As is evident from Table T1, the stratigraphic range of a dinocyst species is rarely synchronous worldwide. This is especially true for the Tertiary, where paleoclimatic control on taxa has been demonstrated by several authors. Bujak and Williams (1979) noted that some species did not have uniform stratigraphic ranges throughout the North Atlantic. For example, Polysphaeridium zoharyi (as Hemicystodinium zoharyi) had a range of early Eocene to Holocene in offshore Florida, whereas on the Labrador Shelf, its LO was in the Oligocene. Williams and Bujak concluded that a worldwide range for a species was not to be expected.
Brinkhuis and Biffi (1993), in an analysis of the Massignano and Monte Cagnero Eocene/Oligocene boundary sections in central Italy, identified lower- and higher-latitude taxa. Bujak and Mudge (1994) distinguished temperature-sensitive species in North Sea Eocene assemblages. They found that warmer-water species include Diphyes colligerum, Diphyes ficusoides, Dracodinium rhomboideum, and Dracodinium pachydermum. Eatonicysta ursulue was inferred to indicate cooler water conditions. Bujak and Brinkhuis (1998) used the abundance of Apectodinium at the Paleocene/Eocene boundary as an indicator of warmer-water conditions. This hypothesis was further advanced in the studies of Crouch et al. (2001), who noted the correspondence of Apectodinium peaks with the Paleocene/Eocene Thermal Maximum. In the Neogene, the recognition of warmer- and colder-water species is becoming extremely sophisticated and is being tied to modern-day modeling of sea-surface temperatures and oceanic currents. Papers highlighting recent developments are de Vernal et al. (2000, 2001), Head (1994, 1996, 1997), Head et al. (2001), McMinn and Wells (1997), Mudie and Rochon (2001), and Rochon et al. (1999).
Several dinocyst papers also deal with the differentiation of Northern and Southern Hemisphere assemblages. Wilson (1967a, 1967b, 1967c, 1988) drew attention to the distinctive nature of some of the New Zealand assemblages and Deflandre and Cookson (1955) and Cookson and Eisenack (1958, 1960a, 1960b, 1962a, 1962b, 1965a, 1965b, 1965c) demonstrated the same for the Australian assemblages. Some of these differences reflect a paucity of studies of higher-latitude Northern Hemisphere assemblages, but some are undoubtedly real (see also Brinkhuis, Sengers, et al., this volume).
The above and other findings convinced us that we had to accommodate latitudinal and hemispherical control of dinocyst assemblages in the Tertiary plots. Accordingly, we give ranges for low, mid-, and high latitudes in both Northern and Southern Hemispheres. Use of the terms low, mid-, and high relates to the present day. But there is a relationship to some extent with the paleogeography, depending on a location's paleolatitude at any given time. Not surprisingly, our data are most comprehensive for the mid-latitudes of the Northern Hemisphere, a reflection of the much greater study of assemblages from these regions.
Uniform climatic conditions are more widespread in the Cretaceous, and thus we have not yet been able to separate many high- and low-latitude taxa. That such differences exist, however, has been documented by, for example, Lentin and Williams (1980), Williams et al. (1990), Mao and Mohr (1992), and Brinkhuis, Sengers, et al. (this volume).