Mega Mechanasaur, also known as "Big-Feet", is a giant robotic dinosaur appearing only in the Super Mario World episode "The Wheel Thing". It was constructed by Kooky von Koopa to be used in an assault on Dome City. Mega Mechanasaur resembled an enormous, robotic Tyrannosaurus Rex with giant wheels in place of legs. It is powered by an actual Tyrannosaurus Rex running on a treadmill inside the lower torso of the mech, and inside the mouth is a Dino-Torch that breathes fire.
After observing the Mario brothers' inventing the wheel and cars for the Cave People, Kooky is inspired to build the Mega Mechanasaur. After its completion, Kooky and King Koopa use it to destroy Dome City. However, the mech is stopped by Mario, Luigi, and the Cave People, setting out logs as speed bumps, traffic lights spitting out fire at it, and potholes dug by Yoshi. After it gets stuck in a pothole, Mega Mechanasaur falls over and is destroyed.