Although the fossil record for monitors is somewhat patchy, Varanus rusingensis has been suggested as a probable close relative of white-throated monitors (Varanus albigularis). – Discovered in Kenya, this fossil traces back to the Early Miocene, making it close to 18 million years old. It is actually the oldest known fossil so far attributed to the genus Varanus.
Varanus rusingensis reached a size of about 6 1/2 feet and had differentiated teeth. Sharp and recurved teeth were in the front, and blunt teeth were in the back — much like modern savannah (Varanus exanthematicus), white-throated and Nile monitors (V. niloticus) have. Unlike white-throats, however, this fossil species is believed to have been aquatic in habit, making it more like Nile and ornate monitors (V. ornatus).
Later Miocene fossils of Varanus are known from Europe and central Asia, and a close fossil relative (V. darevskii) of the desert monitor (V. griseus) was found in Pliocene deposits of Tajikistan.