The Establishment of Continental Ecosystems

The colonization of land was a major evolutionary transition. Following a protracted prelude to the terrestrial invasion during the Ediacaran to Ordovician, the remainder of the Paleozoic experienced an explosion of diversity and the expansion of benthic biotas into new environments through the creation of new niches. This expansion progressed from coastal settings into rivers, floodplains, deserts, and lakes, as well as increasing colonization of infaunal ecospace. A pattern emerges in which colonization of a new environment is followed by rapid filling of available ecospace, after which animals establish new behavioral programs. These programs are represented initially by the creation of original architectural designs, and subsequently modified by a proliferation of ichnogenera representing variation upon these established themes. The overall pattern is consistent with the early burst model of diversification that has been identified for various animal and plant clades, wherein there is a decoupling as an initial expansion in disparity is followed by an increase in diversity.