terrestrial record cannot be viewed independently. The abrupt climatic warming at the end of the Paleocene may have stimulated the evolution of major new mammalian groups such as the artiodactyls, perissodactyls, and the primates (Koch et al., 1992). Within the next few years it should be possible to integrate the terrestrial and marine records of faunal change at sufficient stratigraphic resolution to provide perhaps the best example of biotic change associated with abrupt environmental change.
Originally, observations on biotic change in the Paleocene-Eocene transition were limited to shallow marine invertebrate and terrestrial fossils. It has been generally assumed that, as with other epoch boundaries, changes in the global environment produced the biospheric response. Until recently the character of these changes remained largely unknown. Abrupt global warming and associated environmental changes now known for the end of the Paleocene are clearly implicated as a cause of this biotic crisis.
The oceanic deep-sea sediment record of the Paleocene-Eocene transition is clearly marked by major deep-sea benthic foraminiferal extinctions, perhaps the largest of the past 90 m.y. (Thomas, 1990). This event profoundly affected oceanic benthic communities deeper than the continental shelf (>100 m; neritic zone) resulting in a 35 to 50% species reduction in benthic foraminifera (Thomas, 1990). Deep-sea benthic foraminiferal assemblages radically changed as a result of this event. Late Paleocene assemblages before the extinction are highly diverse and contain genera with long stratigraphic ranges through the Late Cretaceous and Paleocene. Indeed, as pointed out by Thomas (1990, 1992), deep-sea benthic foraminiferal assemblages were little affected during the massive extinctions at the Cretaceous-Tertiary boundary (K/T), about 8 m.y. earlier. Instead many cosmopolitan benthic foraminiferal taxa typical of late Mesozoic and Paleocene assemblages, including all species within certain genera, were eliminated at the end of the Paleocene.
Until recently, the Paleocene-Eocene boundary was not generally recognized as a time of major biotic crisis, because generic-level extinction rates were low (Raup and Sepkoski, 1984). These patterns of extinction, however, are from the shallow marine and terrestrial spheres, not the deep-sea (Thomas, 1992).
The mass extinction that predates the Paleocene-Eocene boundary is located near the middle of a long reversed polarity interval, identified as Magnetochron 24 R (Miller et al., 1987; Stott and Kennett, 1990), within the latest Paleocene. The position of the Paleocene-Eocene boundary appears to be about 40,000 yr younger, but also within Chron 24 R (Kennett and Stott, 1991). Correlation of these respective levels between high and low latitude sequences is still inadequate to establish the precise age and prove synchroneity (for detailed discussion see Thomas, 1990; Kennett and Stott, 1991; Miller et al., 1992). Ages applied to the extinction differ among different sequences, ranging between -57.33 and 58 m.y. ago (Ma) (Miller et al., 1992). However, for several reasons discussed below, we believe that the mass extinction was synchronous and that the different age assignments have resulted from the current inadequacy of biostratigraphic correlations using planktonic microfossils across different latitudes and oceans. This appears, in part, to be the result of diachronism in planktonic microfossil datums and/or insufficient resolution in the biomagnetostratigraphic schemes employed. The age that we previously adopted for the mass extinction was 57.33 Ma (Kennett and Stott, 1991). However, the time scale of the magnetostratigraphic sequence in the vicinity of the extinction is now considered to be 2 m.y. younger (Cande and Kent, 1992).
The mass extinction is marked by four types of change in benthic foraminiferal assemblages: (1) the extinction of many taxa, (2) diversity decrease, (3) changes in the relative abundance of taxa, and (4) a general decrease in test size of taxa within the assemblages. As a result, the benthic faunas were distinctly different before and after the mass extinction.
The extinction removed species within the genera Stensioina, Neoflabellina, Bolivinoides, Pyramidinia, Pullenia, Aragonia, Tritaxia, Gyroidinoides, Neoeponides, Quadratobulimina, Stilostomella, Dorothia, and many other forms making up what has been termed the S. beccariiformis assemblage. Many of the extinct forms were morphologically distinctive, and their loss from the deep-sea record adds to the conspicuousness of this datum level. Epifaunal forms were particularly devastated (Thomas, 1990).
The extinction was first recognized in upper bathyal marine sequences from Trinidad (Beckmann, 1960); the Richenhall and Salzburg Basins, Austria (von Hildebrandt, 1962); and northern Italy (Braga et al., 1975). With the recognition of the extinction in the deep-sea by Tjalsma and Lohmann (1983), as well as Schnitker (1979), Kaiho (1988), Berggren and Miller (1989), Nomura (1991), and Thomas (1990, 1992), its global character was clearly established. It is also evident that a wide range of paleodepths were affected, ranging from bathyal to abyssal depths (Miller et al., 1987).
Despite the global distribution of this extinction horizon, stratigraphic resolution was too low to determine whether the event was geologically instantaneous throughout the oceans or diachronous. More recent biostratigraphic investigations in conjunction with stable isotope stratigra-