The great majority of the published work on the paleontology of the stromatoporoids has appeared since 1950. This influx of information has made possible a fairly clear picture of their evolution. As mentioned earlier by Stearn, stromatoporoids were quite abundant in shallow marine environments from the Middle Ordovician through the Late Devonian. These are referred to as the “Paleozoic stromatoporoids.” The record of Carboniferous stromatoporoids is sparse, but they began to come back in the Permian, and were common again through much of the Mesozoic, until disappearing at the the end of the Cretaceous. The Permian through Cretaceous forms shall be referred to as the “Mesozoic stromatoporoids.”