Class: Reptilia
Order: Squamata
Clade: Ophidia
Suborder: Serpentes

Snakes are elongated, legless, carnivorous reptiles of the suborder Serpentes. Like all squamates, snakes are ectotherms, amniote vertebrates covered in overlapping scales. 

A carpet python snake (Morelia spilota)  at the ACT National Zoo & Aquarium. image: R.Conan-Davies

Bones of snakes

Many species of snakes have skulls with several more joints than their lizard ancestors, enabling them to swallow prey much larger than their heads with their highly mobile jaws.


Drawing of a snake skeleton, The Royal Natural History, 1896

Internal structure of snakes

 To accommodate their narrow bodies, snakes' paired organs (such as kidneys) appear one in front of the other instead of side by side, and most have only one functional lung. Some species retain a pelvic girdle with a pair of vestigial claws on either side of the cloaca. 

Approximate Anatomy of a snake

1. esophagus 2. trachea 3. tracheal lungs 4. rudimentary left lung 5. right lung 6. heart 7. liver 8. stomach 9. air sac 10. gallbladder 11. pancreas 12.spleen 13. intestine 14. testicles 15. kidneys

Compared with legless lizards

Lizards have evolved elongate bodies without limbs or with greatly reduced limbs about twenty five times independently via convergent evolution, leading to many lineages of legless lizards. 

Legless lizards resemble snakes, but several common groups of legless lizards have eyelids and external ears, which snakes lack, although this rule is not universal (see Amphisbaenia, Dibamidae, and Pygopodidae).

Where are snakes found?

Living snakes are found on every continent except Antarctica, and on most smaller land masses; exceptions include some large islands, such as Ireland, Iceland, Greenland, the Hawaiian archipelago, and the islands of New Zealand, and many small islands of the Atlantic and central Pacific oceans.  Additionally, sea snakes are widespread throughout the Indian and Pacific Oceans. 

Types and numbers of species of snakes

More than 20 families are currently recognized, comprising about 520 genera and about 3,600 species. 

The sizes of snakes vary, ancient snakes were even bigger 

 They range in size from the tiny, 10.4 cm -long thread snake to the reticulated python of 6.95 meters in length. The fossil species Titanoboa cerrejonensis was 12.8 meters long. 


An adult Barbados threadsnake, Leptotyphlops carlae. image: Blair Hedges, Penn State/wikipedia

How and when snakes evolved

Snakes are thought to have evolved from either burrowing or aquatic lizards, perhaps during the Jurassic period, with the earliest known fossils dating to between 143 and 167 Ma ago. The diversity of modern snakes appeared during the Paleocene period (c 66 to 56 Ma ago). The oldest preserved descriptions of snakes can be found in the Brooklyn Papyrus.

How venomous are snakes, how else do they kill?

Most species are nonvenomous and those that have venom use it primarily to kill and subdue prey rather than for self-defense. Some possess venom potent enough to cause painful injury or death to humans. Nonvenomous snakes either swallow prey alive or kill by constriction.

Source adapted from: Wikipedia contributors. (2018, July 12). Snake. In Wikipedia, The Free Encyclopedia. Retrieved 02:25, July 16, 2018, from