Q What is a mammal?
— Austin Shiffler, preschool
A Erin Flynn, conservation education curator at Henry Vilas Zoo in Madison, Wis.:
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Mammals such as giraffes, bears, humans and many more are vertebrate animals, meaning they have spines. They’re also warm-blooded, so they produce their own body heat rather than relying on their environment for their body heat. Mammals also make milk for their young and have either fur or hair.
An invertebrate animal, such as an octopus, is not a mammal and has no spine. More specifically, an octopus is a cephalopod, like squid and cuttlefish. They’re some of the smartest invertebrates.
Many people think that giving live birth is also a characteristic of mammals. While giving live birth is a characteristic of most mammals, there are exceptions to the rule.
The egg-laying platypus and the echidna, also known as a spiny anteater of Australia, are very ancestrally old mammals. They lay eggs instead of giving live birth. They’re still considered mammals because they’re warm-blooded, vertebrate animals with fur that make milk for their young.