lepidosauromorphs

Lepidosauromorpha is a major clade of diapsid reptiles that includes the living lepidosaurs—lizards, snakes, and the tuatara’s group Rhynchocephalia—and their fossil relatives. It is one of the two primary lineages of Diapsida, the other being Archosauromorpha, which includes crocodilians, birds, and their extinct relatives.

In modern usage, Lepidosauromorpha encompasses the crown group Lepidosauria and a spectrum of stem lepidosauromorphs that extend back into the Paleozoic era. The two living lineages within Lepidosauria are Rhynchocephalia (tuataras and their relatives) and Squamata (lizards and snakes).

The fossil record for lepidosauromorphs stretches from the Paleozoic onward, with transitional forms that illuminate early lepidosaur evolution. Early members occupied a variety of ecological niches and laid the groundwork for the distinctive body plans, scales, and life histories seen in later lepidosaurs.

Phylogenetically, lepidosauromorphs are important for understanding diapsid evolution because they help define the divergence of lepidosaurs from their extinct relatives and clarify relationships within Rhynchocephalia and Squamata. Some fossil groups once placed with lepidosaurs have been reinterpreted, reflecting ongoing debates and revisions in diapsid phylogeny.

Today, lepidosaurs are widespread and diverse, with more than 7,000 described species of lizards and snakes, plus the sole living rhynchocephalian, the tuatara, which is restricted to New Zealand. The clade exhibits a broad range of sizes, ecologies, and life histories, from burrowers to arboreal and aquatic forms.