''Xenosaurus grandis'', commonly known as the knob-scaled lizard, is a

species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...

of diurnal,

terrestrial Terrestrial refers to things related to land or the planet Earth. Terrestrial may also refer to: * Terrestrial animal, an animal that lives on land opposed to living in water, or sometimes an animal that lives on or near the ground, as opposed to ...

lizard Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia al ...

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found els ...

Mexico Mexico ( Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guate ...

and Guatemala. It primarily inhabits

tropical rainforests Tropical rainforests are rainforests that occur in areas of tropical rainforest climate in which there is no dry season – all months have an average precipitation of at least 60 mm – and may also be referred to as ''lowland equatori ...

. It dwells in rock crevices and eats insects.

Etymology

The scientific name, ''Xenosaurus grandis'', comes from the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

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.Gadow H (1901). ''Amphibia and Reptiles.'' London: Macmillan & Co.

Taxonomy

There are five recognized subspecies, which are spread throughout the species’ range, and the species complex is being reevaluated. Some of the subspecies are currently in the process of being elevated to species status. The species as a whole is listed as vulnerable by the

IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is the world's most comprehensive inventory of the global conservation status of biol ...

and its population is currently decreasing.

Physiology

Appearance

''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.Zuniga-Vega JJ, Valverde T, Rojas-Gonzalez RI, Lemos-Espinal JA (2007)
"Analysis of the population dynamics of an endangered lizard (''Xenosaurus grandis'') through the use of projection matrices"
''Copeia'' 2007 (2): 324-335. 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.Hall D (2007). ''The Ultimate Guide to Snakes and Reptiles''. Kent: Regency House Publishing.

Body size

On average, the snout-vent length (SVL) of ''Xenosaurus grandis'' is 6.8 - 12.9 cm.Smith GR, Lemos-Espinal JA, Ballinger RE (1997). "Sexual dimorphism in two species of knob-scaled lizards (Genus ''Xenosaurus'') from Mexico". ''Herpetologica'' 53: 200-205. While some species of ''Xenosaurus'' do not exhibit

sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...

, ''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.

Body temperature

''Xenosaurus grandis'' is a diurnally active thermal conformer, meaning that its body temperature correlates with substrate and air temperatures. Its average body temperature is 22.7 C.Ballinger RE, Lemos-Espinal J, Sanoja-Sarabia S, Coady NR (1995). "Ecological observations of the lizard, ''Xenosaurus grandis'' in Cuautlapan, Veracruz, Mexico". ''Biotropica'' 27: 128-132. Air and substrate temperatures may be particularly relevant in ''Xenosaurus grandis'' since they are almost exclusively ground and crevice dwellers. Temperatures seem to differ across ''Xenosaurus'' species, possibly because of environment and habitat. ''Xenosaurus grandis'' appears to inhabit more dense tropical forests, where sunlight may not reach the ground as much.Lemos-Espinal JA, Smith GR, Ballinger RE (2003). "Ecology of ''Xenosaurus grandis agrenon'', a knob-scaled lizard from Oaxaca, México". ''Journal of Herpetology'' 37: 192-196. While body temperature is influenced by the lizard's amount of cover and its body position in its crevice, it does not seem to be influenced by sex, month, vegetation type, or any crevice characteristics.

Diet

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.Lemos-Espinal JA, Smith GR, Ballinger RE (2003)
"Diets of three species of knob-scaled lizards (genus Xenosaurus) from Mexico"
''Southwestern Naturalist'' 48: 119-122. Their diet consists primarily of insects, but occasional lizard prey are taken. Their most frequent prey includes coleopterans (beetles),

dipterans Flies are insects of the order Diptera, the name being derived from the Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwings having evolved into advanced ...

(flies), orthopterans (insects such as grasshoppers, crickets, weta, and locusts), and

myriapods Myriapods () are the members of subphylum Myriapoda, containing arthropods such as millipedes and centipedes. The group contains about 13,000 species, all of them terrestrial. The fossil record of myriapods reaches back into the late Silurian, ...

(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.

Behavior

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.

Reproduction

''Xenosaurus grandis'' and the rest of the xenosaurids are

viviparous Among animals, viviparity is development of the embryo inside the body of the parent. This is opposed to oviparity which is a reproductive mode in which females lay developing eggs that complete their development and hatch externally from the ...

, 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.Zúñiga-Vega JJ, Rojas-González RI, Lemos-Espinal JA, Pérez-Trejo ME (2005). "Growth ecology of the lizard ''Xenosaurus grandis'' in Veracruz, México". ''Journal of Herpetology'' 39: 433-443. It is also plausible to say that ''X. grandis'' do not produce young every year.Goldberg, Stephen R. (2009)
"Notes on the reproduction of the knob-scaled lizard, ''Xenosaurus grandis'' (Squamata: Xenosauridae)
from Veracruz, Mexico". ''The Texas Journal of Science'' 61 (4).

Geographic range

There are five major population areas for the ''Xenosaurus grandis'' in Southern Mexico and Guatemala: central

Veracruz Veracruz (), formally Veracruz de Ignacio de la Llave (), officially the Free and Sovereign State of Veracruz de Ignacio de la Llave ( es, Estado Libre y Soberano de Veracruz de Ignacio de la Llave), is one of the 31 states which, along with Me ...

, southern

Oaxaca ) , population_note = , population_rank = 10th , timezone1 = CST , utc_offset1 = −6 , timezone1_DST = CDT , utc_offset1_DST = −5 , postal_code_type = Postal ...

, north-central Oaxaca, the highlands of central

Chiapas Chiapas (; Tzotzil and Tzeltal: ''Chyapas'' ), officially the Free and Sovereign State of Chiapas ( es, Estado Libre y Soberano de Chiapas), is one of the states that make up the 32 federal entities of Mexico. It comprises 124 municipalities ...

, 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''."''Xenosaurus grandis'' (GRAY, 1856)". (2012). Retrieved 10/21/2012
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Habitat

All the subspecies of ''Xenosaurus grandis'' live exclusively in rock crevices, which allows them to live in many habitats, including:

xerophytic A xerophyte (from Greek ξηρός ''xeros'' 'dry' + φυτόν ''phuton'' 'plant') is a species of plant that has adaptations to survive in an environment with little liquid water, such as a desert such as the Sahara or places in the Alps or th ...

vegetation, tropical rainforests,

cloud forests A cloud forest, also called a water forest, primas forest, or tropical montane cloud forest (TMCF), is a generally tropical or subtropical, evergreen, montane, moist forest characterized by a persistent, frequent or seasonal low-level clo ...

, oak forests, and tropical

deciduous In the fields of horticulture and Botany, the term ''deciduous'' () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves, usually in the autumn; to the shedding of petals, a ...

rainforests Rainforests are characterized by a closed and continuous tree canopy, moisture-dependent vegetation, the presence of epiphytes and lianas and the absence of wildfire. Rainforest can be classified as tropical rainforest or temperate rainforest ...

. The lizards have strong attachments to where they live, only living in 1-2 rock crevices for 95% of their entire lives.

Conservation status

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.

Eagle Eagle is the common name for many large birds of prey of the family Accipitridae. Eagles belong to several groups of genera, some of which are closely related. Most of the 68 species of eagle are from Eurasia and Africa. Outside this area, j ...

s 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.

Temperature

Higher temperatures have been associated with higher mortality rates for ''X. grandis''. In the 2003-2004 wet season of Southern Mexico and Guatemala (the habitat regions of the species), the average temperature was 24.3 C. That temperature was in the top 12% of highest recorded temperatures in the past 34 years of record keeping. The mortality rate for yearlings (the youngest age group) increased from 0.1923 to 0.6551 and for adult II (the oldest age group) increased from 0.3956 to 0.5676 for the 2002-2003 and 2003-2004 wet seasons respectively. If temperatures continue to increase, the survival of the species will be further threatened and currently 50% of wet seasons are warm enough to be considered to be unfavorable for the species.

Population and growth rates

As of 2004, ''X. grandis'' had a survival rate of 70.5% and a growth rate of 0.851. Even though the rates may appear to be low, in comparison to other lizard genera and families ''X. grandis'' is doing well. Currently the species is decreasing in population, which is thought to be primarily caused by human development destroying their habitat. If habitat destruction stops, the population should at least be stable, if not prosperous.