The key difference between Prototheria Metatheria and Eutheria is that Prototheria refers to egg-laying mammals while Metatheria refers to marsupials that give birth to partially developed young ones, and Eutheria refers to placental mammals that give birth to well-developed young ones.
Based on the major variations in reproductive systems, mammals can be categorized into three subclasses: Prototheria, Metatheria and Eutheria. Prototheria includes the most primitive mammals, which are egg-laying mammals, especially monotremes. Metatheria includes marsupials while Eutheria includes true placental mammals. In fact, Eutheria is the largest subclass of mammals.
CONTENTS
1. Overview and Key Difference
2. What is Prototheria
3. What is Metatheria
4. What is Eutheria
5. Similarities Between Prototheria Metatheria and Eutheria
6. Side by Side Comparison – Prototheria vs Metatheria vs Eutheria in Tabular Form
7. Summary
What is Prototheria?
The subclass Prototheria contains egg-laying mammals, which are the most ancestral forms in the class Mammalia. There are only three extant species grouped into two families and a single order, the Monotremata. Also, this order is restricted to Australia and New Guinea. These are terrestrial and aquatic species. Moreover, they are endothermic. Besides, they have an unusually low metabolic rate. They maintain their body temperature lower than most other mammals.
Figure 01: Prototheria
Another interesting character Prototheria shows is the large epipubic bones in the pelvic region. Furthermore, all prototherians are carnivorous.
What is Metatheria?
Metatheria is another subclass of mammals. And, this subclass includes marsupials that give birth to the partially developed young one and possess an abdominal pouch. Female marsupials keep their undeveloped young ones inside the pouch and nourish them till they mature. Therefore, the development of young marsupials takes place inside the pouch. Marsupials lack a true placenta, unlike Eutheria.
Figure 02: Metatheria
Most of the Metatheria species are herbivores. However, there are insectivores and predators. Kangaroos, koalas and opossums are few examples for Metatheria.
What is Eutheria?
Eutheria is the largest subclass of mammals. And, this subclass includes mammals that give birth to anatomically complete young ones. They usually have a longer gestation. In addition, they possess a complete or true placenta in order to nourish developing fetus inside her uterus.
Figure 03: Eutheria
After giving birth, the mother animal feeds her young ones with milk for a few months. Therefore, they have well developed mammary glands and abdominal and thoracic nipples. Primates, cats, dogs, bears, hoofed animals, rodents, bats, seals, dolphins, whales and humans are some examples for Eutheria.
What are the Similarities Between Prototheria Metatheria and Eutheria?
- Prototheria, Metatheria and Eutheria are three subclasses of mammals.
- They belong to Kingdom Animalia, Phylum Chordata and Class Mammalia.
- They all are vertebrate animals.
What is the Difference Between Prototheria Metatheria and Eutheria?
Prototheria is a subclass comprised of egg-laying primitive mammals. Metatheria is another subclass of mammals, especially marsupials that give birth to live but partially developed young ones. Eutheria is the largest subclass of mammals including true placental mammals that give birth to well-developed young ones. So, this is the key difference between Prototheria Metatheria and Eutheria.
Moreover, mammals in Prototheria do not have a true placenta while mammals in Metatheria have a simple placenta and mammals in Eutheria have a true and complex placenta. Furthermore, mammals belonging to Prototheria and Eutheria do not have a pouch while mammals belonging to Metatheria have a pouch to keep their young ones and nourish. Therefore, this is another difference between Prototheria Metatheria and Eutheria.
The below infographic summarizes the difference between Prototheria Metatheria and Eutheria.
Summary – Prototheria vs Metatheria vs Eutheria
There are three subclasses of class Mammalia. They are Prototheria, Metatheria and Eutheria. Prototheria includes egg-laying mammals. Metatheria includes marsupials that possess a pouch and give birth to partially developed young ones. Eutheria is the largest subclass of mammals that includes placental mammals that give birth to completely developed young ones. Thus, this is the key difference between Prototheria Metatheria and Eutheria.
Reference:
1. Wund, Matthew, et al. “Prototheria (Egg-Laying Mammals).” Animal Diversity Web, Available here.
2. “Placental Mammal.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 27 June 2018, Available here.
3. “List of Marsupials.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 4 Apr. 2016, Available here.
Image Courtesy:
1. “Ameisenigel” (Public Domain) via Commons Wikimedia
2. “1579629” (CC0) via Pxhere
3. “Eutheria (4831089209)” By Yannick Bammert – 20100228-DSC_3857 (CC BY 2.0) via Commons Wikimedia