Green Iguana - Anatomy and Morphology

Anatomy and Morphology

Despite their name, Green Iguanas can come in different colors. In southern countries of their range, such as Peru, green iguanas appear bluish in color with bold black markings. On islands such as Bonaire, Curaçao, Aruba, and Grenada, a Green Iguana's color may range from green to lavender, black, and even pink. Green Iguanas from the western region of Costa Rica are red and animals of the northern ranges, such as Mexico, appear orange. Juvenile Green Iguanas from El Salvador are often bright blue as babies, however they lose this color as they get older.

Iguana iguana possess a row of spines along their backs and along their tails which helps to protect them from predators. Their whip-like tails can be used to deliver painful strikes and like many other lizards, when grabbed by the tail, the iguana can allow it to break, so it can escape and eventually regenerate a new one. In addition, iguanas have well developed dewlaps which helps regulate their body temperature. This dewlap is used in courtships and territorial displays.

Green Iguanas have excellent vision, enabling them to detect shapes and motions at long distances. As Green Iguanas have only a few Rod cells, they have poor vision in low-light conditions. At the same time, they have cells called “double cone cells” that give them sharp color vision and enable them to see ultraviolet wavelengths. This ability is highly useful when basking so the animal can ensure that it absorbs enough sunlight in the forms of UVA and UVB to produce Vitamin D.

Green Iguanas have a white photosensory organ on the top of their heads called the parietal eye (also called third eye, pineal eye or pineal gland), in contrast to most other lizards, which have lost it. This "eye" does not function the same way as a normal eye does, as it has only a rudimentary retina and lens and cannot form images. It is, however, sensitive to changes in light and dark and can detect movement. This helps the iguana when being stalked by predators from above.

Green Iguanas have very sharp teeth that are capable of shredding leaves and even human skin. These teeth are shaped like a leaf, broad and flat, with serrations on the edge. The similarity of these teeth to those of one of the first dinosaurs discovered led to the dinosaur being named Iguanodon, meaning "iguana-tooth", and the incorrect assumption that it had resembled a gigantic iguana. The teeth are situated on the inner sides of the jawbones which is why they are hard to see in smaller specimens.

Primarily herbivorous, Green Iguanas are presented with a special problem for osmoregulation; plant matter contains more potassium and as it has less nutritional content per gram, more must be eaten to meet metabolic needs. As Green Iguanas are not capable of creating liquid urine more concentrated than their bodily fluids, like birds they excrete nitrogenous wastes as urate salts through a salt gland. As a result, Green iguanas have developed a lateral nasal gland to supplement renal salt secretion by expelling excess potassium and sodium chloride.

Green Iguanas from Guatemala and southern Mexico predominantly have small horns on their snouts between their eyes and their nostrils, whereas others do not. Naturalists once classified these iguanas as a separate subspecies (Iguana iguana rhinolopha); however, this classification has been found to be invalid based on mitochondrial DNA and iguanas with similar nose projections appear randomly in other populations and interbreed freely with those that do not share this trait.

The Green Iguana is a large lizard and is probably the largest species in the iguana family, though a few in the Cyclura genus may match or exceed it in weight. Adults typically grow to 1.2 to 1.7 m (3.9 to 5.6 ft) in length from head to tail. As in all iguanas, the tail comprises much of this length, and the snout-to-vent length of most green iguanas is 30 to 42 cm (12 to 17 in). An average adult male will weigh around 4 kg (8.8 lb) while the smaller adult female will typically weigh 1.2 to 3 kg (2.6 to 6.6 lb). A few large males can reach or exceed 6 to 8 kg (13 to 18 lb) in weight and 2 m (6.6 ft) long. Some specimens have even reportedly been measured at a body weight of greater than 20 lb (9.1 kg).