Abstract: An improved toilet seat usable by either a human or a pet animal, the toilet seat having a rim member with a central aperture and a shelf assembly mounted to the rim member which adjusts the size of the central aperture in a protracted position to support the weight of the pet animal user. A support assembly supports the rim member above a floor surface for training a pet animal user, the support assembly having a leg assembly connected to the rim member by hinges and extendible therefrom for supporting the rim member during animal pet training. A training tray is supportable by the rim member for selectively providing a litter holder cavity below the central aperture.