Hi @jim.rothrock,
Usually, a rigid body consists of one or more rigid shapes. Shapes provide geometric, collision descriptions of the rigid body, while rigid bodies have physics properties associated with them, like mass and inertia tensors. Imaging for example convex decomposition of some object - it has the same mass and properties and a number of rigid convex shapes associated with it.
Without having any information about your URDF it’s pretty hard to understand why you have a smaller number of shapes than rigid bodies.