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TABLE 9.1 The Effect on Different Measures of Diversity for Marine Organisms During the Five Canonical Mass Extinction Episodes of the Phanerozoic

Diversity

Ordovician

Devonian

Permian

Triassic

Cretaceous

Taxic

60/26%

57/22%

82/52%

53/22%

47/16%

Phylogenetic

?

?

High

?

? Medium

Morphologic

High

Medium

High

?

? Medium

Functional

Medium

High

High

Low

Medium

Architectural

Medium

High

High

Medium

Low

Behavioral

?

?

High

Medium

Medium

Developmental

Low

?

Medium

?

?

NOTES: Taxic diversity drops are shown for genera and families from Sepkoski (1996). Estimates of loss of phylogenetic diversity are based on the loss of major clades, as documented by phylogenetic analyses; morphologic disparity is assessed within particular clades, and the loss of major clades; functional diversity is assessed based on published paleoecological studies. Loss of architectural diversity is measured by changes in reef volume and the diversity of reef ecosystems (Wood, 1999; Flügel and Kiessling, 2002). Changes in behavioral diversity were assessed by changes in the complexity of trace fossil assemblages. Developmental diversity was assessed as described. Question marks indicate an absence of sufficient data.

Estimates of the loss of family and generic diversity are from Sepkoski (1996).

One perplexing aspect of the end-Ordovician mass extinction (490 Ma) is that although it is the second largest loss of taxic diversity of marine organisms it had relatively little ecological impact in most groups (Droser et al., 2000). Limited phylogenetic analyses have been produced, mostly for graptolites and gastropods, although some broader studies do span the boundary. The loss of morphologic disparity during this event appears to have been high, whether as measured by the major losses among graptolites, conodonts, brachiopods, and possibly nautiloids or by more quantitative studies of disparity within major clades (Foote, 1991, 1994a; Ciampaglio, 2002, 2004). Using reefs as our measure of architectural complexity, there is a major loss of both reef types and carbonate production although there is little ecological impact (Wood, 1999; Flügel and Kiessling, 2002), hence the medium ranking in Table 9.1. Twitchett and Barras (2004) record only a single study of trace fossils through this interval, too little to estimate the impact on behavioral complexity. Finally, as no major clades completely disappeared the loss of developmental diversity at this time appears to have been fairly low. What developmental complexity was lost was likely in the terminal portions of the networks rather than the highly conserved cores.

The Late Devonian mass extinctions were a series of events best expressed in rocks of Europe (McGhee, 1996). The loss of morphologic



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