Ctenotus inornatus

The bar-shouldered ctenotus (Ctenotus inornatus) is a species of skink found in the Northern Territory, Queensland, Victoria, New South Wales, and Western Australia.

Description
The bar-shouldered ctenotus, scientifically known as Ctenotus inornatus, is a member of the Ctenotus inornatus species group, a putative clade of at least 11 nominal forms of large-bodied skinks that reach similar adult sizes, typically ranging from 85 to 110 millimeters in snout-vent length. Within this species group, they share a common set of color pattern elements and scalation features, creating a distinct and captivating group of reptiles.

One notable characteristic of the Ctenotus inornatus genus is their intricate color patterns, which are typically a complex blend of stripes and spots. Their toes are not significantly compressed or only slightly so, and their subdigital lamellae possess a relatively broad, flat callus, which may have adaptive advantages for their movement.

Their head and facial features have supraciliary scales, a critical phenotypic character that helps distinguish them. In the case of the bar-shouldered ctenotus, an important feature is this arrangement of the supraciliary scales, with the first three scales notably larger than the remainder, which further adds to their distinctive appearance and helps researchers in their identification.

Among the specific features that differentiate the bar-shouldered ctenotus from other members of the C. inornatus species group is the absence of a white subocular stripe and the extent to which dorsal color pattern elements extend anteriorly onto the head and neck region.

Notably, there are instances of intraspecific variation in color patterns within this species. Even as the dorsal patterns become reduced, the lateral pattern elements often remain distinct. This phenomenon has been observed in bar-shouldered ctenotus populations in the Murchison and Gascoyne districts of Western Australia, as well as in the northern Kimberley region of Western Australia, adding an element of diversity to the species' appearance.

Taxonomy
John Edward Gray first classified Ctenotus inornatus in 1845. The Ctenotus (scincid lizards) genus includes more than 100 recognised species and is one of the most species-rich vertebrate clades in Australia.

Several synonyms exist for this species:


 * Ctenotus inornatus (Gray 1845)
 * Ctenotus helenae (Storr, 1969)
 * Ctenotus severus (Storr, 1969)
 * Ctenotus saxatilis (Storr, 1970)
 * Ctenotus brachyonyx (Storr 1971)
 * Ctenotus fallens (Storr 1974)

Distribution
The bar-shouldered ctenotus displays a remarkable degree of geographic variation in color patterns throughout its distribution. This variation can occasionally lead to confusion with several other Ctenotus species in regions of sympatry. However, adult color patterns of the bar-shouldered ctenotus are typically distinct from other Ctenotus species, even in areas where they coexist.

Northern Range and Central Deserts: In the northern reaches of its range and across the central deserts of Australia, the bar-shouldered ctenotus is characterised by a highly reduced pattern. In the Pilbara region, individuals are generally brown with faint striping. Some individuals may only have a faint dark vertebral stripe remaining, while others are nearly unpatterned. In the northern Great Sandy Desert and Tanami Desert, these lizards are often unpatterned, although some may retain weak lateral or dorsal pattern elements. It's essential to note that these patterns are distinctly different from those of C. robustus and C. superciliaris sp. nov., which share parts of their range with the bar-shouldered ctenotus in the Pilbara region. C. robustus and C. superciliaris sp. nov. are characterised by strong patterns in these geographic regions.

Southeast Region: In the southeastern part of its range, bar-shouldered ctenotus (C. inornatus) can potentially be confused with C. spaldingi. To differentiate between the two species in areas where they potentially coexist, you can observe the following combinations of characters:
 * Ctenotus inornatus: Have an unpatterned face with no evidence of striping on the labials and no subocular stripe. The region between the forelimbs and the tympanum is unpatterned (anterior lateral zone), even if pattern elements are present between the forelimbs and hindlimbs. Limbs are generally unpatterned. Laterodorsal and dorsolateral stripes do not extend onto the neck and terminate behind the temporals. Paravertebral stripes are weakly developed or absent, but a bold black vertebral stripe is usually present.
 * Ctenotus spaldingi: In contrast, C. spaldingi is characterised by at least a partial subocular stripe and dark margins (striping) on the labials. The dorsal pattern is generally well-developed with dorsolateral and laterodorsal stripes extending onto the neck and usually reaching the fourth supraocular. Additionally, at least some lateral pattern elements (upper lateral blotches and midlateral stripe) extend anteriorly past the forelimbs. Limbs in C. spaldingi tend to be streaked. In some cases, C. spaldingi from specific regions may display reduced patterns, resembling C. inornatus superficially. However, these individuals differ in several key respects. Some may show minimal or diffuse midlateral lines with small spots or faint blotches in the upper lateral zone. Crucially, patternless bar-shouldered ctenotus (C. inornatus) is defined by an unpatterned neck and face.

Ecology and habitat
The bar-shouldered ctenotus is adapted to the Australian desert ecosystem, and has a particular preference for habitats dominated by spinifex grass (triodea). They exhibit specific foraging behaviors, primarily navigating within or along the edges of dense tussocks of spinifex grass. This behavioral adaptation is likely a response to the structural intricacies and sharp spines of the grass habitat, offering both cover and advantageous positions for capturing prey. They have a versatile palate, with a primary focus on isoptera (termites). Additionally, other prey include formicidae (ants), locustidae (locusts), coleoptera (beetles), various insects, and even parts of vegetation. This diverse dietary range underscores the adaptability of the species to the resources available within its desert habitat, contributing to its ecological success in the Australian arid landscape.

Reproduction
Reproduction for the bar-shouldered ctenotus is timed to the Australian spring and early summer, spanning October to February. The reproductive cycle involves the production of clutches, typically containing up to six eggs, tailored to the desert's seasonal conditions. Sexually mature males undergo testes enlargement and spermatogenesis in October and November. Females display two distinct egg production periods, occurring in spring (September to November) and summer (January and February), with vitellogenesis initiating in July. Continuous low-level reproductive activity persists throughout spring and summer, and there is a possibility of individual females producing multiple clutches within a season.