Corucia of the Solomon Islands, Most Amazing of Skinks

SKINKS! Again.

A captive Corucia in a commercial collection. Image: Darren Naish.

Skinks are an enormous, globally distributed group of lizards. As of December 2019, there are around 1685 recognised species, accounting for about 25% of living lizard diversity (there are about 6780 lizard species in total), and – perhaps unsurprisingly – I’ve written about them quite a lot at TetZoo… though it’s now hard to appreciate this, since the articles concerned have variously been vandalised, curtailed or paywalled by the hosters of TetZoo ver 2 and ver 3. See links below for the wayback machine versions of these articles.

There’s a lot about skinks in the TetZoo archives, please see the links below. Thank Christ for wayback machine.

Among the most remarkable and striking of skinks is the large Solomon Islands skink or Monkey-tailed skink Corucia zebrata, a prehensile-tailed, mostly green, arboreal skink, and the only member of its genus (though read on). Not only is this amazing lizard green, arboreal and equipped with a powerful prehensile tail, it’s also a giant, especially big specimens reaching 72 cm in total length. This makes it the biggest known skink. It first became known to science in 1856 when indefatigable taxonomist John E. Gray tersely described specimens brought to London by John MacGillivray after his voyage aboard the HMS Herald, the type specimens coming specifically from San Christoval (today termed San Cristobal or Makira) in the Solomon Islands (Gray 1856).

The Solomon Islands. Image by OCHA (original here), CC BY 3.0.

The lizards appear widespread throughout the archipelago (Makira is one of the most southerly islands there) and are variable, differing in eye colour, size, and in the configuration and size of their scales. Some experts think that subspecies should be named to reflect this variation, and the smaller, paler-eyed northern form was named C. z. alfredschmidti in 1997 (Köhler 1997). Maverick Australian bad boy herpetologist Raymond Hoser has claimed the existence of several entirely new species of Corucia, one of which he named for his mother. If you want to know more about Mr Hoser (and why he’s a total joke) see the TetZoo article here.

A captive Corucia in a private collection. Note the dark irides which make this individual look different from some of the other animals shown here. Image: S. Hilgers.

So far, all published work on the phylogeography and variation within Corucia finds it and its divergences to be young; as in, younger than about 4 million years old (Hagen et al. 2012). Yet it must have diverged from its closest living relatives 20 million years ago or more (we can infer this because fossils of other members of the same skink group are this old or older), meaning that the vast bulk of its lineages’ history remains completely unknown, for now.

Gray described Corucia as a new member of the ‘fish-scaled’ skink group. This seems a bit odd today, because we don’t refer to any skink by this moniker (to my knowledge). He evidently regarded it as part of the Australasian skink group that includes Egernia, Tiliqua (the blue-tongues) and kin though. Today we think (on the basis of molecular phylogenetics) that this is correct, and that Corucia is a lygosomine skink (Skinner et al. 2011, Pyron et al. 2013).

Representatives of most (but not all) of the skink lineages currently regarded as ‘families’ by Hedges and colleagues. 1: Mabuya, of Mabuyidae. 2: Acontias, of Acontidae (I think it should really be Acontiidae). 3: Ristella, of Ristellidae. 4: Scincus, of Scincidae. 5: Lygosoma, of Lygosomidae. 6: Egernia, of Egerniidae. 7: Eugongylus, of Eugongylidae. These images are from my in-prep textbook, progress of which can be observed here. Images: Darren Naish.

Traditionally, all skinks are combined in the single family Scincidae. Most herpetologists argue that we should stick with this taxonomic system since there’s no dispute that Scincidae is a clade and thus no real need to shake things up. But some argue that putting all the species of this enormous, complex group into the same single ‘family’ obscures and under-emphasises its diversity and disparity and that it would be more realistic to split it into a whole bunch of families (nine in fact: Acontidae, Atechosauridae, Egerniidae, Eugongylidae, Lygosomidae, Mabuyidae, Ristellidae, Scincidae and Sphenomorphidae) (Hedges & Conn 2012, Hedges 2014). I’ve written about this situation before: see the articles below for more. If we follow this revised family-level classification, Corucia is part of Egerniidae.

Substantially simplified cladogram depicting lygosomine skink phylogeny, mostly based on Pyron et al. (2013). Images (top to bottom): Wolfgang Wuster, H. Zell, $Mathe94$, Benjamint444 (all CC BY-SA 3.0), Mark Stevens (CC BY 2.0), W. A. Djatmiko, S. Caut et al. (both CC BY-SA 3.0).

The name Corucia is derived from ‘coruscus’ (meaning shimmering, and referring to the shiny scales), while zebrata is a reference to the stripes present in the specimens Gray was familiar with. Given that Solomon Islanders know this lizard and eat it, there was and is surely indigenous knowledge of the species and probably lore about it, though I haven’t encountered such so far. It’s generic name shouldn’t be confused with that of the Cretaceous fossil lizard Carusia, a possible relative of the living xenosaurids.

Here in the UK, it’s currently not difficult to encounter Corucia in captivity. I should add that it does well if conditions are right: as a canopy-dwelling lizard it needs tall branches with suitable retreats, and some collections (most notably the Philadelphia Zoo) have been breeding Corucia for over 40 years now. They’re not especially active during peak visitor time at zoos, mostly because they’re crepuscular. They’re also exclusively herbivorous and are in fact the only skinks said to be committed to a plant diet. Leaves, shoots, flowers and fruit are all consumed, including those of toxic species. Their dung has a distinctive aroma and it’s apparently possible to locate trees inhabited by this species by smell alone: Harmon (2002) used this technique, making his study “the first documented use of olfactory cues to locate skinks in the wild” (p. 177).

Fine side-eye from this captive Corucia at Bristol Zoo, UK. Image: Darren Naish.

Corucia is viviparous with a 6 to 8 month gestation, but the big deal about its viviparous strategy is that its babies are proportionally enormous, being about half the size of the mother. They can be over 30 cm long and weigh 175 g. Unsurprisingly, only a single baby is normally produced, though rare cases of twins and triplets are on record.

Corucia is also a social skink. In this, it’s far from unique, since egerniids of more than 20 species live together in family groups and even exhibit monogamy, kin recognition, colonial living and co-operation. Juvenile Corucia sometimes stay with their parental group for an extended period and mothers are reported to be highly protective of newborn juveniles (Wright 2007), which is what theory predicts given the substantial material investment involved in growing such a large baby. Also interesting is that not all the adults which form social groups in this species appear related (Wright 1996), and that Corucia groups are even known to allow orphaned juveniles to join their groups (read on…). Some juveniles do apparently leave their parental group to join others (Wright 2007).

Dark-eyed captive Corucia, and here’s proof that this arboreal lizard will - in captivity - drink from standing water (at least some arboreal lizards don’t do this, they rely only on water droplets on leaves). Image: S. Hilger.

Studies of wild-living Corucia on Ugi Island in the Solomon archipelago showed that individuals living less than 150 m apart were likely to be related, but also that individuals wandered for several kilometres (Hagen et al. 2013). Telemetry results obtained in an earlier study (Hagen 2011) indicate that this sort of dispersal is unusual, however, given that Corucia is mostly sedentary with home ranges being equivalent to the canopy of a single tree. Maybe this explains why groups are apparently happy to ‘adopt’ lone youngsters – they may well be related to the members of the group already. After all, we know that kin selection is at play elsewhere in social egerniids.

One of the latest papers discussing social behaviour in these skinks is also among the most shocking, since it reports the occurrence of a Corucia group living together in a deep tree hole, and one that was flooded at its bottom. Remarkably, some of the Corucia in the hole were fully submerged and located beneath the water surface at the time of discovery. To my supreme frustration, I can’t locate this publication right now, even though I recall downloading it (it was a short note in, perhaps, Salamandra or Journal of Herpetology). Let me know if you know the paper concerned. It was such a bizarre report that more information is needed. And I guarantee that it’s legit and that I didn’t dream it.

A captive Corucia at Bristol Zoo. Note the sharply curved claws and interesting nose in these lizards. Image: Darren Naish.

Finally, what does the future hold for this amazing lizard? Unsustainable destruction of forests on the Solomon Islands poses a problem, as does local hunting for the pot and collecting for the pet trade: between 1992 and 1995, 12000 animals were exported for this reason, mostly to the USA (Mann & Meek 2004). Consequently, Corucia is now being considered for inclusion on Appendix I of CITES, with captive breeding likely being crucial to its persistence.

Another captive Corucia. This image is useful and interesting because it shows the cross-sectional shape of the body: note that the side of the body is flat and that there’s an obvious change in angle between the side and dorsal surface. Image: TimVickers (original here), public domain.

A giant, fully herbivorous, slow-breeding, social skink is such a special animal that we must make effort to ensure its survival into the future. And that’s where we must end.

If you enjoyed this article and would like to see me do more, please consider supporting this blog (for as little as $1 per month) at patreon. The more support I receive, the more financially viable this project becomes and the more time and effort I can spend on it. Thank you :)

For previous TetZoo articles on skinks, see…

• Mystery emo skinks of Tonga!, October 2010

• Isopachys: worm-like skinks from Thailand and Myanmar, November 2010

• Hammer-toothed skink SMASH!, November 2012

• Skinks, Skinks, Skinks!, October 2014

• Terror skinks, social skinks, crocodile skinks, monkey-tailed skinks… it's about skinks (skinks part II), October 2014

• Sandfishes and kin: of sand-swimming, placentation, and limb and digit reduction (skinks part III), November 2014

• The Madagascan Skink Amphiglossus Eats Crabs, February 2016

Refs - -

Gray, J. E. 1856. New genus of fish-scaled lizards (Scissosarae) from New Guinea. Annals and Magazine of Natural History (2) 18: 345-346.

Hagen, I. J. 2011. Home ranges in the trees: radiotelemetry of the Prehensile tailed skink, Corucia zebrata. Journal of Herpetology 45, 36-39.

Hagen, I. J., Donnellan, S. C. & Bull, C. M. 2012. Phylogeography of the prehensile-tailed skink Corucia zebrata on the Solomon Archipelago. Ecology and Evolution 2, 1220-1234.

Hagen, I. J., Herfindal, I., Donnellan, S. C. & Bull, C. M. 2013. Fine scale genetic structure in a population of the prehensile tailed skink, Corucia zebrata. Journal of Herpetology 47, 308-313.

Harmon, L. J. 2002. Some observations of the natural history of the Prehensile-tailed skink, Corucia zebrata, in the Solomon Islands. Herpetological Review 33, 177-179.

Hedges, S. B. 2014. The high-level classification of skinks (Reptilia, Squamata, Scincomorpha). Zootaxa 3765, 317-338.

Hedges, S. B . & Conn, C. E. 2012. A new skink fauna from Caribbean islands (Squamata, Mabuyidae, Mabuyinae). Zootaxa 3288, 1-244.

Köhler, G. 1997. Eine neue Unterart des Wickelschwanzskinkes Corucia zebrata von Bougainvillle, Papua-Neuguinea. Salamandra 33 (1), 61-68.

Mann, S. L. & Meek, R. 2004. Understanding the relationship between body temperatureand activity patterns in the giant Solomon Island skink, Corucia zebrata, as a contribution to the effectiveness of captive breeding programmes. Applied Herpetology 1, 287-298.

Pyron, R. A., Burbrink, F. T. & Wiens, J. J. 2013. A phylogeny and revised classification of Squamata, including 4161 species of lizards and snakes. BMC Evolutionary Biology 2013, 13:93.

Skinner, A., Hugall, A. F. & Hutchinson, M. N. 2011. Lygosomine phylogeny and the origins of Australian scincid lizards. Journal of Biogeography 38, 1044-1058.

Wright, K. 1996. The Solomon Islands skink. Reptile & Amphibian Magazine 3 (2), 10-19.

Wright, K. M. 2007. Captivating giants. Reptiles Magazine 15 (12), 54-68.

The Most Amazing TetZoo-Themed Discoveries of 2018

As we hurtle toward the end of the year – always a scary thing because you realise how much you didn’t get done in the year that’s passed – it’s time to look back at just a little of what happened in 2018. This article is not anything like a TetZoo review of 2018 (I’ll aim to produce something along those lines in early 2019), but, rather, a quick look at some of the year’s neatest and most exciting zoological (well, tetrapodological) discoveries. As per usual, I intended to write a whole lot more – there are so many things worthy of coverage – and what we have here is very much an abridged version of what I planned.

Animals we will meet below, a montage. Images: (c) Philippe Verbelen, (c) Kristen Grace, Florida Museum of Natural History, Graham et al. (2018), CC BY-SA 4.0.

Thanks as always to those supporting me at patreon. Time is the great constraint (and finance, of course), and the more support I have, the more time I can spend on producing blog content. Anyway, to business…

The Rote leaf warbler. New passerine bird species are still discovered on a fairly regular basis; in fact three were named in 2018*. One of these is especially remarkable. It’s a leaf warbler, or phylloscopid, endemic to Rote in the Lesser Sundas, and like most members of the group is a canopy-dwelling, insectivorous, greenish bird that gleans for prey among foliage. Leaf warblers are generally samey in profile and bill shape, so the big deal about the new Rote species – the Rote leaf warbler Phylloscopus rotiensis – is that its bill is proportionally long and curved, giving it a unique look within the group. It superficially recalls a tailorbird. Indeed, I think it’s likely that the species would be considered ‘distinct enough’ for its own genus if there weren’t compelling molecular data that nests it deeply within Phylloscopus (Ng et al. 2018).

* The others are the Cordillera Azul antbird Myrmoderus eowilsoni and the Western square-tailed drongo Dicrurus occidentalis.

A Common chiffchaff Phylloscopus collybita encountered in western Europe, a familiar Eurasian-African phylloscopid leaf warbler. Image: Darren Naish.

The story of the Rote leaf warbler’s discovery is interesting in that it’s yet another recently discovered species whose existence and novelty was suspected for a while. Colin Trainor reported leaf warblers on Rote in 2004 but never got a good look at them, Philippe Verbelen observed them in 2009 and realised how anatomically unusual they were, and it wasn’t until 2015 that a holotype specimen was procured (Ng et al. 2018). I’ve mentioned before the fact that documenting and eventually publishing a new species is rarely an instant see it catch it publish it event, but a drawn-out one that can take decades, and here we are again. Also worth noting is that the existence of a leaf warbler on Rote was not predicted based on our prior knowledge of leaf warbler distribution in view of the deep marine channel separating Rote from Timor and lack of any prior terrestrial connection. Yeah, birds can fly, but members of many groups prefer not to cross deep water channels. In this case, this did, however, happen and most likely at some point late in the Pliocene (Ng et al. 2018).

Rote leaf warbler in life, a novel member of an otherwise conservative group. Image: (c) Philippe Verbelen.

Rote has yielded other new passerines in recent years – the Rote myzomela Myzomela irianawidodoae (a honeyeater) was named in 2017 – and it’s possible that one or two others might still await discovery there.

Neanderthal cave art. Hominins don’t get covered much at TetZoo, which is weird given the amazing pace of relevant recent discoveries and the fact that they’re totally part of the remit. I mostly don’t cover them because I feel they’re sufficiently written about elsewhere in the science blogging universe, plus I tend to be preoccupied with other things. Nevertheless, I take notice, and of the many very interesting things published in 2018 was Hoffman et al.’s (2018) announcement of several different pieces of Spanish rock art, seemingly made by Neanderthals Homo neanderthalensis. The art concerned involves hand stencils, abstract lines, squares and amorphous patches of pigment, always marked in red.

Red abstract markings, discovered in several Spanish caves, are old, and in fact were seemingly made by hominins long before H. sapiens moved into Europe. The red sinuous marking and system of squares and lines near the middle of this photo are purported to have been made by Neanderthals (other images, depicting animals and present adjacent to these markings, were seemingly created more recently by H. sapiens individuals). Image: (c) P. Saura.

The main reason for the attribution of this art to Neanderthals is its age: uranium-thorium dating shows that it’s older than 64ka, which therefore makes it more than 20ka older than the time at which H. sapiens arrived in Europe (Hoffman et al. 2018). That seems compelling, and it’s consistent with a building quantity of evidence for Neanderthal cultural complexity which involves the use of shells, pigments, broken stalagmites and so on.

One of the most famous pieces of claimed Neanderthal rock art: the Gorham's Cave ‘hashtag’ from Gibraltar. Image: (c) Stewart Finlayson.

I should add here, however, that I’m slightly sceptical of the use of age as a guide to species-level identification. Why? Well, we have evidence from elsewhere in the fossil record that the range of a hominin species can be extended by around 100ka without serious issue (witness the 2017 announcement of H. sapiens remains from north Africa; a discovery which substantially increased the longevity of our species). In view of this, would a 20ka extension of H. sapiens’ presence in Europe be absolutely out of the question? Such a possibility is not supported by evidence yet, and I don’t mean to appear at all biased against Neanderthals.

A tiny Cretaceous anguimorph in amber, and other Mesozoic amber animals. As you’ll know if you follow fossil-themed news, recent years have seen the discovery of an impressive number of vertebrate fossils in Cretaceous amber, virtually all of which are from Myanmar and date to around 99 million years old. They include tiny enantiornithine birds, various feathers (most recently racquet-like ‘rachis dominated feathers’), the tiny snake Xiaophis, early members of the gecko and chameleon lineages and the small frog Electrorana. Many of these finds were published in 2018 and any one could count as an ‘amazing’ discovery.

The Barlochersaurus winhtini holotype, from Daza et al. (2018).

However, there’s one fossil in particular that I find ‘amazing’, and it hasn’t received all that much coverage. It’s the tiny (SVL* 19.1 mm!), slim-bodied anguimorph Barlochersaurus winhtini, named for a single, near-complete specimen subjected to CT-scanning (Daza et al. 2018). Remarkable images of its anatomical details are included in Daza et al.’s (2018) paper. It has short limbs, pentadactyl hands and feet and a slim, shallow, bullet-shaped skull. Phylogenetic study finds it to be somewhere close to, or within, Platynota (the clade that includes gila monsters and kin, and monitors and kin), or perhaps a shinisaurian (Daza et al. 2018). It could be a specialised dwarf form, or somehow more reflective of the ancestral bauplan for these anguimorph groups. Either way, it’s exciting and interesting. What next from Burmese amber?

* snout to vent length

Barlochersaurus in life. It’s about the size of a paperclip. Image: (c) Kristen Grace, Florida Museum of Natural History (original here).

The Reticulated Siren. Sirens are very special, long-bodied aquatic salamanders with reduced limbs and bushy external gills. They’re very weird. They can reach 95 cm in length (and some fossil species were even larger), lack hindlimbs and a pelvis, have a horny beak and pavements of crushing teeth, and eat plants in addition to gastropods, bivalves and other animal prey. A longish article on siren biology and evolution can be found here at TetZoo ver 3.

A life reconstruction of the Cretaceous siren Habrosaurus, showing features typical of the group. This animal could reach 1.5 m in total length. Image: Darren Naish (prepared for my in-prep texbook The Vertebrate Fossil Record, on which go here).

Until recently, just four living siren species were recognised. But it turns out that indications of a fifth – endemic to southern Alabama and the Florida panhandle – have been around since 1970 at least. Furthermore, they pertain to a big species, similar in size to the Great siren Siren lacertina. Known locally as the ‘leopard eel’ (a less than ideal moniker, given that there’s a real eel that already goes by this name), this animal has been published by Sean Graham and colleagues in the open-access journal PLoS ONE (Graham et al. 2018) wherein it’s formally christened the Reticulated siren S. reticulata. It reaches 60 cm in total length, has dark spots across its dorsal surface and a proportionally smaller head and longer tail than other Siren species.

A museum specimen of the species has been known since 1970 when its finder noted that it did “not conform” to descriptions of known species, and live specimens were collected by David Steen and colleagues in 2009 and 2014. Again, note that discovery and recognition was a drawn-out process. The discovery has, quite rightly, received a substantial amount of media coverage, and many interesting articles about the find are already online. Many of you will already know of David Steen due to his social media presence and Alongside Wild charity (which I’m proud to say I support via pledges at patreon).

The Reticulated siren paratype specimen, as described by Graham et al. (2018). Image: Graham et al. (2018), CC BY-SA 4.0. Original here.

The idea that a new living amphibian species 60 cm long might be discovered anew in North America in 2018 is pretty radical. I’m reminded of the 2009 TetZoo ver 2 article ‘The USA is still yielding lots of new extant tetrapod species’ (which is less fun to look at than it should be, since images aren’t currently showing at ver 2). Furthermore, Graham et al. (2018) discovered during their molecular phylogenetic work that some other siren species are not monophyletic but likely species complexes, in which case taxonomic revision is required and more new species will probably be named down the line.

And that’s where I must end things, even though there are easily another ten discoveries I’d like to write about. This is very likely the last article I’ll have time to deal with before Christmas. As I write, I’m preparing to leave for the Popularising Palaeontology conference which happens in London this week (more info here), and then there are Christmas parties and a ton of consultancy jobs to get done before the New Year. On that note, I’ll sign off with a festive message, as is tradition. Best wishes for the season, and here’s to a fruitful and action-packed 2019. Special thanks once again to those helping me out at patreon.

For previous TetZoo articles relevant to various of the subjects covered here, see…

•  The USA is still yielding lots of new extant tetrapod species, July 2009

• THE AMAZING WORLD OF SALAMANDERS, October 2013

• Chiffchaffs: a view of passerines from the peripheries (part I), August 2014

• The Biology of Sirens, June 2016

Refs - -

Daza, J. D., Bauer, A. M., Stanley, E. L., Bolet, A., Dickson, B. & Losos, J. B. 2018. An enigmatic miniaturized and attenuate whole lizard from the mid-Cretaceous amber of Myanmar. Breviora 563, 1-18.

Graham, S. P., Kline, R., Steen, D. A. & Kelehear, C. 2018. Description of an extant salamander from the Gulf Coastal Plain of North America: the Reticulated Siren, Siren reticulata. PLoS ONE 13 (12): e0207460.

Hoffman, D. L., Standish, C. D., García-Diez, M., Pettitt, P. B., Milton, J. A., Zilhão, J., Alcolea-González, J. J., Cantelejo-Duarte, P., Collado, H., de Balbín, R., Lorblanchet, M., Ramos-Muñoz, J., Weniger, G.-Ch. & Pike, A. W. G. 2018. U-Th dating of carbonate crusts reveals Neandertal origin of Iberian cave art. Science 359, 912-915.

Ng, N. S. R., Prawiradilaga, D. M., Ng, E. Y. X., Suparno, Ashari, H., Trainor, C., Verbelen, P. & Rheindt, F. E. 2018. A striking new species of leaf warbler from the Lesser Sundas as uncovered through morphology and genomics. Scientific Reports 8: 15646.