The Dinobots continued hiding out in the Cascades , stealing fuel from humans and sending Swoop out to spy on the Autobots at the Ark. Learning that Optimus Prime was dead, Grimlock decided to return and seize command for himself. Bursting into the Ark, he denounced Prime's style of leadership as weak and insisted only the strongest should lead but was soundly rebuffed by the assembled Autobots. Meanwhile, Ratbat , the Decepticons' fuel auditor on Cybertron, had sent Trypticon through the space bridge to annihilate the Earthbound Autobots once and for all. Outside the Ark, the Dinobots stood back and watched the slaughter for a while until Trypticon threatened Rachel Becker , a palaeontology student who had taken an interest in the local Transformer activity, which drove Grimlock to defend her. Following their leader's example, the other Dinobots charged, battling Trypticon until his fuel quota for the trip was expended and Ratbat recalled him to Cybertron. For showing courage and compassion in during the battle, the grateful Autobots then elected Grimlock as their new leader. King of the Hill!
After the Ark crashed into the Earth, Grimlock, Snarl and two others remained active and were reformatted to resemble dinosaurs, the planet's dominant lifeforms. Unfortunately the reformatting was a little too thorough and they were left acting like real dinosaurs as well. Rendered inactive by a meteorite strike, they lay dormant beneath what became modern-day Brazil until Grimlock and Snarl were inadvertently awoken by developers from a logging company. Optimus Prime , Jazz and Blaze travelled there to investigate but were ambushed by the Decepticons and Soundwave trapped the Dinobots in a plasma net . Unfortunately for him, the net caused a negative ion feedback which triggered their Transformer circuitry and restored their personalities along with their robot modes . Grimlock and Snarl sent the Decepticons packing but remained in Brazil to look for their missing comrades rather than return to the Ark with the Autobots. The Dinobots!