ABSTRACT In 1896 Charles Deperet described a fauna of dinosaurs from the Upper Cretaceous (?Campanian) Maevarano Formation from the Mahajanga Basin of northwest Madagascar. Among the dinosaurs was a titanosaurid sauropod that he named Titanosaurus madagascariensis. He attributed to the titanosaurid a large, thick circular osteoderm. His referral of an osteoderm to a sauropod was widely doubted until 1980 when Bonaparte and Powell described Saltasaurus loricatus, an armored titanosaurid from Argentina. Since then titanosaurid osteoderms have been recognized from Spain, France and Malawi. In 1996, we collected three isolated and eight associated osteoderms from the Maevarano Formation, confirming Deperet's prescient observation. They range in length from 3 cm to 17 cm, and in thickness up to 6.5 cm. At least one of the two titanosaurids we now recognize from Madagascar was covered with a sparse armor, and that the skin was in places nearly 7 cm thick.