The Noronha skink (Trachylepis atlantica ) is a species of skink from the island of Fernando de Noronha off northeastern Brazil. It is covered with dark and light spots on the upperparts and is usually about 7 to 10 cm (3 to 4 in) in length. The tail is long and muscular, but breaks off easily. Very common throughout Fernando de Noronha, it is an opportunistic feeder, eating both insects and plant material, including nectar from the Erythrina velutina tree, as well as other material ranging from cookie crumbs to eggs of its own species. Introduced predators such as feral cats prey on it and several parasitic worms infect it.
Perhaps seen by Amerigo Vespucci in 1503, it was first formally described in 1839. Its subsequent taxonomic history has been complex, riddled with confusion with Trachylepis maculata and other species, homonyms, and other problems. The species is classified in the otherwise mostly African genus Trachylepis and is thought to have reached its island from Africa by rafting. The enigmatic Trachylepis tschudii, supposedly from Peru, may well be the same species.
The Noronha skink is covered with light and dark spots above, but there is substantial variation in the precise colors. There are no longitudinal stripes. The scales on the underparts are yellowish or grayish. The eyelids are white to yellow. It has a small head with small nostrils, which are placed far to the front at the sides of the head. The mouth contains small and conical teeth and a thin but well-developed tongue. The eyes are small and placed laterally and contain dark, rounded irises. There are three to five well-developed auricular lobules (small projections) in front of the ears; these lobules are absent in true Mabuya. The hindlimbs are longer and stronger than the forelimbs, which are small. The tail is longer than the body and is muscular but very brittle. It is nearly cylindrical in form and tapers towards the end.
In reptiles, features of the scales are important in distinguishing among species and groups of species. In the Noronha skink, the supranasal scales (located above the nose) are in contact, as are the prefrontal scales (behind the nose) in most individuals. The two frontoparietal scales (above and slightly behind the eyes) are not fused. Unlike in T. maculata, the parietal scales (behind the frontoparietals) are in contact with each other. There are four supraocular scales (above the eyes) in almost all specimens and five supraciliary scales (immediately above the eyes, below the supraoculars). The dorsal scales (on the upperparts) have three keels, two fewer than in T. maculata. There are 34 to 40 (mode 38) midbody scales (counted around the body midway between the fore- and hindlimbs), 58 to 69 (mode 63–64) dorsal, and 66 to 78 (mode 70) ventral scales (on the underparts). Mabuya species and T. maculata generally have fewer midbody scales (up to 34). There are 21 to 29 subdigital lamellae under the fourth toe, more than in T. maculata, which has 18. The Noronha skink has 26 presacral vertebrae (located before the sacrum), similar to most Trachylepis, but unlike American Mabuya, which have at least 28.
Although there is substantial variation in measurements within the species, no discrete groups can be detected and it is not possible to separate the sexes unambiguously using measurements alone. Among 15 male and 21 female T. atlantica collected in 2006, snout to vent length was 80.6 to 103.1 mm (3.17 to 4.06 in), averaging 95.3 mm (3.75 in), in males and 65.3 to 88.1 mm (2.57 to 3.47 in), averaging 78.3 mm (3.08 in), in females and body mass was 10.2 to 26.0 g (0.36 to 0.92 oz), averaging 19.0 g (0.67 oz), in males and 6.0 to 15.0 g (0.21 to 0.53 oz), averaging 10.0 g (0.35 oz), in females. Males are significantly larger than females. In 100 specimens collected in 1876, head length was 12.0 to 18.9 mm (0.47 to 0.74 in), averaging 14.8 mm (0.58 in); head width was 7 to 14.4 mm (0.28 to 0.57 in), averaging 9 mm (0.35 in), and tail length was 93 to 170 mm (3.7 to 6.7 in), averaging 117 mm.
The Noronha skink is very abundant throughout Fernando de Noronha, even occurring commonly in houses, and also occurs on the smaller islands that surround the main island of the archipelago. Its abundance may be a result of the absence of ecologically similar competitors. Apart from T. atlantica, the reptile fauna of Fernando de Noronha consists of the indigenous amphisbaenian Amphisbaena ridleyi and two introduced lizards, the gecko Hemidactylus mabouia and the tegu Tupinambis merianae.
The species is found in several microhabitats, but most often on rocks. Although predominantly ground-dwelling, it is a good climber. Nothing is known about its reproduction except that skinks studied in late October and early November, during the dry season, showed little evidence of reproductive activity. The Noronha skink is oviparous (egg-laying), like many Trachylepis, but unlike Mabuya, which are all viviparous (giving live birth).
Trachylepis atlantica is active during the day. Its body temperature averages 32 °C (90 °F), a few degrees higher than the environment temperature. During the day, body temperature peaks at up to 38 °C (100 °F) around midday and is lower earlier and later. In the early morning, the lizard may bask in the sun. During foraging, it spends about 28.4% of its time moving on average, a relatively high value for Trachylepis.
A geologist who visited the island in 1876 noted that the skink is curious and bold:
The Noronha skink is an opportunistic omnivore and "thrives on anything edible". Analysis of stomach contents indicates that it mainly eats plant material, at least during the dry period, but it also feeds on insects, including larvae, termites (Isoptera), ants (Formicidae), and beetles (Coleoptera). Its prey is mostly mobile, rather than sedentary, which is consistent with the relatively high proportion of time it spends moving. Related skink species eat mostly insects, but island populations may often be more herbivorous. Animal prey averages 6.9 mm3 in volume, less than in most other Trachylepis.
When the mulungu tree Erythrina velutina blooms during the dry season, Noronha skinks climb up to 12 m (39 ft) to reach the inflorescences of the tree and to eat the nectar by inserting their heads into the flowers. They probably use the nectar both for its sugar and water content. In this way, the skinks aid in pollinating the tree, as they acquire pollen on their scales and leave pollen on stigmas when visiting a flower. Pollination is rare behavior among lizards, but occurs most frequently in island species. Humans have introduced additional food sources to the island, including Acacia seeds, feces of the rock cavy (Kerodon rupestris ), carrion flies, juvenile Hemidactylus mabouya, and even cookie crumbs given by tourists. The availability of these additional food sources may increase the abundance of the skink. In 1887, H. N. Ridley observed Noronha skinks eating banana skins and yolk from doves' eggs. Several cases of cannibalism have been reported, involving skinks eating eggs, juveniles, and the tail of an adult.
The reptile is thought to be stable in terms of population trends and not under any threat of extinction. However, the climate is rapidly changing, so this could change at any point in time. Although environmental changes do not affect the species in particular, the density of the species is at risk of decreasing should the environment change drastically as well as if tourism trends or more invasive animals are introduced. Additionally, the urbanization of surrounding areas to the lizards habitat could be detrimental, therefore International Union for Conservation of Nature evaluated it as least concern.
