Monotremes And Marsupials, Do They Lay Eggs?

The types of animals that live in Australia and Australasia are some of the most unique animals on the planet. 

Monotremes And Marsupials, Do They Lay Eggs

There are some sub-groups of animals that only exist in Australia which makes it an even more intriguing place.  Two types of animals that live almost exclusively in Australia are monotremes and marsupials(see also: The Waitoreke Of New Zealand – Marsupial or Monotreme?). 

Both of these sub-groups of animals contain multiple species that you have probably heard of.  In this article, we are going to look at the question of whether monotremes and marsupials lay eggs. 

What Are Monotremes?

First things first, what exactly are monotremes?  Monotremes are some of the most primitive mammals on the planet.  They are found only in Australia and New Guinea. 

This is one of the smallest sub-groups of animals that exists in the world.  Monotremes consist of only Platypi and echidnas. 

These animals are classified as mammals, however, they have many differences from most mammals that you will know about. 

What Are Marsupials?

Marsupials are another sub-group of animals that are mainly found in Australia, they have also been found in New Guinea and America. 

Marsupials are another type of mammal that is slightly different from the mammals that you learn about in elementary school. 

The most distinctive feature that marsupials have to help identify them is their pouch which is used to carry their young until they mature.  

Do Monotremes Lay Eggs?

Monotremes do lay eggs to reproduce.  If the egg is unfertilized, they tend to be large in size and with a sizable yolk. 

It is the yolk in eggs that provide the nutrients that are crucial for the potential embryo to develop into a healthy offspring that is strong enough to survive once it has hatched. 

The size of the yolk that has been found in monotreme eggs suggests that their young are hatched with incredible strength for survival. 

Why Do Monotremes Lay Eggs?

As we mentioned above, monotremes are mammals.  However, most mammals don’t lay eggs, in fact, one of the identifying characteristics of mammals is that their young are born. 

Monotremes are different, they are one of the only types of mammals left that still lay eggs.  

Many scientists believe that the existence of monotremes is the result of their ancestors entering the water millions of years ago, making eggs a necessary process to ensure safe reproduction.  

How Do Monotremes Reproduce?

Monotremes sexually reproduce to fertilize their eggs.  This means that all monotreme offspring have two parents.  Monotremes are solitary animals at all times apart from the mating season.  

For echidnas, the mating season tends to fall between July and August.  During the mating season, a single female will be followed by up to ten males that are trying to mate with her. 

After successful copulation in which fertilization happens, an egg will be laid in two weeks.  The egg will hatch after 10 days.  

For a platypus, the mating season falls between June and October.  It is possible for two or three eggs to be fertilized and developed from successful mating. 

These eggs are developed inside the female for about a month.  When the female is ready to lay her eggs, she will seal herself inside a chamber in her burrow.  

It is in this chamber that the female platypus will lay her eggs.  She will then hold the eggs between her body and her tail to keep them warm.  The eggs will hatch in around ten days. 

When the young hatch, they are very small and unable to survive by themselves.  They will suckle from their mother for three to four months until they are able to swim on their own.  

Do Marsupials Lay Eggs?

Marsupials do not lay eggs.  However, neither do they give birth to their young in the same way as many other types of mammals.  Marsupials such as kangaroos do not have the capacity to lay eggs. 

Monotremes And Marsupials, Do They Lay Eggs (1)

The reproductive process for marsupials is unique from almost any other type of animal on the planet.  

How Do Marsupials Reproduce?

The reproduction process of marsupials is one of the most interesting breeding processes on the planet.  For this explanation, we will focus on the specific reproductive habits of kangaroos. 

Kangaroos are considered to be opportunistic breeders.  They have the ability to breed all year round provided that the environment is suitable for them. 

As you will be aware, Australia is a hot and often dry country.  This means that it is prone to periods of drought that can make it difficult to breed.  

Kangaroos require nutrition and hydration to grow their young during gestation.  This can be difficult to obtain when drought hits or when wildfires begin. 

Thankfully, kangaroos are equipped with an incredibly useful and fascinating skill.  These marsupials are able to pause their pregnancy if the conditions become less than favorable. 

It also means that a pregnancy can be paused if the mother is still nursing her last joey.  

When a pregnancy continues for the full 28 – 34 day gestation period, the joey is born.  At birth, the joey is still in an embryo-like state and is completely unable to survive outside of the mother. 

This is where the pouch comes into play.  The tiny joey, weighing only 1g will crawl from the birth canal to the pouch where it will continue to develop. 

The female kangaroo’s pouch is equipped with everything that the joey needs to develop and survive.  There are multiple nipples to supply food and there are sweat glands that provide antimicrobial molecules to protect the baby. 

Each nipple in the pouch is capable of supplying a different type of milk to support different stages of growth and development. 

This also allows a female kangaroo to simultaneously nurse two joeys at different stages of development.  

Frequently Asked Questions

Are Monotremes The Only Mammal That Lays Eggs?

There are three separate types of Mammalia.  Placental mammals, such as humans, cats, dogs, elephants, etc. are mammals that give birth to young that are developed enough to survive outside of the maternal body. 

While the young will still need care and nutrition from the mother, they are capable of surviving outside of the body. 

Marsupial mammals, such as kangaroos, are mammals that give birth to their young before they are fully developed.  The undeveloped young is safely kept inside a pouch until it has grown big and strong enough to leave. 

The majority of development happens after birth, within the pouch of the mother. 

Finally, monotreme mammals, such as the platypus and echidnas, are mammals that lay eggs(see also: Animals That Lay Eggs).  They are the only type of mammal that lays eggs and there are only two species of monotremes left on the planet.  

Final Thoughts

Monotremes and marsupials are both types of mammals, however, they both reproduce in very different ways. 

Marsupials do not lay eggs, instead, they birth their young after a short gestation period and then continue to develop the young in a pouch that is attached to their body. 

Monotremes are the only mammals that reproduce by laying eggs.  Monotremes are the rarest type of mammals on the planet and the sub-group is only made up of platypi and echidnas.

Olivia Kepner