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Skink

(Redirected fromScincidae)
This article is about the reptile. For other uses, seeSkink (disambiguation).

Skinksarelizardsbelonging to thefamilyScincidae,a family in theinfraorderScincomorpha.With more than 1,500 describedspeciesacross 100 different taxonomic genera, the family Scincidae is one of the most diverse families of lizards. Skinks are characterized by their smaller legs in comparison to typical lizards and are found in different habitats except arctic and subarctic regions.[1][2]

Skink
Temporal range:EarlyCenomanianto recent
Trachylepis striata
Scientific classificationEdit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Superfamily: Scincoidea
Family: Scincidae
Gray,1825
Subfamilies

Forgenera,seetext.

Etymology

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The wordskink,which entered the English language around 1580–1590, comes fromclassical Greekskinkosand Latinscincus,names that referred to various specific lizards.[3]

Description

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Skinks look like lizards of the familyLacertidae(sometimes calledtrue lizards), but most species of skinks have no pronounced neck and relatively small legs. Several genera (e.g.,Typhlosaurus) have no limbs at all. This is not true for all skinks, however, as some species such as thered-eyed crocodile skinkhave a head that is very distinguished from the body. These lizards also have legs that are relatively small proportional to their body size.

Skinks' skulls are covered by substantial bony scales, usually matching up in shape and size, while overlapping.[4]Other genera, such asNeoseps,have reduced limbs and fewer than fivetoes(digits) on each foot. In such species, their locomotion resembles that ofsnakesmore than that of lizards with well-developed limbs. As a general rule, the longer the digits, the more arboreal the species is likely to be. A biological ratio can determine the ecological niche of a given skink species. The Scincidae ecological niche index (SENI) is a ratio based on anterior foot length at the junction of the ulna/radius-carpal bones to the longest digit divided by thesnout-to-vent length.[5]

Most species of skinks have long, tapering tails they can shed if predators grab onto them. Such species generally canregeneratethe lost part of a tail, though imperfectly. A lost tail can grow back within around three to four months.[6]Species with stumpy tails have no special regenerative abilities.

Some species of skinks are quite small;Scincella lateralistypically ranges from7.5 to 14.5 cm (3 to5+3⁄4in), more than half of which is the tail.[7]Most skinks, though, are medium-sized, with snout-to-vent lengths around12 cm (4+1⁄2in), although some grow larger; theSolomon Islands skink(Corucia zebrata) is the largest known extant species and may attain a snout-to-vent length of some 35 cm (14 in).

Skinks can often hide easily in their habitat because of their protective colouring (camouflage).[8]

Blood color

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Skinks in the genusPrasinohaemahave green blood because of a buildup of the waste productbiliverdin.[9]

Evolutionary history

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The oldest known skink isElectroscincus zedidescribed from the mid-Cretaceous (lateAlbianto earlyCenomanian)Burmese amberfromMyanmar,dating to around100million years ago.Based on the presence ofosteoderms,Electroscincusappears to belong to the Scincidaecrown group,indicating that some divergence among the extant skink subfamilies must have already occurred by 100 million years ago.[10]Other definitive skink fossils are known from theMiocene.[11][12]

Skink genera known from fossils include the following:[13]

Behavior

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A trait apparent in many species of skink is digging and burrowing. Many spend their time underground where they are mostly safe from predators, sometimes even digging out tunnels for easy navigation. They also use their tongues to sniff the air and track their prey. When they encounter their prey, they chase it down until they corner it or manage to land a bite and then swallow it whole. Despite being voracious hunters at times, all species pose no threat to humans and will generally avoid interaction in the wild. Being neither poisonous or venomous, their bites are also mild and minor.

Diet

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Skinks are generallycarnivorousand in particularinsectivorous.Typical prey includeflies,crickets,grasshoppers,beetles,andcaterpillars.Various species also eatearthworms,millipedes,centipedes,snails,slugs,isopods(woodliceetc), moths, small lizards (includinggeckos), and smallrodents.Some species, particularly those favored as home pets, areomnivorousand have more varied diets and can be maintained on a regimen of roughly 60% vegetables/leaves/fruit and 40% meat (insects and rodents).[14]Species of the genusTristiidonare mainly frugivorous, but occasionally eat moss and insects.

Breeding

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Trachylepis maculilabrismating

Although most species of skinks areoviparous,laying eggs in clutches, some 45% of skink species areviviparousin one sense or another. Many species areovoviviparous,the young (skinklets) developinglecithotrophicallyin eggs that hatch inside the mother'sreproductive tract,and emerging as live births.

In some genera, however, such asTiliquaandCorucia,the young developing in the reproductive tract derive their nourishment from a mammal-likeplacentaattached to the female – unambiguous examples of viviparousmatrotrophy.[15]Furthermore, an example recently described inTrachylepisivensiis the most extreme to date: a purely reptilian placenta directly comparable in structure and function, to aeutherianplacenta.[16] Clearly, such vivipary repeatedly has developed independently in the evolutionary history of the Scincidae and the different examples are not ancestral to the others. In particular, placental development of whatever degree in lizards isphylogeneticallyanalogous,rather thanhomologous,to functionally similar processes in mammals.[15]

Nesting

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Skinks typically seek out environments protected from the elements, such as thick foliage, underneath man-made structures, and ground-level buildings such as garages and first-floor apartments. When two or more skinks are seen in a small area, it is typical to find a nest nearby. Skinks are considered to be territorial and often are seen standing in front of or "guarding" their nest area. If a nest is nearby, one can expect to see 10-30 lizards within the period of a month. In parts of the southern United States, nests are commonly found in houses and apartments, especially along the coast. The nest is where the skink lays its small white eggs, up to 4-8 at a time.[17]

Habitat

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Cape skinknative to South Africa

Skinks are very specific in their habitat as some can depend on vegetation while others may depend on land and the soil.[18]As a family, skinks arecosmopolitan;species occur in a variety ofhabitatsworldwide, apart fromborealand polar regions. Various species occur in ecosystems ranging from deserts and mountains to grasslands.

Afive-lined skinkbasking on a log in Forest Park.

Many species are good burrowers. More species are terrestrial orfossorial(burrowing) thanarboreal(tree-climbing) or aquatic species. Some are "sand swimmers", especially the desert species, such as themole skinkorsand skinkinFlorida.Some use a very similar action in moving through grass tussocks. Most skinks arediurnal(day-active) and typically bask on rocks or logs during the day.

Predators

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Raccoons,foxes,possums,snakes,coatis,weasels,crows,cats,dogs,herons,hawks,lizards,and other predators of small land vertebrates also prey on various skinks. This can be troublesome, given the long gestation period for some skinks, making them an easy target to predators such as themongoose,which often threaten the species to at least near extinction, such as theAnguilla Bank skink.Invasive rodents are a major threat to skinks that have been overlooked, especially tropical skinks.[19]

Skinks are also hunted for food by indigenous peoples inNew Guinea,including by theKalampeople in the highlands ofMadang Province,Papua New Guinea.[20]

Genetics

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Genomic architecture

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Despite making up 15% of reptiles, skinks have a relatively conserved chromosome number, between 11 and 16 pairs.[21]Skink genomes are typically about 1.5 Gb, approximately one-half the size of the human genome. TheChristmas Island blue-tailed skink (Cryptoblepharus egeriae)was sequenced in 2022, representing the first skink reference genome.[22]

Sex determination systems

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Skinks were long thought to have both genetic sex determination (GSD) andtemperature-dependent sex determination(TSD). Despite having sex chromosomes that are not distinguishable with a microscope, all major skink lineages share an old XY system that is over 80 million years old.[23]These X and Y specific regions are highly divergent and contain multiplechromosomal rearrangementsand repetitive sequences.[22]

Genera

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Many genera,Mabuyafor example, are still insufficiently studied, and theirsystematicsare at times controversial, see for example thetaxonomyof thewestern skink,Plestiodon skiltonianus.Mabuyain particular, is being split, many species being allocated to new genera such asTrachylepis,Chioninia,andEutropis.

SubfamilyAcontinae(limbless skinks; 30 species in 2 genera)[24]

SubfamilyEgerniinae(social skinks; 63 species in 9 genera)[25]

SubfamilyEugongylinae(eugongylid skinks; 455 species in 50 genera)[26]

SubfamilyLygosominae(lygosomid skinks; 56 species in 6 genera)[27]

SubfamilyMabuyinae(mabuyid skinks; 226 species in 25 genera)[28]

SubfamilySphenomorphinae(sphenomorphid skinks; 591 species in 41 genera)[29]

SubfamilyScincinae(typical skinks; 294 species in 35 genera)[30]

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See also

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References

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  1. ^Mecke, Doughty & Donnellan (2013)."Redescription ofEremiascincus fasciolatus(Günther, 1867) (Reptilia: Squamata: Scincidae) with clarification of its synonyms and the description of a new species "(PDF).Zootaxa.3701(5): 473–517.doi:10.11646/zootaxa.3701.5.1.PMID26191600.
  2. ^"Skink | lizard".Encyclopedia Britannica.Retrieved2019-05-06.
  3. ^"the definition of skink".www.dictionary.com.Retrieved2019-05-06.
  4. ^Grzimek, Bernhard (1975).Grzimek's Animal Life Encyclopedia Volume 6 Reptiles.New York, NY: Van nostrand reinhold company. p. 242.
  5. ^Schnirel, Brian (2004). "SENI biometric analysis on the extinct Scincidae species:Macroscincus coctei".Polyphemos,Volume 1, Issue 2, May, Florence, South Carolina. pp. 12–22.
  6. ^"10 Creatures That Conveniently Grow Back Body Parts".TreeHugger.Retrieved2019-05-06.
  7. ^"Species Profile: Ground Skink (Scincella lateralis) | SREL Herpetology ".srelherp.uga.edu.Retrieved2019-05-06.
  8. ^"Skink Facts".www.softschools.com.Retrieved2019-05-06.
  9. ^Malhotra, Anita."Some lizards have green blood that should kill them – and scientists can't work out why".The Conversation.Retrieved2019-05-06.
  10. ^Daza, J. D.; Stanley, E. L.; Heinicke, M. P.; Leah, C.; Doucet, D. S.; Fenner, K. L.; Arias, J. S.; Smith, R. D. A.; Peretti, A. M.; Aung, N. N.; Bauer, A. M. (2024)."Compound osteoderms preserved in amber reveal the oldest known skink".Scientific Reports.14.15662.doi:10.1038/s41598-024-66451-w.PMC11231356.
  11. ^Scientific American — Skinks, Skinks, Skinks
    Fossils indicate skinks as a whole are a fairly old group of lizards, the oldest specimens attributed to the group dating to the Lower Cretaceous. The vast majority of early fossil representatives of the group consists of jaw fragments alone. These are certainly from skink-like lizards (from the major lizard group termed Scincomorpha), but they might not all be from skinks proper, and some have been suggested to actually represent other groups (like the armadillo lizards or cordylids, a scincomorph group that also has a possible Cretaceous fossil record). Definite fossil members of modern groups – like blue-tongued skinks – are present in the Miocene.
  12. ^Estes, Richard (1983).Sauria Terrestria, Amphisbaenia. Handbuch der Paläoherpetologie, Part 10A[Sauria Terrestria, Amphisbaenia. Handbook of Paleoherpetology, Part 10A.] (in German). Stuttgart and New York: Gustav Fischer Verlag.ISBN978-3-89937-026-3.
  13. ^"Scincidae Gray 1825".Paleobiology Database.Fossilworks.Retrieved17 December2021.
  14. ^McLeod, Lianne."Keeping Blue Tongued Skinks as Pets".Retrieved2006-08-27.
  15. ^abJustin L. Rheubert; Dustin S. Siegel; Stanley E. Trauth (19 December 2014).Reproductive Biology and Phylogeny of Lizards and Tuatara.CRC Press. pp. 548–.ISBN978-1-4665-7987-3.
  16. ^Blackburn, D. G.; Flemming, A. F. (2011). "Invasive implantation and intimate placental associations in a placentotrophic African lizard,Trachylepis ivensi(Scincidae) ".Journal of Morphology.273(2): 137–59.doi:10.1002/jmor.11011.PMID21956253.S2CID5191828.
  17. ^"Amazing Facts about the Common Garden Skink | OneKindPlanet Animals".OneKindPlanet.Retrieved2019-05-06.
  18. ^Cabrelli, Abigail (August 2017). "Assessing the vulnerability of Australian skinks to climate change".Climate Change.130(2): 223–233.doi:10.1007/s10584-015-1358-6.S2CID153428168– via Energy & Power Source.
  19. ^Thibault, Martin (2017)."Invasive rodents, an overlooked threat for skinks in a tropical island hotspot of biodiversity".New Zealand Journal of Ecology.41:1–10.doi:10.20417/nzjecol.41.9.
  20. ^Bulmer, RNH (1975).Kalam Classification Of Reptiles And Fishes.Journal of the Polynesian Society84(3): 267–308.
  21. ^Giovannotti, M.; Caputo, V.; O'Brien, P. C. M.; Lovell, F. L.; Trifonov, V.; Cerioni, P. Nisi; Olmo, E.; Ferguson-Smith, M. A.; Rens, W. (2009)."Skinks (Reptilia: Scincidae) have highly conserved karyotypes as revealed by chromosome painting".Cytogenetic and Genome Research.127(2–4): 224–231.doi:10.1159/000295002.ISSN1424-859X.PMID20215726.
  22. ^abDodge, Tristram O.; Farquharson, Katherine A.; Ford, Claire; Cavanagh, Lisa; Schubert, Kristen; Schumer, Molly; Belov, Katherine; Hogg, Carolyn J. (2023)."Genomes of two Extinct‐in‐the‐Wild reptiles from Christmas Island reveal distinct evolutionary histories and conservation insights".Molecular Ecology Resources:1755–0998.13780.doi:10.1111/1755-0998.13780.ISSN1755-098X.
  23. ^Kostmann, Alexander; Kratochvíl, Lukáš; Rovatsos, Michail (2021-01-27)."Poorly differentiated XX/XY sex chromosomes are widely shared across skink radiation".Proceedings. Biological Sciences.288(1943): 20202139.doi:10.1098/rspb.2020.2139.ISSN1471-2954.PMC7893288.PMID33468012.
  24. ^Uetz, P.; et al. (eds.)."Acontinae".The Reptile Database.Retrieved10 October2019.
  25. ^Uetz, P.; et al. (eds.)."Egerniinae".The Reptile Database.Retrieved10 October2019.
  26. ^Uetz, P.; et al. (eds.)."Eugongylinae".The Reptile Database.Retrieved10 September2020.
  27. ^Uetz, P.; et al. (eds.)."Lygosominae".The Reptile Database.Retrieved10 October2019.
  28. ^Uetz, P.; et al. (eds.)."Mabuyinae".The Reptile Database.Retrieved10 September2020.
  29. ^Uetz, P.; et al. (eds.)."Sphenomorphinae".The Reptile Database.Retrieved10 October2019.
  30. ^Uetz, P.; et al. (eds.)."Scincinae".The Reptile Database.Retrieved10 October2019.

Sources

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  • De Vosjoli, Philippe (1993)Prehensile-Tailed Skinks.Advanced Vivarium Systems.ISBN1-882770-24-2
  • Hedges, S. Blairand Caitlin E. Conn. 2012. A new skink fauna from Caribbean islands (Squamata, Mabuyidae, Mabuyinae). Zootaxa 3288.
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