Burton's legless lizard
|Burton's legless lizard|
Description and taxonomy
Burton’s legless lizard (Lialis burtonis) is a robust species that grows to around 62 centimetres in length (Cronin, 2001, p. 164). The colouration of this species varies from pale grey or cream to various shades of brown and almost black with a pigmented underside that has dark and pale flecks (Cronin, 2001, p. 164). The snout is distinctly wedge shaped (Cronin, 2001, p. 164). This species is sexually dimorphic with females being larger than males and having a longer snout to vent length (Wall & Shine, 2013, p. 14). Furthermore, this lizard varies ontogenetically in relation to characteristics such as gape size as well (Wall & Shine, 2013, p. 16).
Burton’s legless lizard has significant morphological and behavioural adaptations to enable it to deal with large struggling prey items (Wall & Shine, 2007, p. 719). However, it is the morphological adaptations that will be dealt with here. The first adaptation is a skull with an elongated snout that may be an adaptation to allow a better grip on prey to be obtained and it may promote binocular vision which would allow strikes to be more accurately directed as well (Wall & Shine, 2007, p. 724). The prey of Burton’s legless lizard can also be encircled by its jaws as they are flexible mesokinetic and hypokinetic joints which combined with its pointed, hinged and recurved teeth are another significant adaptation to assist it in holding prey (Wall & Shine, 2007, p. 724). Lastly, the ability of the species to retract its eyes is of key importance as it is a visual predator that relies on eyesight and this adaptation effectively protects them during conflict (Wall & Shine, 2007, p. 725).
Burton’s legless lizard is a member of the genus Lialis within the family Pygopodidae (Wall & Shine, 2013, p. 9). There are approximately 40 species in the family Pygopodidae, however, Burton’s legless lizard and another species (L. jicari) are the only species that fall within genus Lialis (Wall & Shine, 2013, p. 9). Members in genus Lialis are considered analogous to macrostomatan snakes as both groups have developed similar jaws that can accommodate extremely large prey in relation to their body size (Wall & Shine, 2013, p. 9-10).
Members of the family Pygopodidae are often referred to as “pygopod” or “pygopodid” lizards as they lack forelegs and have only rudimentary hind legs (“Pygopod,” 2013). Consequently, Burton’s legless lizard and other pygopod lizards resemble snakes due to their serpentine appearance and phylogenetic convergence (Wall & Shine, 2007, p. 720). There are differences between legless lizards and snakes, however, as legless lizards lack venom glands and the ability to constrict prey, they have a fleshy tongue rather than a forked tongue, they have visible ear holes and legless lizards also have remnant hind limbs (Wall & Shine, 2007, p. 720; Wall & Shine, 2013, p. 9; Cronin, 2001, p. 164).
Distribution and habitat
Burton’s legless lizard occurs almost Australia wide but it is absent in parts of southern Australia including Tasmania (Cogger, 2000, p. 294). In addition, Burton’s legless lizard is even present on Papua New Guinea, although, populations are extremely limited (Cogger, 2000, p. 294).
Burton’s legless lizard is found in a variety of habitats from deserts to the margins of rainforests but not in southern alpine areas and extreme northern deserts as would be expected based on its distribution (Cronin, 2001, p. 164; Cogger, 2000, p. 294). It is usually found in low vegetation or debris on the ground such as leaf litter which has been shown to be important to specimens located in tropical environments (Cogger, 2000, p. 294; Wall & Shine, 2013, p. 19). This was demonstrated by Wall & Shine (2013, p. 19) as they conducted an experiment where individuals were given a choice of several thermally comparable environments and there was an overwhelming preference for leaf litter by specimens from the tropics. In areas where leaf litter is not as readily available this species will use grasses, abandoned burrows and other shelter that it can find as habitat (Cronin, 2001, p. 164).
This species seems to feed exclusively on lizards (Wall & Shine, 2009, p. 265; Cronin, 2001, p. 164; Wall & Shine, 2013, p. 9-10; Cogger, 2000, p. 294). Generally, skinks are the main prey item taken but other lizards such as legless lizards, geckoes and dragons are also a part of the diet of Burton’s legless lizard (Wall & Shine, 2009, p. 265; Cronin, 2001, p. 164). This species also seems to feed rather infrequently according to Wall & Shine (2013, p. 9).
Reproduction seems to be seasonal in populations of Burton’s legless lizard and mating occurs at similar times throughout Australia according to information from Wall & Shine (2013, p. 17) and Cronin (2001, p. 164). Ovulation and mating for the species occurs from September which is during the late dry-season for the populations located in the tropical north of Australia while September is wet in the south which indicates that breeding is not linked to precipitation (Wall & Shine, 2013, p. 17; Cronin, 2001, p. 164). The species is oviparous and eggs are laid under logs or rocks, on the ground under leaf litter and sometimes in the nests of sugar ants (Cronin, 2001, p. 164). This occurs mainly from November to January, however, reproduction can occur outside the common breeding period and females are capable of laying more than one clutch per year (Wall & Shine, 2013, p. 17).
Clutches can be laid in quick succession with each clutch containing a maximum of 2 eggs. Interestingly, nesting can be communal and up to 20 eggs have been found in a nest (Cronin, 2001, p. 164). Another characteristic that has been discovered is the ability of females of this species to either store sperm for reproduction at a later date or to reproduce through parthenogenesis which does not require mating to occur to be successful (Wall & Shine, 2013, p. 17). After hatching, Burton’s legless lizard hatchlings are approximately 13 centimetres long (Cronin, 2001, p. 164).
Burton’s legless lizard is generally diurnal for feeding purposes as prey is most commonly encountered during the day but it can be active at any time (Wall & Shine, 2013, p. 16). This is highlighted as its movements tend to be nocturnal and reasons for this are that surface temperatures are lower in exceedingly hot areas and that the risk of predation from major predators such as raptors is lower at night as many are diurnal (Wall & Shine, 2013, p. 18-19). Another reason for it to move at night is to avoid giving away its ambush position in the day when it has the highest likelihood of encountering prey as this may potentially cost it a meal if it is detected by an otherwise unsuspecting prey item (Wall & Shine, 2013, p. 19). In addition, there is geographic variation in the amount that this species moves and feeds as would be expected for such a widespread species that is located in such a variety of environments with different conditions (Wall & Shine, 2013, p. 19).
This lizard is a visually oriented predator that strikes based on movement (Wall & Shine, 2013, p. 16). This is to be expected, though, as it has a sedentary, ambush habit which involves individuals hiding in suitable shelter so that they are difficult to detect by predators and prey alike (Wall & Shine, 2013, p. 17, 19). However, the thermoregulatory environment provided by the shelter must also be considered (Wall & Shine, 2013, p. 19). Deep leaf litter, for example, is an extremely suitable environment for the species as individuals can bury themselves at an appropriate depth to regulate temperature and it is very good cover (Wall & Shine, 2013, p. 19).
Feeding strategies are a very important behaviour for this species as the lizards it eats can often be large enough to inflict a retaliatory bite that could cause serious harm (Wall & Shine, 2007, p. 719). This is thought to be the reason that this species will modify its strike precision according to prey size as strikes at large prey will be directed at either the head or neck to prevent them from biting back (Wall & Shine, 2007, p. 723). Furthermore, Burton’s legless lizard will hold large prey until it is incapacitated before swallowing to prevent harm to itself whereas it swallows small prey that is still struggling as swallowing live prey costs less energy than waiting for it to be incapacitated (Wall & Shine, 2007, p. 724).
Another important adaptation that this species shares with many other types of lizard is the ability to drop its tail if seized by a predator (Wall & Shine, 2013, p. 19). However, the loss of a tail would be an inconvenience to an individual as there are costs associated with regrowing the tail and if it is seized again soon after losing its tail it will not have another tail to lose and may be preyed on.
Cogger, H. G. (2000). Reptiles and amphibians of Australia. Sydney: Reed New Holland.
Cronin, L. (2001). Key guide: Australian reptiles and amphibians. Annandale, NSW: Envirobook.
Pygopod. (2013). In The free dictionary online. Retrieved from http://www.thefreedictionary.com/Pygopod
Wall, M., & Shine, R. (2007). Dangerous food: Lacking venom and constriction, how do snake-like lizards (Lialis burtonis, Pygopodidae) subdue their lizard prey? Biological Journal of the Linnean Society, 91(4), 719-727. Doi: 10.1111/j.1095-8312.2007.00835.x
Wall, M., & Shine, R. (2013). Ecology and behaviour of Burton’s legless lizard (Lialis burtonis, Pygopodidae) in tropical Australia. Asian Herpetological Research, 4(1), 9-21. doi: 10.3724/SP.J.1245.2013.00009
Wall, M., & Shine, R. (2009). The relationship between foraging ecology and lizard chemoreception: Can a snake analogue (Burton’s legless lizard, Lialis burtonis) detect prey scent? Ethology, 115(3), 264-272. doi: 10.1111/j.1439-0310.2008.01595.x