They are one of the most diverse extant groups of Eureptilia and are sister to Archosauromorphs.
Lepidosauria includes Sphenodontida (tuatara), Sauria (lizards), and Serpentes (snakes) which all share these synapomorphies:
- A transverse cloaca opening
- Notches on their tongues "lingual prehension"
- Full-body ecdysis, the ability to shed all their skin
- Imperforate columella or "stapes" in their ears
- Jaws with teeth attached directly
- Adults with fused pelvic bones
- Caudal vertebrae with fracture planes or "septa"
The top synapomorphies of this group are: fused maxillae; fused parietals; reduced nasals; missing vomerine teeth; special ulna-ulnare, radius-radiale, and ankle joints; developed hemipenes; saccular ovaries; separate Jacobson's organ from the nasal capsule; a lacrimal duct joined to the vomeralnasal duct; egg tooth hatching; and femoral and pre-anal glands.
The right portion of the illustration below shows the skeletal anatomy of a varanid lizard:
Lepidosauria Skull Anatomy: (a) left lateral, (b) dorsal, (c) occipital and (d) palatal views, based mainly on NHMG 8502 and NHMG 9317. Scale bars, 10 mm. A, angular; Ar, articular; Bo, basioccipital; D, dentary; Ec, ectopterygoid; Fr, frontal; J, jugal; L, lacrimal; Mx, maxilla; N, nasal; Ot, oto-occipital; P, parietal; Pa, palatine; Pm, premaxilla; Pfr, postfrontal; Po, postorbital; Prf, prefrontal; Pt, pterygoid; pt.f, pterygoid flange; Q, quadrate; So, supraoccipital; Sp, Splenial; Sq, squamosal; St, supratemporal; Su, surangular; V, vomer.
We observed the following families of squamates in class last week:
Family: Agamidae (Angleheads, Calotes, Dragon Lizards, and Allies)
Subfamiles: Agaminae and Leiolepidinae
Distribution: Africa, Asia and Australia.
Characteristics: Agamids are covered dorsally and ventrally by overlapping juxtaposed scales and do not have osteoderms dorsally or ventrally. All species are limbed and their tails are long to moderately long. The skull has paired nasals, postorbitals, squamosals, frontal and parietal. The specimen we looked at in lab was Draco from the Agaminae subfamily. Dentition of these lizards is acrodont.
The top species Draco on the right picture belongs to this family.
Family: Chamaeleonidae (Chameleons)
Subfamilies: 6 genera
Distribution: Africa, Middle East, Madagascar, Southern Spain, Sri Lanka and India.
Characteristics: Chameleons have strongly laterally compressed bodies, prehensile tails and zygodactylous feet. They have projectile tongues for capturing prey and independently moving eyes. Most species have small juxtaposed scales with no osteoderms dorsally or ventrally. Chameleons have acrodont dentition and their tongue is covered dorsally with reticular papillae.
The middle species in the picture to the right is in this family.
Family: Anguidae (Alligator Lizards, Galliwasps, Glass Lizards and Allies)
Subfamilies: Anguine, Anniellinae, Diploglossinae and Gerrhonotinae.
Distribution: Disjunct, Americas, Europe, Southwest and Southern Asia.
Characteristics: Anguids vary in size to very small to large and some possess limbs while others are limbless. Anguids have large non-overlapping scales with underlying osteoderms dorsally and ventrally on the trunk. Some taxa have a longitudinal ventrolateral groove or fold that allows for body expansion during breathing, feeding and reproduction. Some Anguids have caudal autonomy but not all taxa. The specimen we looked at in lab was Ophisaurus from the subfamily Anguinae. They exhibit extreme limb reduction with a well developed ventrolateral fold, but not all have developed leglessness. Dentition of these lizards is pleurodont. The species on the left belongs to this family.
Family: Gekkonidae (Gekkos and Pygopods)
Subfamilies: Diplodactylinae, Eublepharinae, Gekkoninae and Pygopodinae.
Distribution: Pantropic on all landmasses.
Characteristics: Gekkonoids are covered dorsally and ventrally by small granular scales and some are occasionally interspersed with tubercles. No osteoderms occur ventrally on the trunk but some geckos possess osteoderms ventrally. Some have big distracting tails that store fat and water; caudal autonomy is common among Gekkonoids. Their tongue is covered dorsally with peg-like papillae and lacks lingual scales. The subfamilies we looked at in lab were Eublepharinae and Gekkoninae. They have a single parietal eye on top, spectacle eyelids and sceleral ossicles to adjust their real eyes' lenses. They also have "scansors" or "lamellae" that are useful for climbing. Dentition of these lizards is pleurodont. The species on the left belongs to this family.
Family: Helodermatidae (Gila Monster & Mexican Beaded Lizard)
Subfamilies: One genus Heloderma with 2 species.
Distribution: Southwestern North America southward along the Mexican Pacific coast to Guatemala.
Characteristics: Helodermatids are large lizards and are the only lizards with well-developed venom glands. They have flattened heads, robust bodies, short limbs and short heavy tails. They have thick skin with rounded scales in rows covering the body. Scales are slightly larger and squarish ventrally compared to the dorsal scales. On the ventral side small non-articulate osteoderms are present with none dorsally. Caudal autonomy does not occur. Their tongues have filamentous papillae and the foretongue retracts into the hind tongue. They love eating eggs and spending time underground being antisocial! Dentition of these lizards is pleurodont. The species on the right belongs to this family.
Family: Teiidae (Whiptail Lizards, Tegus and Allies)
Subfamilies: Teiinae and Tupinambinae
Distribution: Americas from northern United States to Argentina and Chile.
Characteristics: Teiids scales are small and granular dorsally but large, rectangular and juxtaposed ventrally. No osteoderms are present dorsally or ventrally on the trunk. Teiids have caudal autonomy and their tails are typically long. The dentition of these lizards is pleurodont. The specimen we observed in lab was Aspidoscelis from the subfamily Teiinae. The species on the left belongs to this family.
Family: Iguanidae* (Anoles, Iguanas, Allies)
Subfamilies: (8) Corytophaninae, Crotophytinae, Hoplocercinae, Iguaninae, Oplurinae, Phrynosomatinae, Polychrotinae, and Tropidurinae.
Distribution: Americas (Ohio!), Madagascar, west-central Pacific islands
Characteristics: Great diversity so wide range of sizes. Scales are large, keeled and overlapping dorsally and ventrally while some have small granular scales, but no osteoderms are exhibited. Very sexually dimorphic. Prominent femoral pores and gular flap in some males. Some change in diet between life stages but mostly opportunistic (insectivore juveniles and herbivorous adults). Exhibit prominent collars and long to moderately long tails. Caudal autonomy occurs through fracture planes in the caudal vertebrae. Dorsal coverage of tongue with reticular papillae without lingual scales and a non-retractable foretongue. Dentition of these lizards is pleurodont.
The species on the right belongs to this family.
*OHIO SPECIES: Pictured to the right: Sceloporus undulates garmani (Northern Fence Lizard).
Family: Scincidae* (Skinks)
Subfamilies: Acontinae and "Scincinae"
Distribution: Nearly worldwide (Ohio!)
Characteristics: Scales are cycloid and smooth, overlapping dorsally and ventrally throughout the trunk and have osteoderms. Limbs can be reduced. They exhibit long to moderately long tails and caudal autonomy is common. Their tongue has filamentous papillae with alternating, serrated, dorsal lingual scales and a non-retractable foretongue. There are both oviparous and viviparous genera. Dentition of these lizards is pleurodont. The species on the left belongs to this family.
OHIO SPECIES: From top to bottom in the picture to the left: Scincella lateralis (Ground Skink), Eumeces fasciatus (Five-Lined Skink), Eumeces laticeps (Broad-Headed Skink), and Eumeces anthracinus (Northern Coal Skink).
Family: Varanidae (Monitors, Goannas and Earless Monitors)
Subfamilies: Lanthanotinae and Varaninae
Distribution: Warm temperate & tropical Africa, Asia, Australia.
Characteristics: They have a blood groove and are venomous lizards. They are generally large and thick-skinned with well-developed limbs. Scales are larger ventrally than dorsally and only have small ventral osteoderms in few species. Their tails are very long but do not have caudal autonomy (cannot regrow tail). Their tongue has filamentous papillae without lingual scales and foretongue that is retractable into the hind tongue. Dentition of these lizards is pleurodont. The species to the right and below are members of this family.
We'll leave you with this picture of Komoto Dragons (Varanidae) chowing down on some prey much larger than themselves, an ox.