Some interesting facts about Squamata are they are the only living reptile group that has both viviparous and ovoviviparous species, as well as the usual oviparous (egg-laying) reptiles.
They also does not include the Tuataras from New Zealand and are a sister group to the squamates.
The Crocodilia are much more distantly related.
Squamatas are also known to all possess and have movable quadrate bones which makes it possible for them to move their upper jaw relative to their braincase.
The percentage of known reptiles that are squamates is (96.3%) which is concentrated in squamates (59% lizards, 35% snakes, and 2% amphisbaenians).
Squamates evolved from Rhynchocephalia in the early Triassic.
A squamate traits are flexible jaw structures also known as movable quadrate bones squamates also have shields instead of secondary palates or shells.
Squamata are defined as being an order of reptiles that comprise of snakes, lizards and sometimes even extinct Pythonomorpha.
Some types of squamates do have legs and other squamates have no legs and some squamates have only front legs and some squamates only have back legs and some squamates have 4 legs.
Most squamata use a special organ on the roof of their mouths to smell and they use the organ to smell by first clicking or picking up chemicals on their tongue.
Most squamata also smell with their noses and taste with their tongues along with the organ on the roof of their mouths.
The families that are in order of Squamata include.
Agamidae (Agamas)
Chamaeleonidae (Chameleons)
Iguanidae (Iguanas) - Includes many subfamilies / subspecies, such as anoles and collared lizards.
Gekkonidae (Geckoes)
Pygopodidae (Legless lizards)
Dibamidae (Blind lizards)
Cordylidae (Spinytail lizards)
Scinidae (Skins)
The sister group to squamates is the Rhynchocephalia (the Tuatara and extinct relatives) which share a common ancestor around 250 million years ago at the start of the Mesozoic.
Together, they form the monophyletic Lepidosauria.
Most squamates have a transparent and rigid structure called brille or spectacle over their eyes.
The thing that all squamates have in common are movable quadrate bones that make it possible for the squamates to move their upper jaw relative to their braincase.
The movable quadrate bones are most visible in snakes that are able to open their mouth very wide to accomodate large prey.
The lepidosauria is the ancestor of Squamata.
The Lepidosauria is a subclass or superorder of reptiles that contains the orders Squamata and Rhynchocephalia.
Squamatas includes snakes, lizards, and amphisbaenians. Squamata contains over 9,000 species, making it by far the most species-rich and diverse order of non-avian reptiles in the present day.
Iguanians were long thought to be the earliest crown group squamates based on morphological data, although genetic data suggest that geckoes are the earliest crown group squamates.
Iguanians are now united with snakes and anguimorphs in a clade called Toxicofera.
The earliest unambiguously identified squamate fossils date from the Middle and Late Jurassic (174–145 Ma), and among them are forms that can be assigned to major modern clades of squamates, including both lizards and snakes (Evans, 1998; Evans, 2003; Caldwell et al., 2015), but many are isolated jaws and skull bones
Squamata is the largest order of reptiles, comprising lizards, snakes, and amphisbaenians, which are collectively known as squamates or scaled reptiles. With over 10,900 species, it is also the second-largest order of extant vertebrates, after the perciform fish.
Class Reptilia includes many diverse species that are classified into four living clades.
Reptilia includes four living clades: Crocodilia (crocodiles and alligators), Sphenodontia (tuataras), Squamata (lizards and snakes), and Testudines (turtles).
There are more than 8,200 living species of reptiles, and they are placed in four orders: Crocodilia, which includes crocodiles and alligators; Sphenodontia, or tuataras; Squamata, which includes lizards and snakes; and Testudines, such as turtles and tortoises.
Gekkota (geckos and pygopods) constitute a diverse and early diverging clade of squamates, but their highly fragmentary fossil record allows only limited insights into their evolutionary history.