This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
October 2014 continues – for no particular reason at all – to be Lizard Month here at Tet Zoo and right now it’s time for more skinks. The previous article is a sort of general introduction to the group as well as a review of the limbless acontiines/acontids and weird feylinines. This time, we move on in the phylogeny, here dealing with the large number of groups conventionally grouped together as the lygosomines...
Lygosomines account for about half of all named skink species and occur across Asia, Africa and Australasia, and also on many island groups across the Indo-Pacific region. Unlike most other skinks, many (but not all) have an extensive bony secondary palate and fused frontal bones (a complete bony palate evolved independently at least twice elsewhere within skinks: in the Seychellean Janetaescincus + Pamelaescincus clade, and in Gongylomorphus from Madagascar). The group has been found to be paraphyletic with respect to Asian and North American eumecines in some studies (Whiting et al. 2003) but monophyletic in others (Brandley et al. 2005, Pyron et al. 2013).
At its core, the group of course includes the writhing skinks (Lygosoma), a massive group that includes species in Africa, India, the Philippines and elsewhere [adjacent photo by W. A. Djatmiko]. Like just about all of those speciose, widespread skink genera (see the previous article for discussion), Lygosoma is almost certainly not a clade. The genus was thought to be even bigger in the past that it is now: Allen Geer noted in one of his articles that Lygosoma was “applied at one time to almost one-half (43%) of all the species in the family” (Greer 1977, p. 515). Skinks included within Lygosoma are – morphologically – somewhat nondescript, being long-bodied, streamlined skinks that are often reddish-brown or golden-brown. The biggest (like the west African Fire skink L. fernandi) reach about 40 cm in total length. And even the modern, restrictive version of Lygosoma isn’t monophyletic: it’s paraphyletic with respect to Lepidothyris and Mochlus (Pyron et al. 2013).
On supporting science journalism
If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
Enough about Lygosoma. In the new taxonomic scheme discussed by Hedges (2014), the disparity and diversity recognised for lygosomines in total is such that the group is now elevated to a ‘higher-level’ clade – Lygosomoidea – that houses the seven ‘family-level’ clades Ateuchosauridae, Sphenomorphidae, Eugongylidae, Lygosomidae, Egerniidae, Ristellidae, and Mabuyidae (Hedges 2014). Mabuyids are one of the youngest groups within this clade.
And I have to resist talking here about the examplar genus of Mabuyidae – the Afroasian-Madagascan-American Mabuya – because... well, there’s a whole world of hurt there [adjacent photo by Lip Kee]. Studies have often suggested that Mabuya sensu lato might not be monophyletic (e.g., Honda et al. 2003) and there’s a push to get the name restricted to American members of the group. Hedges & Conn (2012) erected a full 16 genera for Caribbean species conventionally included within Mabuya and also argued that each of the major clades closely related to Mabuya – the Afro-Madagascan Chioninia and Trachylephis groups and Asian Dasia group – should be recognised as ‘subfamilies’ within Mabuyidae (see Pyron et al. 2013, Hedges 2014). At least some of the 38 or so island-endemic Caribbean mabuyid species are critically endangered or already extinct, predominantly (it's thought) because of mongoose predation (Hedges & Conn 2012).
Phylogenetic studies find the ‘Eugongylus group lygosomines’ of Tasmantis (New Caledonia, New Zealand and Lord Howe Island) to form a clade, with the skinks of New Zealand and Lord Howe Island being nested within an ancestrally New Caledonian clade (Smith et al. 2007) [photo above by Ariefrahman]. This major group is termed Eugongylidae in the new taxonomic scheme (Hedges 2014) and considered to be closely related to Lygosomidae. The young geological age of the taxa concerned indicate that they colonised these islands via over-water dispersal: they are not relicts of Gondwanan fragmentation, as has also been suggested (checks over shoulder for panbiogeographers...).
Where the terror skinks are
Within this eugongylid clade are some of the world’s most interesting skinks. Nannoscincus, for one, has been reported to make squeaking noises when handled (Sadlier et al. 2006).
I’m especially fond of Phoboscincus, predominantly because the gigantic ‘terror skink’ P. bocourti supposedly belongs here (though note that “there is some morphological evidence that it may not be congeneric with P. garnieri” (Smith et al. 2007, p. 1161)). This large skink – reaching 50 cm in total – has especially long, curved anterior teeth and “is probably a fearsome super-predator of lizards and possibly birds” according to one source. In fact, most people only know of this skink because of its mention in Tim Flannery’s notorious book The Future Eaters where we read that “There is no doubt that the terrific skink ruled over the smaller reptiles of New Caledonia as effectively as Tyrannosaurus rex did over the lesser dinosaurs of its era, or the lion does on Africa’s Serengeti today” (Flannery 1994, pp. 48-49). Wow – the T. rex of the skink world! Hold that thought.
P. bocourti was long known only from a single specimen, collected sometime around 1872. In the absence of further specimens or sightings, it was then thought to be extinct for decades. It even features in Flannery’s A Gap In Nature, accompanied by a beautiful Peter Schouten painting.
However, the ‘terror skink’ was rediscovered unexpectedly in 2003, with subsequent expeditions finding another four individuals and seeing (or ‘camera-trapping’) another four (Caut et al. 2013). Still virtually nothing is known about the ecology or behaviour of P. bocourti, however. Its curved teeth certainly indicate that it might prey on smaller lizards, and the isotope analysis performed by Caut et al. (2013) appears to be in agreement with this hypothesis. It’s certainly good news that P. bocourti isn’t extinct, but there’s every indication that it’s extremely rare, and quite plausibly threatened with genuine extinction.
Land mullets, crevice skinks, and sociality
Egernia-group lygosomines (Egerniidae of the Hedges (2014) scheme) are also very neat. Egernia itself is a large, Australian genus, conventionally thought to contain about 30 species of terrestrial, sometimes burrow-dwelling, skinks that tend to be broad-bodied and proportionally short-tailed. [Adjacent photos by Mark Marathon, $Mathe94$, and Liese Coulter.]
As suggested by the common name used for some of these skinks – spiny-tailed skinks – long spines (actually tall keels on the dorsal surfaces of the scales) project from the broad, flattened tails of these lizards, and they use these tails to block the entrances to their burrows or resting crevices (Pianka & Vitt 2003). Some species (like the Pygmy spine-tailed skink E. depressa) have raised, spike-like scales on the head, neck and body as well as the tail. Big species are more herbivorous than the smaller ones.
As is the case with most speciose skink genera, Egernia encompasses a lot of variation in terms of size, proportions, scale anatomy and overall look. Accordingly, some authors have wanted to see it split into four: Egernia proper (the generally large and bulky crevice skinks and spiny-tailed skinks), Bellatorias (containing the brilliantly named Land mullet B. major and kin), Liopholis (the desert and rock skinks), and Lissolepis (the mourning skinks). Furthermore, Gardner et al. (2008) found Egernia in the traditional sense to be paraphyletic with respect to blue-tongued skinks (Tiliqua) and slender skinks (Cyclodomorphus) and recommended application of this revised taxonomy, the ‘Egernia’ clade close to the blue-tongues being Liopholis (see also Pyron et al. 2013).
Anyway, the main reason these skinks are so interesting is that they are highly social, complex, apparently intelligent lizards that typically live in family groups. About 23 of those 30-odd species, in fact, have been reported occurring in social aggregations (Chapple 2003), those of Cunningham’s skink E. cunninghami and the Gidgee skink or Stoke’s skink E. stokesii consisting of up to 17 individuals. Members of some species have been shown to recognise other individuals (and to kill newborns that aren't closely related to them), and several species are monogamous and form pairs that stick together for decades. The Great desert skink Liopholis kintorei constructs complex warren-like tunnel systems that can spread over 13 m and contain 20 entrances. Genetics confirms that the individuals that inhabit these burrow systems are relatives: these are colonial, co-operative lizards (McAlpin et al. 2011). Why this sociality evolved is a good question. Did it originate for the same reason that it did in social, burrow-dwelling mammals, like molerats?
And crocodile skinks and monkey-tailed skinks...
The weird crocodile skinks (Tribolonotus) of New Guinea, the Bismarck Archipelago and the Solomon Islands also belong in this egerniid clade, seemingly as the sister-group to a clade that includes the arboreal Solomon Islands skink or monkey-tailed skink (Corucia), the Cyclodomorphus-Tiliqua complex, and those social skinks (Skinner et al. 2011, Pyron et al. 2013). Given that there are heavily armoured, strongly terrestrial skinks here, specialised arboreal ones, numerous burrowing, desert-dwelling lineages, and short-limbed, massive-headed omnivores, it’s fun to imagine what the ancestral lifestyle and body shape was for the group.
The presence of some egerniids on far-flung islands raises interesting questions about their history. Fossils and molecular distance data indicates that various of these lineages split from one another during the Oligocene, so did they use over-land dispersal to get to various of those island locations? In the case of Corucia, genetics indicate that populations on adjacent islands are not necessarily closely related, and that isolated modern populations are young – the overall pattern indicating that the animals have (again) mostly colonised the islands via overwater dispersal within the last few million years (Hagen et al. 2012). In the case of Corucia, this means that there’s still a massive chunk of its inferred history that remains cryptic. Was it somewhere on the Solomon Islands during all of that time, or did it only colonise the islands recently?
So, there we have it – a very brief whistlestop tour of yet more of the skinks. For a fuller view as goes the diversity and biology of the groups discussed here, do see Eric Pianka and Laurie Vitt’s 2003 book Lizards: Windows the Evolution of Diversity (Pianka & Vitt 2003) if you can. And we’re not done yet; there are more skinks to come...
Tet Zoo now features some fairly reasonable coverage of squamate diversity, but there is still so much to do.
Dibamids and amphisbaenians
Amphisbaenians and the origins of mammals (April 1st article!)
Gekkotans
Gekkota part II: loud voices, hard eggshells and giant calcium-filled neck pouches
Squirting sticky fluid, having a sensitive knob, etc. (gekkotans part III)
300 years of gecko literature, and the ‘Salamandre aquatique’ (gekkotans part VI)
Whence Uroplatus and… there are how many leaf-tailed gecko species now?? (gekkotans part VII)
Ptychozoon: the geckos that glide with flaps and fringes (gekkotans part VIII)
Iguanians
Harduns and toad-heads; a tale of arenicoly and over-looked convergence
The Squamozoic actually happened (kind of): giant herbivorous lizards in the Paleogene
Australia, land of dragons (by which I mean: agamids) (part I)
Lacertids
The New Forest Reptile Centre (on Zootoca and Lacerta)
Skinks and cordylids
Anguimorphs
Pompey and Steepo, the world-record-holding champion slow-worms
Dinosaurs come out to play (so do turtles, and crocodilians, and Komodo dragons)
What I saw at the zoo yesterday... (more brief comments on Komodo dragons)
Perentie tries to swallow echidna. Echidna too spiky, Perentie gets horribly injured. Dies.
“Lean, green and rarely seen”: enthralling prasinoid tree monitors
Snakes
"What was that cute little Mexican snake?", and other musings...
Snake 195 mm long eats centipede 140 mm long. Centipede too big. Snake dies.
Monster pythons of the Everglades: Inside Nature's Giants series 2, part II
The more you know about colubrid snakes, the better a person you are
Love for Mastigodryas, Tomodon, Sordellina and all their buddies: you know it’s right
Refs - -
Flannery, T. F. 1994. The Future Eaters: An Ecological History of the Australasian Lands and People. Reed Press, Port Melbourne, Australia.
Gardner, M. G., Hugall, A. F., Donnellan, S. C., Hutchinson, M. N. & Foster, R. 2008. Molecular systematics of social skinks: phylogeny and taxonomy of the Egernia group (Reptilia: Scincidae). Zoological Journal of the Linnean Society 154, 781-794.
Greer, A. 1977. The systematic and evolutionary relationships of the scincid lizard genus Lygosoma. Journal of Natural History 11, 515-540.
Honda, M., Ota, H., Köhler, G., Ineich, I., Chirio, L., Chen, S.-L. & Hikida, T. 2003. Phylogeny of the lizard subfamily Lygosominae (Reptilia: Scincidae), with special reference to the origin of the New World taxa. Genes & Genetic Systems 78, 71-80.
Pianka, E. R. & Vitt, L. J. 2003. Lizards: Windows the Evolution of Diversity. University of California Press, Berkeley.
Sadlier, R. A., Bauer, A. M. & Smith, S. A. 2006. A new species of Nannoscincus Günther (Squamata: Scincidae) from high elevation forest in Southern New Caledonia. Records of the Australian Museum 58, 29-36.
Skinner, A., Hugall, A. F. & Hutchinson, M. N. 2011. Lygosomine phylogeny and the origins of Australian scincid lizards. Journal of Biogeography 38, 1044-1058.
Smith, S. A., Sadlier, R. A., Bauer, A. M., Austin, C. C. & Jackman, T. 2007. Molecular phylogeny of the scincid lizards of New Caledonia and adjacent areas: evidence for a single origin of the endemic skinks of Tasmantis. Molecular Phylogenetics and Evolution 43, 1151-1166.
Whiting, A. S., Bauer, A. M. & Sites, J. W. 2003. Phylogenetic relationships and limb loss in sub-Saharan African scincine lizards (Squamata: Scincidae). Molecular Phylogenetics and Evolution 29, 582-598.