Knob-scaled lizard
Xenosaurus grandis, commonly known as the knob-scaled lizard, is a species of diurnal, terrestrial lizard endemic to Mexico and Guatemala. It primarily inhabits tropical rainforests. It dwells in rock crevices and eats insects.
The scientific name, Xenosaurus grandis, comes from the Greek words xenos, meaning “alien”, “stranger”, or “foreigner”, saurus, meaning “lizard”, and grandis, meaning “grand” or “great”.Its common name, “knob-scaled lizard”, refers to the bumpy, “knob-like” scales found on the upper portion of its body.
Xenosaurus grandis has a flattened head and body and is nearly always found in rock crevices, or at least with a portion of the body in a crevice.Its flattened physiology is most likely an adaptation to allow it to squeeze into narrow crevices. Its color ranges from dark grey to dark brown, with lighter bands or blotches. It has a forked tongue, and small, sharp, fang-like teeth.
On average, the snout-vent length (SVL) of Xenosaurus grandis is 6.8 - 12.9 cm. While some species of Xenosaurus do not exhibit sexual dimorphism, Xenosaurus grandis, among other species, is one that does.In Xenosaurus grandis, males and females do not differ significantly in body size, but males have proportionately larger heads (in length and width) than females. Males and females of X. grandis do not exhibit a significant difference in femur length or head shape.
There are five major population areas for the Xenosaurus grandis in Southern Mexico and Guatemala: central Veracruz, southern Oaxaca, north-central Oaxaca, the highlands of central Chiapas, and central Guatemala. The separate population areas have given rise to five subspecies of X. grandis. The five subspecies are X. g. grandis, X. g. agrenon, X. g. arboreus, X. g. rackhami, and X. g. sanmartinesis.
All the subspecies of Xenosaurus grandis live exclusively in rock crevices, which allows them to live in many habitats, including: xerophytic vegetation, tropical rainforests, cloud forests, oak forests, and tropical deciduous rainforests. The lizards have strong attachments to where they live, only living in 1-2 rock crevices for 95% of their entire lives.
The Knob-scaled lizard is diurnal, meaning it is active during the day. Due to its diet of Orthoptera and Lepitdoptera larvae, Xenosaurus grandis is an ambush predator. It waits in its rocky crevice home and strikes with the element of surprise. It is a very solitary and aggressive species and will often fight with members of its own species over territory.
Lizards in the genus Xenosaurus are exclusively found in crevices. Such a lifestyle suggests that the diets of these lizards might be opportunistic, and they eat whatever crawls or flies past or into their crevice. Their diet consists primarily of insects, but occasional lizard prey are taken. Their most frequent prey includes coleopterans (beetles), dipterans (flies), orthopterans (insects such as grasshoppers, crickets, weta, and locusts), and myriapods (terrestrial arthropods such as millipedes and centipedes). On the basis of number, they consume the most dipterans, but on the basis of volume, they consume the most orthopterans.
Xenosaurus grandis and the rest of the xenosaurids are viviparous, which means offspring are birthed live rather than in eggs. Young are birthed after a 9-month gestation period. The majority of litters contain only three offspring, but litters ranging from two to seven offspring have also been observed. Male knob-scaled lizards reach maturity at 28 months, while females reach maturity a little later, at 32 months. It is also plausible to say that X. grandis do not produce young every year.
Currently Xenosaurus grandis is categorized as a vulnerable species according to the IUCN. The species was given this status because of fragmented populations, decreasing population size, and decreasing habitat quality and area, covering only 20,000 square km. The greatest threats to the survival of the species in the wild are habitat destruction and trapping for international pet trade. Eagles are the greatest natural predator of X. grandis, but they are not considered a threat to the survival of the species as a whole. Also, warmer temperatures in their habitat have been shown to cause greater mortality rates among the lizards, posing another potential threat to the species.
