Fill in the Blanks All about mammals!Online version Let's play! by Naiara Muñoz Pérez 1 Mammals include - blooded animals , and they have a backbone , which makes them . One of their characteristics is that they have hair and a well - developed , more than other types of . The blue is the biggest animal on Earth . They feed on krill , which makes them , and they live in the ocean . They often swim in groups or alone . The African elephant is also considered a . They feed on , so they are herbivores . As well as the blue whale , the Elephant lives in society . The Brown Bear is a , too . They feed on salmon and plants , meaning they are grouped under the type of animals . They live up to 25 . Another characteristic of mammals is that they feed their young with . We , , belong to this group , too .