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Squamata

Squamata is the largest order of reptiles, with about 6,000 species, accounting for more than 90% of existing reptiles. It is divided into two orders, including the lizards and snakes. The body surface is covered with keratinous scales, generally without bony plates, and the body is mostly long. The front and rear limbs are well developed or degenerate.

I. Introduction to Squamata

1. Definition and Key Characteristics

  • Taxonomic Placement
    Squamata is the largest order of Reptilia (reptiles), comprising all lizards (in a broad sense), snakes, and amphisbaenians (worm lizards). With over 10,000 described species, they inhabit a range of environments (deserts, rainforests, grasslands, coastlines, etc.) worldwide, excluding the polar regions.

  • Morphological and Physiological Traits

    • Scaled Skin: Squamates have keratinized scales that reduce water loss and provide protection. Many species shed these scales periodically during growth.

    • Flexible Jaws: Most squamates have a relatively kinetic skull and jaw articulation; notably, snakes can disarticulate their jaws extensively to swallow large prey.

    • Locomotion Variations: Lizards typically have four limbs (though some groups like glass lizards have reduced limbs). Snakes have lost limbs entirely and move by lateral undulation or other specialized methods. Amphisbaenians (worm lizards) also lack visible limbs, with segmented bodies adapted to burrowing.

  • Lifestyle Diversity

    • Diet: Ranges from strict herbivory (e.g., iguanas) and insectivory to carnivory (e.g., large constrictors, venomous snakes) or specialized feeding.

    • Reproduction: Most are oviparous (egg-laying), though some exhibit ovoviviparity or viviparity (e.g., some vipers and skinks).

2. Ecological and Human Relevance

  • Role in Food Webs
    Many lizards and snakes act as medium-level predators, controlling insect or rodent populations, and serving as prey for birds or larger carnivores. Herbivorous lizards may help in seed dispersal and plant community dynamics.

  • Economic and Cultural Value

    • Pest Control and Balance: Snakes can significantly reduce rodent populations in agricultural areas.

    • Medicinal and Ornamental: Some snakes (e.g., cobras, pit vipers) are used in traditional medicine, while various lizards (e.g., green iguana) and snakes (e.g., ball pythons, kingsnakes) are popular in the pet trade.

    • Negative Impacts: A few venomous species pose safety risks; some introduced lizards (e.g., green iguanas) can become invasive in non-native regions.


II. Evolutionary History

  1. Origins and Early Evolution

  • Squamates trace back to Jurassic–Cretaceous ancestors (~150–100 million years ago). They derived from older diapsid reptiles, diversifying widely through the Mesozoic era.

  • Snakes (Serpentes) evolved from a particular lineage of limbless or limb-reduced lizards, though whether this occurred primarily in a burrowing terrestrial environment or a marine environment was long debated. Current evidence favors a terrestrial or fossorial (burrowing) origin.

  1. Modern Diversification and Global Spread

  • Geological and climatic changes (e.g., continental drifts, sea-level changes) from the Cretaceous onward allowed lizards and snakes to expand nearly worldwide, except the coldest polar areas.

  • Different groups have successfully adapted to terrestrial, arboreal, fossorial, freshwater, or even marine environments (such as marine iguanas or sea snakes).


III. Major Classification Table of Squamata

Traditionally, lizards (Lacertilia / Sauria), snakes (Serpentes), and amphisbaenians (Amphisbaenia) are recognized as three major lineages. Below is a concise list of prominent families and representative genera. Please note that molecular research continues to refine family-level boundaries.

A. Lizards (Broadly, “Lacertilia/Sauria”)

FamilyRepresentative GeneraExample SpeciesDistribution & Notes
Gekkonidae (Geckos)Gekko (Tokay gecko), Hemidactylus (House gecko), etc.Tokay gecko (Gekko gecko), Common house gecko (Hemidactylus frenatus), etc.Typically small, nocturnal lizards with adhesive toe pads for climbing walls and ceilings.
Scincidae (Skinks)Eumeces (Skinks), Scincus (Sand skinks), etc.Blue-tailed skink (Plestiodon/ Eumeces laticeps), etc.Many have cylindrical bodies and smooth scales; some exhibit limb reduction or viviparity.
Agamidae (Agamas)Pogona (Bearded dragons), Draco (Flying dragons), etc.Central bearded dragon (Pogona vitticeps), Flying lizard (Draco volans), etc.Found in Africa, Asia, and Australia; popular as pets (bearded dragons); Draco can glide among trees.
Chamaeleonidae (Chameleons)Chamaeleo, Furcifer, Calumma, etc.Panther chameleon (Furcifer pardalis), Veiled chameleon (Chamaeleo calyptratus), etc.Africa & Madagascar primarily; famous for projectile tongues, independently rotating eyes, vivid coloration.
Iguanidae (Iguanas)Iguana, Amblyrhynchus (Marine iguana), etc.Green iguana (Iguana iguana), Galápagos marine iguana (Amblyrhynchus cristatus), etc.Mostly New World; some species herbivorous (e.g., green iguana), others specialized (marine iguana dives for algae).
Helodermatidae (Beaded lizards)Heloderma (Gila monster, Beaded lizard)Gila monster (Heloderma suspectum), Mexican beaded lizard (H. horridum)North American desert dwellers; possess venomous glands, injecting toxin via grooved teeth.
Varanidae (Monitor lizards)Varanus (Monitors)Komodo dragon (Varanus komodoensis), Asian water monitor (Varanus salvator), etc.Africa, Asia, Oceania distribution; often large-bodied; Komodo dragon is among the world’s largest lizards.

B. Snakes (Serpentes)

FamilyRepresentative GeneraExample SpeciesDistribution & Notes
Pythonidae (Pythons)Python, Morelia, Liasis, etc.Burmese python (Python bivittatus), Reticulated python (Malayopython reticulatus), etc.Old World distribution, typically large constrictors; some can exceed 6 meters in length.
Boidae (Boas & Anacondas)Boa, Eunectes, etc.Boa constrictor (Boa constrictor), Green anaconda (Eunectes murinus), etc.New World distribution, parallel to pythons in function (constrictors); anacondas among the heaviest snakes.
Colubridae (Typical snakes)Natrix (Grass/Water snakes), Elaphe (Ratsnakes), Pantherophis, etc.Grass snake (Natrix natrix), King ratsnake (Elaphe carinata), etc.The largest snake family worldwide; most are non-venomous or only mildly venomous; highly diverse ecologically.
Elapidae (Cobras, Kraits, Mambas, Coral snakes, etc.)Naja (Cobra), Ophiophagus (King cobra), Micrurus (Coral snakes), etc.King cobra (Ophiophagus hannah), Indian cobra (Naja naja), etc.Possess potent neurotoxic venom, found in Africa, Asia, Australia, and the Americas (e.g., coral snakes).
Viperidae (Vipers & Pit vipers)Vipera, Crotalus (Rattlesnakes), Bothrops (Lanceheads), etc.Timber rattlesnake (Crotalus horridus), Gaboon viper (Bitis gabonica), etc.Venomous snakes with cytotoxic or hemotoxic venom; common morphological traits include triangular heads and vertical pupils.
(Sea Snakes: Subfamily Hydrophiinae under Elapidae)Hydrophis, Laticauda, etc.Banded sea krait (Laticauda colubrina), Short-headed sea snake (Hydrophis curtus), etc.Fully or partially marine, primarily in Indo-Pacific warm seas; often highly venomous.

C. Amphisbaenians (Worm Lizards)

FamilyRepresentative GeneraExample SpeciesDistribution & Notes
AmphisbaenidaeAmphisbaena, Zygaspis, etc.Various “worm lizards” (Amphisbaena alba, etc.)Africa and the Americas; elongate and limbless, adapted for fossorial (burrowing) life with a reinforced skull.
TrogonophidaeTrogonophis, Parea, etc.Moroccan worm lizard (Trogonophis wiegmanni), etc.Found in North Africa/Middle East; ringed body segments, head-tail similarity for burrowing.
BipedidaeBipes (Two-legged worm lizards)Mexican mole lizard (Bipes biporus), etc.Endemic to arid regions of Mexico, unique among amphisbaenians in retaining forelimbs but no hind limbs.

(Note: The amphisbaenian suborder is less commonly encountered but evolutionarily significant.)


IV. Conclusion

  1. Multiple Adaptations and Global Distribution

  • Squamata represents over 95% of extant reptile species. Fossil and molecular data indicate they underwent major diversification from the Late Jurassic to the Cretaceous, dispersing via land bridges and sea-level changes to inhabit most warm regions worldwide.

  1. Ecological and Human Interactions

  • Squamates often occupy mid-level trophic positions, helping maintain ecological balance (e.g., snakes controlling rodents).

  • Some species are harvested for food or traditional medicine, while others are valuable in the pet trade. However, invasive species introductions, potential venomous risks, and habitat encroachment are ongoing concerns.

  1. Conservation Challenges

  • Habitat loss, pollution, overharvesting, and climate change imperil many squamate species (e.g., island-endemic lizards, rare vipers).

  • Legislation, education, regulated pet trade, and habitat conservation are crucial for preserving squamate diversity and ecological stability.


Summary

This overview provides a brief introduction to the history of the order Squamata, its major classifications, and its role in ecology and human society. For more in-depth species-level or regional information, refer to professional herpetology books, field manuals, and the latest molecular systematics papers. I hope that this "Squamata Classification" will provide you with detailed and easy-to-understand scientific information to help readers understand the fascinating world of the three major groups of reptiles: lizards, snakes, and caecilians.

Testudines Squamata Crocodilia Lizardia
Emydocephalus ijimae

Emydocephalus ijimae

Emydocephalus ijimae,Egg sea snake, Turtle head sea snake

Features:The ventral scales are small and their width is no more than 2 times the adjacent body scales.

The Latin name of the turtle-headed sea snake is Emydocephalus ijimae, which is a reptile of the genus Emydocephalus in the family Elapidae.The turtle-headed sea snake lives in seawater. It is ovoviviparous. It feeds on fish.The turtle-headed sea snake is an animal with striking white stripes. But i...

Laticauda semifasciata

Laticauda semifasciata

Laticauda semifasciata,Semi-ringed flat-tailed sea snake

Features:Mild in nature, highly toxic

The Latin name of the semi-ringed flat-tailed sea snake is Laticauda semifasciata. It is a reptile of the genus Laticauda in the family Elapidae, with no subspecies.The semi-ringed flat-tailed sea snake lives in water most of the time, but also enters land for mating, digesting food, resting and lay...

Laticauda colubrina

Laticauda colubrina

Laticauda colubrina,Gray sea snake, fire snake, gray-blue flat-tailed sea snake

Features:In water, it uses its paddle-like tail to move back and forth to propel itself forward.

The gray-blue flat-tailed sea snake, whose Latin name is Laticauda colubrina, belongs to the genus Laticauda of the family Elapidae.The blue-grey flat-tailed sea snake is a good swimmer and spends most of its time in the ocean, but it also spends 25 to 50% of its time on land to mate, lay eggs, dige...

Acrochordus granulatus

Acrochordus granulatus

Acrochordus granulatus,Wart-scaled snake

Features:It is a species of snake that lives entirely in water.

Little wart snake (pinyin: luǒ lín shé), English name: Little wart snake, is a snake species that lives entirely in water.The main food of the scrofula is fish, but there are a lot of these snakes, and they live in groups, so when fishermen fish, they will also salvage the scrofula, and many fish...

Ptyas carinatus

Ptyas carinatus

Ptyas carinatus,Green black snake, dragon bone rat snake, black web black snake

Features:The subspecies is mainly green in color, very beautiful, a large non-venomous snake

The black-netted snake is called Ptyas carinatus in foreign language. It is the largest type of snake.The black-netted snake is timid by nature, extremely agile, good at climbing, and loves to move, but has little ability to entangle, and is mostly active during the day.The main food of the black-ne...

Thermophis baileyi

Thermophis baileyi

Thermophis baileyi,Hot Spring Snake

Features:The snake that lives at the highest altitude

The hot spring snake, whose Latin name is Thermophis baileyi, is the only snake species with the highest vertical distribution (4,350 m) in my country and is unique to the Tibetan Plateau in my country.Currently, little is known about the living habits of hot spring snakes. It is only known that it...

Rhynchophis boulengeri

Rhynchophis boulengeri

Rhynchophis boulengeri,Gonyosoma boulengeri,Rhinoceros rat snake, Cone-nosed snake,

Features:There is an upward protrusion at the front of the snout.

The sharp-beaked snake, whose Latin name is Rhynchophis boulengeri, is a small snake of the family Colubridae.The sharp-beaked snake is a tree-dwelling non-venomous snake. Like other tree-dwelling snakes such as the green snake, it lives in trees all year round and feeds on some lizards, insects, an...

Elaphe perlacea

Elaphe perlacea

Elaphe perlacea,Euprepiophis perlacea,Elegant female snake, horizontal striped jade snake, horizontal striped jade snake

Features:It is gentle and non-venomous, and is known as the most beautiful non-venomous snake.

The Latin name of the Elaphe perlacea is Elaphe perlacea, which is a specialty animal in western Sichuan, China.The Elaphe perlacea mainly preys on lizards and rodents. It is oviparous and non-toxic.In 1929, American scholar Stejneger.L first discovered this snake in Ya'an, Sichuan, China, captu...

Elaphe davidi

Elaphe davidi

Elaphe davidi,Black-rimmed rat snake, flower worm

Features:The back of the body is brown, non-toxic, with three rows of dark brown oval spots with black edges in the center and on both sides of the back, like a bunch of flowers

The Latin name of the Elaphe davidi is Elaphe davidi, a reptile of the genus Elaphe in the family Colubridae.The Elaphe davidi preys on lizards, rodents and bird eggs, and is oviparous. It is violent and its head becomes triangular when it is frightened. It is often mistaken for a venomous snake. It...

Tri-rope beauty snake

Tri-rope beauty snake

Tri-rope beauty snake,White flower snake, white flower snake, three-line snake, Guang snake (ni Guang), three-line snake, three-line snake

Features:It has a violent temperament and its front body maintains an "S" shape when in an attacking state.

Tri-rope beauty snake is a non-venomous snake of the genus Elaphe in the family Colubridae.The hibernation period of the Elaphe striata is from November to March of the following year. It mainly hibernates in rat holes in fields or cemeteries to the south, either alone or in groups, and sometimes wi...

Achalinus jinggangensis

Achalinus jinggangensis

Achalinus jinggangensis

Features:It is a species endemic to China

Achalinus jinggangensis is a small snake, which is unique to my country. Most of the snakes in the family Colubridae are non-venomous snakes, and the same is true for Jinggangshan Ridge Snake.There is very little research data on Jinggangshan Ridge Snake, and the number is also scarce. Only four ind...

Python bivittatus

Python bivittatus

Python bivittatus,Python, King snake, Anaconda, Southern snake, Burmese snake, King snake, Lyre snake, Burmese python, Plum snake

Features:Likes heat and fears cold, is good at climbing, and can live in water for a long time

Python bivittatus is a large reptile of the family Python and genus Python.Pythons are good at climbing, can live in water for a long time, are sleepy, nocturnal, and omnivorous. This species likes heat and is afraid of cold. It is generally active at 25℃; very active at 30℃ or above; inactive or...

Eryx tataricus

Eryx tataricus

Eryx tataricus,Earth stick

Features:There are circular spots of the same color across the sides

The Eastern Sand Boa is a reptile of the genus Eryx tataricus in the family Python, commonly known as the Earth Stick.Compared with other species, the Eastern Sand Boa is very active and very docile - but some young individuals and male individuals in general estrus are exceptions.Sand boas have a w...

Eryx miliaris

Eryx miliaris

Eryx miliaris,Earthen stick, both ends even, red sand python

Features:The neck is not clearly distinguished, the tail is short and blunt at the end

The scientific name of the red sand python is Eryx miliaris. It is a relatively primitive small to medium non-venomous snake.The red sand python is a common species abroad, but some subpopulations are on a downward trend. The number in China is unknown. Many taxonomists regard the red sand python an...

Xenopeltis unicolor Reinwardt

Xenopeltis unicolor Reinwardt

Xenopeltis unicolor Reinwardt,Sun snake, flaming snake

Features:The scales are lustrous and can shine with electric blue, sapphire green, blood red, purple and copper under sunlight.

The Latin name of the glitter snake is Xenopeltis unicolor Reinwardt, which belongs to the genus Xenopeltis of the family Xenopeltis.The glitter snake has a small head and eyes, and its scales are shiny. Under sunlight, it can shine with electric blue, emerald green, blood red, purple red and copper...

Cylindrophis ruffus

Cylindrophis ruffus

Cylindrophis ruffus,Red-tailed pipe snake,Red-tailed pipe snake, two-headed snake

Features:Small head, flat back and abdomen; brown body, with 40 pairs of white horizontal stripes on the sides

Cylindrophis ruffus is a species of snake in the family Shieldtail Snake.The red-tailed tube snake is a genuine burrowing snake. It usually stays in the soft soil of the rice field park and only appears on the ground when hunting. The function of this flat tail is only to imitate the flat head and n...

Typhlopslazelli

Typhlopslazelli

Typhlopslazelli,Indotyphlops lazelli,Rasmus's blind snake

Features:Small snakes, shaped like earthworms, with a small head and short tail, cylindrical in shape, and the same thickness from head to tail

Hong Kong blind snake (scientific name: Typhlops lazelli) is a reptile of the genus Typhlops in the family Typhlopidae, also known as Lazelli's blind snake, and is endemic to Hong Kong.This species is named after James D. Lazell to honor his contribution to the study of reptile communities in su...

Dibamus bogadeki

Dibamus bogadeki

Dibamus bogadeki,Bowman's Diplodocus,Bogadek's burrowing lizard

Features:It was discovered and named by amateur amphibian and herpetologist Father Bo Jiatian in 1987.

Bogadek's burrowing lizard is a reptile unique to Hong Kong.In 2012, the Hong Kong SAR government included the islands of Dawn Island and Shek Kwu Chau, where the species was discovered in 2011, in the government's reclamation research plan and incinerator plan. Some environmental groups bel...

Scincella huanrenensis

Scincella huanrenensis

Scincella huanrenensis,,Huanren dwarfskinkGolden Horse Snake

Features:The body is small and slender, and the scales are smooth and without edges.

Huanren dwarfskink is called Huanren dwarfskink in foreign language, and has no subspecies.Huanren dwarfskink mainly feeds on mosquitoes, flies, spiders, earthworms, insect larvae and moths. Individuals in artificial breeding also eat mealworm larvae, but their preference for them is slightly lower....

Varanus salvator

Varanus salvator

Varanus salvator,Common Water Monitor,Five-clawed golden dragon, monitor lizard, four-legged snake, scale insect, big four-legged snake

Features:Aggressive and ferocious. Good at swimming and climbing trees.

Common Water Monitor, with 5 subspecies.Unlike other animals, Common Water Monitor is active both day and night, but it goes out most frequently in the early morning and evening, swimming in the water or climbing up trees to find food. The round-nosed monitor has a wide range of diets, from fish, fr...

Varanus bengalensis,

Varanus bengalensis,

Varanus bengalensis,Bengal Monitor Lizard,Common Indian monitor lizard, Bengal monitor lizard

Features:It has strong survival ability and mainly lives on the ground, but can also climb trees.

Bengal Monitor Lizard, also known as Bengal Monitor Lizard, has 3 subspecies.Bengal Monitor Lizard mainly lives on the ground and also climbs trees. Males are more active than females (males: 4.5 hours/day, females: 2.85 hours/day). The male has an activity range of 53,000m2 and the female has an ac...