Monitor Lizards.
A juvenile Indian clouded monitor, Varanus nebulosus.

Varanids are more widely known as monitors. In some places they are also known as leguaans or goannas, terms derived from the Carib "iguana," for the distantly related large iguanas. 

Monitors are characterized by elongate heads, moveable eyelids, external ear openings, four well-developed limbs with five digits and claws, a long, bifid and retractile tongue, and a visible parietal eye. Ventral scales are rectangular and arranged in rows. All monitors are egg layers. They range in size from about 8 inches (18 cm) to a confirmed record of 10 feet, 2 inches (3 m). 

The Varanidae has a fossil record stretching back at least 70 million years (Late Cretaceous), and distinct varanoids are known from as far back as the Jurassic. Many herpetologists believe that ancestral monitors evolved into snakes.

Found in Africa, southern Asia, Indo-Australia, and Australia.

A mangrove monitor alert on the Bensbach River, basking on the bank. 
These large lizards are very difficult to see unless they are moving.