Many know that mammals (including humans) grow hair, differentiating them from other types in the animal world. External variations in skin type provide a good starting point. However, several other differences separate mammals from reptiles and amphibians. Body temperature, metabolism, hearts and breathing methods also stand as distinctions between the three types. These variations often determine the environments necessary for these animals to survive.
Amphibians begin as larvae (such as tadpoles) and undergo a metamorphic entrance into adulthood (frogs). Mammals give live birth and reptiles generally lay hard-shell eggs upon land. Amphibians lay their gel-like eggs in the water.
Body Temperature and Metabolism
Mammals, classified as warm-blooded, regulate their own body temperature. External temperature determines the body temperatures of reptiles and amphibians, both known as cold-blooded creatures. Warm-blooded animals mostly use food as energy to maintain body temperature rather than for size. Cold-blooded animals' food goes mostly toward their body mass, resulting in a smaller need for food. Changing body temperatures help make cold-blooded creatures less susceptible to viruses, which find it difficult to grow in fluctuation conditions.
Mammals grow hair and fur on their skin. Reptiles feature scales on their skin. Amphibians possess a moist skin, essential to their existence. Should an amphibian's skin dry out, the animal will die.
Mammals and reptiles breathe through lungs throughout their lives. Amphibians breathe through gills in the water as larvae. As adults, amphibians absorb oxygen through their skin.
Amphibians need a moist environment to survive. Both amphibians and reptiles demand warmer climates, as they do not regulate their own body temperatures. Mammals can thrive in cold climates.
Hearts of mammals contain four chambers: two atria and two ventricles. Reptiles and amphibians possess three-chambered hearts, bearing two atria and one ventricle.
The duck-billed platypus, defined as a mammal, lays eggs rather than giving live birth to its young. The crocodile, classified as a reptile, runs on a four-chambered heart. Not all mammals completely maintain their body temperature; bats cool down when inactive, and animals such as bears and gophers, can lose up to 10 degrees C when hibernating.