There are over 1.8 million different species of animals that have been identified by scientists, but only around 70% of them have been given a classification. The largest class of animals is mammals, which includes humans and other creatures like whales, bears, and tigers. Other classes include birds, reptiles (e.g., snakes), amphibians (e.g., frogs), fish (e.g., trout) spiders (such as tarantulas), insects such as ladybugs or ants).
They make up nearly half the total number of classified species in existence today, with more than 454 mammal species found so far.
Mammals are the only class of animals that nourish their young with milk produced by mammary glands. Most mammals also have hair, three middle ear bones, and a neocortex (a portion of the brain), which is believed to be the most evolved part of the brain in humans. The largest mammal on Earth today is the blue whale, which can grow to lengths of 30 meters (nearly 100 feet) and weigh more than 180 metric tons (almost 400,000 pounds).
Other large mammals include the African elephant, polar bear, Indian rhinoceros, and hippopotamus.