Squamata

Squamata is the largest order of reptiles, comprising the majority of lizards and snakes, as well as amphisbaenians. With thousands of described species, it encompasses a wide range of forms—from tiny geckos and skinks to large pythons and monitor lizards. Members occupy nearly every terrestrial habitat and many freshwater environments, from deserts and forests to grasslands and urban areas.

Key features include keratinized scales that shed (ecdysis), a kinetic skull with a highly movable jaw, and, in males, paired hemipenes. Limb reduction or loss has produced serpentine and legless forms. Movable eyelids are common in lizards, while snakes typically have a fixed transparent spectacle over the eye.

Taxonomy: Squamata is traditionally divided into Lacertilia (lizards) and Serpentes (snakes); Amphisbaenia is often treated as a separate lineage within Squamata. Molecular studies recognize major clades such as Iguania (iguanas, chameleons, agamids) and Scleroglossa (geckos, skinks, monitors, snakes and relatives).

Ecology and reproduction: Diet ranges from insects to vertebrates; venom is present mainly in snakes, with some lizard lineages (Helodermatidae) possessing venom. Reproduction is diverse, with both egg-laying and live birth across groups; many lizards guard eggs or young, while some snakes give birth to live young.

Conservation and importance: Many species face habitat loss and collection; some groups are threatened or endangered, highlighting the need for habitat protection and research on their diversity. Squamates play essential roles as predators and prey in many ecosystems.