Global taxonomic richness is affected by variation in three components: within-community, or alpha, diversity; between-community, or beta, diversity; and between-region, or gamma, diversity. A data set consisting of 505 faunal lists distributed among 40 stratigraphic intervals and six environmental zones was used to investigate how variation in alpha and beta diversity influenced global diversity through the Paleozoic, and especially during the Ordovician radiations. As first shown by Bambach (1977), alpha diversity increased by 50 to 70 percent in offshore marine environments during the Ordovician and then remained essentially constant for the remainder of the Paleozoic. The increase is insufficient, however, to account for the 300 percent rise observed in global generic diversity. It is shown that beta diversity among level, soft-bottom communities also increased significantly during the early Paleozoic. This change is related to enhanced habitat selection, and presumably increased overall specialization, among diversifying taxa during the Ordovician radiations. Combined with alpha diversity, the measured change in beta diversity still accounts for only about half of the increase in global diversity. Other sources of increase are probably not related to variation in gamma diversity but rather to appearance and/or expansion of organic reefs, hardground communities, bryozoan thickets, and crinoid gardens during the Ordovician.

Being of especially high quality, the Neogene fossil record of planktonic foraminifera offers special opportunities for assessing patterns of extinction and speciation. A variety of metrics indicates that within this group the mean duration of lineages has been much shorter (rate of extinction has been higher) for the globorotaliid clade than for the globigerinid clade. Furthermore, in the globorotaliid clade rates of extinction and speciation have not been closely linked to changes in diversity, but rather have been relatively high even at times when diversity has undergone little change. Thus, the globorotaliid clade has undergone more rapid evolutionary turnover than the globigerinid clade. Data for living species reveal that neither geographic range nor temperature tolerance is the primary factor controlling lineage duration. On the other hand, there is evidence that lineages marked by low abundance (small population size) are relatively short-lived. The reason that globorotaliid lineages have generally survived for shorter intervals, on the average, may be that their populations have been less abundant and less stable. Usually they live deeper in the water column, where food is often sparse, and many flourish only in areas of upwelling. Furthermore, the globorotaliids lack symbiotic algae for nutritional support. The same ecological factors may have accelerated speciation in the globorotaliid clade, by causing species to be patchily distributed. Thus, population size and structure have been more important than geographic range in determining rates of extinction and speciation. This parallels the situation for Neogene marine bivalves.

For planktonic foraminifera, as for Western Atlantic Bivalvia, the normal pattern of extinction was reversed in late Pliocene time, apparently in response to climatic cooling. The globigerinids suffered a sudden pulse of extinction. The deeper dwelling globorotaliids fared better; probably many of their species benefited from elevation of the seasonal thermocline into the photic zone. At the same time, rate of speciation declined in the globorotaliid clade, which supports the idea, inferred from the evolutionary history of marine bivalves, that an increase in the size and stability of populations should depress both rate of extinction and rate of speciation.

The Late Devonian extinction event was not geologically “instantaneous,” in that extinctions during the epoch are not concentrated into a single sharp pulse at the end of the Frasnian. Extinction rates are elevated for a period of at least 2 to 4 m.y. during the middle and late phases of the Frasnian, with maximum rates occurring generally 2 m.y. before the terminal Frasnian. Neither was the Late Devonian biotic crisis a “gradual” event. In the analysis of the evolution of ecosystems, it is misleading to consider the pattern of extinction rates alone. Frasnian marine ecosystems flourished during the same time interval characterized by elevated extinction rates because origination rates of new species are higher, per time interval, than corresponding extinction rates. This pattern of relative origination/extinction rates abruptly reversed during the latest Frasnian—precipitating a rapid loss of species diversity. Within limits of current stratigraphic correlation, the ecosystem collapse appears to have occurred simultaneously in such widespread geographic regions as New York State (U.S.A.) and the southern Urals (U.S.S.R.).

In viewing the Late Devonian event from an ecological perspective, the most important question is not “What triggered the elevated extinction rates?”, but rather “What was the inhibiting factor that caused the cessation of new species originations?”

Cohort analysis is used to investigate survivorship of trilobites originating during the Cambrian and Ordovician. Using a time-homogeneous branching model, it is estimated that trilobite genera and species originating during the Ordovician survived three times longer than Cambrian genera and species. Monte Carlo simulation of survivorship is used to show that (1) Cambrian and Ordovician survivorship are significantly different, (2) Ordovician cohorts conform more closely to the time-homogeneous model than do Cambrian cohorts, and (3) deviations from temporal homogeneity are more often produced by extraordinary extinction than by unusually slow turnover.

When Early Ordovician cohorts are decomposed into genera within families that originated in the Cambrian versus the Ordovician, no evidence that Cambrian and Ordovician survivorship differences are clade-specific can be found. Ordovician genera of Cambrian affinity and of Ordovician affinity become extinct at similar rates.

Some of the ultimate causes of these differences in survivorship include (1) taxonomic inconsistency, (2) greater environmental stability in the Ordovician, and (3) more highly structured ecosystems in the Ordovician that may have led to the weeding out of extinction-prone taxa.

Nipponites, a Late Cretaceous nostoceratid ammonite, shows a peculiar meandering shell growth in the middle-late stage. Assuming neutral buoyancy, and a constant aperture angle relative to the sea bottom, meandering growth of this ammonite was modeled by computer simulation. In this model, the meandering shell growth is controlled by regulation of life orientation. The remarkable similarity in the coiling modes and rib obliquity patterns between the computer-simulated and actual specimens strongly suggests a free living mode of life in Nipponites with an approximately neutral buoyancy. The simulation also suggests that morphological saltation from a simple helicoid form like Eubostrychoceras japonicum to a meandering shell form like Nipponites occurred abruptly without any intermediate form by minor change of the upper and lower limits of growth direction.

Modern ruminant species have traditionally been placed in three broad dietary categories (browsers, grazers and intermediates) based on their observed feeding habits. Shape analysis of premaxillary outlines of 31 species of ruminants shows that their premaxillae differ according to their dietary category. Browsers have pointed premaxillae and grazers square ones. Intermediate feeders have intermediate outlines.

The Miocene giraffid Samotherium boissieri has always been viewed as a specialized browser similar to the modern okapi, Okapia johnstoni. However, the premaxillary shape of S. boissieri falls very close to the mean of the grazers and is most similar to that of the African buffalo (Syncerus caffer), a committed grazer.

Quantitative analyses of the microscopic wear patterns on the molars reveal significant differences between three modern species from the three dietary groups. S. boissieri has more microscopic scratches on its teeth than either the modern giraffe Giraffa camelopardalis (a browser) or Grant's gazelle Gazella granti (an intermediate feeder). In this respect, it is indistinguishable from the wildebeest Connochaetes taurinus which is a committed grazer.

Both of these analyses suggest that this extinct giraffid was a grazer, although we cannot rule out the possibility that it was an intermediate feeder. It was definitely not a specialized browser as are both living members of the Giraffidae.

Megafossil remains of conifers allied to taxa of the high montane fir-spruce-hemlock-white pine zone often occur in relatively lowland Tertiary floras together with taxa typical of the mixed-conifer and broadleaved sclerophyll forest zones. Even though these forests are now separated in elevation by fully 1,000 m and in distance by 10–20 km or more, it has been generally accepted that the structures of the high montane conifers were transported to the basins of deposition from distant, high mountains. Several lines of evidence show that montane conifers were regular members of both mixed-conifer and montane conifer forests. They were restricted to higher elevations in the late Neogene–Quaternary; as summers became drier and hotter, the germinating seedlings failed to become established in the mixed-conifer forest zone. They were further isolated from the broadleaved sclerophyll zone, which was confined to lower levels as winters became colder and snow more frequent.