Sampling bias, gradual extinction patterns and catastrophes in the fossil record

Abstract

Catastrophic hypotheses for mass extinctions are commonly criticized because many taxa gradually disappear from the fossil record prior to the extinction. Presumably, a geologically instantaneous catastrophe would not cause a reduction in diversity or a series of minor extinctions before the actual mass extinction. Two types of sampling effects, however, could cause taxa to appear to decline before their actual biotic extinction. The first of these is reduced sample size provided in the sedimentary record and the second, which we examine in greater detail, is artificial range truncation. The fossil record is discontinuous in time and the recorded ranges of species or of higher taxa can only extend to their last known occurrence in the fossil record. If the distribution of last occurrences is random with respect to actual biotic extinction, then apparent extinctions will begin well before a mass extinction and will gradually increase in frequency until the mass extinction event, thus giving the appearance of a gradual extinction. Other factors, such as regressions, can exacerbate the bias toward gradual disappearance of taxa from the fossil record. Hence, gradual extinction patterns prior to a mass extinction do not necessarily eliminate catastrophic extinction hypotheses. The recorded ranges of fossils, especially of uncommon taxa or taxa in habitats not represented by a continuous record, may be inadequate to test either gradual or catastrophic hypotheses.

When and how did the terrestrial mid-Permian mass extinction occur? Evidence from the tetrapod record of the Karoo Basin, South Africa

“…Because preserved ranges underestimate true ranges [34], the severity of extinction can be independently and more finely resolved using CONOP. Several equally good solutions all reveal a significant clustering of last appearances, which supports the existence of coordinated extinctions and indicates that genus richness was lost as a result of an increased extinction rate, not merely a drop in originations (figure 3b).…”

Ice-age megafauna in Arctic Alaska: extinction, invasion, survival

“…Estimating extinction times is problematic because we will never discover and date the last surviving individual (Signor and Lipps, 1982) and because taphonomic processes can change over time. Also, megafaunal populations probably fluctuated in size over time, particularly at high latitudes and especially given the rapid tempo of climate changes during the ice age.…”

“…People arrived in arctic Alaska only recently compared to the Eurasian Arctic, where they first appeared >34,000 years ago (Pitulko et al, 2004;Slimak et al, 2011). The earliest archaeological date from the North Slope has a 2s range of 13.7e13.3 cal ka BP (Kunz and Reanier, 1994;Mann et al, 2001) (Fig.…”

Radiocarbon Chronologies and Extinction Dynamics of the Late Quaternary Mammalian Megafauna of the Taimyr Peninsula, Russian Federation

“…For example, one important concern is that, from an epistemological standpoint, any given ''last'' occurrence date is merely a provisional and minimum estimate of the true extinction date ). Except in the most contrived hypothetical cases, extinction dates can only be presented in the form of probability statements (Signor & Lipps, 1982).…”