The olive legless lizard (Delma inornata) is a species of legless gecko from the Pygopodidae family. This species is commonly found throughout the Australian Capital Territory, New South Wales, Queensland, Victoria and southeastern South Australia, mostly inhabiting areas consisting of dry to temperate southern grasslands and grassy woodlands.
Taxonomy Delma inornata is also commonly referred to as the patternless delma, olive snake-lizard, plain snake-lizard, olive delma lizard, patternless legless lizard, and common delma. The species is a member of the Pygopodidae gecko family, which consists of approximately thirty legless, snake-like species endemic to Australia, with only two species found outside of mainland Australia. These Pygododid lizards are closely related to the Diplodactylidae family of geckos. Distinguishing features include the absence of forelimbs, and replacement of hindlimbs for scaly-flaps, accompanied by snake-like, lidless eyes. The Delma genus, described by John Edward Gray in 1831, currently contains 22 described species. This group of terrestrial legless lizards is characterised by well-developed hindlimb flaps, external ear openings and a broad, rounded tongue. Head scales are relatively symmetrical and enlarged, with body scales consisting of 20 or fewer rows. Delma inornata has 36 chromosomes. Unlike its close relatives, its Y chromosome is much larger than its X chromosome due to the gradual accumulation of repetitive DNA sequences. The Y chromosome is also its largest chromosome.
Phylogeny The olive legless lizard is most closely related to Delma grayii, Delma nasuta, and Delma butleri. The inornata clade, as a rule, lack the broad prominent banding of other Delma. They are also larger, and have comparatively elongate & narrow head, longer & sharper snouts, and small parietal scales. This clade is a widely geographically distributed group, and diverged from other Delma during the drying out of Australia during the Miocene (~15mya), with rapid speciation occurring between 10mya and 5mya. Indeed, the widely separated archaic members Delma grayii and Delma inornata suggest a once wider range for ancestral members of the group. Raymond Hoser believes that populations of Delma inornata in southern New South Wales and South Australia should be separate species, but herpetologists reject his work.
Description
Morphology Delma inornata is one of the largest species of the Delma genus, with an average snout-to-vent length of 13.3 centimetres (5.2 in). The tail is typically 2-4 times the length of the body, and up to 2/3 of its total length. The absence of a uniform pattern or unique features drove the naming of this species, as these features are often a characterizing trait of Delma. The dorsal colouration of this species is grey, grey-brown or olive brown, with specimens often sporting a yellow throat. Delma inornata resembles Pygopus, and their gekkonid relatives, in their invertebrate-heavy diet, rounded head shape, peglike & crushing dentition and low degree of cranial kinesis. Delma inornata is better suited to a slower and more powerful bite to crush and pierce arthropod cuticles.
Scales The smooth scales are in typically 16 rows but can range from 15-18, with ventral scales being wider than the adjacent body scales. Delma inornata is further identifiable by three enlarged pre-anal scales and 3-5 scales on the lower hindlimb flap. Scales are characterised by a dark outlining border, with ventral scales being a lighter whitish colouration. Juveniles have been observed with darker scales on top of the head.
South Australia The population of olive legless lizard in South Australia are rare, and likely isolated from the main population in Victoria and New South Wales. For example, although 90% of olive legless lizard have 2 supranasal scales, a study of South Australian specimens revealed that 78% of individuals had 1 supranasal scale.
Differentiation The species which most closely resembles Delma inornata, and which overlaps in distribution, is the (occasionally stripe-less) striped legless lizard, (Delma impar). The best known difference between these taxa is the fusion or partial fusion of the nasal and first supra-labial scale in Delma impar, and the clear separation of these scales in Delma inornata. However, this is inconsistent, with some specimens of Delma impar having clearly separated nasal and first supra-labial scales. Despite this, experienced workers are able to identify specimens of either species. Delma butleri has also been misidentified as Delma inornata.
Hemipenis The hemipenis is a consistent differentiating morphology between species of Delma. The olive legless lizard has a fully extended, bi-lobed, bulb-shaped hemipenis, with poorly differentiated apical lobes. The inner lobe is larger than outer lobe and the surface is covered by bumps, with the sulcus being forked. A moderate asymmetrical ornamentation and bi-lobed design is also found in Delma grayii, Delma butleri, and Delma nasuta. Except for Delma nausta, this group is typified by micro-ornamentation restricted to the lobes, far from the sulcus. The sulcus terminates laterally onto shallow broad sulcal pads, which are also lack ornamentation. Convergences with Delma fraseri and Delma petersoni suggest that an approximately symmetrical, bi-lobed, and relatively unornamented hemipenis may be the ancestral condition of Delma.
Distribution This species has a relatively wide distribution, spanning across much of the interior of the east coast of Australia. Delma inornata ranges from the region of Darling Downs in south-east Queensland, then extends down south, to the west of the Great Dividing Range in New South Wales to the south-east region of South Australia. There have been records of isolated populations in Northern Queensland and Central Queensland.
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