Robert Broom's most important discoveries were made in the Sterkfontein valley of South Africa. It was there in 1936 that he found the first known adult Australopithecus africanus while excavating in Sterkfontein cave. In 1938, he discovered more fossil remains of africanus and other early hominins in Kromdraai cave.Some of these fossils were larger boned and more muscular with powerful jaws.t was there in 1936 that he found the first known adult Australopithecus africanus while excavating in Sterkfontein cave. In 1938, he discovered more fossil remains of africanus and other early hominins in Kromdraai cave. Some of these fossils were larger boned and more muscular with powerful jaws.