The Savage Land is a secret jungle paradise on the coast of Antarctica that is home to many monstrous, prehistoric creatures. It is not, however, Dinobot Island. That's a different secret jungle paradise that is home to many monstrous, prehistoric creatures.
Marvel Comics continuity
Four million years ago Shockwave followed the crashing Ark down to the planet Earth, but instead of prehistoric Oregon, he landed in the Savage Land where he spent his time productively by fighting dinosaurs. The Ark's barely-functioning computer detected his presence there and reactivated five Autobots to deal with the threat. Rebuilt with altmodes resembling the Savage Land's dinosaurs, these newly-minted Dinobots took one of the Ark's shuttles to Antarctica and battled Shockwave but the mission was only a partial success - while they succeeded in defeating Shockwave and burying him under rock, the Dinobots fell into a tar pit and sank without trace. Slag would later flash back to this whilst in a coma.
In 1984, Huffer learned of these events and had Ratchet despatch one of the Ark's probes to investigate. However, instead of locating the missing Dinobots, the probe reactivated Shockwave who crushed it and then flew to Mount St. Hilary where he promptly defeated any Autobots left standing. Nice going, Huffer.
As the only functional Autobot (he was moonlighting at the hospital when Shockwave attacked) Ratchet needed to bolster troop numbers, so he took a shuttle containing his mobile repair bay to the Savage Land to revive the Dinobots. After digging them out of the tar pit, he replayed the events that led to their subterranean incarceration (for the benefit of the reader) by tapping into Slag's memories. Once reactivated, the Dinobots accepted Ratchet's offer of a second chance to take down Shockwave and they left with him for the Ark.
Marvel UK future timelines
Later, the Savage Land's dinosaurs fell victim to a disease that drove them to madness and death. Professor Embrey, a paleontologist stationed there, discovered the Dinobots' shuttle and used a control crystal he found to create a healing machine. He also established a quarantine zone, using the shuttle's weapons to defend his healthy dinosaurs from the sick ones. In 1992 the Dinobots returned to the Savage Land in the hope of transferring Snarl's mind into the control crystal, to buy him some time while they searched for a cure for his apparently untreatable Corrodia Gravis. At first they were none too impressed by Embrey's appropriation of their technology, but after he pleaded for the lives of his dinosaurs the Dinobots formed a new plan and transferred their stricken comrade's mind into the body of a healthy Stegosaurus. They then departed the Savage Land, leaving Snarl in Embrey's care.
The Savage Land was mentioned as part of the origin of the Dinobots very early in the Marvel Comics Transformers series, during the brief period of time in which the Transformers comic took place in the main Marvel Universe. The Savage Land of the mainstream Marvel Universe first appeared in the X-Men comic in the 1960s, and is sustained by alien technology. The explanation for the existence of a jungle full of dinosaurs in Antarctica in the Transformers comic continuity is unknown, but is presumably similar.