Is a snake simply a long legless lizard? It's not really easy to distinguish snakes and lizards...
Snakes have no external limbs.
Exceptions: Boas and pythons have vestigial hind limbs that show up as tiny spurs (left). Lizards have well-developed front and back limbs.
Exceptions: Of the 17 families of lizards, 6 families include legless members. Most of them are either burrowers or live in grasslands, where legs would just get in the way. A fascinating example is the Cape Legless Skink (Acontias meleagris): a burrowing skink which is not only long and legless but like snakes, also has no external ears!
Snakes have flexible jaws to swallow large prey.
Lizards have jaws that are rather rigid.
Exception: some Monitor Lizards like the Komodo Dragon have flexible jaws.
Snakes do not have external ears or eardrums.
But they have inner ears. Although these are not as well developed, they can sense ground vibrations. For more about how snakes hear. Lizards have external ears openings with visible eardrums.
Exceptions: some burrowing lizards have no visible eardrums too. The Earless Monitor Lizard (Lanthonotus borneensis) of Borneo, as its name implies, has no external ears. A burrower, it also has small limbs. When it swims, it too moves by undulating its body.
Many snakes are venomous.
Exceptions: Many snakes do not produce any venom at all. Some don't even have teeth, e.g., the Egg-eating snake. Most lizards are not venomous.
Exceptions: Beaded lizards and Gila Monsters in the family Helodermatidae are the only venomous lizards. Venom glands feed through ducts into the lower teeth which have grooves in the front. Venom is introduced with the bite, but not injected through hollow fangs as in snakes. These lizards eat eggs and defenceless prey and use their venom for self-defence rather than to hunt prey. Komodo Dragons have a deadly bite, used to kill prey. But they rely on the introduction of bacteria into the wound to do the damage, and Komodos don't produce venom.
Snakes have no movable eyelids. Their eyes are protected by a transparent scale.
Lizards have movable eyelids.
Snakes have short tails and don't drop them off in self-defence. Although snakes appear to be just one long tail, their real tail is the portion of the body without vertebrae.
Lizards have long tails and many can drop them off to distract predators.
The most reliable way to distinguish snakes and lizards is from the structure of bones in the head and internal body features.
Snakes' brains are completely enclosed by skull bones
Lizards' brains are not completely enclosed by skull bones
Snakes do not have urinary bladders
Lizards have urinary bladders
Some other interesting comparisons
Snakes are "younger" than lizards: they appeared about 130 million years ago! Lizards appeared more than 250 million years ago
How did snakes come about? Some studies suggest snakes evolved from burrowing lizards that lost their limbs and re-emerged to live above ground. Some limbless lizards look very much like snakes. These lizards are distinguished from snakes only by their movable eyelids and external ears. Another suggestion is that they arose from the same family of lizards as the monitors (Varanids) which also have a forked tongue.
Whatever the case may be, snakes are now found in a much wider range of habitats than lizards, suggesting that snakes' adaptations are better.
Why are snakes so successful? Snakes are the most streamlined and stripped down of the vertebrates. It just has the bare necessities of a mouth and a belly, a skull and spinal column. The snake lacks limbs, wings, flippers or other appendages that other vertebrates rely on for movement, feeding and life in general.
But as a group, snakes can do nearly everything other vertebrates do: move on all kinds of terrain from slippery mud and shifting sand to dense growths and steep rocky slopes. They can tunnel underground. They can swim, some even living permanently at sea. Among the trees, they can climb and move silently among the branches. Some even glide between trees, while others have prehensile tails like other arboreal vertebrates. Snakes can kill and eat relatively large prey and are fearsomely efficient in this task!
There area about 2,600 known snake species, 2,800 if we count subspecies. Classification of snakes continue to be in dispute. It is usually based on: Scales their arrangement, number, shape, jaw structure and how much they can expand, tooth and fang structure and behaviour
INFRAORDER SCOLECOPHIDIA (Blindsnakes): 300 species. This group of snakes are the most primitive and least diversified. All are well adapted specialised burrowers.
INFRAORDER ALETHINOPHIDIA: 2,400 species or 90% of snakes. Represents the snakes that re-emerged from burrowing and readapted to a wide range of habitats. Main differences from Scolecophidia: jaws can dislocate more extensively, teeth and fangs better developed.
SUPERFAMILY ANILIOIDS: most primitive Alethinophidians. Only slight differentiation between head and body, jaw expansion limited, belly scales only slightly enlarged.
SUPERFAMILY BOOIDS (Pythons and Boas): They, especially Boidae, were the dominant snake species about 65 to 25 million years ago (Tertiary Era) and were huge; 10-15m! Most have since disappeared. Their features include a clear differentiation between head and body, large belly scales, flexible upper jaw.
SUPERFAMILY ACROCHORDOIDS (Filesnakes): Aquatic snakes. Large but streamlined head-flattened and widens to the back-distinct from body. Mobile jaws. Small belly scales. No vestigial pelvis or hind limbs. Scales don’t overlap, the only snakes to have small tubercles with small hairs, function still unknown. Give birth to live young.
SUPERFAMILY COLUBROIDS: The major group of snakes to develop venom, about 40 million years ago.
More about snakes
- What are snakes?
- Are snakes cold?
- Why are snakes long?
- What do snakes eat? Do they drink?
- How do snakes swallow?
- How do snakes hunt?
- Why and how do snakes kill?
Snake predators and how do snakes protect themselves?
Snake mating, eggs and babies
Where are snakes found?
Fascinating snake adaptations to various habitats
Snake bites and first aid
Snakes in danger: role and conservation and snakes in human culture
Snake records: biggest, smallest, deadliest and more
- More snakes
- More animals
- General snake links and references
Further informations in german can be found here!