Skull tree iguana  (Liolaemus occipitalis)

The skull tree iguana is classified as Vulnerable (VU) on the IUCN Red List (1).

The skull tree iguana (Liolaemus occipitalis) is a small, greyish or greyish-tan lizard of sand dune habitats on the coastal beaches of eastern Brazil. Its colouration provides good camouflage against the sandy substrate, while a wedge-shaped snout may help it to rapidly dive into sand to escape predators (2). This species has long, slightly curved claws and its tail makes up just over half of its total length (2).

The upperparts of the skull tree iguana are usually relatively plain or have indistinct patterning, although adult males develop a dark stripe along the sides, which is widest above the forelimbs (2) (3). Juvenile skull tree iguanas usually have white underparts, while adult females have a yellow throat, and males have dark spots on the throat and abdomen (2) (3). The yellow of the female’s throat usually intensifies during the breeding season (2) (3), and can also sometimes be seen on young individuals (3). In the second year of life, some females develop dark spots on the throat or a black stripe along the sides (3). Male skull tree iguanas grow larger than females (3) (4) and are usually slightly darker in colour (3).

A population of skull tree iguanas occurring on the island of Ilha de Santa Catarina differs slightly from the mainland population in its appearance and genetics (5) (6).

This species is endemic to the coast of southeast Brazil, where it occurs in the states of Santa Catarina and Rio Grande do Sul (1) (2). The northern limit of the skull tree iguana’s range is Ilha de Santa Catarina, off the coast of Santa Catarina state (5) (6).

The skull tree iguana inhabits sand dunes in shrubby coastal habitat known as ‘restinga’ (5), part of the unique Atlantic forest ecosystem of eastern South America. It appears to prefer areas of dry, loose sand, where it is best camouflaged and can easily bury into the substrate (5). This species does not move inland further than the open dunes, and its coastal range may therefore not exceed an area about five kilometres in width (2).

The skull tree iguana is active during the day (7) (8) (9), with most activity occurring on warm, sunny days (7). This species is less active during the winter (8) (9). The skull tree iguana feeds mainly on insects, which it hunts using a ‘sit and wait’ strategy, lying in wait to ambush passing prey (4) (10).

If threatened, the skull tree iguana typically flees into vegetation or buries itself in the sand (2) (7) (8), and if caught by a predator it may shed its tail to escape (8). This species also constructs burrows in which to shelter at night or during the hottest part of the day. The burrow is usually built next to sand dunes with patches of vegetation, and can measure around 20 to 30 centimetres in length (2) (7). Skull tree iguanas may also use the burrows of other animals (2).

During the breeding season, a male and female skull tree iguana can sometimes be found within the same burrow (2), but males are aggressive towards each other and may fight (3) (8) (10). Individuals in captivity have been shown to use signalling behaviour, such as flexing the feet and shaking the head, to mark the territory or court mates (10). The skull tree iguana usually breeds between September and December (11), although some populations may have a longer breeding season, with high numbers of juveniles appearing between March and April (6). Males reach sexual maturity at a snout-vent length of around 5 centimetres, and females at about 4.5 centimetres (4) (11).

The major threat to the skull tree iguana is the destruction of its beach habitat, mainly due to urban expansion (1). The coastal ‘restingas’ of Brazil are under severe threat from trampling, recreation, tourism, housing developments and other humans activities (5) (12), and the Ilha de Santa Catarina has already lost over 80 percent of its original vegetation (5). As a result of this destruction, the skull tree iguana population is decreasing (1), and the species is listed as Vulnerable on the list of threatened Brazilian fauna (13).

The most important conservation measure for the skull tree iguana would be improved legal protection of restinga habitats, to prevent their degradation and to stop the encroachment of human developments onto the sand dunes (5) (12). On Ilha de Santa Catarina, the sand dunes of Praia da Joaquina occur within the Parque Municipal das Dunas da Lagoa da Conceição, although this area needs better supervision and more personnel if it is to be properly protected (5).

Find out more about conservation in the Atlantic forest region:

• Conservation International: Biodiversity Hotspots - Atlantic Forest: 
  http://www.biodiversityhotspots.org/xp/Hotspots/atlantic_forest/Pages/default.aspx
• WWF: Atlantic Forests: 
  http://wwf.panda.org/about_our_earth/ecoregions/atlantic_forests.cfm
• SOS Mata Atlântica:
  http://www.sosmatatlantica.org.br/
• The Nature Conservancy:
  http://www.nature.org/wherewework/southamerica/brazil/work/art5080.html
• World Land Trust:
  http://www.worldlandtrust.org/projects/brazil.htm