Distribution: Jamaica, Goat I, Little Goat I
Type locality: Jamaica.
The rhinoceros iguana (Cyclura cornuta) is a threatened species of lizard in the family Iguanidae that is primarily found on the Caribbean island of Hispaniola, shared by the Republic of Haiti and the Dominican Republic. They vary in length from 60 to 136 centimetres (24 to 54 in) and skin colors range from a steely gray to a dark green and even brown. Their name derives from the bony-plated pseudo-horn or outgrowth which resembles the horn of a rhinoceros on the iguana's snout.
The rhinoceros iguana is a species of lizard belonging to the genus Cyclura. The generic name (Cyclura) is derived from the Ancient Greek cyclos (κύκλος) meaning "circular" and ourá (οὐρά) meaning "tail", after the thick-ringed tail characteristic of all Cyclura. The rhinoceros iguana's specific name, cornuta, is the feminine form of the Latin adjective cornutus, meaning "horned" and refers to the horned projections on the snouts of males of the species. The species was first identified by Pierre Joseph Bonnaterre in 1789.
In addition to the nominate race (Cyclura cornuta cornuta) found on Hispaniola, there are two other subspecies of Cyclura cornuta, the Mona ground iguana (Cyclura cornuta stejnegeri) and the Navassa Island iguana (Cyclura cornuta onchiopsis), although the latter subspecies is believed to be extinct in the wild.
Anatomy and morphology
The rhinoceros iguana, like other members of the genus Cyclura, is a large-bodied, heavy-headed lizard with strong legs and a vertically flattened tail. A crest of pointed horned scales extends from the nape of their neck to the tip of their tail. Their color is a uniform gray to brown drab. Most adults weigh 4.56 kilograms (10.1 lb) to 9 kilograms (20 lb)
These iguanas are characterized by the growth of bony prominent tubercles on their snouts which resemble horns. Dr. Thomas Wiewandt, who spent an extended period on Mona Island studying Cyclura cornuta stejnegeri, suggested that the horns, along with lateral spines and prominent parietal bulges, function as protective armor against sharp rocks or as defensive tools to facilitate the escape of males from the grasp of one another. Males possess an adipose pad in the form of a helmet on the occipital region of the head, and a large dewlap. This species, like other species of Cyclura, is sexually dimorphic; males are larger than females, and have more prominent dorsal crests and "horns" in addition to large femoral pores on their thighs, which are used to release pheromones.
Distribution and habitat
Ranging throughout Hispaniola, Haiti and the Dominican Republic; rhinoceros iguana populations are stable only on Isla Beata and the extreme of the Barahona Peninsula inside Parque Nacional Jaragua. There are moderately dense populations in the southeastern region of Haiti and its offshore islands including the saltwater lake of Etang Saumatre. Populations in Haiti are even more endangered due to the deforestation and human clearing practices. In general, the iguanas are found most abundantly in, although not restricted to, scrub woodland, dry forests characterized by xeric, rocky habitats of eroded limestone in coastal terraces and lowlands of the mainland and several offshore islands and small cays in a variety of subtropical life zones and habitat types. An individual was photographed on May 4, 2008 on the Limbe Island in Northern Haiti. It had been caught by a group of fishermen from Bas-Limbe, Bord de Mer village. The rhinoceros iguanas caught on Limbe Island are eaten by the local population. This sighting represents a new area previously not thought to be in the range of Cyclura cornata.
The rhinoceros iguana is a diurnal species living primarily in rocky outcroppings with little vegetation for cover. Although quick to flee when attacked or threatened, they will aggressively attack by biting and repeatedly striking with their thick tail if cornered.
The rhinoceros iguana, like most Cyclura species is primarily herbivorous, consuming leaves, flowers, berries, and fruits from different plant species. A study in 2000 by Dr Allison Alberts of the San Diego Zoo revealed that seeds passing through the digestive tracts of Cycluras germinate more rapidly than those that do not. These seeds in the fruits consumed by cycluras have an adaptive advantage by sprouting before the end of very short rainy seasons. The rhinoceros iguana is also an important means of distributing these seeds to new areas (particularly when females migrate to nesting sites) and, as the largest native herbivores of their island's ecosystem, they are essential for maintaining the balance between climate and vegetation. Rhinoceros iguanas do appear to be opportunistic carnivores as individual animals have been observed eating small lizards, snakes, and insects.
Male rhinoceros iguanas, unlike other members of the genus Cyclura, reach sexual maturity at four to five years of age. Females become sexually mature at two to three years of age. Male rhinoceros iguanas are territorial and the most aggressive males will have the largest range of territory. Mating takes place at the beginning of, or just prior to, the first rainy season of the year (May to June) and lasts for two to three weeks. Females lay from 2 to 34 eggs, with an average clutch size of 17, within 40 days. Females guard their nests for several days after laying their eggs, and incubation lasts approximately 85 days. It has been noted that their eggs are among the largest lizard eggs produced in the world.
Although rhinoceros iguanas are the most common species of Cyclura kept in captivity there remain approximately 10-16,000 of these animals in the wild. A successful breeding program existed at the Parque Zoológico Nacional of the Dominican Republic (ZooDom) from 1974 to 1994, with an average of 100 babies hatching annually. These efforts included reintroductions of captive-bred "head-started" young to several protected areas in the southwest Dominican Republic in order to reduce the odds of predation by snakes and feral animals such as mongoose or cats. The program has not continued since 1995, due to an administrative change at the zoo.
The rhinoceros iguana is well established in captivity, both in public and private collections. Rhinoceros iguanas in captivity throughout the United States total 39 males, 32 females, and 36 undetermined individuals at 20 zoological institutions, with an additional 533 animals of unassigned subspecies, reported by seven American Zoological and Aquarium Association institutions. The actual number may be much higher considering animals kept at European and Asian zoos and the many kept as pets in private collections. As a result, the demand for wild-caught animals to supply zoos and the pet trade has been reduced.
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Cyclura is a genus of lizards from the family Iguanidae. Members of this genus are known as "cyclurids" or more commonly as rock iguanas and only occur on islands in the West Indies. Rock iguanas have a high degree of endemism, with a single species or subspecies restricted to individual islands.
- Turks and Caicos rock iguana, Cyclura carinata
- Jamaican iguana, Cyclura collei
- Rhinoceros iguana, Cyclura cornuta
- Northern Bahamian rock iguana, Cyclura cychlura
- Grand Cayman blue iguana, Cyclura lewisi
- Cuban iguana, Cyclura nubila
- Anegada ground iguana, Cyclura pinguis
- Ricord's iguana, Cyclura ricordi
- San Salvador iguana, Cyclura rileyi
Rock iguanas most often inhabit subtropical areas of West Indian dry forest biomes characterized by eroded limestone and sparse vegetation ranging from only moderately dry acacia forest to much drier mesquite and cactus habitats. These are nonvolcanic islands made up of heavily eroded limestone which form natural caves that the iguanas use as retreats.
Diet and longevity
All rock iguanas are herbivorous, consuming leaves, flowers, berries, and fruits from different plant species. A study in 2000 by Allison Alberts of the San Diego Zoo revealed that seeds passing through the digestive tracts of rock iguanas germinate more rapidly than those that do not. These seeds in the fruits consumed by cycluras have an adaptive advantage by sprouting before the end of very short rainy seasons. The iguanas are an important means of distributing these seeds to new areas (particularly if females migrate to nesting sites) and, as the largest native herbivores of many island ecosystems, they are essential for maintaining the balance between climate and vegetation. Their diet is very rarely supplemented with insect larvae, crabs, slugs, dead birds, and fungi; individual animals do appear to be opportunistic carnivores.
Like other herbivorous lizards, the rock iguanas are presented with a special problem for osmoregulation: plant matter contains more potassium and has less nutritional content per gram than meat so more must be eaten to meet the lizard's metabolic needs. Unlike mammals, reptile kidneys cannot concentrate urine to save on water intake. Instead reptiles excrete toxic nitrogenous wastes as solid uric acid through their cloaca. In the case of the rock iguana which consumes large amounts of vegetation, these excess salt ions are excreted through their salt gland in the same manner as birds.
The record for the longest lived captive-born rock iguana is held by a Lesser Caymans iguana, which lived for 33 years in captivity.
A blue iguana captured on Grand Cayman in 1950 by naturalist Ira Thompson was imported to the United States in 1985 by Ramon Noegel and sold to reptile importer and breeder, Tom Crutchfield. Crutchfield loaned this iguana to the Gladys Porter Zoo in Brownsville, Texas in 1997. The lizard was named Godzilla by the zoo staff and was kept until his death in 2004. Thompson estimated the iguana to be 15 years of age at the time of its capture. This lizard may have been the word's longest-living recorded lizard at 69 years of age, having spent 54 years in captivity.
All speciesof Cyclura are sexually dimorphic; males are larger than females, and have more prominent dorsal crests as well as larger femoral pores on their thighs, which are used to release pheromones.
Although the particulars vary slightly among species and subspecies, the rock iguanas reach sexual maturity at three to seven years of age. Females become sexually mature at two to five years of age. Males can be highly territorial with the notable exception of the Exuma Island iguana. Mating takes place at the beginning of or just prior to the first rainy season of the year (May to June) and lasts for two to three weeks. Females lay from 2 to 34 eggs, with an average clutch size of 17 within 40 days. Females of most species guard their nests for several days after laying their eggs, and incubation lasts approximately 85 days. It has been noted that Cyclura eggs are among the largest lizard eggs produced in the world.
Every species and subspecies of rock iguana is endangered. Nine of these taxa are Critically Endangered, meaning there are fewer than 250 of each species or subspecies left in wild populations and in danger of Extinction, four taxa are endangered and three species have been identified as Vulnerable, one species is believed to be extinct in the wild. In addition to small numbers typical of endemic island-dwelling animals, wild populations of these lizards are directly and indirectly impacted by land development, overgrazing by domestic and feral livestock and predation by humans and feral mammals such as hogs, cats, rats, dogs, and mongooses.
In 1990, the American Zoo and Aquarium Association (AZA) designated the genus Cyclura as their highest priority. Their first project was a captive breeding program for the Grand Cayman iguana, which at the time was the most critically endangered of all the species of Cyclura.
The Indianapolis Zoo is involved in research and conservation of all 16 taxa of West Indian iguanas. This includes collaborative work on establishing baseline biological values in captive and wild iguanas, and scientific investigation, conservation efforts, field research and captive breeding programs. The Indianapolis Zoo has been involved in the Dominican Republic for almost ten years and will continue its research and conservation efforts with the Ricord's iguana.
The project's goals are:
- to work with the Ricord’s Iguana Recovery Group to implement the ISG’s Species Recovery Plan.
- to conduct a census of iguanas on Isla Cabritos, Dominican Republic.
- to determine vitamin D status of captive West Indian iguanas at the Zoo before and after exposure to sunlight.
- to continue to develop long-term captive breeding programs for Grand Cayman Island Blue iguanas and Jamaican iguanas at the Indianapolis Zoo.
- to work in partnership with ZOODOM (the national zoo of the Dominican Republic) to develop a long-term captive breeding and husbandry program for Ricord’s iguanas.
- to develop an education program for West Indian iguanas and their habitats.
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