The Tar Pits is a limited-time premium building that was released on February 18, 2015, as part of the Superheroes 2015 Event. Upon completion, Petroleus Rex is unlocked.
It was re-released on June 20, 2016 for the Superheroes 2016 Event. It returned again on September 12, 2018 during the Super Powers 2018 Event. It was a possible prize in the Mystery Box The Sequel.
Tar Pits with Petroleus Rex
Springfield Tar Pits Sign in the show
Springfield Tar Pits from "Bart Gets an Elephant"