That Reptile Blog – Reptile, Amphibian and Exotic Pet Care and Information

Please see Part I of this article for notes on other aspects of skink care (temperature, light, etc.) and taxonomy. Read More »

With over 1,200 species, the skink family (Scincidae) is the lizard world’s largest, and in it we find some very unusual creatures.  Yet one, the Crocodile Skink (Tribolonotus gracilis), stands out as being particularly unique even in this odd assemblage of reptiles.  Originally thought to be a difficult animal to keep, we are now learning more and more about it, and captive reproduction is no longer a rarity.  Let’s take a look at how this skink distinguishes itself.

Description

This species departs radically from the typical skink body plan.  The head is enlarged, triangular in shape and capped with helmet-like scales, while four rows of thick, pointed scales line the back.  Its color is dark brown to black, with a striking red or orange area about the eye.  Crocodile Skinks average 6.5-7.8 inches in length.

Range

The Crocodile Skink is found only in Papua New Guinea and on the nearby Admiralty Islands.  One additional species, the Spiny Skink, T. novaeguinea, (which also appears in the pet trade) inhabits New Guinea, and 6 other species within the genus are found on the Solomon Islands and in New Caledonia.

Habitat

Crocodile Skinks frequent damp, shaded mountain valleys near streams and, in contrast to most skinks (and lizards in general!), they prefer temperatures of 66-75 F.

Again unlike most skinks, they are largely nocturnal or crepuscular (active in early mornings and evenings).  Although declining in some areas, recent observations indicate that piles of coconut husks on farms provide important habitat, and may help populations to increase.

Reproduction

Here again the rules are broken, with females laying only 1 egg at a time.  Oddly, the left ovary and oviduct are somewhat regressed in development as compared to the right.  The single egg developing on the left side is not laid until approximately 60 days after the right ovary’s egg has been laid.   This is true for 7 of the 8 species of Tribolonotus…Schmidt’s Helmet Skink (T. schmidti) gives birth to a single live offspring.   Well-fed female Crocodile Skinks may produce up to 6 eggs each year.

Female Crocodile Skinks guard their eggs during the 70 day incubation period.  In captivity they cover the eggs with substrate when foraging and lunge at intruders.  The hatchlings stay in close proximity to the female for approximately 2 weeks.  Further study may reveal an even greater degree of social behavior, as males kept in the same enclosure are not hostile to the young or to the female.

Other Unusual Characteristics

Crocodile Skinks are unique among lizards in having glands under the abdominal scales, on the surface of the hands, and on the undersides of the feet.  The function of these glands is not completely understood.

They also vocalize when disturbed – producing quite a loud “squawk” for such a small creature – and feign death when stressed.  I can attest that both behaviors are very surprising to the uninitiated!  Some vocalizations may be in response to egg disturbance – another lizard “first” (please see article below).

Further Reading

An interesting article detailing work carried out at the Dallas Zoo on Crocodile Skink vocalizations is posted here.

To read more about the largest lizard family, please see my article Skinks: an Overview.

A video of rarely seen display behavior is posted here.

I’ll cover the care of these most unusual lizards in a future article. 

Introduction
The family Scincidae, the skinks, contains over 1,200 species – more than any other family of lizards.  Skinks range throughout the Eastern and Western Hemispheres, reaching their greatest diversity in Southeast Asia, Australia and Africa.  Among its members we find some of our most common pet reptiles and least-known lizards.  The following information is meant to introduce you to their wonderful diversity of forms and lifestyles.

The Unusual Giant
The group’s largest member, the Prehensile-Tailed Skink, Corucia zebrata, reaches 28 inches in length and is unique in a number of ways – it is entirely arboreal, has a prehensile tail, is limited in range to the Solomon and surrounding islands, feeds on leaves, gives birth to 1 (rarely 2) large offspring after a gestation period of 8-9 months, and seems to have a complex social structure that includes parental care of the young.

Lifestyle and Diet
Typical skinks are elongated in form with small legs and shiny scales.  Most are secretive and, although often diurnal (active by day), spend a good deal of time below rocks, logs or leaf litter.  Legs are absent or reduced in many species, including the various African and Middle Eastern “Sandfish” (Shenops and other genera) which seem to swim as they wriggle through shifting sand dunes.  Most skinks are insectivorous, but many also take fruit, carrion and small mammals, birds, reptiles and amphibians.  Several consume vegetation exclusively.

Skink Reproduction
Almost half of the known species bear live young, and a number of these have evolved a primitive placenta.  Many oviparous (egg-laying) skinks guard their eggs, and there is evidence that females may move the egg clutch in response to disturbances.

A Few That Break the Mold
Quite a few skink species depart from the group’s typical body plan and lifestyle.  New Guinea’s Fojia Skink, Fojia bumui, for example, has plate-like scales down the center of the back and granular scales along the sides.  It clings to vertical rock surfaces along streams, dives after small invertebrates that swim by, and climbs into bushes to sleep on large, sturdy leaves.  The genus Egernia contains at least 23 species that live in extended family groups and exhibit complex social behavior.  There are also aquatic, arboreal and fossorial skinks, some of which have scale-covered, sightless eyes.

Carl Kauffeld and New York City’s Lizards
While growing up in NYC, I was pleased to learn that New York State is home to 2 skink species – the Five-Lined Skink, Eumeces fasciatus and the Coal Skink, E. anthracinus. They are, in fact, the state’s only native lizards – Staten Island’s Eastern Fence Lizards were introduced there by none other than the Staten Island Zoo’s famed reptile man, Carl Kauffeld (to provide a source of food for lizard-eating snakes) and the Italian Wall Lizard of the Bronx, Queens and Nassau County is a pet trade escapee (I have observed free-living Wall Lizards for some time now…more on them to come).

Further background information on skinks, with links to individual species, is available at:
http://www.tigr.org/reptiles/families/Scincidae.html