Features of Mammals
Mammals are considered as the dominant vertebrates on earth. They exist in diverse forms, size and adaptations. The approximate number of mammals is not known yet. However, more than 4500 living mammals have been discovered and they are grouped in to 21 subclasses including marsupials, primates, cetaceans, bats, elephants, carnivores, ungulates and rodents. Even though they differ in looks, they share some features in common. One of the important features of mammals is the existence of backbone or spinal cord. The back bone makes for the structure of their body and is made of several individual bones. Mammals are warm blooded animals which mean they can maintain a constant body heat. They do not depend on any external source to regulate the temperature. They consume energy from food which helps in their metabolic activities. They develop hair from the follicles on skin that provides warmth and protection in harsh conditions. In the case of aquatic mammals, hair is not found, but they grow hair at some point in their lives.
Mammals are tetrapods which mean they have four limbs. Some mammals are adapted to walk with four or two limbs while others do both. Mammals have one bone on the either sides of their lower jaw which is directly attached to skull. Their middle ear features three bones namely, malleus, incus and stapes. They possess an efficient circulatory system with a four chambered heart. They breathe air and have a pair of lungs. Another defining feature of mammals is the way they reproduce. Female mammals give birth to young ones and feed with milk produced from mammary glands. No other animals possess diaphragm which is an exceptional feature of mammals. Also they hold diphyodonty, replacement of teeth once in a life. All these features make mammals more advanced in the animal Kingdom and they can survive in any landmass on earth.