Magnedon

Magnedons were metallic, lizard-like creatures native to Skaro. They were similar in shape to a crocodile, but with eyes on stalks and spines along their back. Their bodies were held together by an internal magnetic field and the First Doctor believed that they could attract other metallic creatures to prey on them. Many magnedons were killed during the Thousand Year War, though their bodies were kept in relatively the same conditions. Their metallic physiology prevented them from decaying, thus leaving them intact. The Thals used their bodies to recharge their hand lights. (TV: The Daleks)

The Seventh Doctor encountered a weaponised Magnedon. (GAME: Dalek Attack)

A magnedon was kept on Station 7 by the Space Security Service in the petrified jungle, where it was found by the Eleventh Doctor and Amy Pond. (COMIC: The Only Good Dalek)

Behind the scenes
A magnedon also appears in the Dr. Who film Dr. Who and the Daleks, which is a remake of The Daleks. The magnedon appears as a huge petrified lizard-like beast. The exemplar featured is destroyed when Ian Chesterton falls into the pit where it is.