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Classes of vertebrates

Once an organism is categorised into a phylum, we can further group them into a class. This becomes more specifies, and the animals in a class have more in common than those in a phylum. In this section, we’ll focus on classes in the phylum Chordata, specifically those that are vertebrates. 


  1. What is a class
  2. What are examples of classes in Chordata
  3. What are the characteristics of animals in these classes.  

Class Mammalia

Animals in this class: 

  • are vertebrates, 
  • have hair or fur, 
  • maintain a constant body temperature (endotherms),
  • give birth to live young, and 
  • feed them with their mothers milk. 

We can further break this class into 3 subgroups. The difference between them relates to how their young develop. Click here to learn about how the Platypus confused the scientific community.



There are only five living monotreme species and only in Australia and New Guinea. Monotremes are different from other mammals because they lay eggs and have no teats. The milk is provided for their young by being secreted by many pores on the female’s belly.



Marsupials give birth to their young prematurely. Their young continues to develop while attached to the nipples on the mother's lower belly.



Placental mammals carry their fetus in their uterus where it is nourished via the placenta. They also give birth to their young much later in their development.

While hair might not be the first thing to come to mind when thinking of whales and dolphins, most of them have hair when they are first born. Most whales have their hair follicles where land-mammals would have whiskers today.  To learn more check out this website

Pause & Think

Which subclass of mammals do you think we belong too? Why do you think that?


Class Aves

Animals in this class: 

  • are vertebrates, 
  • are covered in feathers, 
  • have scaly legs,
  • lay hard shelled eggs, and
  • are endotherms. 

Class Reptilia

Animals in this class: 

  • are vertebrates,
  • usually have their body covered in scales, 
  • use their lungs to breath, and
  • are ectotherms (require the environment to help regulate their body temperature).


Look at the image below. Select all the animals that belong to class Aves.

Class Pisces

Animals in this class: 

  • are vertebrates, 
  • use gills to breath,
  • covered in scales, 
  • have fins, and
  • are ectotherms. 

We can further divide fish into 2 categories, those with skeletons made of cartilage (Sharks and rays) and those with more bony skeletons.

Class Amphibia

Animals in this class: 

  • are vertebrates, 
  • use gills to breath in the first part of their life and as they get older they develop lungs,
  • lay eggs without shells, 
  • have soft, slimy skin, and
  • are ectotherms.


  • A class is the next level of grouping after phylum. The organisms here are more closely related then the organisms in a phylum. 

  • Mammalia, Aves, Reptilia, Amphibia and Pisces are all examples of classes in the Chordata phylum. 

  • Each class has a specific set of requirements for the animals to belong to it. 

  • Endotherms are able to regulate their own body temperature.
  • Ectotherms rely on the environment to help regulate their body temperature. 

Test your knowledge

Click the ‘question mark’ to test your knowledge with some questions and activities.


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