dominantly microbial. From the Middle Ordovician radiation through the Late Devonian mass extinctions, stromatoporoids (coralline sponges) and corals were the primary reef builders, with important contributions from other sponges in the early part of the interval. Latest Devonian through Early Permian reefs are often described as “mud mounds” because of the absence of abundant framework builders in these primarily algal and microbial systems. In the Early to Middle Permian, between five and seven different reef types have been described with sponges, brachiopods, corals, and bryozoans being prominent components of different types. Scleractinan corals become the major reef builders in the Late Triassic, with significant contributions from bivalves during some intervals. Indeed, post-Aptian Cretaceous reefs were built largely by rudist bivalves. Cenozoic reefs were constructed by scleractinian corals and coralline red algae. These gross patterns obscure Phanerozoic trends of changing ecology, including higher nutrient requirements toward the recent (Kiessling, 2002). An important issue for further exploration is the extent to which these different reef types were ecosystem builders that enhanced the diversity of other groups. For example, the phylloid algal mounds of the Lower Permian of West Texas apparently were so dense that they excluded many other organisms (Toomey, 1976), whereas later scleractinian reefs appear to have enhanced diversity. On land, trees and forests often provide a similar architectural structure to reefs in the ocean.
The social and behavioral complexity of extinct animals might seem irretrievably lost (other than what might be inferred from morphology or the known history of social clades). In fact, the preservation of tracks, trails, and burrows provides insights into behavior, with the constraint that such trace fossils can rarely be uniquely associated with particular species (Seilacher, 2007). More commonly, particular trace fossils could be produced by many distantly related species. Worms of several different phyla can produce similar burrows. Nonetheless, trace fossils can provide considerable insight into the complex behavioral repertoires of their makers. Vertebrate trace fossils on land provide similar insights, for example, into herding behavior among some dinosaurs, or burrowing among Late Permian dicynodonts in South Africa (personal observation). Other evidence of behavioral complexity comes from the characteristic patterns preserved in fossil leaves by herbivorous insects, reflecting both the behavior and mouthpart morphology of various herbivorous insect groups (Labandeira, 2006). One means to track changes in behavioral complexity during a mass extinction is by documenting changes in trace fossil abundance and diversity.