Skink

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Skink
Temporal range: Paleocene - Recent
Blue-toungued skink444.jpg
Eastern blue-tongued lizard
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Superfamily: Scincoidea
Family: Scincidae
Gray, 1825
Subfamilies

For genera, see text.

Skinks are lizards belonging to the family Scincidae, a family in the infraorder Scincomorpha. With more than 1,500 described species across 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]

Contents

Description

Skinks look like lizards of the family Lacertidae (sometimes called true 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 the red-eyed crocodile skink have 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. [3] Other genera, such as Neoseps , have reduced limbs and fewer than five toes (digits) on each foot. In such species, their locomotion resembles that of snakes more 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 the snout-to-vent length. [4]

Most species of skinks have long, tapering tails they can shed if predators grab onto them. Such species generally can regenerate the lost part of a tail, though imperfectly. A lost tail can grow back within around three to four months. [5] Species with stumpy tails have no special regenerative abilities.

Some species of skinks are quite small; Scincella lateralis typically ranges from 7.5 to 14.5 cm (3 to 5+3⁄4 in), more than half of which is the tail. [6] Most skinks, though, are medium-sized, with snout-to-vent lengths around 12 cm (4+1⁄2 in), although some grow larger; the Solomon 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). [7]

Blood color

Skinks in the genus Prasinohaema have green blood because of a buildup of the waste product biliverdin. [8]

History

The word skink, which entered the English language around 1580–1590, comes from classical Greek skinkos and Latin scincus, names that referred to various specific lizards. [9]

Skink-like lizards first appear in the fossil record about 140 million years ago, during the early Cretaceous, mostly in the form of jawbones that appear very skink-like. Definitive skink fossils appear later, during the Miocene period. [10] [11]

Skink genera known from fossils include the following: [12]

Behavior

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

Skinks are generally carnivorous and in particular insectivorous. Typical prey include flies, crickets, grasshoppers, beetles, and caterpillars. Various species also eat earthworms, millipedes, centipedes, snails, slugs, isopods (woodlice etc), moths, small lizards (including geckos), and small rodents. Some species, particularly those favored as home pets, are omnivorous and have more varied diets and can be maintained on a regimen of roughly 60% vegetables/leaves/fruit and 40% meat (insects and rodents). [13] Species of the genus Tristiidon are mainly frugivorous, but occasionally eat moss and insects.

Breeding

Trachylepis maculilabris mating Trachylepis maculilabris mating.jpg
Trachylepis maculilabris mating

Although most species of skinks are oviparous, laying eggs in clutches, some 45% of skink species are viviparous in one sense or another. Many species are ovoviviparous, the young (skinklets) developing lecithotrophically in eggs that hatch inside the mother's reproductive tract, and emerging as live births.

In some genera, however, such as Tiliqua and Corucia , the young developing in the reproductive tract derive their nourishment from a mammal-like placenta attached to the female – unambiguous examples of viviparous matrotrophy. [14] Furthermore, an example recently described in Trachylepis ivensi is the most extreme to date: a purely reptilian placenta directly comparable in structure and function, to a eutherian placenta. [15] 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 is phylogenetically analogous, rather than homologous, to functionally similar processes in mammals. [14]

Nesting

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. [16]

Habitat

Cape skink native to South Africa Cape Skink Flowers.jpg
Cape skink native 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. [17] As a family, skinks are cosmopolitan; species occur in a variety of habitats worldwide, apart from boreal and polar regions. Various species occur in ecosystems ranging from deserts and mountains to grasslands.

Many species are good burrowers. More species are terrestrial or fossorial (burrowing) than arboreal (tree-climbing) or aquatic species. Some are "sand swimmers", especially the desert species, such as the mole skink or sand skink in Florida. Some use a very similar action in moving through grass tussocks. Most skinks are diurnal (day-active) and typically bask on rocks or logs during the day.

Predators

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 the mongoose, which often threaten the species to at least near extinction, such as the Anguilla Bank skink. Invasive rodents are a major threat to skinks that have been overlooked, especially tropical skinks. [18]

Skinks are also hunted for food by indigenous peoples in New Guinea, including by the Kalam people in the highlands of Madang Province, Papua New Guinea. [19]

Genetics

Genomic architecture

Despite making up 15% of reptiles, skinks have a relatively conserved chromosome number, between 11 and 16 pairs. [20] Skink genomes are typically about 1.5 Gb, approximately one-half the size of the human genome. The Christmas Island blue-tailed skink (Cryptoblepharus egeriae) was sequenced in 2022, representing the first skink reference genome. [21]

Sex determination systems

Skinks were long thought to have both genetic sex determination (GSD) and temperature-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. [22] These X and Y specific regions are highly divergent and contain multiple chromosomal rearrangements and repetitive sequences. [21]

Genera

Many genera, Mabuya for example, are still insufficiently studied, and their systematics are at times controversial, see for example the taxonomy of the western skink, Plestiodon skiltonianus. Mabuya in particular, is being split, many species being allocated to new genera such as Trachylepis , Chioninia , and Eutropis .

Subfamily Acontinae (limbless skinks; 30 species in 2 genera) [23]

Subfamily Egerniinae (social skinks; 63 species in 9 genera) [24]

Subfamily Eugongylinae (eugongylid skinks; 455 species in 50 genera) [25]

Subfamily Lygosominae (lygosomid skinks; 56 species in 6 genera) [26]

Subfamily Mabuyinae (mabuyid skinks; 226 species in 25 genera) [27]

Subfamily Sphenomorphinae (sphenomorphid skinks; 591 species in 41 genera) [28]

Subfamily Scincinae (typical skinks; 294 species in 35 genera) [29]

Related Research Articles

<i>Egernia</i> Genus of lizards

Egernia is a genus of skinks that occurs in Australia. These skinks are ecologically diverse omnivores that inhabit a wide range of habitats. However, in the loose delimitation the genus is not monophyletic but an evolutionary grade, as has long been suspected due to its lack of characteristic apomorphies.

<i>Emoia</i> Genus of lizards

Emoia is a genus of skinks, lizards in the subfamily Eugongylinae. The genus Emoia belongs to a group of genera mainly from the southwestern Pacific-Australian region.

<i>Eugongylus</i> Genus of lizards

Eugongylus is a genus of skinks in the subfamily Eugongylinae. It was previously recognised as namesake of the Eugonglyus group of genera within Lygosominae, where it occupied a quite basal position. Members of this genus are commonly called mastiff skinks or short-legged giant skinks.

<i>Lampropholis</i> Genus of lizards

Lampropholis is a genus of skinks, commonly known as sunskinks, in the lizard subfamily Eugongylinae of the family Scincidae. The genus Lampropholis was previously found to belong to a clade with the genera Niveoscincus, Leiolopisma and others of the Eugongylus group within Lygosominae. All species of Lampropholis are endemic to Australia. For similar skinks see genera Bassiana, Pseudemoia, and Niveoscincus.

Lobulia is a genus of skinks in the subfamily Eugongylinae. The genus Lobulia is endemic to New Guinea.

<span class="mw-page-title-main">Blue-tongued skink</span> Genus of lizards

Blue-tongued skinks comprise the Australasian genus Tiliqua, which contains some of the largest members of the skink family (Scincidae). They are commonly called blue-tongued lizards or simply blue-tongues or blueys in Australia or panana in Indonesia. As suggested by these common names, a prominent characteristic of the genus is a large blue tongue that can be bared as bluff-warning to potential enemies. The type of predator/threat that is near will determine the intensity of colour present in the tongue. The tongue can also deform itself and produce a thick mucus in order to catch prey. They are relatively shy in comparison with other lizards, and also significantly slower due to their shorter legs.

<i>Scincella reevesii</i> Species of lizard

Scincella reevesii is a species of skink, a lizard in the family Scincidae. The species is endemic to Asia.

<span class="mw-page-title-main">Whitaker's skink</span> Species of lizard

Whitaker's skink, also known commonly as Whitaker's New Zealand skink, is an endangered species of skink, a lizard in the family Scincidae. The species is found only in New Zealand.

Acontinae is a subfamily of limbless skinks within the family Scincidae.

<span class="mw-page-title-main">Lygosominae</span> Subfamily of lizards

Lygosominae is the largest subfamily of skinks in the family Scincidae. The subfamily can be divided into a number of genus groups. If the rarely used taxonomic rank of infrafamily is employed, the genus groups would be designated as such, but such a move would require a formal description according to the ICZN standards.

<span class="mw-page-title-main">Scincinae</span> Subfamily of lizards

Scincinae is a subfamily of lizards. The subfamily contains 33 genera, and the genera contain a combined total of 284 species, commonly called skinks. The systematics is at times controversial. The group is probably paraphyletic. It is one of three subfamilies of the family Scincidae, the other two being Acontinae and Lygosominae.

<i>Trachylepis striata</i> Species of lizard

The African striped skink, commonly called the striped skink, is a species of lizard in the skink family (Scincidae). The species is widespread in East Africa and Southern Africa. It is not a close relation to the Australian striped skink, Ctenotus taeniolatus.

<i>Saiphos</i> Species of reptile

Saiphos equalis, commonly known as the yellow-bellied three-toed skink or simply three-toed skink, is a species of burrowing skink found in eastern Australia. It is the only species classified under the genus Saiphos.

<i>Trachylepis homalocephala</i> Species of lizard

Trachylepis homalocephala, commonly known as the red-sided skink, is a small, slender species of skink in the subfamily Mabuyinae.

<span class="mw-page-title-main">Stokes's skink</span> Species of lizard

Egernia stokesii is a gregarious species of lizard of the Scincidae family. This diurnal species is endemic to Australia, and is also known as the Gidgee skink, spiny-tailed skink, Stokes's skink and Stokes's egernia. The species forms stable, long-term social aggregations, much like the social groups seen in mammalian and avian species. This characteristic is rarely found in the Squamata order, but is widespread within the Australian subfamily of Egerniinae skinks. Populations of E. stokesii are widely distributed, but fragmented, and occur in semi-arid environments. There are three recognised subspecies. The conservation status for the species is listed as least concern, however, one subspecies is listed as endangered.

<span class="mw-page-title-main">Eugongylinae</span> Subfamily of skinks

Eugongylinae is a subfamily of skinks within the family Scincidae. The genera in this subfamily were previously found to belong the Eugongylus group in the large subfamily Lygosominae.

<span class="mw-page-title-main">Egerniinae</span> Subfamily of skinks

Egerniinae is the subfamily of social skinks within the family Scincidae. The genera in this subfamily were previously found to belong the Egernia group in the large subfamily Lygosominae.

<span class="mw-page-title-main">Mabuyinae</span> Subfamily of skinks

Mabuyinae is a subfamily of skinks within the family Scincidae. The genera in this subfamily were previously found to belong the Mabuya group in the large subfamily Lygosominae.

<span class="mw-page-title-main">Sphenomorphinae</span> Subfamily of skinks

Sphenomorphinae is a large subfamily of skinks, lizards within the family Scincidae. The genera in this subfamily were previously found to belong to the Sphenomorphus group in the large subfamily Lygosominae.

Trachylepis hemmingi, also known commonly as the Somali mabuya, is a species of skink, a lizard in the subfamily Mabuyinae of the family Scincidae. The species is endemic to Somalia.

References

  1. ↑ Mecke, Doughty & Donnellan (2013). "Redescription of Eremiascincus 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. PMID   26191600.
  2. ↑ "Skink | lizard". Encyclopedia Britannica. Retrieved 2019-05-06.
  3. ↑ Grzimek, Bernhard (1975). Grzimek's Animal Life Encyclopedia Volume 6 Reptiles. New York, NY: Van nostrand reinhold company. p. 242.
  4. ↑ 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.
  5. ↑ "10 Creatures That Conveniently Grow Back Body Parts". TreeHugger. Retrieved 2019-05-06.
  6. ↑ "Species Profile: Ground Skink (Scincella lateralis) | SREL Herpetology". srelherp.uga.edu. Retrieved 2019-05-06.
  7. ↑ "Skink Facts". www.softschools.com. Retrieved 2019-05-06.
  8. ↑ Malhotra, Anita. "Some lizards have green blood that should kill them – and scientists can't work out why". The Conversation. Retrieved 2019-05-06.
  9. ↑ "the definition of skink". www.dictionary.com. Retrieved 2019-05-06.
  10. ↑ 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.
  11. ↑ 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. ISBN   978-3-89937-026-3.
  12. ↑ "Scincidae Gray 1825". Paleobiology Database. Fossilworks. Retrieved 17 December 2021.
  13. ↑ McLeod, Lianne. "Keeping Blue Tongued Skinks as Pets" . Retrieved 2006-08-27.
  14. 1 2 Justin L. Rheubert; Dustin S. Siegel; Stanley E. Trauth (19 December 2014). Reproductive Biology and Phylogeny of Lizards and Tuatara. CRC Press. pp. 548–. ISBN   978-1-4665-7987-3.
  15. ↑ 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. PMID   21956253. S2CID   5191828.
  16. ↑ "Amazing Facts about the Common Garden Skink | OneKindPlanet Animals". OneKindPlanet. Retrieved 2019-05-06.
  17. ↑ 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. S2CID   153428168 – via Energy & Power Source.
  18. ↑ 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 .
  19. ↑ Bulmer, RNH (1975). Kalam Classification Of Reptiles And Fishes. Journal of the Polynesian Society 84(3): 267–308.
  20. ↑ 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. ISSN   1424-859X. PMID   20215726.
  21. 1 2 Dodge, 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 . ISSN   1755-098X.
  22. ↑ 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. ISSN   1471-2954. PMC   7893288 . PMID   33468012.
  23. ↑ Uetz, P.; Freed, P.; Hošek, J. (eds.). "Acontinae". The Reptile Database . Retrieved 10 October 2019.
  24. ↑ Uetz, P.; Freed, P.; Hošek, J. (eds.). "Egerniinae". The Reptile Database . Retrieved 10 October 2019.
  25. ↑ Uetz, P.; Freed, P.; Hošek, J. (eds.). "Eugongylinae". The Reptile Database . Retrieved 10 September 2020.
  26. ↑ Uetz, P.; Freed, P.; Hošek, J. (eds.). "Lygosominae". The Reptile Database . Retrieved 10 October 2019.
  27. ↑ Uetz, P.; Freed, P.; Hošek, J. (eds.). "Mabuyinae". The Reptile Database . Retrieved 10 September 2020.
  28. ↑ Uetz, P.; Freed, P.; Hošek, J. (eds.). "Sphenomorphinae". The Reptile Database . Retrieved 10 October 2019.
  29. ↑ Uetz, P.; Freed, P.; Hošek, J. (eds.). "Scincinae". The Reptile Database . Retrieved 10 October 2019.

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