Are Snakes Mammals?

Snakes are reptiles. They are not mammals. Mammals have hair or fur, while snakes are covered with overlapping scales. Mammals are warm-blooded, which means their bodies regulate their own heat. Snakes are cold-blooded, which means the heat of their bodies is regulated by their environment. But the thing that really separates mammals from snakes is that mammals have mammary glands used to nurse their young while snakes do not nurse their young and lack this anatomical feature.

Snakes also lack limbs that all mammals have, even if a few species have limbs that evolved into flukes and flippers, such as those of sirenians or cetaceans. Though reptiles are older than mammals, snakes are younger than mammals, having evolved from lizards only about 143 to 167 million years ago. Mammals diverged from reptiles over 200 million years ago.

While snakes and mammals have seemingly little in common, they actually share ancestors, both evolving from ancient reptiles. Yes, mammals evolved from reptiles, specifically the reptilian order Therapsida, over 200 million years ago. Therapsids are one of the earliest known reptilian groups and over time evolved from primarily predation to herbivory as well. Their dentition also evolved into heterodontism, teeth separated into categories of molar, incisor, or canine, similar to mammalian dentition. Mammals also retain other traits from their reptilian ancestors, such as an efficient four-chambered heart, an airway that allows them to breathe and eat simultaneously, and hair, correlating to endothermy (warm-bloodedness). The evolution from reptile to mammal was not linear and involved what is known as a “mosaic” pattern of evolution, meaning at any point in time animals existed with characteristics of both reptiles and mammals, hybrids, if you will.

Like mammals, some reptiles experience live birth, having incubated and hatched their eggs internally, and protecting their babies for a short while. The king cobra mother is the only snake known to build a nest. Still, no snake nurses its young. Many mammal babies are also born underdeveloped and helpless, while baby snakes are ready to care for themselves the moment they enter the world. Some snakes, like baby king cobras, are as or more venomous than their parents.

Venom is another thing that separates snakes from mammals, though there are some exceptions. While most of these reptiles do not have venom, there are many that do. Some have venom potent enough to kill a human. However, venomous mammals do exist, including the solenodon and the northern short-tailed shrew. The male platypus, a supremely fascinating mammal in several ways, contains venom in spurs on the backs of the feet. The slow loris of Southeast Asia is believed to be the only venomous primate.