Difference Between Monotremes and Marsupials

Main Difference – Monotremes vs Marsupials

Mammals are warm-blooded animals with a backbone. They belong to the phylum Chordata. Mammals are characterized by the presence of mammary glands to feed their babies milk from the mother’s body. Mammals can be classified into three types based on the way they develop their babies. They are placentals, monotremes, and marsupials. The babies of placentals are developed inside the mother’s womb. The main difference between monotremes and marsupials is that monotremes lay eggs whereas marsupials give birth to the live young ones that further develop inside a pouch of the mother’s body.

Key Areas Covered

1. Monotremes
– Definition, Facts, Characteristics
2. Marsupials
– Definition, Facts, Characteristics
3. What are the Similarities Between Monotremes and Marsupials
– Outline of Common Features
4. What is the Difference Between Monotremes and Marsupials
– Comparison of Key Differences

Key Terms: Egg, Mammals, Marsupials, Milk, Monotremes, Placenta, Pouch, Undeveloped Young

Monotremes – Definition, Facts, Characteristics

Monotremes refer to a primitive mammal that lays large yolky eggs. Only five type of monotremes can be identified: platypus and four species of Echidna. They consist of a bird-like skull, primitive snouts and beaks. Monotremes have no teeth. They chew food by the bony plate at the roof of the mouth. Monotremes are mainly distributed in Australia, Tasmania, and New Guinea. A short-beak Echidna is shown in figure 1.

Difference Between Monotremes and Marsupials

Figure 1: A Short-Beak Echidna

The body temperature of monotremes is the lowest among mammals. It is 30 °C. The female monotreme lays a single egg directly into a shallow pouch located in her belly. The egg hatches in about ten days. Generally, monotremes do not have any nipples. The milk seeps out of pores located in the female’s abdomen and is lapped up by the baby. Monotremes have long periods of maternal care. They produce one offspring per year.

Marsupials – Definition, Facts, Characteristics

Marsupials refer to mammals that give birth to incompletely developed young who are typically carried in a pouch on the mother’s belly. The group of marsupials consists of approximately 334 species including kangaroos, possums, koalas, and bandicoots. Marsupials have more teeth in their mouth than placental mammals. However, they develop only a single set of teeth during their lifetime. A baby kangaroo inside the mother’s pouch is shown in figure 2.

Figure 2: Kangaroo’s Pouch

Marsupials have both a uterus and a placenta. The placenta is simple and more like a yolk sac. The baby is attached to the placenta for a very short time period. Hence, marsupials give birth to a young that is very small and undeveloped. The young is blind at birth and lacks ears and back legs. However, it has strong and stumpy front legs that help it to crawl to the nipples located in the mother’s pouch. The pouch of the kangaroos opens up at the top while, in bandicoot, it opens on the bottom. The baby remains attached to the mother’s nipples until it develops into a young animal.

Similarities Between Monotremes and Marsupials

Monotremes and marsupials are two types of mammals.
Both monotremes and marsupials are warm-blooded animals.
Both monotremes and marsupials have mammary glands.
Both monotremes and marsupials have different types of pouches.
Both monotremes and marsupials have hair surrounding their body.

Definition

Monotremes: Monotremes refer to a primitive mammal that lays large yolky eggs.

Marsupials: Marsupials refer to mammals that give birth to incompletely developed young, typically carried in a pouch on the mother’s belly.

Number of Species

Monotremes: Only five species of monotremes have been identified so far.

Marsupials: Around 334 species of marsupials have been identified.

Development of Babies

Monotremes: Monotremes lay eggs.

Marsupials: Marsupials give birth to undeveloped young.

Placenta

Monotremes: Monotremes do not have a placenta.

Marsupials: Marsupials have a simple placenta.

Type of Pouches

Monotremes: Monotremes have a pouch to carry the eggs.

Marsupials: Marsupials have a pouch to carry the undeveloped young.

Lactation

Monotremes: Monotremes do not have nipples.

Marsupials: Marsupials have nipples.

Body Temperature

Monotremes: The body temperature of monotremes is 30 °C.

Marsupials: The body temperature of marsupials is 35 °C.

Metabolism

Monotremes: Monotremes have basal metabolic rates 25-30% lower than placentals.

Marsupials: Marsupials have basal metabolic rates 30% lower than placentals.

Teeth

Monotremes: Monotremes do not have teeth.

Marsupials: Marsupials have more teeth than placentals.

External Ears

Monotremes: Monotremes do not have external ears.

Marsupials: Undeveloped marsupials lack external ears.

Conclusion

Monotremes and marsupials are two types of mammals with mammary glands. Monotremes lay eggs, and the eggs hatch into the pouch in the mother’s body. Marsupials give birth to undeveloped young that are developed inside the pouch. The main difference between monotremes and marsupials is the way the offspring are developed.

Reference:

1. “Monotremes.” Introduction to the Monotremata, Available here.
2. “Marsupial.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 3 Jan. 2018, Available here.

Image Courtesy:

1. “Tachyglossus aculeatus side on” By JJ Harrison ([email protected]) – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Baby kangaroo in pouch” By Johnscotaus – Own work (CC BY-SA 4.0) via Commons Wikimedia