By Jennifer Okafor, BSc.

Jen’s a passionate environmentalist and sustainability expert. With a science degree from Babcock University Jen loves applying her research skills to craft editorial that connects with our global changemaker and readership audiences centered around topics including zero waste, sustainability, climate change, and biodiversity.

Elsewhere Jen’s interests include the role that future technology and data have in helping us solve some of the planet’s biggest challenges.

Photo by Cowirrie on iNaturalist CC0 1.0 (Public Domain)
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