This invention is directed to EP4 receptor selective prostaglandin agonists of the Formula I, ##STR00001## wherein R.sup.2, X, Z and Q are as defined in the specification. This invention is also directed to pharmaceutical compositions containing those compounds. This invention is also directed to methods of treating conditions which present with low bone mass, particularly osteoporosis, frailty, an osteoporotic fracture, a bone defect, childhood idiopathic bone loss, alveolar bone loss, mandibular bone loss, bone fracture, osteotomy, bone loss associated with periodontitis, or prosthetic ingrowth in a mammal comprising administering those compounds.