The Crocodile Skink

Distribution: Northern Papua New Guinea including off-shore islands.

Habitat: Coconut plantations and tropical forests near creeks.

Diet: Soft-bodied insects, possibly termites.

Max.length: 88-100mm SVL (192mm TL).

Reproductive strategy: Oviparous with a clutch of 1 egg.

The genus Tribolonotus contains eight species from New Guinea to the Solomon Islands but only two species occur on the New Guinea mainland and its continental islands, T.gracilis and T.novaeguineae, but whether they are separate species or represent geographical populations of the same species, as I am inclined to believe, has yet to be determined.

The crocodile skink is relatively common on Karkar Island and is far more frequently encountered there, in the husk piles, than in forest habitats on the mainland where only five specimens were found under scattered debris along a forest creek. This is a very unusual lizard which differs considerably from the typical smooth scaled, or weakly-keel scaled,  and plain (unadorned) ‘skink blue-print’. The New Guinea crocodile skink has rugose skin with irregular tuberculate scales and four rows of large, elevated vertebral scales. The head is large and protrudes posteriorly as a slightly spinous casque, especially so in males. Colouration is drab brown, lighter below, with a contrasting orange-red pigmented area of skin around the eye and a yellow ring in the iris. Hatchlings have a pale brown head cap and vertebral stripe.  

Curious volar pores are also present on the palmar (palm) and plantar (sole) regions of male New Guinea crocodile skinks, with abdominal glands present in both sexes, though larger in the males.

The purpose of these glands and their secretions has not yet been determined. Female New Guinea crocodile skinks possess two ovaries but only the right oviduct, the result being that an egg developing in the left oviduct must migrate across the body cavity prior to oviposition. Only a single, elongate leathery-shelled egg is laid, incubation taking approximately 60 days.

A further unusual characteristic of the New Guinea crocodile skink is its ability to vocalize, producing an extraordinarily loud sound for such a relatively small species. The ability to vocalize may be increased by an enlarged larynx-like structure in the throat area, again especially pronounced in males.

Crocodile skinks are secretive, they try to escape to cover when disturbed in the coconut husk piles and do not appear to bask, as they have been said to do in captivity.

Sources for more information:

Greer A.E. & F.Parker 1968 A new species of Tribolonotus (Lacerilia: Scincidae) from Bougainville and Buka, Solomon Islands, with comments on the biology of the genus. Breviora 291 pp.1-23.

Hartdegen R.W., MJ.Russell, B.Young & R.D.Reams 2001 Vocalization of the crocodile skink, Tribolonotus gracilis (de Rooy, 1909), and evidence of parental care. Contemporary Herpetology 2001(2)1-9.

McCoy M. 1980 Reptiles of the Solomon Islands. Wau Ecology Handbook No.7. vi+80.

Mys B. 1988 The zoogeography of the scinicid lizards from North New Guinea (Reptilia: Scinicidae). I. The distribution of the species. Bulletin de l'Institute des Sciences naturalles de Belgique, Biologie 58: p.147-149, figs. 69-71.

O’Shea M. 1994 The herpetofauna of coconut husk piles on Kar Kar island, madang Province, Papua New Guinea: The initial surveys. ASRA Journal 1994:51-72.

Rooji N. de 1909 Tribolonotus gracilis n. sp. pp. 381-382 in Reptilien (Eidechsen, Scildkröten und Krokodile) in Wichmann A. (ed.) Nova Guinea. Résultants de l'Expédition Scientific Néerlandaise à la Nouvelle-Guinée. Leiden 5 Zoologie pp. 375-383.

Russell M.J. 1996 Notes on the natural history, captive husbandry and reproduction of crocodile skinks (Tribolonotus gracilis) at the Dallas Zoo. pp.69-74 in P.D. Strimple (ed.) Advances in Herpetoculture. Spec. Publ. Int. Herp. Symposium No.1.

— 1997 Husbandry notes on a juvenile crocodile skink, Tribolonotus gracilis. Case Report 5. Assoc Reptilian Amphibian Vet. 7(4):9.

— L.A.Mitchell 1995 Crocodile skink (Tribolonotus novaeguineae) hatches at the Dallas Zoo.  American Zoo and Aquarium Assoc. Communique Dec. 1995:18.

Zweifel R.G. 1980 Tribolonotus gracilis p. 422 in Results of the Archbold Expeditions. No. 103. Frogs and lizards from the Huon Peninsula, Papua New Guinea. Bulletin of the American Museum of Natural History 165 (5): 387-434.