Pictures of Animals

Thousands of free, original pictures of baby, cute, dangerous, and endangered animals--and so much more!

Because not all of the traits are easy to see, classifying a mammal can sometimes be difficult. Regardless, there are six traits that set mammals apart from other types of animals:

  1. All mammals have hair or fur at some point in their life. Even dolphins are born with a few hairs on their nose that sort of look like whiskers.
  2. Mammals produce milk to feed their young. The word “mammal” came from the glands that produce milk, mammary glands.
  3. Mammals lower jaw is made up of one bone.
  4. All mammals have three little bones in their middle ear (the stirrup, anvil, and hammer)
  5. The mammals heart consists of one primary artery that bends to the left (unlike some animals that have a main artery that curves to the left).
  6. All mammals have a diaphragm as a part of their respiratory system.

There are about 5,500 species of mammals. Most mammals belong to the placental group, which means that they use a placenta during gestation. However, 5 species of mammals lay eggs including the duck billed platypus and the Echidna. Mammals have a very large range of sizes. The smallest mammal is a 1 inch long Bumblebee Bat, and the largest mammal is a 100 ft blue whale! The three largest orders of mammals are the Primates (which humans and apes belong to), Cetartiodactyla (Whales and even-toed hoofed animals), and carnivore (dogs, cats, seals).

Bowhead whales are thought to be the longest living mammal. Some have been estimates to be over 200 years old! Meanwhile, opossums only live to be about a year old.