A fossil hyrax from the Upper Fossil Wood Zone, Jebel el Qatrani formation is described. It represents a new genus and species Thyrohyrax domorictus. The type specimen as well as two referred specimens exhibit an internal mandibular fenestra whereas four referred mandibular fragments do not. One nearly complete mandible with an internal mandibular fenestra has extremely inflated horizontal rami which enclose swollen ovoid chambers opening at the fenestra. This inflated ramus, which is believed to be unique among all mammals, and the internal mandibular fenestra are thought to be sexual characters. Evidence from other genera of the Saghatheriinae suggests these characters are found in females; not in males.