Sea-level change and rock-record bias in the Cretaceous: a problem for extinction and biodiversity studies

The association between mass extinction in the marine realm and eustatic se a-level change in the Mesozoic is well documented, but perplexing, because it seems implausible that sealevel change could actually cause a major exti nction. However, large-scale cycles of sea-level change can and do alter th e ratio of shallow to deep marine continental-shelf deposits preserved in t he rock record both regionally and globally. This taphonomic megabias alone could be driving patterns of first and last occurrence and standing divers ity because diversity and preservation potential both change predictably wi th water depth, We show that the Cenomanian/Turonian faunal event in wester n Europe has all the predicted signatures expected if taphonomic megabias w as the cause. Grade taxa terminating in pseudoextinction and Lazarus taxa a re predominantly found in the onshore facies that disappear for extended pe riods from the rock record. Before other mass extinctions are taken at face value, a much more careful analysis of biases in the rock record needs to be carried out, and faunal disappearances need to be analyzed within a phyl ogenetic framework.