Ctenophorus spinodomus Sadlier, Colgan, Beatson & Cogger, 2019

Common Name and Distinction

Ctenophorus spinodomus, commonly called the Eastern Mallee dragon, has physical features that set it apart from other agamid lizards and support its survival.

Male Femoral Pores

Adult males have a continuous row of 15–22 femoral pores on each side, arranged in an arch toward the midline.

Dorsal Surface Pattern

Their dorsal surface is pale brown to medium sandy orange, with a pale dorsolateral stripe bordered by dark edges, plus dark blotches on the dorsal surface and large dark markings on the upper-lateral surface.

Mid-Lateral Stripe

A pale stripe, sometimes with scattered flecks, runs along the mid-lateral surface.

Tail Pattern

The tail has pale spots along its dorsolateral edge; the side of the tail is dark, forming a distinct stripe bordered by a pale stripe across its basal third.

Male Ventral Pattern

The ventral surface is pale, with scattered dark speckling on the throat and a dark chest patch broken by white flecks that may align along the midline to form a poorly defined T-shape.

Female Patterning

Adult females have a similar patterning but in lighter tones, and their ventral surface lacks significant dark markings.

Shared Identification Feature

Both sexes can be identified by a fine, typically uninterrupted pale dorsolateral stripe that extends from the neck to just past the hind limbs.

Total Length Range

Eastern Mallee dragons are relatively small, with a typical total length of 15.5–18 cm.

Sexual Size Dimorphism

Adult females are generally larger in body size than males, while adult males have longer tails and hind limbs: male tail length is approximately 2.1–2.4 times body length, compared to 1.95–2.15 times body length in females.

Endemic Range

The Eastern Mallee dragon is endemic to the eastern Mallee region of Australia.

Geographical Distribution

Its range covers red sand plains and Mallee woodlands of south central and south western New South Wales, extending along the northern side of the Murray River into South Australia.

Spinifex Habitat Association

It is well adapted to the arid and semi-arid landscapes of this region, and its range is highly restricted to areas with Spinifex hummock grass (Triodia), which it uses for foraging, shelter, and social interactions.

Substrate Requirement

Spinifex grows as a groundcover in Mallee woodland habitat known as Triodia Mallee vegetation, and Eastern Mallee dragons also require this habitat to be paired with a red sand substrate, which provides nesting and overwintering sites.

Life Cycle Length

Eastern Mallee dragons are diurnal, terrestrial agamid lizards that mostly follow an annual life cycle, though some individuals live into a second season, and very rarely into a third.

Adult Mortality Period

A large rise in adult mortality starts in late December and continues through January, killing as much as 85% of the population during this period.

Adult Home Range Sizes

Males have larger home ranges on average, around 0.032 hectares, while females have smaller average home ranges of about 0.015 hectares.

Juvenile Home Range Size

Juveniles have even smaller ranges, approximately 0.007 hectares, than adults.

Territoriality and Migration

There is very little change in home range size, negligible migration, and no observed territorial behaviour in this species.

Habitat Preference Correlates

The species is more common in landscapes with extensive Triodia Mallee vegetation, and its presence is strongly linked to substantial Spinifex coverage and large, healthy Spinifex hummocks.

Post-Fire Population Dynamics

These conditions typically develop 20–50 years after fire, with population peaking around 35 years post-fire; after this peak, population densities gradually decline.

Diel Activity Cycle

The species follows a 24-hour diel cycle tied to using Spinifex clumps at different times of day.

Thermoregulation Strategy

Like many reptiles, Eastern Mallee dragons are ectothermic and rely on external heat to regulate body temperature.

Basking Behaviour

They are often seen basking in the sun, especially in the morning and late afternoon.

Spinifex Shelter Use

At night, individuals shelter inside Spinifex clumps, and they bask among the clump's spines to reach a suitable body temperature for activity.

Hot Weather Behaviour

After emerging, they usually stay within a few meters of the clump, and during the hottest part of the day they retreat into the nearest Spinifex clump, where humidity is higher than the surrounding environment and temperature is notably cooler than the surroundings, especially the substrate.

Winter Shelter Behaviour

During winter, few individuals stay inactive within Spinifex; instead, observations indicate they dig into the soil to shelter underground.

Reproductive Mode

Eastern Mallee dragons are oviparous, meaning they lay eggs.

Breeding Season Timing

Their breeding season falls in the warmer months of the year, with egg-laying usually occurring in late spring or early summer, and peak egg deposition around mid-November.

Male Mating Displays

Males compete through combat displays that include head-bobbing and tail-waving, to establish dominance and attract females.

Clutch and Nesting Details

Females usually lay clutches of 2–3 eggs, which they bury in a carefully prepared underground nest chamber that is constructed and sealed the same day as laying.

Incubation and Hatching

Incubation occurs in the warm, protected nest environment, and hatching takes place in under 8 weeks.

Hatchling Survival

Hatchlings are independent from birth and must fend for themselves; on average, only 20% of hatchlings reach reproductive maturity.