Pathfinder RPG: Ultimate Wilderness - Rules of Play says:

Pathfinder RPG Ultimate Wilderness gives players the tools to survive the wilds. A new 20-level base class, the shifter, puts animalistic powers into the hands—or claws—of player characters and villains alike, with new class features derived from animalistic attributes. Overviews of druidic sects and rituals, as well as new archetypes, character options, spells, and more, round out the latest contribution to the Pathfinder RPG rules!