Mammalian Diversity Part 3: Placentals
Professor Dave Explains · 2026-05-13
💡 Quick Take
1. Placental mammals make up about 95% of all extant mammals.
2. Placental mammals are divided into 19 proposed orders.
3. The most widely accepted groups of placental mammals are Afrosoricida, Macroscelidea, Tubulidentata, Hyracoidea, Proboscidea, and Sirenia.
4. Afrotheria is the most diverse order of placental mammals.
5. Order Afrosoricida contains about 55 species, including golden moles, otter shrews, and tenrecs.
6. Order Macroscelidea includes about 20 species of "elephant shrews" that are neither shrews nor elephants.
7. Order Tubulidentata contains a single extant species, the aardvark.
8. Order Hyracoidea contains 5 species of hyraxes native to Africa and Arabia.
9. Order Proboscidea includes 3 extant species of elephants.
10. Order Sirenia includes 4 species of sea cows or sirenians.
11. Xenarthra includes 2 orders of placental mammals: Cingulata and Pilosa.
12. Order Cingulata includes armadillos, while Order Pilosa includes anteaters and tree sloths.
13. Laurasiatheria includes orders Eulipotyphla, Pholidota, Carnivora, Perissodactyla, Artiodactyla, Cetacea, and Chiroptera.
14. Order Eulipotyphla includes true shrews, hedgehogs, and moles.
15. Order Pholidota includes pangolins or scaly anteaters.
16. Order Carnivora includes cats, dogs, bears, and other carnivorous mammals.
17. Order Perissodactyla includes odd-toed ungulates, such as horses and rhinos.
18. Order Artiodactyla includes even-toed ungulates, such as cattle and pigs.
19. Order Cetacea includes whales, dolphins, and porpoises.
20. Order Chiroptera includes bats, which are the second most diverse order of mammals.
21. Euarchontoglires includes orders Dermoptera, Primates, Scandentia, Lagomorpha, and Rodentia.
22. Order Dermoptera includes flying lemurs or colugos.
23. Order Primates includes lemurs, lorises, tarsiers, and great apes.
24. Order Scandentia includes tree shrews or "banxrings".
25. Order Lagomorpha includes hares, rabbits, and pikas.
26. Order Rodentia includes rodents, which are the most diverse of all mammalian orders.
📊 Detailed Explanation
Placental mammals make up about 95% of all extant mammals. This is because they have a more complex placenta that allows for a longer gestation period and more developed young. This has given them a significant advantage over other mammals, such as marsupials and monotremes.
The 19 proposed orders of placental mammals are a result of ongoing research and classification. These orders are based on molecular data and are subject to revision as new information becomes available.
Afrotheria is the most diverse order of placental mammals, with 6 suborders and over 100 species. This order includes a wide range of mammals, from the small golden moles to the large elephants.
Order Afrosoricida contains about 55 species, including golden moles, otter shrews, and tenrecs. These mammals are characterized by their small size, long snouts, and powerful limbs.
Order Macroscelidea includes about 20 species of "elephant shrews" that are neither shrews nor elephants. These mammals are characterized by their long, flexible snouts and elongated limbs.
Order Tubulidentata contains a single extant species, the aardvark. This mammal is characterized by its long snout, unique tongue, and lack of teeth.
Order Hyracoidea contains 5 species of hyraxes native to Africa and Arabia. These mammals are characterized by their small size, thick fur, and short tails.
Order Proboscidea includes 3 extant species of elephants. These mammals are characterized by their large size, trunks, and thick skin.
Order Sirenia includes 4 species of sea cows or sirenians. These mammals are characterized by their fully aquatic lifestyle, fusiform bodies, and heavy bones.
Xenarthra includes 2 orders of placental mammals: Cingulata and Pilosa. Order Cingulata includes armadillos, while Order Pilosa includes anteaters and tree sloths.
Laurasiatheria includes orders Eulipotyphla, Pholidota, Carnivora, Perissodactyla, Artiodactyla, Cetacea, and Chiroptera. These orders are characterized by their diverse range of mammals, from the small shrews to the large whales.
Order Eulipotyphla includes true shrews, hedgehogs, and moles. These mammals are characterized by their small size, long snouts, and powerful limbs.
Order Pholidota includes pangolins or scaly anteaters. These mammals are characterized by their large, protective keratinized scales and long tails.
Order Carnivora includes cats, dogs, bears, and other carnivorous mammals. These mammals are characterized by their diverse range of adaptations, from the large size of the bears to the small size of the cats.
Order Perissodactyla includes odd-toed ungulates, such as horses and rhinos. These mammals are characterized by their single-toed hooves and diverse range of adaptations.
Order Artiodactyla includes even-toed ungulates, such as cattle and pigs. These mammals are characterized by their two-toed hooves and diverse range of adaptations.
Order Cetacea includes whales, dolphins, and porpoises. These mammals are characterized by their fully aquatic lifestyle, streamlined body shape, and large size.
Order Chiroptera includes bats, which are the second most diverse order of mammals. These mammals are characterized by their unique forelimbs adapted to flight and diverse range of adaptations.
Euarchontoglires includes orders Dermoptera, Primates, Scandentia, Lagomorpha, and Rodentia. These orders are characterized by their diverse range of mammals, from the small flying lemurs to the large great apes.
Order Dermoptera includes flying lemurs or colugos. These mammals are characterized by their nocturnal tree-dwelling lifestyle and ability to glide for great distances.
Order Primates includes lemurs, lorises, tarsiers, and great apes. These mammals are characterized by their diverse range of adaptations, from the small size of the lemurs to the large size of the great apes.
Order Scandentia includes tree shrews or "banxrings". These mammals are characterized by their small size, long snouts, and powerful limbs.
Order Lagomorpha includes hares, rabbits, and pikas. These mammals are characterized by their diverse range of adaptations, from the large size of the hares to the small size of the pikas.
Order Rodentia includes rodents, which are the most diverse of all mammalian orders. These mammals are characterized by their single pair of continuously growing incisors and diverse range of adaptations.
🎯 Expert Opinion
As an expert in the field of mammalogy, I can say that the diversity of placental mammals is truly remarkable. From the small golden moles to the large elephants, these mammals have evolved a wide range of adaptations to survive and thrive in their environments.
One of the most interesting aspects of placental mammals is their ability to adapt to different environments. For example, the elephants have adapted to live in a variety of habitats, from the savannas of Africa to the forests of Asia. Similarly, the bats have adapted to live in a wide range of environments, from the deserts of North America to the rainforests of South America.
Another interesting aspect of placental mammals is their social behavior. Many of these mammals are highly social, living in complex societies with hierarchies and communication systems. For example, the elephants are known for their complex social behavior, with matriarchal herds and strong family bonds.
As we look to the future, it is likely that placental mammals will continue to evolve and adapt to their environments. With the ongoing threat of climate change and habitat destruction, it is more important than ever that we work to conserve and protect these amazing animals.
One area of research that I believe is particularly promising is the study of placental mammal evolution. By studying the fossil record and molecular data, we can gain a better understanding of how these mammals have evolved over time and how they have adapted to different environments.
Another area of research that I believe is particularly important is the study of placental mammal conservation. With many of these mammals facing threats such as habitat destruction, climate change, and human persecution, it is more important than ever that we work to protect and conserve these amazing animals.
Overall, the diversity of placental mammals is truly remarkable, and I believe that continued research and conservation efforts are essential to protecting these amazing animals for future generations.
Kanal: Professor Dave Explains