Planet Dragons, like their namesake celestial bodies, are known to walk orbital laps around the heaviest objects in their proximity. Heavier Caretakers have been offended by this behavior, and place boulders near the habitats as a preventative measure.
Like tectonic plates floating above a planet's molten core, as Planet Dragons mature, the brown coloring on their backsides drift closer together, forming one massive, mostly contiguous spot.
One ancient dragon scholar wrote of Planet Dragons: To eat, to drift, to feast, to fly, behold the Planet Dragon's cry. He knows the source of land and sea, and for some food he will tell me.
While not known for their flight abilities, it is written that ancient Epic Form Planet Dragons left this planet for space, and as they feasted on solar energy and interstellar dust, grew to become planets orbiting around distant stars.