Research
The Orange-bellied Burrowing Skink, Simiscincus aurantiacus, a subterranean lizard species?
Ross A. Sadlier and Aaron M. Bauer
Introduction
Noumèa from Mt Koghis.
Simiscincus aurantiacus, note the bright lateral colouration (top), and ventral colouration and markings (bottom).
A view of the rainforest patch on Mt Koghis from which Simiscincus aurantiacus was collected.
Closed forest habitat on Mt Koghis.
Dorsal views of the head of Simiscincus aurantiacus (line space 5 mm).
Our research over the past decade has identified that almost half the lizard species from New Caledonia are either:
- moderately well known but restricted in distribution
- or known only from a few specimens collected from a few or single localities.
Among the latter group of apparently 'rare' species are several morphologically 'bizarre' species. The Orange-bellied Burrowing Skink, Simiscincus aurantiacus was only recently discovered from a closed forest habitat on Mt Koghis, on the outskirts of the capital, Noumèa. It is an unusual species known only from a single specimen, cannot be readily assigned to any existing group of species.
Other unusual species of New Caledonian skinks are:
- Bocourt's Giant Skink, Phoboscincus bocourti
- Meier's Skink, Geoscincus haraldmieri
- Gracile Burrowing Skink, Graciliscincus shonae
All show a number of unusual characteristics not seen in other related species of skink.
Morphology
In overall morphology Simiscincusaurantiacus appears to be most closely related to Graciliscincusshonae, another burrowing, monotypic New Caledonian skink. Both have broad snouts characterised by wide frontonasal scales (more than two times as broad as long), and share several unusual features of head scalation (an enlarged nasal scale and moderately small widely separated prefrontal scales). They also have elongate bodies and markedly reduced limbs (hind limb length 20-25% of body length in Graciliscincus, 30% in Simiscincus), and share certain skeletal features including fusion of the atlantal arches to the intercentrum in the first vertebrae.
In other aspects of their morphology Simiscincus and Graciliscincus differ markedly, and in general Simiscincus would appear to be the more primitive of the two. Simiscincus has a large ear opening, a condition considered primitive to the diminutive ear opening of Graciliscincus. In osteology Simiscincus has only 29 presacral vertebrae whereas Graciliscincus with 36 presacral vertebrae is highly derived for this character. The elevated number of 19 premaxillary teeth in Simiscincus is unique among skinks, and is clearly derived compared with the 13 premaxillary teeth in Graciliscincus.
Terms
- Monotypic – a group that has only a single representative e.g. a genus represented by a single species.
- Frontonasal - large scale on top of the head near the snout, bordering the rostral and nasal scales anteriorly, and the paired prefrontal scales posteriorly.
- Atlantal Arches and Intercentrum - The atlantal vertebrae is a ring shaped structure comprising three elements, two neural arches and the underlying intercentral arch.
- Presacral vertebrae - those vertebra of the neck and body anterior to the sacral vertebrae that attach to the pelvic girdle.
- Premaxillary teeth – teeth located in the front of the upper jaw.
Survey Area
The area on Mt Koghis from which Simiscincus aurantiacus was collected is one of our most intensively surveyed areas in New Caledonia (in terms of number of visits over the past 10 years). Conservatively we estimate to have spent a minimum of 24 person hours of collecting time on daytime searches in this area, yet Simiscincus aurantiacus was only very recently discovered (in August 1994). Other small skinks such as the burrowing species the Earless Dwarf Skink, Nannoscincus mairiei or litter dwelling species Deplanche’s Shiny Skink Sigaloseps deplanchiei have been commonly encountered on all occasions at this site. It would appear that traditional log and rock turning techniques used for reptile surveys may not adequately or consistently sample certain elements of the reptile `in-fauna' (meaning the reptile fauna that lives underground).
Behaviour
The behaviour of Simiscincus aurantiacus when it was uncovered indicated this species uses existing tunnel-ways through the subsoil. By contrast the species of Nannoscincus when uncovered attempt to escape using a swimming motion that pushes them through loose soil and leaf debris until they are covered, though they will utilise existing cracks in the earth when these are encountered. While observations on Simiscincus aurantiacus and Graciliscincus in the wild are very limited it seems as though there is a correspondence between the morphology of the snout region in Simiscincus aurantiacus and Nannoscincus and the way they move through their `subterranean' environment.
The recent discovery of Simiscincus aurantiacus hints at a possibly greater species diversity among these morphologically bizarre elements of the reptile `in-fauna', and has been one of the more interesting and exciting aspects to our fieldwork in New Caledonia.
Acknowledgements
The authors thank the New Caledonian authorities for permission to collect and conduct research in New Caledonia, particularly Monsieur M. Boulet, Le Chef du Service de l'Environment et de la Gestion des Parcs et Reserves. Logistical support and encouragement was provided by Jean Chazeau of ORSTOM Centre de Noumea, and Alain Renevier and family. Special thanks to Peter Rowland for his assistance and company in the field.
References
- Bauer A.M. and Sadlier R.A. 1994. Systematics, biogeography and conservation of the lizards of New Caledonia. Biodiversity Letters 1: 107-122.
- Sadlier R.A. and Bauer A.M. 1997. A new genus and species of lizard (Reptilia: Scincidae) from New Caledonia, southwest Pacific. Pacific Science 51(1): 91-96.
Copyright © Australian Museum, 2002
