How large of a shell would a World Turtle need to have to have most of the major types of biomes on its shell, including but not limited to swamp, jungle, temperate forest, and polar forest?
Also assume the different parts of the turtle can be eco-regions such as: legs, neck, tail, and head.
Assume the shell has a large mountain like ridge along its spine.
Gravity: Gravity pulls objects downward, not towards the center of the turtle
Water: Assume water comes from springs in the turtles shell, so no bodies of water larger than a lake
Air: Assume the air is thinner at higher elevations like on Earth, and that the atmospheric conditions are Earth-like.