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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
Naja naja

Naja naja

Naja naja

Features:The stripes on the back look like a smiling face

The Indian cobra (Latin name: Naja naja) is a species of snake in the genus Naja of the family Elapidae, and is also an important representative species in the genus Naja. The keyword "Naja" in the scientific name of this snake species and the entire genus Naja comes from the snake god &qu...

Varanus komodoensis

Varanus komodoensis

Varanus komodoensis,dragon、komodo dragon

Features:The Komodo dragon is the largest lizard known to exist.

The largest lizard on earth is the Komodo dragon. The Komodo dragon, scientifically known as Varanus komodoensis (Ouwens, 1912), is a species of Varanus in the Varanidae family. Also known as the Komodo dragon, it is the largest lizard known to exist today. The Komodo dragon is ferocious, and adults...

Atheris hispida

Atheris hispida

Atheris hispida,Hairy tree pit viper, scaly tree pit viper

Features:The body is covered with dense and sharp thorn-like scales, making it the most dragon-like snake.

The Kivu tree viper (scientific name: Atheris hispida), also known as the hairy tree viper and the scaly-skinned tree viper, is a venomous snake species under the Viperidae family of the suborder Serpentes.The Kivu tree viper is an expert at climbing trees. It lives mainly on trees, but also climbs...

Vipera renardi

Vipera renardi

Vipera renardi,Oriental Viper

Features:Very similar in appearance to the Vipera

Oriental viper belongs to the family Viperidae of the order Squamata. It is a small viper.Oriental viper is gentle and does not actively attack humans. Even if people want to kill it, it will not fight back, but only run away. It mainly feeds on small rodents, lizards, and insects.Oriental viper was...

Vipera berus

Vipera berus

Vipera berus,Northern Viper,Dragon viper, Arctic viper

Features:It is the only snake found within the Arctic Circle.

The Vipera berus is the most widely distributed land snake.The Vipera berus is a solitary animal. It rarely stays with other individuals except during mating and hibernation. Its activity time is mainly concentrated at sunset. They start hibernation between September and October every year, wake up...

Protobothrops mangshanensis

Protobothrops mangshanensis

Protobothrops mangshanensis,White-tailed snake, rare snake, small green dragon, Mangshan iron-headed snake

Features:The head is slightly triangular, slightly larger, with cheek pits, and looks like a piece of iron, hence the name.

The Latin name of the Mangshan pit viper Protobothrops mangshanensis is a giant venomous snake species unique to China, commonly known as "Little Green Dragon".The Mangshan pit viper is carnivorous. They will track their prey in a timely manner and find the right opportunity to prey. Under...

Protobothrops cornutus

Protobothrops cornutus

Protobothrops cornutus,Horned iron, horned pit viper

Features:Head with a pair of horns

The Latin name of the horned pit viper Protobothrops cornutus is very rare and its whereabouts in the wild are secretive.The horned pit viper is a highly venomous snake. In addition to the common attributes of these venomous snakes, it also has its own unique "killer move". The fangs of th...

Gloydius shedaoensis

Gloydius shedaoensis

Gloydius shedaoensis,Agkistrodon acutus, Agkistrodon acutus, Agkistrodon acutus, Agkistrodon acutus

Features:The body color is mostly silver and gray, with light black stripes.

The scientific name of the snake island pit viper is Gloydius shedaoensis. It is one of the famous venomous snakes in China. Its distribution area "Snake Island" is named after the abundance of snake island pit vipers.The migratory bird season is the season for the activity of the snake is...

Daboia russelii siamensis

Daboia russelii siamensis

Daboia russelii siamensis,Leopard, leopard, coin spot, ancient coin window, round-spotted viper

Features:Slow in movement, fierce in nature, and extremely poisonous

Daboia russelii siamensis is a venomous viper belonging to the genus Viper in the subfamily Viperidae of the suborder Viperidae. There are three subspecies, among which the Thai viper (Daboia russelii siamensis) is a second-level key protected animal in my country.The round-spotted viper moves slowl...

Praescutata viperina

Praescutata viperina

Praescutata viperina,Black-tailed sea snake, Sea viper

Features:The head and neck are not clearly distinguished; the body is relatively short and thick, slightly flattened laterally, and the tail is flattened laterally

The Latin name of the sea viper is Praescutata viperina, which is a species of the genus Praescutata in the family Elaphedae.Sea vipers live in the ocean, often in shallow waters. They feed on fish. They are ovoviviparous.Listed in the "National List of Terrestrial Wildlife with Important Econo...

Hydrophis jerdonii

Hydrophis jerdonii

Hydrophis jerdonii

Features:Short head, olive-colored back with black rings

The sea snake is a species of the genus Sea Snake in the family Elaphedae. It is highly venomous and poses a great threat to fishermen.It preys on eels and other fish. It is ovoviviparous. Listed in the "National List of Terrestrial Wildlife with Important Economic and Scientific Research Value...

Hydrophis platurus

Hydrophis platurus

Pelamis platurus,Hydrophis platurus

Features:The most widespread sea snake

Long-nosed sea snakes live in the ocean and can stay away from the coast. They are the most widely distributed species of sea snakes.Long-nosed sea snakes mainly feed on various small fish and crustaceans. They are ovoviviparous.Listed in the "National List of Terrestrial Wildlife with Importan...

Microcephalophis gracilis

Microcephalophis gracilis

Graceful sea snake,Microcephalophis gracilis,Small-headed sea snake

Features:The head is extremely small, the front part of the body is extremely thin and cylindrical, and the back part is thick and laterally flattened.

Microcephalophis gracilis, Latin name of the small-headed sea snake, is a reptile of the genus Microcephalophis in the family Elapidae.The small-headed sea snake lives in the ocean. It is ovoviviparous. It has a very small head and feeds on long small fish and fish eggs. The venom is stronger than o...

Lapemis eurtus

Lapemis eurtus

Lapemis eurtus,Spiny sea snake, flat-chinned sea snake

Features:Back side is green-brown or yellow-olive with wide dark olive horizontal stripes

The Latin name of the flat-chinned sea snake is Lapemis eurtus, a species of the genus Lapemis eurtus in the family Elapidae, a front-grooved venomous snake.The flat-chinned sea snake lives in the ocean. It eats fish. It is ovoviviparous.Listed in the "National List of Terrestrial Wildlife with...

The Dwarf Sea Snake

The Dwarf Sea Snake

Hydrophiidea,The Dwarf Sea Snake,Gray sea snake

Features:One of the three common sea snakes along the coast of China (blue-gray sea snake, blue-ringed sea snake, light-gray sea snake)

The Dwarf Sea Snake is a reptile of the genus Cobra in the family Elapidae.The Dwarf Sea Snake will not actively attack humans, and will mostly hurt people when they are harassed.The venom of the blue-gray sea snake is a neurotoxin similar to cobra venom, but it mainly harms human voluntary muscles...

Hydrophis stokesii

Hydrophis stokesii

Hydrophis stokesii

Features:The longest fang of a sea snake

The sea snake is one of the heaviest and most robust sea snakes, and has the longest fangs among sea snakes. Its fangs are sharp enough to pierce a diving suit. Although the sea snake is venomous, bites and is aggressive, there is no record of human casualties caused by the sea snake.During the bree...

Acalyptophis peronii

Acalyptophis peronii

Acalyptophis peronii,Horned sea snake, Spiny sea snake

Features:The tail is not as slender as a whip like a land snake, but is flattened like a paddle.

Acalyptophis peronii is a venomous sea snake.Spiny-canthus sea snakes often move in caves and crevices in the sea. Night is the most active period for Spiny-canthus sea snakes. They mainly eat shrimp gobies and other small fish.The sea snake is a viviparous snake. The female gestation period is 6-7...

Hydrophis ornatus

Hydrophis ornatus

Hydrophis ornatus,Black-spotted sea snake, pale grey sea snake

Features:The back of the head is black, olive or gray, and the back of the body and tail is light gray or olive with wide black or dark ring spots

The Latin name of the pale gray sea snake Hydrophis ornatus is a reptile of the genus Hydrophis in the family Elapidae.The pale gray sea snake lives in the ocean. It eats eels and also eats dead fish when it is raised. It is ovoviviparous.Listed in the second level of the "List of National Key...

Hydrophis melanocephalus

Hydrophis melanocephalus

Hydrophis melanocephalus,Black-headed sea snake

Features:The back of the head has yellowish-white spots, the back of the body is olive or gray, and the abdomen is yellowish-white with black rings.

The black-headed sea snake is mainly Hydrophis melanocephalus, an animal of the genus Hydrophis in the family Elapidae.The black-headed sea snake mainly lives in tropical to subtropical waters. It is a completely aquatic snake and has difficulty moving on land. They are mostly seen during the day an...

Hydrophis fasciatus

Hydrophis fasciatus

Hydrophis fasciatus,Sea Snake,Ringed sea snake

Features:Back side dark grey with black rings

The Latin name of the ringed sea snake is Hydrophis fasciatus, which is a highly venomous snake.The ringed sea snake lives in the sea and mainly feeds on small eels and squids.The sea snake is ovoviviparous. In September, a baby snake of 350 to 400 mm was collected in Hainan (the umbilicus was still...

Hydrophis cyanocinctus

Hydrophis cyanocinctus

Hydrophis cyanocinctus,Sea snake, sea snake

Features:The venom is more than 20 times that of a king cobra.

The Latin name of the blue-ringed sea snake is Hydrophis cyanocinctus, a highly venomous snake of the front groove class.The blue-ringed sea snake mainly preys on snake eels. Most of the food is sharp-nosed snake eels. Occasionally there are other eels and fish. Food is mainly swallowed from the hea...