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End Ordovician extinctions : a coincidence of causes.

Harper, D.A.T.; Hammarlund, E.U.; Rasmussen, C.M.Ø


E.U. Hammarlund

C.M.Ø Rasmussen


The end Ordovician (Hirnantian) extinction was the first of the five big Phanerozoic extinction events, and the first that involved metazoan-based communities. It comprised two discrete pulses, both linked in different ways to an intense but short-lived glaciation at the South Pole. The first, occurring at, or just below, the Normalograptus extraordinarius graptolite Biozone, mainly affected nektonic and planktonic species together with those living on the shallow shelf and in deeper water whereas the second, within the N. persculptus graptolite Biozone, was less focused, eradicating faunas across a range of water depths. In all about 85% of marine species were removed. Proposed kill mechanisms for the first phase have included glacially-induced cooling, falling sea level and chemical recycling in the oceans, but a general consensus is lacking. The second phase is more clearly linked to near-global anoxia associated with a marked transgression during the Late Hirnantian. Most recently, however, new drivers for the extinctions have been proposed, including widespread euxinia together with habitat destruction caused by plate tectonic movements, suggesting that the end Ordovician mass extinctions were a product of the coincidence of a number of contributing factors. Moreover, when the deteriorating climate intensified, causing widespread glaciation, a tipping point was reached resulting in catastrophe.


Harper, D., Hammarlund, E., & Rasmussen, C. (2014). End Ordovician extinctions : a coincidence of causes. Gondwana Research, 25(4), 1294-1307.

Journal Article Type Article
Acceptance Date Dec 12, 2012
Online Publication Date Jan 21, 2013
Publication Date 2014-05
Deposit Date Jan 29, 2013
Journal Gondwana Research
Print ISSN 1342-937X
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 25
Issue 4
Pages 1294-1307
Keywords End Ordovician, Extinction, Hirnantian, Isotopes, Palaeogeography.