Here is a comprehensive summary of the Wikipedia article on snakes:

Snakes are limbless, carnivorous reptiles belonging to the suborder Serpentes, distinguished from lizards by their highly flexible skulls (cranial kinesis) that allow them to swallow prey much larger than their heads, and their lack of eyelids and external ears. They are found on every continent except Antarctica, with around 4,170 species ranging from the tiny 10.4 cm Barbados threadsnake to the 6.95 m reticulated python, though the extinct Titanoboa cerrejonensis reached a staggering 12.8 meters in length. Thought to have evolved from burrowing or aquatic lizards during the Jurassic period (with the earliest fossils dating to 143–167 million years ago), their modern diversity exploded after the Cretaceous–Paleogene extinction event roughly 66 million years ago. While most species are non-venomous and subdue prey by constriction, venomous snakes deliver potent toxins—including neurotoxins and hemotoxins—through specialized fangs primarily to paralyze prey, though some can be lethal to humans. The English word "snake" traces back to the Proto-Indo-European root (s)nēg-o- meaning "to crawl," and taxonomically, all modern snakes are grouped within the order Squamata, though their precise evolutionary placement remains a subject of scientific debate.