Welcome to our Mammal Encyclopedia Page

Gazell in a grass field

Major Categories of Mammals

Monotremes are egg-laying mammals and represent the most primitive reproductive condition in mammals. This subclass includes only one order:

Platypus swimming

Order Monotremata

This order includes species like the echidnas and the duck-billed platypus.

Subclass Theria (Live-bearing Mammals)

Theria is divided into two infraclasses based on their reproductive strategies: Metatheria and Eutheria.

Marsupials give birth to highly altricial young after a short gestation period. They are characterized by their unique reproductive system where the young are typically carried and nursed in a pouch.

Placental mammals have a longer gestation period, allowing the young to develop more fully before birth. This is the largest subclass of mammals, comprising 19 orders.

Tasmanian devil with an open mouth

Order Dasyuromorphia

Includes the Tasmanian devil and quolls.

Opossum in a tree

Order Didelphimorphia

Includes opossums.

Kangaroo and Joey

Order Diprotodontia

Includes kangaroos, koalas, and wombats.

Rodent on a branch

Order Microbiotheria

Includes the monito del monte.

blind Marsupial Mole

Order Notoryctemorphia

Includes marsupial moles.




Little shrew opossum

Order Paucituberculata

Includes shrew opossums.




Bandicoot in a field

Order Peramelemorphia

Includes bandicoots and bilbies.



Sketch of extinct Coheni

Order Yalkaparidontia

This is an extinct order known only from fossils found in Australia. It is represented by a single species, Yalkaparidon coheni, which lived during the Miocene epoch.

Blind golden mole

Order Afrosoricida

(Golden Moles and Tenrecs):

Small insectivorous mammals.

Giraffe and baby

Order Artiodactyla

(Even-Toed Hoofed Mammals):
Includes pigs, deer, and giraffes.

Bear in a cave

Order Carnivora

(Carnivores):
This order includes animals like lions, bears, and domestic dogs and cats.

Dolphin swimming

Order Cetacea

(Whales, Dolphins, and Porpoises):
Aquatic mammals adapted to life in water.

Bat in a tree

Order Chiroptera

(Bats):
Bats are the only mammals capable of sustained flight.

Close up of an armadillo

Order Cingulata

(Armadillos):
Placental mammals with a leathery armor shell.

Colugos at night

Order Dermoptera

(Colugos): Also known as flying lemurs, these are gliding mammals found in Southeast Asia.

Hedgehog closeup

Order Eulipotyphla

(Hedgehogs, Solenodons, and Shrews):
Small, primarily insectivorous mammals.

A rock hyrax on a path

Order Hyracoidea


Small, thickset, herbivorous mammals.

Little pika

Order Lagomorpha

(Pikas and Rabbits):
Includes rabbits, hares, and pikas.

Elephant Shrews

Order Macroscelidea

(Elephant Shrews):

Small insectivorous mammals native to Africa.

A Rino in a field

Order Perissodactyla

(Odd-Toed Hoofed Mammals):
Includes horses, rhinos, and tapirs.

Armored pangolin

Order Pholidota

(Pangolins):

Mammals known for their protective keratin scales.

Anteater in grass

Order Pilosa

(Sloths and Anteaters):

Neotropical mammals with long snouts.

Orangutan in a tree

Order Primates

(Primates):
Includes humans, apes, monkeys, and lemurs.

elephant in Africa

Order Proboscidea

(Elephants):

Large mammals with trunks.

Squirrel on the ground

Order Rodentia

(Rodents):
The largest order of mammals, including mice, rats, and squirrels

Tree shrew on the ground

Order Scandentia

(Tree Shrews):

Small, arboreal mammals found in Southeast Asia.

Dugong swimming

Order Sirenia

(Dugongs and Manatees):

Aquatic, herbivorous mammals.

Walking aardvark

Order Tubulidentata

(Aardvark):

A single species known for its unique teeth structure.

Classification of Mammals

Key characteristics of Mammals:

  1. Hair or fur: All mammals have at least some hair during their life.
  2. Warm-blooded: Mammals can keep their body temperature steady, no matter how hot or cold it is outside.
  3. Live birth: Most mammals give birth to live young (except for monotremes like platypus, which lay eggs).
  4. Milk production: Female mammals make milk to feed their babies.
  5. Four-chambered heart: This helps pump blood efficiently through their bodies.
  6. Lungs for breathing: All mammals breathe air using lungs.
  7. Large brain: Mammals generally have larger brains compared to their body size than other animals.
  8. Specialized teeth: Most mammals have different types of teeth for different jobs (cutting, grinding, etc.).
  9. Middle ear bones: Mammals have three tiny bones in their ears that help them hear well.
  10. Lower jaw made of one bone: Unlike reptiles, the mammal’s lower jaw is one single bone.
  11. Sweat glands: Many mammals have these to help cool their bodies.
  12. Neocortex in the brain: This part of the brain helps with higher-order thinking.
  13. Diaphragm: A muscle that helps mammals breathe.
  14. Endothermic: Mammals can produce their own body heat.
  15. Care for young: Mammals often take care of their babies for a long time after birth.

These features have helped mammals live in many different places all over the world. From the hottest deserts to the coldest arctic areas, from deep in the oceans to high in the trees, mammals have found ways to survive and thrive. Their ability to keep warm, care for their young, and adapt to different foods and habitats has made them very successful. Mammals play important roles in nature, both as animals that hunt and as food for other animals. They’ve also developed complex behaviors and social systems, making them some of the most interesting animals to study.

Conclusion

Mammals are a highly diverse class of animals with complex classification systems. By understanding the major categories and orders within the class Mammalia, we can better appreciate the diversity and evolutionary history of these fascinating creatures. This classification helps in organizing an animal encyclopedia by grouping similar kinds together, making it easier to study and understand the vast array of mammalian species.


  1. Wilson, D. E., & Reeder, D. M. (2005). Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Johns Hopkins University Press. 2,142 pages.
  2. Hilton-Taylor, C. (2000). 2000 IUCN Red List of Threatened Species. No preview available.
  3. McKenna, M. C., & Bell, S. K. (1997). Classification of Mammals: Above the Species Level. Columbia University Press.

Articles and Papers

  1. Reeder, D. M., Helgen, K. M., & Wilson, D. E. (2007). Global Trends and Biases in New Mammal Species Discoveries. Occasional Papers, Museum of Texas Tech University, 269:1-36.

Online Resources

  1. Mammal Species of the World. Bucknell University. http://www.departments.bucknell.edu/biology/resources/msw3/
  2. Library Guides @ VIU: Taxonomy and the Classification, Identification, and Nomenclature of Organisms: Reference Materials. Vancouver Island University. https://library.viu.ca/c.php?g=188912&p=1247823
  3. Vertebrate References. NatureServe. https://help.natureserve.org/biotics/content/record_management/Element_Files/Element_Tracking/ETRACK_Vertebrate_References.htm
  4. Mammalian Classification. University of Texas at El Paso. https://www.utep.edu/leb/classification/mammclassification.htm
  5. Classification of Mammals. Columbia University Press. http://cup.columbia.edu/book/classification-of-mammals/9780231110136
  6. Mammal – Classification, Class Mammalia, Monotremes, Marsupials & Placental Mammals. Britannica. https://www.britannica.com/animal/mammal/Classification
  7. Strauss, B. (2021). The 21 Basic Mammal Groups. ThoughtCo. https://www.thoughtco.com/basic-mammal-groups-4088057