Green Iguana

Iguana's are a family of large lizards with a spiny back, generally found in South America . The photograph is of a green Iguana; these reptiles are green during their younger days and lose colour as they grow older.
The spines on the back grow upto the tail and they use it as a defense mechanism by whipping the tail. The Iguana can make it's tail break off and grow a new one like many other lizards.
The loose skin that you see below the lower jaw is called a 'dewlap', it is similar to the loose skin on many other animals like Cow, Ox( Zebu) or dog (mastiff). It is of different use to different species from cooling, scaring predators to storing fat. For the iguana, it helps in regulating body temperature and also uses it for display during mating.