Iguana

Iguana (/ɪˈɡwɑːnə/, Spanish: ) is a genus of herbivorous lizards that are native to tropical areas of Mexico, Central America, South America, and the Caribbean. The genus was first described in 1768 by Austrian naturalist Josephus Nicolaus Laurenti in his book Specimen Medicum, Exhibens Synopsin Reptilium Emendatam cum Experimentis circa Venena. Two species are included in the genus Iguana: the green iguana, which is widespread throughout its range and a popular pet, and the Lesser Antillean iguana, which is native to the Lesser Antilles and endangered due to habitat destruction, introduced feral predators, hunting, and hybridization with introduced green iguanas. The word 'iguana' is derived from the original Taino name for the species, iwana. In addition to the two species in the genus Iguana, several other related genera in the same family have common names of the species including the word 'iguana'. Iguanas can range from 1.5 to 1.8 metres (5 to 6 ft) in length, including their tail. The two species of lizard within the genus Iguana possess a dewlap and a row of elongated scales running from the midline of their necks down to their tails. Iguanas have varying types of scales covering different areas of their body, for example, there are some large round tuberculate scales scattered around the lateral region of the neck among smaller, overlapping scales. The scales on the dorsal trunk of their body are also thicker and more tightly packed than those on the ventral side. These scales may be a variety of colors and are not always visible from close distances. They have a large round scale on their cheeks known as a sub-tympanic shield. Iguanas have keen vision and can see shapes, shadows, colors, and movement at long distances. Their visual acuity enables them to navigate through crowded forests and to locate food. They employ visual signals to communicate with other members of the same species. The tympanum, the iguana's eardrum, is located above the sub-tympanic shield (or 'ear shield') behind each eye. Iguanas are often hard to spot, as they tend to blend into their surroundings and their coloration enables them to hide from larger predators. Like most reptiles, an iguana has a three-chambered heart with two atria, one ventricle, and two aortae with a systemic circulation. The muscles of an iguana are very light in color, this is due to the high proportion of fast glycolytic muscle fibers. These fibers are not very vascularized and are low in myoglobin, giving them their pale look. This high density of fast glycolytic muscle fibers allows iguanas to move very quickly for a short period of time, which facilitates short bursts of movement but is inefficient for long duration movement, since cellular respiration in fast glycolytic muscle fibers is anaerobic.