The appearance of the Crocodile Skink is unusual amongst reptiles, with the first thing you notice being its heavily armoured, almost plastic-like, prehistoric look. This is unique amongst skinks. Its impressive triangular-shaped head and rectangular body, along with the four rows of enlarged, pointed, ridged bony scales are more reminiscent of a crocodilian, and help to explain the common name of this genus. These lizards are truly a miracle of the natural world.

Telling the two popular species apart is simple.  An adult T. gracilis has a ring of red scales around its eyes, whereas T. novaeguineae only has a small patch of light orange to yellow colouration restricted to the areas at the front of the eyes.  In addition, their vertebral scale shapes are different. The four rows of spines in the case of T. gracilis point backwards towards the tail, whereas T. novaeguineae is more heavily keeled on its flanks, with the vertebral spines having a more vertical shape. (Carl .J. Franklin)

                                        Tribolonotus novaeguineae                                                     Tribolonotus gracilis

The average life expectancy of a Trib is currently unclear. Captive-bred specimens are still uncommon, but I would suggest it would be approximately 12 to 15 years, as a result of their quite slow metabolism and the relatively cool climate which they favour. This view is also based on the fact they are slow to mature. Females will be at least three years old before they breed for the first time, with this period being slightly shorter in the case of males.

·         Tribolonotus gracilis

Young of this species measure approximately  2.4in (6cm) when they hatch. They are not conspicuously coloured, but as with most other reptile species, this is more than likely just to camouflage them at such a vulnerable age. The head on a baby T. gracilis is a light yellow to cream colour with a few patches of reddish orange. The lower jaw has black and cream vertical markings, and even at this age, they already have the small yellow slit on the inside of their eye socket. The eye itself has a round pupil. The majority of the skink’s base colour is a deep brown, but this is broken by variable cream colouration that is present on the head as a faint stripe running from the back of the neck to the tip of the tail. This does fade and disappear within 6 months of hatching however, and by this age, the distinctive red eye scales will be well on the way to becoming fully developed. 

Adult T. gracilis have a snout to vent length of 3.7in (9cm), with an overall length of 7.2 -7.8in (18-20cm). They have an average weight of 1.3-1.6oz (38-45g) with the males being slightly larger and heavier than females. At this size, the red rings surrounding the eyes are now fully developed, although it’s unknown why they have this marking around the eye socket. It has been suggested it may deter predators, and/or it may serve as a means of species’ recognition, but as yet, no-one really knows. Mature specimens will also have developed an orange-coloured marking on the underside of the chin. As far as I can tell, this is clear sign of the skink’s sexual maturity. The body is a dark brown to black colour all over, with a collar of lighter brown behind the neck, while the underbelly can vary from cream to white. Some captive-bred specimens of T. gracilis may also develop a golden yellow colouration on the tips of their toes but the reason for this is unknown. It could be genetic, but it’s most probably to do with the different types of food given to them in captivity.

·               Tribolonotus novaeguineae

Baby T. novaeguineae hatch at an average length of 2.2in (5.5cm). The head is a light brown colour with a small splash of cream on the nose. The body is again a light brown but seems to have a more faded look than T. gracilis do at this age. They posses a faint stripe from the back of the neck to the tip of their tail. Both flanks have pale cream bands.  As with T. gracilis babies, they have a small yellow slit on the inside their eye socket, with the eye itself having a round pupil.

T. novaeguineae average 7.4-7.8in (19-20cm) in terms of their total length when adult, with the males again being slightly larger and stockier than females. With most specimens weighing no more than 1.6oz (45g), they are smaller overall than T. gracilis. Colouration in mature specimens is a medium brown on the back, head and flanks. A pale cream collar has now developed and this colour continues along the belly. But very occasionally in the summer months, when their quarters have been sprayed heavily, a few of those which I’ve kept have developed a vibrant orange glow. During these periods, the individuals have been producing and protecting eggs.