What Are the Only Two Mammals That Lay Eggs Rather Than Give Live Birth?


Mammals are separated from other animal classes by characteristics such as milk-producing mammary glands, for feeding their young, and live birth. Animals in one small group of mammals, the monotremes, do not give birth to live young. The spiny anteater and the duckbill platypus, the only members of this order, are the only egg-laying mammals.

Duckbill Platypus

  • The duckbill platypus has a body and tail that are relatively flat, like a beaver's. Its mouth is formed into a soft beak, giving the animal its duckbill name. Duckbills are amphibious creatures and capable swimmers. Platypus' sense of smell enables them to forage for food underwater. They are found only in Australia.

Spiny Anteater

  • There are two living species of echidna, the spiny anteater; both of them live in Australia. They have prickly and stiff fur along the back, giving them an appearance similar to hedgehogs or porcupines. The spiny anteater eats ants and termites, like the more familiar giant anteater, to which it is not related. For defense, a spiny anteater rolls itself into a ball and displays sharp prickly spines. Although the spiny anteater is a terrestrial animal, fossil records indicate that this species originally developed from the amphibious platypus.

Survival of Egg-Laying Mammals

  • Egg-laying mammals are living fossils, having survived evolutionary pressures for millions of years. The emergence of marsupials in Australia led to the disappearance of many egg-laying species that are known only through fossil records. However, the duckbill platypus and spiny anteater survived. A theory about the survival of the platypus and the spiny anteater stems from the fact that present-day monotremes are descended from amphibious animals; for defense against more highly developed animals, egg-laying mammals simply headed to the water, out of reach of predatory creatures.

Shared Characteristics

  • The platypus and the spiny anteater both lay eggs. Other common characteristics are the lack of teats for hatched young to suckle milk. Instead, infants lick the region of the mammary glands, where milk is secreted through the mother's skin. Lack of development of front and rear legs inhibits rapid movement to flee from predators. However, well-developed muscles in the forelegs allow platypuses to be extremely efficient swimmers, and spiny anteaters can burrow in world-record fashion.

Relationship to Other Animals

  • The evolutionary record considers monotremes to be the first mammals, exhibiting characteristics similar to both reptiles and mammals. The shape of the appendages and egg-laying are distinctly reptilian traits. Compared to other mammals, monotremes have half the number of genes devoted to olfactory development. Like other mammals, monotremes have fur, mammary glands, sweat-producing glands and the developed region of the brain known as the neocortex -- a particularly mammalian trait. Egg-laying mammals are considered the link between reptiles and the emergence of marsupials.

Related Searches


  • Photo Credit Tom Brakefield/Stockbyte/Getty Images
Promoted By Zergnet



You May Also Like

  • Why Are Dolphins Classified as Mammals?

    Although dolphins swim with the fish, they are classified as mammals, meaning they are vertebrates -- or organisms with a spine --...

  • What is Oviparous?

    Oviparous is a word that literally means "egg bearing" and refers to animals that produce and lay eggs. This should not be...

  • The Life Cycle of Mammals

    Mammals life cycles can vary, especially in some varieties of mammals that may not be so obvious, such as dolphins and platypuses....

  • Milkweed & Milk Thistle

    The words "milkweed" and "milk thistle" are often used interchangeably by those who do not study plants. They are, in fact, two...

  • How to Make Milk

    Mammals make milk to feed their young. Domestic animals bred to produce milk for humans make far more milk than most animals....

  • How to Remove Hair With Ant Egg Oil

    Excessive hair can be an embarrassment. Many products and services claim to remove unwanted hair, however they can be painful and expensive....

  • Reptiles that Give Live Birth

    A reptile is a vertebrate that is covered in scales and breathes air through lungs. Reptiles can be divided into three major...

  • Which Reptiles Do Not Lay Eggs?

    Birthing live young, as opposed to laying eggs, seems to fall almost completely in the domain of mammals. With only two exceptions,...

  • What are the Differences Between Reptiles, Amphibians and Mammals?

    An overview of the differences between reptiles, amphibians and mammals, with separate perspectives of care approach for each.

  • List of Characteristics of Mammals

    There are seven major characteristics that distinguish the 4500 unique species of mammals from other animals. Mammals are air-breathing, warm-blooded and have...

Related Searches

Check It Out

How to Travel For Free With Reward Points

Is DIY in your DNA? Become part of our maker community.
Submit Your Work!