Origination, extinction, and mass depletions of marine diversity

Abstract

In post-Cambrian time, five events-the end-Ordovician, end-Frasnian in the Late Devonian, end-Permian, end-Triassic, and end-Cretaceous-are commonly grouped as the ''big five'' global intervals of mass extinction. Plotted by magnitude, extinction intensities for all Phanerozoic substages show a continuous distribution, with the five traditionally recognized mass extinctions located in the upper tail. Plotted by time, however, proportional extinctions clearly divide the Phanerozoic Eon into six stratigraphically coherent intervals of alternating high and low extinction intensity. These stratigraphic neighborhoods provide a temporal context for evaluating the intensity of extinction during the ''big five'' events. Compared with other stages and substages in the same neighborhood, only the end-Ordovician, end-Permian, and end-Cretaceous extinction intensities appear as outliers. Moreover, when origination and extinction are considered together, only these three of the ''big five'' events appear to have been generated exclusively by elevated extinction. Low origination contributed more than high extinction to the marked loss of diversity in the late Frasnian and at the end of the Triassic. Therefore, whereas the ''big five'' events are clearly times when diversity suffered mass depletion, only those at the end of the Ordovician, Permian, and Cretaceous periods unequivocally qualify as globally distinct mass extinctions. Each of the three has a unique pattern of extinction, and the diversity dynamics of these events differ, as well, from the other two major diversity depletions. As mass depletions of diversity have no common effect, common causation seems unlikely.

Interdependence of specialization and biodiversity in Phanerozoic marine invertebrates

“…They corroborate earlier work suggesting that high ecological specialization is related to elevated rates of speciation 20,21,38,39 as well as the notion that losses in diversity can be driven by a lack of origination 6,40 . Furthermore, they confirm a general positive relationship between standing diversity and specialization and thus contribute to the ongoing debate on the role of biotic and abiotic factors as primary drivers of biodiversity dynamics.…”

Extinction as the loss of evolutionary history

“…This effort identifies at least three of the five canonical mass extinctions below. However, like other work (32,33) it raises questions about the magnitude of other extinction events.…”

Geochemical evidence for widespread euxinia in the Later Cambrian ocean

“…We suggest that anoxic water masses occurred widely in the subsurface of the later Cambrian ocean (i.e., below the wind-mixed surface layer), a view that finds qualitative support in the stratigraphic distribution of organic-rich, pyritic black shales, which peak in abundance in later Cambrian successions 24 . If correct, the high rates of biological turnover 25 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 11 …”