Long-term, within-habitat species replacement is either evolutionary or ecological in nature. Ecological replacement of dominant species by unrelated species which sham essentially the same niche requirements is a very characteristic feature of Early Jurassic benthic shelf faunas from northern Chile. More than that, an examination of the relevant literature reveals that the process was significant in Mesozoic benthic shelf ecosystems on the whole. It occurred among all important guilds and in a broad range of environmental subdivisions (salinity-controlled environments, coarse-grained and fine-grained shallow shelf, mid to outer shelf, and oxygen-controlled environments). In contrast, evolutionary replacement of dominant faunal elements appears to have been limited to restricted basins. Faunal replacement was the underlying process of several distinctive patterns in the temporal distribution of Mesozoic benthic shelf faunas, that is the evolutionary stability of dominant morphotypes, the widespread occurrence of parallel associations and the persistence of guild-assemblages through time. Fluctuations of relative sea-level are regarded as a substantial controlling factor of within-habitat species replacement.
