Lizardia
There are about 3,750 known species in the order Lizardia, and about 9 families and more than 150 species are known in China. Most are small and medium-sized reptiles. Generally, species have well-developed limbs, 5 fingers and toes, and claws at the end, which are suitable for crawling and digging. A few species have degenerate or missing limbs and long tails. They have shoulder straps and sternums, movable eyelids, flat tongues that can be retracted, but no tongue sheaths. There are also terrestrial, arboreal, semi-aquatic or burrowing species. The tails of some species often break off when encountering enemies, and they can move for a period of time after breaking off to divert the enemy's attention and escape; the tail can be regenerated, and the regenerated tail is different from the original tail in appearance.
It should be noted that in modern reptile classification, lizards (in a broad sense), snakes and caecilians are generally classified as "Squamata". Among them, "Lacertilia / Sauria" is often regarded as "Luzardia" in morphology or traditional classification, but from a phylogenetic perspective, lizards are a paraphyletic group because snakes evolved from some "legless lizard" groups. For the convenience of popular science and retrieval, the name of "Luzardia" is still used here to introduce and classify the traditional "lizards" and other scaly reptiles.
I. Introduction to the “Lizard Order” (Lacertilia / Sauria)
1. Definition and Main Characteristics
Traditional Taxonomic Status
Historically, any squamate with (usually) four limbs (or reduced limbs), but neither a snake nor an amphisbaenian, has been called a “lizard.” This group, consisting of over 7,000 species (excluding snakes and amphisbaenians), is distributed worldwide (except in polar regions) across diverse habitats.
Morphology and Physiology
Body and Limb Structure: Most lizards have four limbs (some groups, e.g. glass lizards, have partially or entirely reduced limbs). They typically have a spindle- or dorsoventrally flattened body and a relatively long tail.
Skin: Covered in keratinized scales that reduce water loss and protect against physical damage; periodic ecdysis (shedding) accompanies growth.
Jaw and Movement: Lizards generally have less skull and jaw mobility than snakes, though some (e.g. chameleons) have highly specialized feeding mechanisms (projectile tongues).
Behavior: Both diurnal and nocturnal species exist. Many rely on visual cues (color patterns, head-bobbing, dewlap displays) for communication. Males often exhibit bright colors or ornamental structures during courtship or territorial defense.
Habitat and Diet
Habitat Diversity: Lizards occupy a range of environments—from tropical rainforests and deserts to coastal cliffs and high-elevation grasslands—and may be arboreal, terrestrial, saxicolous (rock-dwelling), burrowing, or semiaquatic.
Feeding: Most are insectivorous or feed on small arthropods, but certain lineages are herbivorous (e.g., many iguanas) or omnivorous (some skinks). Large species (e.g. Komodo dragons) may prey on vertebrates.
2. Ecology and Human Relevance
Mid-Level Predators
Lizards act as important predators of insects or other small arthropods, while serving as prey for birds, snakes, and mammals. Some herbivorous lizards influence plant regeneration and seed dispersal.
Economic and Cultural Importance
Pets and Ornamental: Many species (green iguanas, bearded dragons, chameleons, geckos) are popular in herpetoculture.
Medicinal or Commercial: In certain regions, lizards are used in traditional medicine or harvested for skins. Large species (e.g. monitor lizards) may be hunted for meat or perceived as threats.
Negative Impacts: Introduced lizards (e.g., green iguanas) can become invasive. Some large carnivorous lizards (e.g., Komodo dragons) occasionally pose a safety risk to humans or livestock.
II. Evolutionary History of Lizards
Origins and Early Evolution
Tracing back to the Middle/Late Jurassic–Early Cretaceous, the earliest lizard-like ancestors diverged among the squamate lineages.
Together with snakes and amphisbaenians, lizards share a common “Squamata” ancestor. Snakes branched off during the mid- to late Cretaceous from certain limb-reduced lizard stock.
Relationship with Snakes and Amphisbaenians
Molecular data confirm that “lizards” form a paraphyletic group within Squamata, as snakes (Serpentes) arose from within the “lizard” line. Nonetheless, morphological and ecological differences (limbs, external ear openings, eyelids, etc.) distinguish most lizards from snakes/amphisbaenians.
Modern Diversity and Distribution
Continental shifts and climate changes from the late Mesozoic into the Cenozoic facilitated their global spread.
Present-day lizards display tremendous variety—from chameleons with ballistic tongues to monitor lizards as apex predators, and from iguanid herbivores to highly specialized skinks—underscoring remarkable morphological and ecological adaptability.
III. Major Families and Representative Genera
Below is a traditional classification summary of “lizards” (excluding snakes and amphisbaenians) with selected families and genera as examples. Note that molecular systematics continues to refine boundaries at the family or subfamily level.
1. Geckos and Allies (Family Gekkonidae & related families)
| Family | Representative Genera | Example Species | Distribution & Notes |
|---|
| Gekkonidae (Geckos) | Gekko (Tokay gecko), Hemidactylus (House gecko), etc. | Tokay gecko (Gekko gecko), Common house gecko (Hemidactylus frenatus) | Typically nocturnal, climb walls using adhesive toe pads; tropical-subtropical. |
| Eublepharidae (Eyelid geckos) | Eublepharis (Leopard gecko), etc. | Leopard gecko (Eublepharis macularius) | Popular in the pet trade, have movable eyelids (unlike many other geckos). |
2. Skinks (Family Scincidae)
| Representative Genera | Example Species | Distribution & Notes |
|---|
| Eumeces / Plestiodon (Blue-tailed skinks) | Blue-tailed skink (Plestiodon laticeps), etc. | Cylindrical bodies, smooth scales; widespread in North America & East Asia; some with vivid tail coloration. |
| Scincus (Sand skinks) | Sandfish skink (Scincus scincus), etc. | Found in North Africa & Middle East deserts; can “swim” through sand. |
3. Agamids (Family Agamidae) / Chameleons (Family Chamaeleonidae)
| Family | Representative Genera | Example Species | Distribution & Notes |
|---|
| Agamidae (Agamas) | Draco (Flying lizards), Pogona (Bearded dragons), etc. | Flying lizard (Draco volans), Bearded dragon (Pogona vitticeps), etc. | Africa, Asia, Oceania distribution; Draco uses patagial membranes to glide, Pogona is popular as a pet. |
| Chamaeleonidae (Chameleons) | Chamaeleo, Furcifer, Calumma, etc. | Veiled chameleon (Chamaeleo calyptratus), Panther chameleon (Furcifer pardalis), etc. | Mostly in Africa & Madagascar; known for projectile tongues, independently rotating eyes, striking coloration. |
4. “True Lizards” (Lacertidae), Tegus (Teiidae), Iguanas (Iguanidae), etc.
| Family | Representative Genera | Example Species | Distribution & Notes |
|---|
| Lacertidae (Wall lizards, etc.) | Lacerta, Podarcis (Wall lizards) | Green lizard (Lacerta viridis), Common wall lizard (Podarcis muralis), etc. | Common in Europe, Africa, Asia; mostly insectivorous or omnivorous, often found on walls/rocks. |
| Teiidae (Whiptails, Tegus) | Tupinambis (Tegus), Aspidoscelis (Whiptails), etc. | Argentine black and white tegu (Salvator merianae), Six-lined racerunner (Aspidoscelis sexlineata), etc. | Found in the Americas; swift, ground-dwelling; tegus can grow large and are sometimes kept as pets. |
| Iguanidae (Iguanas) | Iguana (Green iguana), Amblyrhynchus (Marine iguana), etc. | Green iguana (Iguana iguana), Galápagos marine iguana (Amblyrhynchus cristatus), etc. | Primarily in the New World; many are herbivorous, some large-bodied. Marine iguana is the only marine herbivorous lizard. |
5. Monitor Lizards (Family Varanidae)
| Representative Genera | Example Species | Distribution & Notes |
|---|
| Varanus (Monitors) | Komodo dragon (Varanus komodoensis), Asian water monitor (V. salvator), etc. | Native to Africa, Asia, Oceania; apex or near-apex predators/scavengers. Komodo dragon can exceed 3 meters in length. |
6. Beaded Lizards (Family Helodermatidae)
| Representative Genera | Example Species | Distribution & Notes |
|---|
| Heloderma (Beaded lizards) | Gila monster (Heloderma suspectum), Mexican beaded lizard (H. horridum) | Found in arid regions of southwestern North America; possess venom glands, delivering toxin via grooved teeth. |
7. Limb-Reduced Lizard Groups: Glass Lizards, Slowworms, etc.
| Family | Representative Genera | Example Species | Distribution & Notes |
|---|
| Anguidae (Glass lizards, Alligator lizards) | Ophisaurus (Glass lizard), Anguis (Slowworm), etc. | Eastern glass lizard (Ophisaurus ventralis), Slowworm (Anguis fragilis), etc. | Limbless or limb-reduced, serpentiform body but with external ear openings. Found in the Americas, Europe, Asia. |
(Additional lesser-known or region-specific families include Cordylidae [Girdled lizards in Africa], Xantusiidae [Night lizards], etc.)
IV. Conclusion
Multiple Adaptations and Worldwide Distribution
Lizards, in the broad sense, underwent significant diversification from the late Jurassic onward. Geographic and climatic changes facilitated their colonization of almost all warm regions on Earth. This yielded numerous convergent evolutions (e.g., limb reduction, arboreal gliding).
Ecology and Human Interaction
Most lizards serve as insect or small-vertebrate predators, benefiting ecosystems by controlling pest populations; herbivorous species can shape vegetation dynamics.
They are widely used as pets, in some regions as food or medicine, and in ecotourism. Yet, invasive species or large predatory lizards can create environmental or safety concerns.
Conservation and the Future
Habitat loss, climate shifts, illegal trade, and invasive competition threaten certain lizard populations, especially island endemics or specialized desert/rainforest species.
Effective habitat protection, regulated reptile trade, and ongoing research/education are essential to sustain lizard diversity.
Summary
This overview provides a comprehensive introduction to the historical development, main classification systems and ecological status of the "Lizards" (the traditional concept of "Lacertilia / Sauria"). If you need to know more about specific families, genera or species (such as morphological characteristics, geographical distribution, and conservation status), you can refer to professional herpetology materials, field observation manuals, and the latest molecular systematic research literature. I hope that this "Lizards Classification Encyclopedia" can provide you with practical and detailed scientific information, so that more people can know and cherish these colorful reptiles.
