ELSEVIER Marine Micropaleontology 29 (1997) 65 103

MicroNotes

The Cretaceous-Tertiary boundary: the El Kef blind test

Jere H. Lipps

University of California, Museum of Paleontology, Berkeley, CA 94720, USA

Received 12 April 1996; accepted 12 June 1996

The famous Asteroid Impact Hypothesis for the extinction of dinosaurs, shallow-water invertebrates and oceanic plankton (Alvarez et al., 1980) remains controversial (Glen, 1994). While many scientists accept the geological, mineralogical, and chemical evidence that an asteroid hit Earth at the end of the Cretaceous, others are dubious that it caused simul- taneous extinctions of so many unrelated organisms. In the enthusiasm for the hypothesis, many very ten- uous so-called evidential links were made but few actually provided strong inference in support of the hypothesis. Some of the most tenuous evidence has been from the fossil record, yet inordinate attention has been heaped on it, both by scientists and the media. The hypothesis still needs careful framing to develop potential tests of disproof rather than contin- ued accumulation of highly-touted, possible proof. Can the fossil record provide such a test? I think not.

Dinosaurs from the very start were intimately intertwined in the hyperbole of the hypothesis, al- though they carry no evidential weight one way or the other with regard to the hypothesis of an impact. Their record is simply too poor, and too many other extinction mechanisms seem probable to suggest that the dinosaurs could ever contribute a significant test. Other groups of less spectacular organisms, like planktic foraminifera and calcareous nannoplankton, have much better fossil records, a fact well known to most paleontologists if not other geoscientists. Even with these organisms, however, two differing views have emerged.

Central to these divergent views are observations on the mode of extinction of planktic foraminif- era across the K/T boundary. Some workers have maintained that planktic foraminifera disappeared at the boundary, while others thought they disap- peared gradually or step-wise before and/or across the boundary. These views seemed easy to test - just have several independent experts study the same identical samples without knowing their stratigraphic position, a so-called ‘blind test’. How could this not easily clarify which view is correct, and thus con- tribute to a test of the primary hypothesis of impact and extinction? Actually, several reasons confuse the results and interpretations.

(1) Phil Signor and I (1982) noted that the fossil record near any boundary is inadequate to show true extinction patterns because of ecologic and tapho- nomic factors, including scientists’ errors and omis- sions (the Signor-Lipps effect, so named by David Raup). The Signor-Lipps effect has been ignored or countered on the basis that additional sampling or searching will yield a better record. They will not, however, because the effect includes fundamental ecologic biases that removed species entirely from the area sampled, hence make a compiled record ap- pear gradual no matter what actually occurred. Even agreement between scientists may not reflect true events in this case.

(2) Systematic assignments are critical in any comparison of stratigraphic occurrences. Without identical species identifications, no meaningful com-

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66 El Kef blind test/Marine Micropaleontology 29 (1997) 65-103

parisons can be made. Individual opinion reigns Robert Ginsburg reports herein, but because of what strong in these kinds of determinations, even when the test may say about how our science works. type specimens are available for direct comparison. Ginsburg notes that we need better quality control With simple morphologies in widely varying popula- and more replicable tests by independent workers tions, species determinations are bound to be contro- in earth sciences, a truly good idea. The blind test, versial. The definitions of species will therefore be therefore, may provide insights into how such con- imprecise and result in confusion in any test. trols might be constructed in the future.

(3) Determination of reworking is essential across any boundary as well. If range extensions are found, do these represent individuals that were alive during the later intervals or are they reworked? Evidence for one or the other is independent of a test such as proposed, but the status of these specimens must be resolved before the test’s results can be mean- ingfully interpreted. Other factors may enter into the tabulation and interpretation of the results of such a blind test that are not so obvious. The mind sets and sociology of the scientists performing the test will always play an important, but undefined, role.

A ‘blind test’ was devised for planktic foraminif- era at the K/T boundary, and its results are included in the following reports. Marine Micropaleontology publishes them, not because they produced a clear consensus of the testers, as test-organizer Professor

To me, the politics, sociology and behavior of science and scientists may have a good deal more to do with the results and interpretations than the data. Certainly, in most scientific controversies, these fac- tors play an extraordinary role. The Impact Hypoth- esis too has been highly charged by scorn, threats, scientific exile, praise, honors, and a host of other negative and positive reinforcements. Those in favor of the idea for whatever reason win, while those not in favor of it lose. While this particular debate requires much further analysis, Glen (in Glen, 1994) has begun its examination. They are routinely dealt with by sociologists of science in other disciplines. We should welcome both rigorous new approaches in our science and an understanding of why we do what we do in science. We will all be the better for it!