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Cenozoic |
1 Department of Geology and Geological Engineering, University of North Dakota, Grand Forks ND 58202-8358, USA
2 Department of Geology, Western Washington University, Bellingham, WA 98225, USA
Naticid gastropods have been important shell-drilling predators of molluscs since the Cretaceous. Preliminary compilations of drilling frequencies by Vermeij (1987) were used to support his hypothesis of escalation, involving temporal increase in the hazard of predation and in adaptation to this hazard.
A comprehensive survey of naticid predation on molluscs in the Cretaceous and Palaeogene of the North American Coastal Plain revealed a complex pattern of escalation influenced by mass extinctions and recoveries. Data from more than 46 000 specimens from 17 formations show that dynamics of the naticid predator-prey system were affected significantly by the Cretaceous-Tertiary and Eocene-Oligocene mass extinctions. In the Cretaceous, drilling was low for gastropod prey (4–6%) and moderate for bivalves (13–19%). Drilling frequencies significantly increased above the K/T boundary in an initial recovery phase that lasted no more than 1–3 Ma. Recovery from the Eocene-Oligocene extinction also involved a significant increase in drilling, especially on bivalves (from 8% to 24%).
Based on these data (and similar patterns reported for fossil ostracode prey), we propose a model of cyclic escalation of the naticid predator-prey system, in which mass extinctions perturb the system and initiate cycles. Drilling frequencies in recovery faunas are greatly increased, possibly owing to preferential extinction of highly escalated prey. As the recovery proceeds, escalation of prey defences causes drilling frequencies to stabilize or decline. Reorganization of the predator-prey system also involves reduction in predator behavioural stereotypy after mass extinctions, followed by gradual recovery.
