Squamata

Squamata is the largest order of reptiles, comprising lizards, snakes and amphisbaenians (worm lizards), which are collectively known as squamates or scaled reptiles. With over 10,000 species,[3] it is also the second-largest order of extant (living) vertebrates, after the perciform fish, and roughly equal in number to the Saurischia (one of the two major groups of dinosaurs). Members of the order are distinguished by their skins, which bear horny scales or shields. They also possess movable quadrate bones, making it possible to move the upper jaw relative to the neurocranium. This is particularly visible in snakes, which are able to open their mouths very wide to accommodate comparatively large prey. Squamata is the most variably sized order of reptiles, ranging from the 16 mm (0.63 in) dwarf gecko (Sphaerodactylus ariasae) to the 5.21 m (17.1 ft) green anaconda (Eunectes murinus) and the now-extinct mosasaurs, which reached lengths of over 14 m (46 ft).

Among other reptiles, squamates are most closely related to the tuatara, which superficially resembles lizards.

Squamata
Temporal range:
Early JurassicPresent, 199–0 Ma[1]
Blue-toungued skink444
Eastern blue-tongued lizard (Tiliqua scincoides scincoides)
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder: Lepidosauria
Order: Squamata
Oppel, 1811
Subgroups[2]

Evolution

Slavoia darevskii
Slavoia darevskii, a fossil squamate

Squamates are a monophyletic sister group to the rhynchocephalians, members of the order Rhynchocephalia. The only surviving member of Rhynchocephalia is the tuatara. Squamata and Rhynchocephalia form the subclass Lepidosauria, which is the sister group to Archosauria, the clade that contains crocodiles and birds, and their extinct relatives. Fossils of rhynchocephalians first appear in the Early Triassic, meaning that the lineage leading to squamates must have also existed at the time.[4] Scientists believe crown group squamates probably originated in the Early Jurassic based on the fossil record.[4] The first fossils of geckos, skinks and snakes appear in the Middle Jurassic.[5] Other groups like iguanians and varanoids appeared in the Cretaceous. Polyglyphanodontians, a distinct clade of lizards, and mosasaurs, a group of predatory marine lizards that grew to enormous sizes, also appeared in the Cretaceous.[6] Squamates suffered a mass extinction at the Cretaceous–Paleogene (K–PG) boundary, which wiped out polyglyphanodontians, mosasaurs and many other distinct lineages.[7]

The relationships of squamates is debatable. Although many of the groups originally recognized on the basis of morphology are still accepted, our understanding of their relationships to each other has changed radically as a result of studying their genomes. Iguanians were long thought to be the earliest crown group squamates based on morphological data,[6] however, genetic data suggests that geckoes are the earliest crown group squamates.[8] Iguanians are now united with snakes and anguimorphs in a clade called Toxicofera. Genetic data also suggests that the various limbless groups; snakes, amphisbaenians and dibamids, are unrelated, and instead arose independently from lizards.

A study in 2018 found that Megachirella, an extinct genus of lepidosaur that lived about 240 million years ago during the Middle Triassic, was a stem-squamate, making it the oldest known squamate. The phylogenetic analysis was conducted by performing high-resolution microfocus X-ray computed tomography (micro-CT) scans on the fossil specimen of Megachirella to gather detailed data about its anatomy. This data was then compared with a phylogenetic dataset combining the morphological and molecular data of 129 extant and extinct reptilian taxa. The comparison revealed Megachirella had certain features that are unique to squamates. The study also found that geckos are the earliest crown group squamates not iguanians.[9][10]

Reproduction

Trachylepis maculilabris mating
Trachylepis maculilabris skinks mating

The male members of the group Squamata have hemipenes, which are usually held inverted within their bodies, and are everted for reproduction via erectile tissue like that in the human penis.[11] Only one is used at a time, and some evidence indicates that males alternate use between copulations. The hemipenis has a variety of shapes, depending on the species. Often it bears spines or hooks, to anchor the male within the female. Some species even have forked hemipenes (each hemipenis has two tips). Due to being everted and inverted, hemipenes do not have a completely enclosed channel for the conduction of sperm, but rather a seminal groove that seals as the erectile tissue expands. This is also the only reptile group in which both viviparous and ovoviviparous species are found, as well as the usual oviparous reptiles. Some species, such as the Komodo dragon, can reproduce asexually through parthenogenesis.[12]

Elaphe quadrivirgata
The Japanese striped snake has been studied in sexual selection

There have been studies on how sexual selection manifests itself in snakes and lizards. Snakes use a variety of tactics in acquiring mates.[13] Ritual combat between males for the females they want to mate with includes topping, a behavior exhibited by most viperids, in which one male will twist around the vertically elevated fore body of its opponent and forcing it downward. It is common for neck biting to occur while the snakes are entwined.[14]

Facultative parthenogenesis

Central fusion and terminal fusion automixis
The effects of central fusion and terminal fusion on heterozygosity

Parthenogenesis is a natural form of reproduction in which the growth and development of embryos occur without fertilization. Agkistrodon contortrix (copperhead snake) and Agkistrodon piscivorus (cotton mouth snake) can reproduce by facultative parthenogenesis. That is, they are capable of switching from a sexual mode of reproduction to an asexual mode.[15] The type of parthenogenesis that likely occurs is automixis with terminal fusion (see figure), a process in which two terminal products from the same meiosis fuse to form a diploid zygote. This process leads to genome wide homozygosity, expression of deleterious recessive alleles and often to developmental abnormalities. Both captive-born and wild-born A. contortrix and A. piscivorus appear to be capable of this form of parthenogenesis.[15]

Reproduction in squamate reptiles is ordinarily sexual, with males having a ZZ pair of sex determining chromosomes, and females a ZW pair. However, the Colombian Rainbow boa, Epicrates maurus, can also reproduce by facultative parthenogenesis resulting in production of WW female progeny.[16] The WW females are likely produced by terminal automixis.

Inbreeding avoidance

When female sand lizards mate with two or more males, sperm competition within the females reproductive tract may occur. Active selection of sperm by females appears to occur in a manner that enhances female fitness.[17] On the basis of this selective process, the sperm of males that are more distantly related to the female are preferentially used for fertilization, rather than the sperm of close relatives.[17] This preference may enhance the fitness of progeny by reducing inbreeding depression.

Evolution of venom

Recent research suggests that the evolutionary origin of venom may exist deep in the squamate phylogeny, with 60% of squamates placed in this hypothetical group called Toxicofera. Venom has been known in the clades Caenophidia, Anguimorpha, and Iguania, and has been shown to have evolved a single time along these lineages before the three groups diverged, because all lineages share nine common toxins.[18] The fossil record shows the divergence between anguimorphs, iguanians, and advanced snakes dates back roughly 200 Mya to the Late Triassic/Early Jurassic.[18] But the only good fossil evidence is from the Jurassic.[1]

Snake venom has been shown to have evolved via a process by which a gene encoding for a normal body protein, typically one involved in key regulatory processes or bioactivity, is duplicated, and the copy is selectively expressed in the venom gland.[19] Previous literature hypothesized that venoms were modifications of salivary or pancreatic proteins,[20] but different toxins have been found to have been recruited from numerous different protein bodies and are as diverse as their functions.[21]

Natural selection has driven the origination and diversification of the toxins to counter the defenses of their prey. Once toxins have been recruited into the venom proteome, they form large, multigene families and evolve via the birth-and-death model of protein evolution,[22] which leads to a diversification of toxins that allows the ambush predators the ability to attack a wide range of prey.[23] The rapid evolution and diversification is thought to be the result of a predator–prey evolutionary arms race, where both are adapting to counter the other.[24]

Humans and squamates

Bites and fatalities

Number of snake envenomings
Map showing the global distribution of venomous snakebites

An estimated 125,000 people a year die from venomous snake bites.[25] In the US alone, more than 8,000 venomous snake bites are reported each year.[26]

Lizard bites, unlike venomous snake bites, are not fatal. The Komodo dragon has been known to kill people due to its size, and recent studies show it may have a passive envenomation system. Recent studies also show that the close relatives of the Komodo, the monitor lizards, all have a similar envenomation system, but the toxicity of the bites is relatively low to humans.[27] The Gila monster and beaded lizards of North and Central America are venomous, but not deadly to humans.

Conservation

Though they survived the Cretaceous–Paleogene extinction event, many squamate species are now endangered due to habitat loss, hunting and poaching, illegal wildlife trading, alien species being introduced to their habitats (which puts native creatures at risk through competition, disease, and predation), and other anthropogenic causes. Because of this, some squamate species have recently become extinct, with Africa having the most extinct species. However, breeding programs and wildlife parks are trying to save many endangered reptiles from extinction. Zoos, private hobbyists and breeders help educate people about the importance of snakes and lizards.

Classification and phylogeny

DesertIguana031611
Desert iguana from Amboy Crater, Mojave Desert, California

Historically, the order Squamata has been divided into three suborders:

Of these, the lizards form a paraphyletic group,[28] since "lizards" excludes the subclades of snakes and amphisbaenians. Studies of squamate relationships using molecular biology have found several distinct lineages, though the specific details of their interrelationships vary from one study to the next. One example of a modern classification of the squamates is[2][29]

Squamata
Dibamia

Dibamidae

Bifurcata
Gekkota
Pygopodomorpha

Diplodactylidae Underwood 1954Hoplodactylus pomarii white background

Pygopodidae Boulenger 1884The zoology of the voyage of the H.M.S. Erebus and Terror (Lialis burtonis)

Carphodactylidae

Gekkomorpha

Eublepharidae

Gekkonoidea

Sphaerodactylidae Underwood 1954

Phyllodactylidae Phyllodactylus gerrhopygus 1847 - white background

Gekkonidae

Unidentata
Scinciformata
Scincomorpha

ScincidaeBilder-Atlas zur wissenschaftlich-populären Naturgeschichte der Wirbelthiere (Plate (24)) Tribolonotus novaeguineae

Cordylomorpha

Xantusiidae

GerrhosauridaeGerrhosaurus ocellatus flipped

CordylidaeIllustrations of the zoology of South Africa (Smaug giganteus)

Episquamata
Laterata
Teiformata

Gymnophthalmidae Merrem 1820PZSL1851PlateReptilia06 Cercosaura ocellata

Teiidae Gray 1827Bilder-Atlas zur wissenschaftlich-populären Naturgeschichte der Wirbelthiere (Tupinambis teguixin)

Lacertibaenia
Lacertiformata

Lacertidae Brockhaus' Konversations-Lexikon (1892) (Lacerta agilis)

Amphisbaenia

Rhineuridae Vanzolini 1951

Bipedidae Taylor 1951Bilder-Atlas zur wissenschaftlich-populären Naturgeschichte der Wirbelthiere (Bipes canaliculatus)

Blanidae Kearney & Stuart 2004Blanus cinereus flipped

Cadeidae Vidal & Hedges 2008

Trogonophidae Gray 1865

Amphisbaenidae Gray 1865Amphisbaena microcephalum 1847 - white background

Toxicofera
Anguimorpha
Paleoanguimorpha
Shinisauria

Shinisauridae Ahl 1930 sensu Conrad 2006

Varanoidea

Lanthanotidae

VaranidaeZoology of Egypt (1898) (Varanus griseus)

Neoanguimorpha
Helodermatoidea

Helodermatidae Gray 1837Gila monster ncd 2012 white background

Xenosauroidea

Xenosauridae

Anguioidea

Diploglossidae

Anniellidae

Anguidae Gray 1825

Iguania
Acrodonta

ChamaeleonidaeZoology of Egypt (1898) (Chamaeleo calyptratus)

Agamidae Gray 1827Haeckel Lacertilia (Chlamydosaurus kingii)

Pleurodonta

Leiocephalidae

IguanidaeStamps of Germany (Berlin) 1977, Cyclura cornuta

Hoplocercidae Frost & Etheridge 1989

Crotaphytidae

Corytophanidae

Tropiduridae

Phrynosomatidae

Dactyloidae

Polychrotidae

Liolaemidae

Leiosauridae

Opluridae

Serpentes
Scolecophidia

Leptotyphlopidae Stejneger 1892Epictia tenella 1847 -white background

Gerrhopilidae Vidal et al. 2010

Xenotyphlopidae Vidal et al. 2010

Typhlopidae Merrem 1820Typhlops vermicularis3 white background

Anomalepididae

Alethinophidia
Amerophidia

Aniliidae

Tropidophiidae Brongersma 1951

Afrophidia
Booidea

UropeltidaeUropeltis ceylanica (2) flipped

Anomochilidae

CylindrophiidaeCylind resplendens Wagler white background

Xenopeltidae Bonaparte 1845

Loxocemidae

Pythonidae Fitzinger 1826Python natalensis Smith 1840 white background

BoidaeBoa Iconographia Zoologica white background

Xenophidiidae

Bolyeriidae Hoffstetter 1946

Caenophidia

Acrochordidae Bonaparte 1831

Xenodermidae

Colubroidea

Pareidae

ViperidaeOur reptiles and batrachians; a plain and easy account of the lizards, snakes, newts, toads, frogs and tortoises indigenous to Great Britain (1893) (Vipera berus)

Proteroglypha

Homalopsidae

ColubridaeXenochrophis piscator 1 Hardwicke white background

Lamprophiidae

ElapidaeBilder-Atlas zur wissenschaftlich-populären Naturgeschichte der Wirbelthiere (Naja naja)

All recent molecular studies[18] suggest that several groups form a venom clade, which encompasses a majority (nearly 60%) of squamate species. Named Toxicofera, it combines the groups Serpentes (snakes), Iguania (agamids, chameleons, iguanids, etc.), and Anguimorpha (monitor lizards, Gila monster, glass lizards, etc.).[18]

List of extant families

The over 10,000 extant squamates are divided into 58 families.

Amphisbaenia
Family Species count Common names Example species Example photo
Amphisbaenidae
Gray, 1865
Over 120 Tropical worm lizards Darwin's worm lizard (Amphisbaena darwinii)
Bipedidae
Taylor, 1951
4 Bipes worm lizards Mexican mole lizard (Bipes biporus) Bipes biporus
Blanidae 7 Mediterranean worm lizards Mediterranean worm lizard (Blanus cinereus) Culebra Ciega - panoramio
Cadeidae
Vidal & Hedges, 2008[30]
2 Cuban worm lizards Cadea blanoides
Rhineuridae
Vanzolini, 1951
1 North American worm lizards North American worm lizard (Rhineura floridana) Amphisbaenia 1
Trogonophidae
Gray, 1865
5 Palearctic worm lizards Checkerboard worm lizard (Trogonophis wiegmanni)
Gekkota (incl. Dibamia)
Family Species count Common names Example species Example photo
Dibamidae
Boulenger, 1884
23 Blind lizards Dibamus nicobaricum
Gekkonidae
Gray, 1825 (paraphyletic)
About 1,000 Geckos Thick-tailed gecko (Underwoodisaurus milii) Underwoodisaurus milii
Pygopodidae
Boulenger, 1884
44 Legless lizards Burton's snake lizard (Lialis burtonis) Lialis burtonis
Iguania
Family Species count Common names Example species Example photo
Agamidae
Spix, 1825
Over 300 Agamas Eastern bearded dragon (Pogona barbata) Bearded dragon04
Chamaeleonidae
Gray, 1825
202 Chameleons Veiled chameleon (Chamaeleo calyptratus) Chamaelio calyptratus
Corytophanidae
Frost & Etheridge, 1989
9 Casquehead lizards Plumed basilisk (Basiliscus plumifrons) Plumedbasiliskcele4 edit
Crotaphytidae
Frost & Etheridge, 1989
12 Collared and leopard lizards Common collared lizard (Crotaphytus collaris) Collared lizard in Zion National Park
Hoplocercidae
Frost & Etheridge, 1989
16 Wood lizards or clubtails Enyalioides binzayedi Holotype of Enyalioides binzayedi - ZooKeys-277-069-g007-top
Iguanidae 40 Iguanas Marine iguana (Amblyrhynchus cristatus) Marineiguana03
Leiosauridae
Frost et al., 2001
21 Darwin's iguana (Diplolaemus darwinii)
Liolaemidae
Frost & Etheridge, 1989
Over 200 Swifts Shining tree iguana (Liolaemus nitidus) Atacama lizard1
Opluridae
Frost & Etheridge, 1989
8 Madagascan iguanas Chalarodon (Chalarodon madagascariensis) Chalarodon madagascariensis male
Phrynosomatidae
Frost & Etheridge, 1989
136 Earless, spiny, tree, side-blotched and horned lizards Greater earless lizard (Cophosaurus texanus) Reptile tx usa
Polychrotidae
Frost & Etheridge, 1989 (+ Dactyloidae)
7 Anoles Carolina anole (Anolis carolinensis) Anolis carolinensis
Tropiduridae
Frost & Etheridge, 1989
At least 130 Neotropical ground lizards (Microlophus peruvianus) Mperuvianus
Lacertoidea (excl. Amphisbaenia)
Family Species count Common Names Example Species Example Photo
Alopoglossidae
Goicoechea, Frost, De la Riva, Pellegrino, Sites Jr., Rodrigues, & Padial, 2016
23 Ptychoglossus vallensis Ptychoglossus vallensis
Gymnophthalmidae
Fitzinger, 1826
Over 270 Spectacled lizards Bachia bicolor Bachia bicolor
Lacertidae
Oppel, 1811
Over 300 Wall or true lizards Ocellated lizard (Lacerta lepida) Perleidechse-20
Teiidae 151 Tegus or whiptails Gold tegu (Tupinambis teguixin) Goldteju Tupinambis teguixin
Neoanguimorpha
Family Species count Common names Example species Example photo
Anguidae
Oppel, 1811
About 100 Glass lizards, alligator lizards and slowworms Slowworm (Anguis fragilis) Anguidae
Anniellidae
Gray, 1852
6 American legless lizards California legless lizard (Anniella pulchra) Anniella pulchra
Helodermatidae 5 Gila monsters Gila monster (Heloderma suspectum) Gila.monster.arp
Xenosauridae
Cope, 1866
10 Knob-scaled lizards Mexican knob-scaled lizard (Xenosaurus grandis)
Paleoanguimorpha or Varanoidea
Family Species count Common names Example species Example photo
Lanthanotidae 1 Earless monitor Earless monitor (Lanthanotus borneensis) Real Lanthanotus borneensis
Shinisauridae 1 Chinese crocodile lizard Chinese crocodile lizard (Shinisaurus crocodilurus) Chin-krokodilschwanzechse-01
Varanidae 75 Monitor lizards Perentie (Varanus giganteus) Perentie Lizard Perth Zoo SMC Spet 2005
Scincoidea
Family Species count Common Names Example Species Example Photo
Cordylidae About 70 Spinytail lizards Girdle-tailed lizard (Cordylus warreni) Cordylus breyeri1
Gerrhosauridae 34 Plated lizards Sudan plated lizard (Gerrhosaurus major) Gerrhosaurus major
Scincidae
Oppel, 1811
Over 1500 Skinks Western blue-tongued skink (Tiliqua occipitalis) Tiliqua occipitalis
Xantusiidae 34 Night lizards Granite night lizard (Xantusia henshawi) Xantusia henshawi
Alethinophidia
Family Species count Common names Example species Example photo
Acrochordidae
Bonaparte, 1831[31]
3 File snakes Marine file snake (Acrochordus granulatus) Wart snake 1
Aniliidae
Stejneger, 1907[32]
1 Coral pipe snakes Burrowing false coral (Anilius scytale) False Coral Snake (Anilius scytale) close-up (13929278050)
Anomochilidae
Cundall, Wallach and Rossman, 1993.[33]
3 Dwarf pipe snakes Leonard's pipe snake, (Anomochilus leonardi)
Boidae
Gray, 1825[31] (incl. Calabariidae)
49 Boas Amazon tree boa (Corallus hortulanus) Corallushortulanus
Bolyeriidae
Hoffstetter, 1946
2 Round Island boas Round Island burrowing boa (Bolyeria multocarinata)
Colubridae
Oppel, 1811[31] sensu lato (incl. Dipsadidae, Natricidae, Pseudoxenodontidae)
Nearly 2,000 Colubrids Grass snake (Natrix natrix) Natrix natrix (Marek Szczepanek)
Cylindrophiidae
Fitzinger, 1843
8 Asian pipe snakes Red-tailed pipe snake (Cylindrophis ruffus) Cylindrophis rufus
Elapidae
Boie, 1827[31]
325 Cobras, coral snakes, mambas, kraits, sea snakes, sea kraits, Australian elapids King cobra (Ophiophagus hannah) Ophiophagus hannah2
Homalopsidae
Bonaparte, 1845
Over 50
Lamprophiidae
Fitzinger, 1843[34]
315 Bibron's burrowing asp (Atractaspis bibroni)
Loxocemidae
Cope, 1861
1 Mexican burrowing snakes Mexican burrowing snake (Loxocemus bicolor) Loxocemus bicolor
Pareatidae
Romer, 1956
20
Pythonidae
Fitzinger, 1826
31 Pythons Ball python (Python regius) Ball python lucy
Tropidophiidae
Brongersma, 1951
34 Dwarf boas Northern eyelash boa (Trachyboa boulengeri)
Uropeltidae
Müller, 1832
About 50 Shield-tailed snakes, short-tailed snakes Cuvier's shieldtail (Uropeltis ceylanica) Silybura shortii
Viperidae
Oppel, 1811[31]
224 Vipers, pitvipers, rattlesnakes European asp (Vipera aspis)
Xenodermatidae
Fitzinger, 1826
About 18
Xenopeltidae
Gray, 1849
2 Sunbeam snakes Sunbeam snake (Xenopeltis unicolor) XenopeltisUnicolorRooij
Scolecophidia (incl. Anomalepidae)
Family Common names Example species Example photo
Anomalepidae
Taylor, 1939[31]
15 Dawn blind snakes Dawn blind snake (Liotyphlops beui)
Gerrhopilidae
Vidal et al., 2010[30]
Over 16
Leptotyphlopidae
Stejneger, 1892[31]
87 Slender blind snakes Texas blind snake (Leptotyphlops dulcis) Leptotyphlops dulcis
Typhlopidae
Merrem, 1820[35]
Over 200 Blind snakes European blind snake (Typhlops vermicularis) Typhlops vermicularis
Xenotyphlopidae
Vidal et al., 2010[30]
2 Xenotyphlops grandidieri

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  22. ^ Fry, B. G.; Scheib, H.; Young, B.; McNaughtan, J.; Ramjan, S. F. R.; Vidal, N. (2008). "Evolution of an arsenal". Molecular & Cellular Proteomics. 7 (2): 215–246. doi:10.1074/mcp.m700094-mcp200. PMID 17855442.
  23. ^ Calvete, J. J.; Sanz, L.; Angulo, Y.; Lomonte, B.; Gutierrez, J. M. (2009). "Venoms, venomics, antivenomics". FEBS Letters. 583 (11): 1736–1743. doi:10.1016/j.febslet.2009.03.029. PMID 19303875.
  24. ^ Barlow, A.; Pook, C. E.; Harrison, R. A.; Wuster, W. (2009). "Coevolution of diet and prey-specific venom activity supports the role of selection in snake venom evolution". Proceedings of the Royal Society B: Biological Sciences. 276 (1666): 2443–2449. doi:10.1098/rspb.2009.0048. PMC 2690460. PMID 19364745.
  25. ^ "Snake-bites: appraisal of the global situation" (PDF). Who.com. Retrieved 30 December 2007.
  26. ^ "First Aid Snake Bites". University of Maryland Medical Center. Retrieved 30 December 2007.
  27. ^ "Komodo dragon kills boy, 8, in Indonesia". msnbc. Retrieved 30 December 2007.
  28. ^ Reeder, Tod W.; Townsend, Ted M.; Mulcahy, Daniel G.; Noonan, Brice P.; Wood, Perry L.; Sites, Jack W.; Wiens, John J. (2015). "Integrated Analyses Resolve Conflicts over Squamate Reptile Phylogeny and Reveal Unexpected Placements for Fossil Taxa". PLOS ONE. 10 (3): e0118199. doi:10.1371/journal.pone.0118199. PMC 4372529. PMID 25803280.
  29. ^ Zheng, Yuchi; Wiens, John J. (2016). "Combining phylogenomic and supermatrix approaches, and a time-calibrated phylogeny for squamate reptiles (lizards and snakes) based on 52 genes and 4162 species". Molecular Phylogenetics and Evolution. 94 (Pt B): 537–547. doi:10.1016/j.ympev.2015.10.009. PMID 26475614.
  30. ^ a b c S. Blair Hedges. "Families described". Hedges Lab | Evolutionary Biology.
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  32. ^ "Aniliidae". Integrated Taxonomic Information System. Retrieved 12 December 2007.
  33. ^ "Anomochilidae". Integrated Taxonomic Information System. Retrieved 13 December 2007.
  34. ^ "Atractaspididae". Integrated Taxonomic Information System. Retrieved 13 December 2007.
  35. ^ "Typhlopidae". Integrated Taxonomic Information System. Retrieved 13 December 2007.

Further reading

  • Bebler, John L.; King, F. Wayne (1979). The Audubon Society Field Guide to Reptiles and Amphibians of North America. New York: Alfred A. Knopf. p. 581. ISBN 978-0-394-50824-5.
  • Capula, Massimo; Behler (1989). Simon & Schuster's Guide to Reptiles and Amphibians of the World. New York: Simon & Schuster. ISBN 978-0-671-69098-4.
  • Cogger, Harold; Zweifel, Richard (1992). Reptiles & Amphibians. Sydney: Weldon Owen. ISBN 978-0-8317-2786-4.
  • Conant, Roger; Collins, Joseph (1991). A Field Guide to Reptiles and Amphibians Eastern/Central North America. Boston, Massachusetts: Houghton Mifflin Company. ISBN 978-0-395-58389-0.
  • Ditmars, Raymond L (1933). Reptiles of the World: The Crocodilians, Lizards, Snakes, Turtles and Tortoises of the Eastern and Western Hemispheres. New York: Macmillan. p. 321.
  • Evans, SE (2003). "At the feet of the dinosaurs: the origin, evolution and early diversification of squamate reptiles (Lepidosauria: Diapsida)". Biological Reviews, Cambridge. 78 (4): 513–551. doi:10.1017/S1464793103006134. PMID 14700390.
  • Evans SE. 2008. The skull of lizards and tuatara. In Biology of the Reptilia, Vol.20, Morphology H: the skull of Lepidosauria, Gans C, Gaunt A S, Adler K. (eds). Ithaca, New York, Society for the study of Amphibians and Reptiles. pp1–344. Weblink to purchase
  • Evans, SE; Jones, MEH (2010). The origin, early history and diversification of lepidosauromorph reptiles. In Bandyopadhyay S. (ed.), New Aspects of Mesozoic Biodiversity. 27 Lecture Notes in Earth Sciences. Lecture Notes in Earth Sciences. 132. pp. 27–44. doi:10.1007/978-3-642-10311-7_2. ISBN 978-3-642-10310-0.
  • Freiberg, Dr. Marcos; Walls, Jerry (1984). The World of Venomous Animals. New Jersey: TFH Publications. ISBN 978-0-87666-567-1.
  • Gibbons, J. Whitfield; Gibbons, Whit (1983). Their Blood Runs Cold: Adventures With Reptiles and Amphibians. Alabama: University of Alabama Press. p. 164. ISBN 978-0-8173-0135-4.
  • McDiarmid, RW; Campbell, JA; Touré, T (1999). Snake Species of the World: A Taxonomic and Geographic Reference. 1. Herpetologists' League. p. 511. ISBN 978-1-893777-00-2.
  • Mehrtens, John (1987). Living Snakes of the World in Color. New York: Sterling. ISBN 978-0-8069-6461-4.
  • Rosenfeld, Arthur (1989). Exotic Pets. New York: Simon & Schuster. p. 293. ISBN 978-0-671-47654-0.

External links

Amphipholis squamata

Amphipholis squamata, common names brooding snake star and dwarf brittle star, is a species of brittle star in the family Amphiuridae.

Barremian

The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 129.4 ± 1.5 Ma (million years ago) and 125.0 ± 1.0 Ma). It is a subdivision of the Early Cretaceous epoch (or Lower Cretaceous series). It is preceded by the Hauterivian and followed by the Aptian stage.

Cyrtodactylus

Cyrtodactylus (Greek κυρτος kurtos "curved", from κυπτω kuptō "to stoop"; δακτυλος daktulos "finger, toe") is a diverse genus of Asian geckos, commonly known as bent-toed geckos or bow-fingered geckos. It has at least 250 described species at present, which makes it the largest of all gecko genera.

Gekkonidae

Gekkonidae is the largest family of geckos, containing over 950 described species in 61 genera. Many common geckos are member of this family, including house geckos (Hemidactylus), true geckos (Gekko), day geckos (Phelsuma), and web-toed geckos (Gehyra). Gekkonid geckos occur globally and are particularly species-rich in tropical areas.

Hemipenis

A hemipenis (plural hemipenes) is one of a pair of intromittent organs of male squamates (snakes, lizards and worm lizards). Hemipenes are usually held inverted within the body, and are everted for reproduction via erectile tissue, much like that in the human penis. They come in a variety of shapes, depending on species, with ornamentation, such as spines or hooks.

Iguanomorpha

Iguania is an infraorder of squamate reptiles that includes iguanas, chameleons, agamids, and New World lizards like anoles and phrynosomatids. Using morphological features as a guide to evolutionary relationships, the Iguania are believed to form the sister group to the remainder of the Squamata. However, molecular information has placed Iguania well within the Squamata as sister taxa to the Anguimorpha and closely related to snakes. Iguanians are largely arboreal and usually have primitive fleshy, non-prehensile tongues, although the tongue is highly modified in chameleons. The group has a fossil record that extends back to the Early Jurassic (the oldest known member is Bharatagama, which lived about 190 million years ago in what is now India).

Juniperus squamata

Juniperus squamata (flaky juniper or Himalayan juniper; Chinese: 高山柏 gao shan bai) is a species of juniper native to the Himalayas and China, from northeastern Afghanistan east to western Yunnan in southwestern China, and with disjunct populations north to western Gansu and east to Fujian. It grows at 1,600-4,900 m altitude. It represents the provincial tree of Khyber Pakhtunkhwa (unofficial).

It is a coniferous evergreen shrub (rarely a small tree) reaching 2–10 m tall (rarely 15 m), with flaky brown bark, and a prostrate to irregularly conical crown. The leaves are broad needle-like, 3–9 mm long, arranged in six ranks in alternating whorls of three, and often strongly glaucous blue-green in colour. The cones are berry-like, globose to ovoid, 4–9 mm long and 4–6 mm diameter, glossy black, and contain one seed; they are mature in about 18 months. The male cones are 3–4 mm long, and shed their pollen in early spring. It is largely dioecious, with pollen and seed cones produced on separate plants, but occasionally monoecious.The Latin specific epithet squamata means small, scale-like leaves.Three to five varieties are accepted, with treatment differing between different authors:

Juniperus squamata var. squamata - leaves mostly 5–9 mm. Throughout the range.

Juniperus squamata var. fargesii Rehder & E.H.Wilson - leaves mostly 3–5 mm. Confined to the eastern half of the range in China.

Juniperus squamata var. hongxiensis Y.F.Yu & L.K.Fu; often included in var. squamata.

Juniperus squamata var. parviflora Y.F.Yu & L.K.Fu; often included in var. squamata.Juniperus morrisonicola Hayata from Taiwan is often treated as a synonym, or a variety Juniperus squamata var. morrisonicola (Hayata) H.L.Li & H.Keng, but is better treated as a distinct species as it has a distinct DNA profile.

Lepidosauria

The Lepidosauria (from Greek meaning scaled lizards) are reptiles with overlapping scales. This subclass includes Squamata and Rhynchocephalia. It is a monophyletic group and therefore contains all descendants of a common ancestor. Squamata includes snakes, lizards, and amphisbaenia. Rhynchocephalia was a widespread and diverse group 220-100 million years ago; however, it is now represented only by the genus Sphenodon, which contains a single species of tuatara, native to New Zealand. Lepidosauria is the sister taxon to Archosauria, which includes Aves and Crocodilia. Lizards and snakes are the most speciose group of lepidosaurs and, combined, contain over 9,000 species. There are many noticeable distinguishing morphological differences between lizards, tuataras, and snakes.

Lepidosauromorpha

Lepidosauromorpha is a group of reptiles comprising all diapsids closer to lizards than to archosaurs (which include crocodiles and birds). The only living sub-group is the Lepidosauria: extant lizards, snakes, amphisbaenians and tuataras.

Lepidosauromorpha are distinguishable from Archosauromorphs (archosaurs) by their primitive sprawling gait, which allows for the same sinusoidal trunk and tail movement seen in fish, the sliding "joint" between the coracoids and the sternum (for a longer stride), and their pleurodont dentition. In contrast, Archosauromorphs possess a parasagittal gait, a reduction in their dermal girdle, a reduction and/or loss of the sternum, and a more thecodont dentition.

Lepidosauromorpha have retained cold blood because of their low-energy sprawling stance.

List of reptiles of Colombia

Colombia is the sixth richest country in the world for reptiles, and third richest in the Western Hemisphere.

Lorica squamata

The lorica squamata is a type of scale armour used by the ancient Roman military during the Roman Republic and at later periods. It was made from small metal scales sewn to a fabric backing.It is typically seen on depictions of standard bearers, musicians, centurions, cavalry troops, and auxiliary infantry, as well as regular legionaries. The Roman victory triumph depicting Trajan's victory over the Dacians, the Tropaeum Traiani, shows the majority of legionaries wearing loricae squamatae. A shirt of scale armour was shaped in the same way as a mail lorica hamata, mid-thigh length with the shoulder doublings or cape. This depiction may be in line with historical events, as Trajan had to re-equip his soldiers wearing lorica segementata with other forms of armor such as the lorica hamata (chainmail) and lorica squamata (scale) during the Dacian Wars. The individual scales (squamae) were either iron or bronze, or alternating metals on the same shirt. They could be tinned as well, one surviving fragment showing bronze scales that were alternately tinned and plain. The metal was generally not very thick, 0.50 mm to 0.80 mm (.020" to .032") perhaps being a common range. Since the scales overlapped in every direction, however, the multiple layers gave good protection. The size ranged from as small as 6.3 mm wide by 9.5 mm tall (1/4" × 3/8") up to about 5 cm wide by 8 cm tall (2" × 3"), with the most common sizes being roughly 1.3 cm by 2.5 cm (1/2" × 1"). Many have rounded bottoms, while others are pointed or have flat bottoms with the corners clipped off at an angle. The scales could be flat, or slightly domed, or have a raised midrib or edge. All the scales in a shirt would generally be of the same size; however, scales from different shirts may vary significantly.

The scales were wired or laced together in horizontal rows that were then laced or sewn to the backing. Therefore, each scale had from four to 12 holes: two or more at each side for wiring to the next in the row, one or two at the top for fastening to the backing, and sometimes one or two at the bottom to secure the scales to the backing or to each other.

There was also a rare type where the backing was a mail lorica hamata, effectively giving two layers of defence, but at the cost of greater weight and expense.It is possible that the shirt could be opened either at the back or down one side so that it was easier to put on, the opening being closed by ties. Much has been written about scale armour's supposed vulnerability to an upward thrust, but this may be exaggerated.

No examples of an entire lorica squamata have been found, but there have been several archaeological finds of fragments of such shirts and individual scales are quite common finds—even in non-military contexts.

The type of armour in which the scales are laced to each other and need no backing at all is known as lamellar armour, while to confuse the matter there is also locking scale in which the scales are wired together without a backing. It can be difficult to tell which type of armour a single scale might have come from, as the Romans did not necessarily have different terms for each type. The typical scale had a vertical pair of holes at each side near the top, plus one or two holes at the top.

Monitor lizard

The monitor lizards are large lizards in the genus Varanus. They are native to Africa, Asia, and Oceania, but are now found also in the Americas as an invasive species. Currently, 79 species are recognized.

Monitor lizards have long necks, powerful tails and claws, and well-developed limbs. The adult length of extant species ranges from 20 cm (7.9 in) in some species, to over 3 m (10 ft) in the case of the Komodo dragon, though the extinct varanid known as Megalania (Varanus priscus) may have been capable of reaching lengths more than 7 m (23 ft). Most monitor species are terrestrial, but arboreal and semiaquatic monitors are also known. While most monitor lizards are carnivorous, eating eggs, smaller reptiles, fish, birds, and small mammals, some also eat fruit and vegetation, depending on where they live.

Mosasaur

Mosasaurs (from Latin Mosa meaning the 'Meuse river', and Greek σαύρος sauros meaning 'lizard') comprise a group of extinct, large marine reptiles containing 38 genera in total. Their first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764. Mosasaurs probably evolved from an extinct group of aquatic lizards known as aigialosaurs in the Early Cretaceous. During the last 20 million years of the Cretaceous period (Turonian-Maastrichtian ages), with the extinction of the ichthyosaurs and pliosaurs, mosasaurs became the dominant marine predators. They became extinct as a result of the K-Pg event at the end of the Cretaceous period, about 66 million years ago.

Ophidia

Ophidia (also known as Pan-Serpentes) is a group of squamate reptiles including modern snakes and all reptiles more closely related to snakes than to other living groups of lizards.

Ophidia was defined as the "most recent common ancestor of Pachyrhachis and Serpentes (modern snakes), and all its descendants" by Lee and Caldwell (1998: 1551). The latter author has used Ophidia in a manner inconsistent with this definition, using it to incorporate other more basal stem-snakes, such as the Late Cretaceous Najash rioegrina or the Jurassic Diablophis and Portugalophis.

The clade name Ophidia derives from the Ancient Greek word ὀφίδιον (ophídion), meaning "small snake".

Roman military personal equipment

Roman military personal equipment was produced in small numbers to established patterns, and it was used in an established manner. These standard patterns and uses were called the res militaris or disciplina. Its regular practice during the Roman Republic and Roman Empire led to military excellence and victory. The equipment gave the Romans a very distinct advantage over their barbarian enemies, especially so in the case of armour. This does not mean that every Roman soldier had better equipment than the richer men among his opponents. According to Edward Luttwak, Roman equipment was not of a better quality than that used by the majority of Rome's adversaries.Initially, they used weapons based on Greek and Etruscan models. On encountering the Celts, they based new varieties on Celtic equipment. To defeat the Carthaginians, they constructed an entire fleet de novo based on the Carthaginian model. Once a weapon was adopted, it became standard. The standard weapons varied somewhat during Rome's long history, but the equipment and its use were never individual.

Scleroglossa

Scleroglossa is a clade (evolutionary group) of lizards that includes geckos, autarchoglossans (scincomorphs, anguimorphs, and varanoids), and amphisbaenians. Scleroglossa is supported by phylogenetic analyses that use morphological features (visible anatomical features). According to most morphological analyses, Scleroglossa is the sister group of the clade Iguania, which includes iguanas, chameleons, agamids, and New World lizards. Together, Scleroglossa and Iguania make up crown group Squamata, the smallest evolutionary grouping to include all living lizards and snakes.

The name Scleroglossa is derived from the Greek, skleros, meaning "hard" and glossa, meaning "tongue". The split between Scleroglossa and Iguania can be based on features of the tongue; iguanians have a muscular tongue and use lingual prehension to capture food, whereas scleroglossans have hard tongues and use teeth-and-jaw prehension to capture food, freeing the tongue for chemosensory activity.

Recent phylogenetic analyses based on molecular data (such as DNA sequences) nest iguanians deeper within Squamata along with snakes and anguimorphs. Under this phylogeny, Scleroglossa is not a valid grouping. A new clade Bifurcata (bifurcated tongue) has been proposed to include Iguania as a sister taxon to Anguimorpha.

Toxicofera

Toxicofera (Greek for "those who bear toxins") is a proposed clade of scaled reptiles (squamates) that includes the Serpentes (snakes), Anguimorpha (monitor lizards, gila monster, and alligator lizards) and Iguania (iguanas, agamas, and chameleons). Toxicofera contains about 4,600 species, (nearly 60%) of extant squamata. It encompasses all venomous reptile species, as well as numerous related non-venomous species. There is little morphological evidence to support this grouping, however it has been recovered by all molecular analyses as of 2012.

Varanidae

The Varanidae are a family of lizards in the superfamily Varanoidea. The family, a group of carnivorous and frugivorous lizards, includes the living genus Varanus, the extinct Megalania (the largest known land-dwelling lizard), and a number of other extinct taxa. Varanus includes the Komodo dragon (the largest living lizard), the crocodile monitor and Savannah monitor, the goannas of Australia and Southeast Asia, and various other species with a similarly distinctive appearance. Their closest living relatives are the anguid and helodermatid lizards.

Violet-necked lory

The violet-necked lory (Eos squamata) is a species of parrot in the family Psittaculidae. It is endemic to Indonesia, where it is found in the northern Maluku Islands and west Papuan islands. Its natural habitats are tropical moist lowland forests and tropical mangrove forests.

Extinct squamate genera
Extant reptile orders by subclass
Diapsida
Extant chordate classes
Olfactores

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