Evolutionary change during the interval in which a fossil sample accumulates will inflate the variance of that sample relative to the population-level standing variation. If this effect is widespread and severe, paleontological samples will not provide reliable estimates of population variation. Although the few published studies conducted to test this possibility have found similar levels of variation in samples differing greatly in temporal acuity, the paucity of case studies prevents assessing the generality of this pattern. In this paper, two independent, literature-based approaches are used to greatly expand the data available to address this issue. The first approach compares morphometric variability in Quaternary mammal samples with samples from related modern populations. The second approach artificially lumps separate samples from evolving lineages and calculates the variance effects of this analytical time-averaging. Both approaches yield consistent results indicating that variance observed in time-averaged samples is typically only slightly inflated (approximately 5%) relative to population-level values. This finding suggests that rates of evolution are typically slow when scaled to within-population variation, providing support for relative stasis as the dominant mode of within-lineage evolution. An important practical consequence of these findings is that time-averaged fossil samples generally show trait variances and covariances that are similar to population-level parameters, which has been an important but implicit assumption in many paleontological studies of phenotypic variation.

Biodiversity has two principal components: richness (the number of taxa) and evenness (the distribution of individuals among taxa). Both of these attributes are critical in defining community composition and structure, but evenness may be particularly important for ecological reasons, especially in the context of a possible evolutionary increase in richness. Here I examine abundance data in well-preserved Cambrian and Ordovician benthic marine assemblages from mixed carbonate-shale and shale lithofacies deposited below normal wave base in North America. Evenness increases significantly from the Cambrian to the Ordovician in these assemblage data. The increase cannot easily be attributed to differences in sample size, lithology, water depth, or other sample characteristics. There is relatively little variation in evenness among stages within the Cambrian and Ordovician periods. Much of the within-period variance in evenness appears to arise from environmental and / or taphonomic differences that may exist between stratigraphic formations, but some variance may also be ascribed to the degree of taxonomic and / or ecological overlap among dominant taxa. Specifically, assemblages that are co-dominated by taxa from the same class or order tend to have lower evenness than assemblages dominated by genera from different higher taxa, but the effect is not strong in these data.

The Cambrian and Paleozoic evolutionary faunas show similar, but out-of-phase, patterns of evenness within assemblages. Both faunas have comparably low evenness early in their history but then increase to similar, higher evenness values. In the case of the Cambrian fauna, the increase occurs in the Late Cambrian or Early Ordovician. In the Paleozoic fauna, the increase appears to occur after the lower Arenigian.

Paleontologists increasingly appreciate the importance of studying the ecological context of fossil species and communities. Measuring abundance is a vital component not just for describing this context, but also for evaluating biases related to preservation and sampling and for estimating species richness (Jackson et al. 1999; Jackson and Johnson 2001; Kidwell 2001). Our purpose here is to identify a previously unrecognized problem that could lead to incorrect interpretation of observed patterns of abundance.

We present a quantitative analysis of megafloral turnover across the Cretaceous/Paleogene boundary (K/T) based on the most complete record, which comes from the Williston Basin in southwestern North Dakota. More than 22,000 specimens of 353 species have been recovered from 161 localities in a stratigraphic section that is continuous across and temporally calibrated to the K/T and two paleomagnetic reversals. Floral composition changes dynamically during the Cretaceous, shifts sharply at the K/T, and is virtually static during the Paleocene. The K/T is associated with the loss of nearly all dominant species, a significant drop in species richness, and no subsequent recovery. Only 29 of 130 Cretaceous species that appear in more than one stratigraphic level (non-singletons) cross the K/T. Only 11 non-singletons appear first during the Paleocene. The survivors, most of which were minor elements of Cretaceous floras, dominate the impoverished Paleocene floras. Confidence intervals show that the range terminations of most Cretaceous plant taxa are well sampled. We infer that nearly all species with last appearances more than about 5 m below (approximately 70 Kyr before) the K/T truly disappeared before the boundary because of normal turnover dynamics and climate changes; these species should not be counted as K/T victims. Maxima of last appearances occur from 5 to 3 m below the K/T. Interpretation of these last appearances at a fine stratigraphic scale is problematic because of local facies changes, and megafloral data alone, even with confidence intervals, are not sufficient for precise location of an extinction horizon. For this purpose, we rely on high-resolution palynological data previously recovered from continuous facies in the same sections; these place a major plant extinction event precisely at the K/T impact horizon. Accordingly, we interpret the significant cluster of last appearances less than 5 m below the K/T as the signal of a real extinction at the K/T that is recorded slightly down section. A maximum estimate of plant extinction, based on species lost that were present in the uppermost 5 m of Cretaceous strata, is 57%. Palynological data, with higher stratigraphic but lower taxonomic resolution than the megafloral results, provide a minimum estimate of a 30% extinction. The 57% estimate is significantly lower than previous megafloral observations, but these were based on a larger thickness of latest Cretaceous strata, including most of a globally warm interval, and were less sensitive to turnover before the K/T. The loss of one-third to three-fifths of plant species supports a scenario of sudden ecosystem collapse, presumably caused by the Chicxulub impact.

Paleontologists have a long tradition of the use of mathematical models to assist in describing and understanding patterns of diversification through time (e.g., Raup et al. 1973; Stanley 1975; Sepkoski 1978; Raup 1985; Foote 1988; Gilinsky and Good 1989). This is natural, as the information, phylogenetic and otherwise, that paleontologists work with comes equipped with a temporal dimension, albeit approximate, which endows these phylogenies with information about the tempo of evolution as well as the genealogical relationships among the lineages. Mathematical and statistical modeling are the tools for unlocking the quantitative information in the phylogenies.

Marshall (1995) used the distribution of the endpoints of 50% range extensions added to the stratigraphic ranges of individual taxa to bracket the position of an extinction boundary. Here we describe two improvements to Marshall's method. First, we show that more precise estimates of the position of such a boundary may be obtained using range extensions with confidence levels of less than 50% (e.g., 20%). Second, we introduce a new method of calculating confidence intervals that explicitly takes into account the position of the highest fossil find. Incorporating these improvements leads to confidence intervals for simulated data sets that are approximately four times more precise than those obtained by using Marshall's (1995) original method and approximately twice as precise as those using other published methods. We provide a look-up table that shows for different numbers of taxa the confidence level that should be used to maximize the precision of the estimated position of the extinction boundary, while ensuring that the boundary still lies within the stratigraphic interval bounded by at least one range extension. Unlike some other methods, our method is nonparametric and does not make the restrictive assumption of uniform preservation and recovery potential. We apply the method to Macellari's (1986) ammonite data from the late Cretaceous of Seymour Island, Antarctica.

Although the causes of mass extinctions have been studied in detail, recoveries have received little attention until recently. In this study, I examine the influence of extinction versus recovery intervals on ecological patterns across the end-Cretaceous (K/T) event in veneroid bivalves. Systematic and stratigraphic data were collected for 140 subgenera of veneroids, ranging from the Late Cretaceous through Oligocene of North America and Europe. Morphological data were collected for 1236 specimens representing 101 subgenera. Extinction selectivity and differential recovery were assessed with respect to morphology, and by extension, burrowing ecology in these bivalves. Eighty-one percent of veneroid subgenera went extinct at the K/T and diversity did not return to preextinction levels until 12 million years later. Despite the severity of the K/T extinction, I found little evidence of morphological or ecological selectivity. The K/T recovery, in contrast, was strongly biased toward taxa with deep pallial sinuses (i.e., toward deeper burrowers). For veneroids, the morphological and ecological effects of the K/T event are not tied to the extinction itself, but to the recovery that followed. The K/T recovery initiated a trend toward deeper burrowing that helped to establish veneroids as one of the most abundant and successful groups of modern marine bivalves.

For more than 60 years, evolutionary biologists have debated the issue of whether the processes of genetic change observable within populations (microevolution) can provide an adequate explanation for the large-scale patterns in the history of life (macroevolution). In general, population geneticists have argued in favor of microevolutionary extrapolation, whereas paleontologists have sought to establish an autonomous and hierarchical macroevolutionary theory based on the operation of selection at several levels of biological organization (especially species). The massive variation in eukaryotic genome sizes (haploid nuclear DNA contents, or “C-values”) has similarly been a subject of debate for more than half a century, and it has become clear that no one-dimensional explanation can account for it. In this article, the basic concepts of macroevolutionary theory are reviewed and then applied to the long-standing puzzle of genome size variation (the “C-value enigma”). Genome size evolution provides a clear example of hierarchy in action and therefore lends support to the theoretical approach of macroevolutionists. Perhaps more importantly, it is apparent that genome evolution cannot be understood without such a hierarchical approach, thereby providing an intriguing conceptual link between the most reductionistic and expansive subjects of evolutionary study.

In post-Cambrian time, five events-the end-Ordovician, end-Frasnian in the Late Devonian, end-Permian, end-Triassic, and end-Cretaceous-are commonly grouped as the “big five” global intervals of mass extinction. Plotted by magnitude, extinction intensities for all Phanerozoic substages show a continuous distribution, with the five traditionally recognized mass extinctions located in the upper tail. Plotted by time, however, proportional extinctions clearly divide the Phanerozoic Eon into six stratigraphically coherent intervals of alternating high and low extinction intensity. These stratigraphic neighborhoods provide a temporal context for evaluating the intensity of extinction during the “big five” events. Compared with other stages and substages in the same neighborhood, only the end-Ordovician, end-Permian, and end-Cretaceous extinction intensities appear as outliers. Moreover, when origination and extinction are considered together, only these three of the “big five” events appear to have been generated exclusively by elevated extinction. Low origination contributed more than high extinction to the marked loss of diversity in the late Frasnian and at the end of the Triassic. Therefore, whereas the “big five” events are clearly times when diversity suffered mass depletion, only those at the end of the Ordovician, Permian, and Cretaceous periods unequivocally qualify as globally distinct mass extinctions. Each of the three has a unique pattern of extinction, and the diversity dynamics of these events differ, as well, from the other two major diversity depletions. As mass depletions of diversity have no common effect, common causation seems unlikely.

Ammonoid taxonomic history is a well-documented series of diversity “booms and busts”, but the effect of this taxonomic pattern on morphological evolution has not received as much attention. We know particularly little about the effects of the Permo-Triassic mass extinction on the subsequent morphological evolution of the ammonoids.

Morphological data from 322 Triassic ammonoid genera (322 species) were combined with previously published data for Late Paleozoic ammonoids. This data set of 601 specimens was subjected to PCA to assess (1) the effects of the Permo-Triassic taxonomic bottleneck on ammonoid morphological evolution, by comparing the strength and sign of correlations in the Paleozoic and in the Triassic, and (2) whether the Triassic ammonoids immediately shifted to Jurassic morphologies, retained Paleozoic morphologies, or evolved in a more “mosaic” fashion.

The Triassic ammonoids recapitulate the late Paleozoic W-D distribution, but in S-D space their distribution closely foreshadows that of the Lower Jurassic ammonites. Given these findings it is clear that at even the level of shell geometry the Triassic ammonoids evolved in a mosaic fashion

The Triassic ammonoids reoccupy, and extend, the volume of morphospace occupied by the Paleozoic ammonoids. Overall, Triassic correlations between pairs of characters are weaker, but not significantly so.

Tracking the geometry of all 597 ammonoid genera from the Lower Devonian into the Lower Triassic, a 145–Myr period that spans three mass extinctions, shows that Paleozoic ammonoid shell geometries were strongly biased for a few combinations of whorl expansion (W), whorl overlap (D), and whorl shape (S). Just three modal combinations accommodated approximately 432 genera (72% of total) and just one combination accommodated 239 genera (40%). All three primary modal forms have similar low expansion rates (W ≈ 1.75) and differ only in coiling tightness (D). These geometries resulted in long body chambers (≈400°) with Nautilus-like static in-life aperture orientations (≈30°) for the great majority (>80%) of Paleozoic ammonoids. The ancestral clade Agoniatitida included a unique spectrum of openly coiled geometries that went extinct at the Frasnian/Famennian boundary (and were not seen again until the Triassic). The Devonian/Mississippian extinction terminated the brief, explosive radiation of the Clymeniida (64 genera). The dominant Paleozoic clade, the Goniatitida (ca. 130 Myr, 374 genera [64% of total]), survived both the F/F and D/M extinctions, but began declining well before the Permian/Triassic crisis. The long-lived Prolecanitida (40 genera [7%]) appeared shortly after the D/M extinction, persisted as a low-diversity clade through the Carboniferous, and gave rise to the Ceratitida in the mid-Permian, from which were derived all Mesozoic ammonoids. After each major extinction event the phylogenetic composition of ammonoid stocks was fundamentally reordered and geometries were recanalized. Without external disturbances, as the relatively uninterrupted Mississippian through Permian record shows, the history of ammonoid shell geometry would probably have been a record of much greater constancy, perhaps tied much more closely to the Lower Devonian geometric landscape.

Recent molecular analyses indicate that many reef coral species belong to hybridizing species complexes or “syngameons.” Such complexes consist of numerous genetically distinct species or lineages, which periodically split and/or fuse as they extend through time. During splitting and fusion, morphologic intermediates form and species overlap. Here we focus on processes associated with lineage fusion, specifically introgressive hybridization, and the recognition of such hybridization in the fossil record. Our approach involves comparing patterns of ecologic and morphologic overlap in genetically characterized modern species with fossil representatives of the same or closely related species. We similarly consider the long-term consequences of past hybridization on the structure of modern-day species boundaries.

Our study involves the species complex Montastraea annularis s.l. and is based in the Bahamas, where, unlike other Caribbean locations, two of the three members of the complex today are not genetically distinct. We measured and collected colonies along linear transects across Pleistocene reef terraces of last interglacial age (approximately 125 Ka) on the islands of San Salvador, Andros, and Great Inagua. We performed quantitative ecologic and morphologic analyses of the fossil data, and compared patterns of overlap among species with data from modern localities where species are and are not genetically distinct.

Ecologic and morphologic analyses reveal “moderate” overlap (>10%, but statistically significant differences) and sometimes “high” overlap (no statistically significant differences) among Pleistocene growth forms (= “species”). Ecologic analyses show that three species (massive, column, organ-pipe) co-occurred. Although organ-pipes had higher abundances in patch reef environments, columnar and massive species exhibited broad, completely overlapping distributions and had abundances that were not related to reef environment. For morphometric analyses, we used multivariate discriminant analysis on landmark data and linear measurements. The results show that columnar species overlap “moderately” with organ-pipe and massive species. Comparisons with genetically characterized colonies from Panama show that the Pleistocene Bahamas species have intermediate morphologies, and that the observed “moderate” overlap differs from the morphologic separation among the three modern species. In contrast, massive and columnar species from the Pleistocene of the Dominican Republic comprise distinct morphologic clusters, similar to the modern species; organ-pipe species exhibit “low” overlap (<10%, only at species margins) with columnar and massive species.

Assuming that “moderate” overlap implies hybridization and “high” overlap implies more complete lineage fusion, these results support the hypothesis of hybridization among species within the complex in the Bahamas during the Pleistocene. Hybridization involved introgression of three distinct evolutionary lineages, in association with Pleistocene sea level and temperature fluctuations, and appears to have been limited geographically primarily to the Bahamas and the northern Caribbean. Thus, not only does the structure of species boundaries within the complex vary geographically, but these geographic differences may have persisted since the Pleistocene.

The relative proportions of Sepkoski's Cambrian, Paleozoic, and Modern evolutionary faunas in Cambrian-Ordovician benthic marine assemblages from mixed carbonate-shale and shale lithofacies deposited below normal wave base (herein, deep subtidal) in North America are strongly positively correlated with global relative genus richness in Sepkoski's global compendium. The correlation between local and global faunal proportions is robust regardless of how proportions are calculated, including when local proportions are based on number of specimens. Like the global pattern, the transition between the Cambrian and Paleozoic evolutionary faunas appears to occur gradually, in that Lower Arenigian (Ibexian) deep subtidal assemblages contain approximately equal proportions of Cambrian and Paleozoic faunal elements. In agreement with previous work, an onshore-offshore differentiation of faunas is evident both within Ordovician deep subtidal communities and across a larger environmental gradient.

Within the deep subtidal assemblages studied here, the Paleozoic fauna tends to have a greater proportion of individuals for a given proportion of genera than the Cambrian fauna, although both tend to accrue genera at similar rates with increasing relative abundance. The Modern evolutionary fauna appears to accrue genera more rapidly with increasing local relative abundance. The extent to which these differences reflect ecological factors such as biomass, metabolic requirements or larval recruitment patterns, taxonomic practices stemming from variable morphospace saturation, or taphonomy-related counting biases remains unclear, but it suggests the possibility that Sepkoski's evolutionary faunas may share ecological characteristics that influence both local relative abundance and global rates of taxonomic evolution.

High-resolution (annual to decadal) paleoecological records of community composition can contribute a long-term perspective to conservation biology on baseline ecological variability and the response of communities to environmental change. We present here a detailed comparison of species assemblage characteristics (species richness, abundance, composition, and occurrence frequency) in live, dead, and recent fossil ostracode samples from Lake Tanganyika, East Africa. This study calibrates the fidelity of paleoecological samples (i.e., both death and fossil assemblages) to live diversity patterns for the purpose of reconstructing community dynamics through time.

Both life and death assemblages were collected from rocky sites in a mixed substrate habitat (total of ten sampling visits over 22-month period) over spatial scales of less than a meter to about 3–12 meters. Fossil assemblages were derived from sediment cores collected in sandy substrates adjacent to the rocky sites. Species richness in paleoecological assemblages is comparable to that in a year's accumulation of life assemblages sampled approximately monthly. The temporal resolution of the fossil samples in Lake Tanganyika could thus be as short as one year. Species abundance distributions were statistically indistinguishable among data sets. Rank abundance tests demonstrated that death and fossil assemblages were quite similar, although life assemblages differed substantially in the composition of their dominant species. Species composition differences between life and paleoecological assemblages appear to reflect the area of spatial integration represented by an assemblage—i.e., death and fossil assemblages are integrated over multiple habitat types, whereas life assemblages dominantly represent the rocky habitats where they were collected. Species occurrence frequencies in paleoecological data identified ecologically persistent species and may be useful for delimiting local species pools. Analysis of sampling efficiency indicates that approximately 28% of species in each paleoecological assemblage are “unique”; i.e., they are not likely to be present in an additional subsample from the same sample. Ordination reveals that life assemblages of ostracodes are characterized by high spatiotemporal heterogeneity. Variability in species composition was lower in paleoecological assemblages, presumably as a result of spatial and temporal averaging.

Death and fossil assemblages of Lake Tanganyika appear to preserve many characteristics of living benthic ostracode assemblages with high fidelity. Spatiotemporal averaging allows paleoecological assemblages to render information about the average composition of ostracode communities over short timescales, at spatial scales of several meters, and across habitat types. Sampling shell assemblages in surficial sediments thus represents a more efficient way of assessing the average ecological conditions at a locality than repeated live sampling. Furthermore, paleoecological analyses can generate novel insights into long-term community variability and membership with direct relevance to conservation.

The siliciclastic succession of the late Neoproterozoic Vendian Group in the White Sea area demonstrates a wide range of lithofacies, some recurring in a vertical succession. Significantly, each lithofacies contains a distinct assemblage of Ediacaran fossils that represents in situ benthic paleocommunities smothered in life position. These lithofacies define (1) a monospecific Inaria assemblage, restricted to the lower-shoreface muds; (2) a Charnia assemblage, within the middle-shoreface graded siltstone-shale couplets; (3) a Dickinsonia-Kimberella assemblage, confined to the interstratified sandstone and shale of prodelta; and (4) a Onegia-Rangea assemblage, preserved within channelized sandstone beds of the distributary-mouth bar.

In the White Sea area a strong correlation exists between taxonomic composition, biostratinomic features, and paleoecological context of the Ediacaran fossil assemblages. Facies-controlled distribution is also evident in other Ediacaran localities, demonstrating the recurrence of similar facies relationships on a global scale. This pattern is interpreted as representing Ediacaran biofacies with Avalon-type biotas distributed in deep marine habitats, Ediacara-type biotas inhabiting microbial biofilms in shallow marine prodeltaic settings, and infaunal Nama-type biotas found in distributary-mouth bar shoals. This in turn reveals a marked degree of environmental sensitivity and ecological specialization. Correspondence between depositional environment and taxonomic composition speaks against any obvious biogeographic provinciality of the Ediacaran biotas, and also casts doubt on claims of substantial evolutionary change.

Better understanding of the functional biology of early angiosperms may clarify ecological factors surrounding their origin and early radiation. Phylogenetic studies identify Amborella, Nymphaeales (water lilies), Austrobaileyales, and Chloranthaceae as extant lineages that branched before the radiation of core angiosperms. Among living plants, these lineages may represent the best models for the ecology and physiology of early angiosperms. Here we combine phylogenetic reconstruction with new data on the morphology and ecophysiology of these plants to infer early angiosperm function. With few exceptions, Amborella, Austrobaileyales, and Chloranthaceae share ecophysiological traits associated with shady, disturbed, and wet habitats. These features include low and easily light-saturated photosynthetic rates, leaf anatomy related to the capture of understory light, small seed size, and clonal reproduction. Some Chloranthaceae, however, possess higher photosynthetic capacities and seedlings that recruit in canopy gaps and other sunny, disturbed habitats, which may have allowed Cretaceous Chloranthaceae to expand into more diverse environments. In contrast, water lilies possess ecophysiological features linked to aquatic, sunny habitats, such as absence of a vascular cambium, ventilating stems and roots, and floating leaves tuned for high photosynthetic rates in full sun. Nymphaeales may represent an early radiation into such aquatic environments. We hypothesize that the earliest angiosperms were woody plants that grew in dimly lit, disturbed forest understory habitats and/or shady streamside settings. This ecology may have restricted the diversity of pre-Aptian angiosperms and living basal lineages. The vegetative flexibility that evolved in the understory, however, may have been a key factor in their diversification in other habitats. Our inferences based on living plants are consistent with many aspects of the Early Cretaceous fossil record and can be tested with further study of the anatomy, chemistry, and sedimentological context of Early Cretaceous angiosperm fossils.

Historical changes in the coastline of Kikai Island of the Ryukyu Islands in the southeast part of Japan were estimated by using a numerical simulation based on a glacio-hydro-isostasy model. Temporal changes in the area of the island during the last 40 Kyr were compared with temporal changes in species diversity in fossil land snails of the island. The species number in the past was theoretically estimated by the area of Kikai Island in the past and a species-area relationship among the modern land snail fauna of the Ryukyu Islands. The theoretical species numbers are very close to the actual ones. This suggests that the change in island area is the main cause of the change in species diversity in Kikai Island. In addition, we discuss causes other than the area, such as island elevation, distance to the nearest large island, climate change, human activity, and imperfection of fossil data. We also discuss the change in Fisher's alpha and body size against the change in the area.

Fossil samples almost always accumulate on timescales much longer than the life spans of individual organisms. This time-averaging has the potential to inflate the variability of fossil samples because phenotypic changes may occur during the interval of sample accumulation. Although many have realized that this effect may increase the variance of fossil samples, only qualitative predictions have been possible thus far. In this paper, I assume a simple but general Markovian model of evolution to derive expressions that predict the effects of time-averaging on trait variance and covariance. For lineages evolving as an unbiased random walk, phenotypic variance in samples increases linearly with the duration of time-averaging, at a slope that is proportional to the evolutionary rate. Although based on a very simple model of specimen input into time-averaged samples, the expressions relating variance, time-averaging, and evolutionary rate prove to be robust or adaptable to more realistic assumptions.

The theoretical findings are applied to analyze variation in a set of samples of the deep-sea ostracode Poseidonamicus miocenicus that vary greatly in temporal acuity. The relationship between duration of time-averaging and morphological variance is used to estimate evolutionary rates of two morphological traits in these ostracodes. These rate estimates are similar to those calculated independently from differences between presumed ancestor-descendant pairs of populations. Consistent with other studies of variability and time-averaging, these data suggest that phenotypic variance tends to increase rather slowly with the duration of time-averaging, indicating that greatly inflated variance is expected only in samples that have accumulated over many tens of thousands of years.

Ecological polarities are theoretical roles of organisms, reflected in evolved behaviors and characters. Ecological polarity includes what has been called life history strategies, functional types, habitat templates, and r and K selection. Three common ecological polarities emphasize reproduction, agonistic behavior, and withstanding harsh conditions. Such organisms can be called breeders, competitors, and tolerators, respectively. Polarities of ecospace can be envisaged graphically as apices of a triangular diagram within which each species occupies a particular region. Quantitative studies of ecological polarities rely on proxy measurements of specific morphological features, such as the proportional functional area of canines (for competitors), molars (for tolerators), and incisors (for breeders) among mammals. Such proxy measures of morphospace or chemospace are traditionally judged successful by the degree to which they reveal adaptive differences between species. This approach to approximating ecological polarity is here applied to modern soils, plants, snails, and mammals, as well as to comparable fossils of the Clarno and John Day Formations (Eocene and Oligocene) of central Oregon. An advantage of this approach is that adaptive similarities can be tested quantitatively, as shown here for Oligocene oaks and maples, rather than assuming that extinct species were comparable to related living plants. Paleosols that supported fossil creatures provide useful supporting evidence of past selection pressures for ecologically significant adaptations. Degree of hardship can also be quantified from paleosol features. For example, fossil snails had narrower apertures in paleosols of drier climates as revealed by their shallower calcic horizons, and leaves of extinct relatives of Meliosma and Oreomunnea were sclerophyllous in paleosols showing evidence of waterlogging, nutrient-deficiency, and metal toxicity. Evolutionary trends of ecological specialization revealed by this approach include molarization (interpreted as evolution toward the tolerator pole) in ungulates. Adaptive breakthroughs that initiated evolutionary radiations also can be reassessed by using these approximations of ecospace, for example, the convergent evolution by bears of degree of caninization previously evolved in an extinct creodont (Hemipsalodon). Ecological polarities provide new concepts and metrics for ordering morphological, chemical, and ecological characters of fossil and modern organisms, and for reassessing evolutionary trends.