Animasaurus rex can be purchased from the Abyssal Knight Quartermaster at the Shattered Worlds area in Lumbridge Swamp for 58,000,000 Shattered anima. However, all lower tiers of this pet must be unlocked first which adds up to a cumulative total of 175,700,000 Shattered anima. This version of the anima pet is the highest tier (9) and cannot be upgraded any further.
Examining the pet shows its owner's highest achieved world in Shattered Worlds. However, when using it to override familiars, it will only show's the familiar's usual examine information.