Discussion on Lazarus taxa and fossil abundance at times of biotic crisis Journal, Vol. 156, 1999, pp. 453–456

Abstract

R. J. Twitchett writes: Palaeontologists grudgingly accept that the fossil record of most taxa is very patchy and incomplete. A particular taxon will appear in the fossil record, and then disappear for any number of millions of years, only to reappear again, apparently unchanged, in younger strata. This disappearance and reappearance is termed the Lazarus effect. Thus, in any particular interval of time a Lazarus taxon is one that is not present in the fossil record, but which we know must have existed by virtue of the presence of older and younger specimens. ⇓Wignall & Benton (1999) are concerned with the importance of the Lazarus effect during extinction‐recovery intervals. Traditional explanations for this phenomenon are: (i) a reduction in the quality of the fossil record, and/or (ii) a migration of taxa into (as yet) undiscovered refugia. Wignall & Benton make the novel suggestion that the Lazarus effect is, instead, due to periods of low abundance. Implicit in this argument is the hypothesis that population size has to exceed a critical threshold before a taxon stands any chance of becoming fossilized. Below this threshold the population remains viable, but we simply have no record of its existence. They make the reasonable assumptions that this threshold will vary between environments (presumably also between taxa), and is essentially ‘impossible to quantify’. While I agree that this is a credible explanation for the Lazarus effect, I do not consider that the tests constructed by Wignall & Benton are sufficiently rigorous to disprove the traditional alternatives. #### Testing the ‘quality’ of the fossil record For the Permian–Triassic event the authors use the number of fossiliferous, shallow‐marine formations from each stage as a measure of the quality of the fossil record. As there is no change in the number of formations from the Changxingian to the Griesbachian, they infer that the quality of …