The latest Aalenian–early Bajocian time interval (ca. 171-169 Ma) is marked by a global reorganization of oceanic plates with the Central Atlantic opening and the formation of the Pacific plate. This time interval is also marked by a global geochemical perturbation of δ13C with a negative excursion at the Aalenian/Bajocian boundary and a positive excursion during the early Bajocian. Evolutionary diversifications of marine invertebrate taxa, namely ammonites, radiolarians, and coccolithophorids, are recorded at that time. Concerning coccolithophorids, this interval witnesses the diversification and expansion of the most successful Mesozoic genus: Watznaueria. In this study, we explore the potential environmental, ecological, and biological forcing at the origin of Watznaueria diversification and its effect on the coccolith assemblages through quantification of the absolute and relative abundances of calcareous nannofossils in two Middle Jurassic key sections: Cabo Mondego (Portugal) and Chaudon-Norante (France). In both sections, we find an increase in nannofossil absolute abundance and flux at the beginning of the lower Bajocian, coeval with an increase in absolute and relative abundances of Watznaueria spp., followed by a plateau in the middle and upper part of the lower Bajocian. The increase of Watznaueria spp. is synchronous with a decrease in relative abundance of other major coccolith taxa, whereas the absolute abundance of these species did not decrease. During the climatically driven early Bajocian eutrophication event, Watznaueria spp. integrated into the calcareous nannoplankton community in two successive evolutionary steps involving first W. contracta and W. colaccicchii, and second W. britannica and W. aff. manivitiae. Step 1 was driven by an increase in niche carrying capacities linked to the early Bajocian eutrophication. Step 2 was driven by specific adaptation of the newly evolved Watznaueria species to bloom in nutrient-rich environments not exploited before. These evolutionary events have initiated the 100-Myr reign of Watznaueria over the calcareous nannoplankton community.

Allometric analysis of the size-shape relationships in the Pliocene-Pleistocene planktic foraminiferal Globorotalia (Globoconella) puncticulata-inflata plexus reveals several heterochronic modes underlying the morphological evolution of the clade. The ancestral lineage, G. puncticulata, is a peramorphocline, showing a pre-displacement mode of heterochrony between 3.5 Ma and 3.0 Ma and an acceleration mode from 3.0 to 2.7 Ma. A different peramorphosis process, isometric giantism (hypermorphosis), in the ontogeny of the ancestral stocks of Globoconella occurred at about 3.5 Ma and gave rise to the G. inflata lineage. The descendant lineage, G. inflata, appears to have adopted a paedomorphosis trend by delaying the onset of the neanic stage in ontogeny during the period of 3.5 to 2.35 Ma, resulting in a series of transposition allometries. During the interval of 2.4 to 1.73 Ma, the allometries shifted to the opposite direction, signifying a pre-displacement trend. Evolutionary stasis marks the evolution during 1.73 to 0.25 Ma. Neoteny concluded the final evolutionary stage of the G. inflata lineage during the latest Quaternary (0.26 to 0.05 Ma). The enormous plasticity and fluctuations in morphology of G. inflata are attributed to the highly positive allometric growth during the ontogeny and the wide-range transposing allometries in the phyletic history. The major changes in heterochronic mode coincide with paleoceanographic events, suggesting that the morphological evolution in the Globoconella clade has been modulated by changes in paleoceanographic conditions.

The mammalian fossil record of Spain is long and taxonomically well resolved, offering the most complete record of faunal change for the Neogene of Europe. We evaluated changes in diversification, composition, trophic structure, and size structure of large mammals over the middle and late Miocene with methods applied to this record for the first time, including ordination of fossil localities to improve temporal resolution and estimation of confidence intervals on taxa temporal ranges. By contrast, analysis within the traditional Mammal Neogene (MN) biochronology obscures important aspects of diversification. We used inferred temporal ranges of species and evaluated per capita rates of origination, extinction, diversification, and turnover over 0.5-Myr time intervals.

Three periods of significant faunal change occurred between 12.0 and 5.5 Ma: (1) From 12.0 to 10.5 Ma, elevated origination rates led to an increase in diversity without significant change in ecological structure. Immigrants and geographic-range shifts of species to lower latitudes during an interval of global cooling contributed to these faunal changes. (2) From 9.5 to 7.5 Ma, high extinction rates followed by high origination rates coincided with significant changes in taxonomic composition and ecological structure. These changes represent the Vallesian Crisis, with replacement of a fauna of forest affinities (with frugivores and browsers) by a fauna of open woodlands (with grazers and mixed feeders). (3) From 6.5 to 5.5 Ma, high extinction rates reduced diversity without substantial changes in ecological structure, and large mammal faunas became highly endemic across the northern Mediterranean region. This interval includes the Messinian Salinity Crisis, the desiccation of the Mediterranean basin. Extinction may have been caused by geographic isolation and aridification, with evolution of endemic lineages giving rise to new species in the early Pliocene. These distinct macroevolutionary patterns of faunal change correspond to different geographic scales of inferred climatic and tectonic drivers.

Given estimates of the variation in total standing species richness through the periods of the Phanerozoic, mean species duration, and the relative intensity of the sampling of the fauna from each of the periods, the expected number of described species can be predicted for each period of the Phanerozoic using an analytic sampling model. This model is based on the assumption that the relative abundances of species in any geologic period can be approximated by the canonical (lognormal) species-abundance distribution.

Three commonly cited models of standing species richness (Valentine, 1973; Gould et al., 1977; Bambach, 1977) each suggest different patterns of species richness in the Phanerozoic. By assuming that sampling of the fossil record is proportionate to sediment volume, it can be shown with the sampling model that the Empirical, Equilibrium, and Species-Richness Models each predict that the number of described species will be strongly correlated with sediment volume. Equally high correlations are predicted if it is assumed that sampling is proportionate to sediment area or to paleontological interest. The correlations predicted for each of the three models are remarkably similar. The impact of sampling effects is so strong that the variations in species richness postulated by these three models are almost completely obscured. Preservational biases will probably only further obscure the relationship between the number of described species and total species richness. Therefore, it seems likely that analysis of trends in the total number of described species will be of little use in determining trends in worldwide species richness in the Phanerozoic.

Comparison of the actual patterns of variation in the number of described species and the expected numbers of described species predicted by the sampling model reveals that more species are known from the Cenozoic than would be predicted from the abundance of Cenozoic sediments or from the amount of paleontological interest in the Cenozoic. This might have resulted from the Cenozoic sediments remaining relatively free of diagenetic effects which might have destroyed the fossils entombed in the sediments.

The set of environmental conditions under which a taxon can survive and maintain viable populations, known as the ecological niche, is a fundamental determinant of a taxon's distribution. Because of the central importance of ecological niches, they have been assumed to remain relatively stable during intervals of morphological stasis. However, the assumption of niche stability has rarely been tested directly with fossil data spanning multiple temporal intervals. Thus, the conditions under which this assumption is likely to be accurate are not well understood. In this study, we use ecological niche modeling (ENM) to reconstruct the ecological niche for 11 genera of marine benthos (crinoids, trilobites, molluscs, bryozoans, and corals) from the Type Cincinnatian Series (Late Ordovician, Katian Stage) across nine temporal intervals spanning approximately three million years. This interval includes both abiotic environmental change (gradual sea-level fall) and biotic change (rapid pulses of the Richmondian Invasion), thus allowing the relative effect of different environmental perturbations to be constrained. A previous symmetrical analysis of niche stability of brachiopod species recovered an increase in niche evolution following the Richmondian Invasion. Herein we test the generality of the brachiopod pattern within the community. Niche stability was evaluated in geographic space, ecological space, and niche parameter space. Niche stability varied through time; during the Pre-Invasion interval, taxa exhibited niche stability during gradual shallowing of sea level in the basin, whereas niche evolution became more common during the Richmondian Invasion. Taxa adjusted to the increased competition by altering aspects of their niche. Notably, surviving taxa contracted their niche into a subset of their previous niche parameters. This represents an adaptive response to increased competition for resources with the newly established invader taxa, and it was employed most successfully by generalist taxa. Patterns of niche evolution were congruent between clades, among feeding styles, and across taxonomic levels.

Cladistic analysis of osteological and dental characters in a monophyletic group of Miocene and younger tayassuids demonstrates a pattern of changes in the degree of sexual dimorphism in canine tooth diameter and zygomatic arch width, and in phenotypic correlations between these characters. Primitively, tayassuids have canine teeth that are sexually dimorphic and discretely bimodal in size, and zygomatic arches that are narrow in both sexes. Many late Miocene and Pliocene tayassuids have broad, winglike zygomatic processes. In some species, these processes are large in both sexes, but in others, those of females are much smaller than those of males. The presence of large processes in both sexes is primitive relative to the condition of strong sexual dimorphism. In five separate clades, the zygomatic processes of both sexes become reduced in size, and the degree of sexual dimorphism in canine size becomes reduced as well. The pattern is congruent with predictions derived from a theoretical model of the evolution of sexual dimorphism, and it further indicates the emergence of a new phenotypic correlation between two previously uncorrelated characters, canine size and zygoma size. The advent of this new correlation coincides with the advent of pronounced sexual dimorphism in zygomatic processes. Although such a pattern could be explained by genetically modifying phenotypic expression of homologous characters in one sex or the other, an epigenetic modification of expression is equally plausible: the evolution of sexual dimorphism in homologous characters could be accomplished by placing phenotypic expression of an originally monomorphic character under the control of steroid sex hormones. This hypothesis is consistent with evidence from many vertebrate groups, and it provides testable predictions.

The exceptionally preserved Triassic (Anisian) Grès à Voltzia fauna from the Vosges of northeastern France is compared with four major Carboniferous Konservat-Lagerstätten. The problem of comparing faunas with different types of preservation and degrees of taxonomic determination is addressed with a newly devised similarity coefficient. This coefficient quantifies and combines data from different levels in the taxonomic hierarchy and allows comparisons between biotas in a consistent direction regardless of relative diversity. The rank order of similarity between the four Carboniferous Konservat-Lagerstätten and the Grès à Voltzia is as follows: 1. Mazon Creek (Westphalian D) of Illinois; 2. Glencartholm (Visean) of southern Scotland; 3. Bear Gulch (Namurian) of Montana; and 4. Blanzy-Montceau (Stephanian) of France. These occurrences represent conditions transitional between nearshore fully marine and fresh water. The Grès à Voltzia fauna is significantly closer to the Mazon Creek fauna than to the others; the taxonomic overlap with Blanzy-Montceau and Bear Gulch is limited.

Stratigraphic age has an insignificant influence on the result; indeed, the fauna closest in age to the Grès à Voltzia, that of Blanzy-Montceau, is least similar. Taphonomic factors are important in determining the range of organisms preserved. The Glencartholm fauna is represented only by forms with either mineralized or robust chitinous skeletons, implying a greater degree of decay prior to the onset of diagenetic mineralization than in the other Konservat-Lagerstätten. Environment, however, is the major control on similarity. The Mazon Creek biota, like that of Grès à Voltzia, represents settings transitional between terrestrial and marine-influenced delta. Groups common to both Konservat-Lagerstätten include medusae, brachiopods, polychaetes, bivalve and gastropod molluscs, limulids, scorpions, spiders, branchiopods, ostracodes, malacostracans, cycloids, euthycarcinoid and myriapod uniramians, insects, fish, and tetrapods. There is a striking continuity between the faunas of Carboniferous and Triassic transitional sedimentary environments. Groups that were adapted to fluctuating conditions (e.g., shifting salinity) show strong congruence at the family and lower levels and were little affected by Permian extinctions. The major taxonomic contrasts are in the eumalacostracans and insects: many of the groups represented in the Grès à Voltzia appeared in the Permian and radiated across the Permo-Triassic boundary as Paleozoic forms became extinct.

Magadina cumingi (Davidson) lives in an environment of high current energy and mobile sediments using the pedicle as an elevating device. This previously undescribed substrate relationship is reflected in pedicle form, the muscular system, distribution of secondary thickening and characters of the beak. The cardinalia provide the evidence of key differences in the muscular system from an attached species Magellania australis (Quoy and Gaimard) and a free lying species with atrophied pedicle Neothyris lenticularis (Deshayes). The possession of an open foramen in articulate brachiopods is not synonymous with permanent attachment.

Micropaleontology is a peculiar subject: it is not easily defined, it focuses on geologic problems, and it ignores fundamental paleontologic and evolutionary questions it could best attack. As a result of its historic development, micropaleontology is directed to the solution of stratigraphic, paleoceanographic and paleoclimatologic problems, but it has seldom addressed paleobiologic or evolutionary ideas. It is a tradition rather than a discipline. The term “micropaleontology” and all it signifies should be abandoned, for it obscures natural relationships, attracts people with geologic rather than biologic approaches, isolates its practitioners in a blanket of systematics, biostratigraphies, and terminologies, and, as a result, discourages outsiders with other viewpoints or contributions from utilizing its fine fossil record. The growth of the field has been exponential in people-power and literature but not in the development of fundamentally new ideas. Micropaleontology has therefore contributed little to recent paleobiologic or evolutionary hypotheses, in spite of the possession by the many organisms relegated to it of biological properties and fossil records which have much potential for the generation and testing of such hypotheses. Microfossil studies have served geology powerfully and they should continue in that role, but they should also be used to fulfill their promise in the interpretation of paleobiogeography, paleoecology, morphology, evolutionary processes and the origin of new groups and ground plans.

In this paper we present a method for estimating soil pCO2 in ancient environments using the measured carbon-isotope values of pedogenic carbonates and plant-derived organic matter. The validity of soil pCO2 estimates proves to be highly dependent on the organic δ13C values used in the calculations. Organic matter should be sourced from the same paleosol profiles as sampled carbonates to yield the most reliable estimates of soil pCO2. In order to demonstrate the potential use of soil pCO2 estimates in paleoecological and paleoenvironmental studies, we compare samples from three Upper Jurassic localities. Soil pCO2 estimates, interpreted as a qualitative indicator of primary paleoproductivity, are used to rank the Late Jurassic terrestrial environments represented by the Morrison Formation in western North America, the informally named Lourinhã formation in Western Europe, and the Stanleyville Group in Central Africa. Because modern terrestrial environments show a positive correlation between primary productivity and faunal richness, a similar relationship is expected in ancient ecosystems. When the relative paleoproductivity levels inferred for each study area are compared with estimates of dinosaur generic richness, a positive correlation emerges. Both the Morrison and Lourinhã formations have high inferred productivity levels and high estimated faunal richness. In contrast, the Stanleyville Group appears to have had low primary productivity and low faunal richness. Paleoclimatic data available for each study area indicate that both productivity and faunal richness are positively linked to water availability, as observed in modern terrestrial ecosystems.

Cheilostome bryozoans that grew as rigidly erect arborescent colonies dominate many bryozoan-rich assemblages of Tertiary age, in which they are found most commonly as small dissociated fragments. The regularity with which branching and branch thickening occur in intact colonies of living species provides a basis for quantitative reconstruction of these growth processes in fossils. We propose models to describe branch thickening, develop methods to extend both thickening and branching models to fossils, investigate the thickening and branching properties of four Paleocene and five Oligocene species and compare the properties of these fossils to those of nine living species.

The properties investigated are largely mutually independent and species specific irrespective of geologic age and have similar numerical ranges among different assemblages of coeval species. Species are evenly distributed across the range of possible morphologies between observed extremes, without obvious gaps. Statistically significant trends through time are identified in gradients of branch thickening, which have implications for the resistance of colonies to mechanical stress, and in angles of bifurcation, that are important in the way growing colonies occupy space.

One of the most enduring evolutionary metaphors is Van Valen's (1973) Red Queen. According to this metaphor, as one species in a community adapts by becoming better able to acquire and defend resources, species with which it interacts are adversely affected. If those other species do not continuously adapt to compensate for this biotically caused deterioration, they will be driven to extinction. Continuous adaptation of all species in a community prevents any single species from gaining a long-term advantage; this amounts to the Red Queen running in place. We have critically examined the assumptions on which the Red Queen metaphor was founded. We argue that the Red Queen embodies three demonstrably false assumptions: (1) evolutionary adaptation is continuous; (2) organisms are important agents of extinction; and (3) evolution is a zero-sum process in which living things divide up an unchanging quantity of resources. Changes in the selective regime need not always elicit adaptation, because most organisms function adequately under many “suboptimal” conditions and often compensate by demonstrating adaptive flexibility. Likewise, ecosystems are organized in such a way that they tend to be robust and capable of absorbing invasions and extinctions, at least up to a point. With a simple evolutionary game involving three species, we show that Red Queen dynamics (continuous adaptation by all interacting species) apply in only a very small minority of possible outcomes. Importantly, cooperation and facilitation among species enable competitors to increase ecosystem productivity and therefore to enlarge the pool and turnover of resources. The Red Queen reigns only under a few unusual circumstances.

656 mandibles and isolated teeth of the bovid Pachytragus solignaci Robinson from two localities in the Miocene Beglia Formation, Gafsa, Tunisia, have been individually aged on the basis of ontogenetic development and state of dental wear. The sample probably represents normal but seasonally restricted mortality. Life table analysis indicates an annual mortality rate of 25–30%, increasing in old animals. Dental dimensions are affected by stabilizing selection which sets in as the tooth comes into function, earlier mortality being nonselective in that respect.

Evidence is presented that primitive artiodactyls had a diploid number of 14. The higher diploid numbers of most living artiodactyls are interpreted as resulting from karyotypic fissioning at the times of past adaptive radiations. The fossil record appears to support this contention.

An evolutionary sequence of unusual X chromosome transformations has been deduced from the differences that exist among extant species. From these, and from interrelationships of karyotypes, certain phylogenetic revisions are suggested.

Insect taphonomy is a topic that has drawn interest because of its potential biases on diversity patterns and the ecological information recorded by ancient insect faunas. Other than the onset of common amber fossilization in the Cretaceous, very little is known about long-term trends in the nature and quality of insect preservation and, as a result, the effects of taphonomic biases are poorly constrained. We assembled a database of nearly 7000 Carboniferous–Pliocene insect adpression (compression and impression) species from the primary literature to assess changes in insect taphonomy over time and test biotic and environmental controls on preservation. We grouped the fossils into 10-Myr bins and scored preservation of holotype specimens as either articulated bodies or isolated wings; articulated specimens with a body implied a generally higher quality of preservation. Paleozoic and Triassic insect holotypes are known overwhelmingly from isolated wings (only 12% articulated bodies), but our database shows a significant increase in the percentage preserved as articulated bodies, to more than 70%, beginning about 160 Myr ago in the Late Jurassic. This transition could reflect variations in the robustness of different insect orders and shifts in the taxonomic composition of insect faunas, but all the major orders in the database exhibit significant increases in articulation. Instead, a shift to increased preservation in lacustrine paleoenvironments, which contain a greater proportion of articulated body fossils, explains most of the trend. The pronounced Late Jurassic increase in articulation has implications for evolutionary and ecological reconstructions, for example, suggesting that preserved insect diversity may be biased downward in the earlier part of their history when articulation was poor.

The centric diatom Stephanodiscus yellowstonensis Theriot and Stoermer is endemic to Yellowstone Lake, where it can be an important component of the summer phytoplankton assemblage. Its close relative, Stephanodiscus niagarae Ehrenberg, is abundant in nearby lakes and regional reservoirs. We used the stratigraphic record of Yellowstone Lake to investigate the evolution of S. niagarae to S. yellowstonensis and to describe the limnologic and climatic conditions associated with its evolution. A dramatic morphological shift took place between about 13.7 and 10.0 Ka, but morphology remained stable from 10 Ka to the present. Coincident with morphological change in the S. niagarae/S. yellowstonensis complex were changes in the diatom species assemblage, biogenic silica concentrations, sediment lithology, and regional vegetation. These changes suggest an environment that experienced progressive warming following the retreat of continental glaciers. We could not identify a specific selective factor driving evolution. Nevertheless, nonrandom morphological evolution strongly associated with continuous environmental change suggests that directional selection is a reasonable hypothesis to account for evolution of S. yellowstonensis. Protists are presumed to evolve gradually after speciation events because of large population size, high dispersal capacity, and low reproductive barriers. However, published diatom examples and the evolution of S. yellowstonensis suggest that it is premature to generalize about rates of evolution in protists, or at least to include diatoms in this generalization.

The evolutionary history of shell geometry of Early Jurassic ammonoids during the Pliensbachian–Toarcian second-order mass extinction is explored at both adult and ontogenetic levels. The ontogenetic approach builds on the concept of allometric space to get insights into the developmental aspects of morphological evolution. Investigation of the deployment of taxa in adult morphospace and allometric space allows the appraisal of the temporal evolution of morphological and allometric disparities. Curves of taxonomic diversity, adult morphological disparity, allometric disparity, and average adult size are contrasted. Results show that during the Pliensbachian–Toarcian interval, ammonoids underwent two successive and drastic declines in taxonomic diversity. Patterns of morphospace and allometric space occupancy suggest nonselective extinction at both morphological and developmental levels. Another measure of allometric disparity suggests the occurrence of two heterochronic trends, a peramorphocline followed by a paedomorphocline, during the Toarcian. These trends are concomitant with changes in average adult size that compensate for the heterochronic effects and explain the striking stability of morphological disparity despite changes in diversity. The results also emphasize the existence of two contrasted evolutionary dynamics in Pliensbachian and Toarcian ammonoids. Methodologically, the allometric disparity approach appears to be a fruitful tool to analyze the rather understudied clade-wide ontogenetic aspects of morphological evolution. Combining multiple approaches to describe clade morphological dynamics leads to a better characterization and understanding of the diversity-disparities relationships and a better distinction of the potential processes driving these macroevolutionary patterns.

Here I test the hypothesis that temporal variation in geographic range size within genera is affected by the expansion and contraction of their preferred environments. Using occurrence data from the Paleobiology Database, I identify genera that have a significant affinity for carbonate or terrigenous clastic depositional environments that transcends the Database's representation of these environments during the stratigraphic range of each genus. These affinity assignments are not a matter of arbitrarily subdividing a continuum in preference; rather, genera form distinct, nonrandom subsets with respect to environmental preference. I tabulate the stage-by-stage transitions in range size within individual genera and the stage-by-stage changes in the extent of each environment. Comparing the two shows that genera with a preference for a given environment are more likely to increase in geographic range, and to show a larger average increase in range, when that environment increases in areal extent, and likewise for decreases in geographic range and environmental area. Similar results obtain for genera with preferences for reefal and non-reef settings. Simulations and subsampling experiments suggest that these results are not artifacts of methodology or sampling bias. Nor are they confined to particular higher taxa. Genera with roughly equal preference for carbonates and clastics do not have substantially broader geographic ranges than those with a distinct affinity, suggesting that, at this scale of analysis, spatial extent of preferred environment outweighs breadth of environmental preference in governing geographic range. These results pertain to changes over actual geologic time within individual genera, not overall average ranges. Recent work has documented a regular expansion and contraction when absolute time is ignored and genera are superimposed to form a composite average. Environmental preference may contribute to this pattern, but its role appears to be minor, limited mainly to the initial expansion and final contraction of relatively short-lived genera.

Vertebrate microfossil bonebeds (VMBs)—localized concentrations of small resilient vertebrate hard parts—are commonly studied to recover otherwise rarely found small-bodied taxa, and to document relative taxonomic abundance and species richness in ancient vertebrate communities. Analyses of taphonomic comparability among VMBs have often found significant differences in size and shape distributions, and thus considered them to be non-isotaphonomic. Such outcomes of “strict” statistical tests of isotaphonomy suggest discouraging limits on the potential for broad, comparative paleoecological reconstruction using VMBs. Yet it is not surprising that sensitive statistical tests highlight variations among VMB sites, especially given the general lack of clarity with regard to the definition of “strict” isotaphonomic comparability. We rigorously sampled and compared six VMB localities representing two distinct paleoenvironments (channel and pond/lake) of the Upper Cretaceous Judith River Formation to evaluate biases related to sampling strategies and depositional context. Few defining distinctions in bioclast size and shape are evident in surface collections, and most site-to-site comparisons of sieved collections are indistinguishable (p≤0.003). These results provide a strong case for taphonomic equivalence among the majority of Judith River VMBs, and bode well for future studies of paleoecology, particularly in relation to investigations of faunal membership and community structure in Late Cretaceous wetland ecosystems. The taphonomic comparability of pond/lake and channel-hosted VMBs in the Judith River Formation is also consistent with a formative model that contends that channel-hosted VMBs were reworked from pre-existing pond/lake assemblages, and thus share taphonomic history.

Kelps and other fleshy macroalgae—dominant reef-inhabiting organisms in cool seas—may have radiated extensively following late Cenozoic polar cooling, thus triggering a chain of evolutionary change in the trophic ecology of nearshore temperate ecosystems. We explore this hypothesis through an analysis of body size in the abalones (Gastropoda; Haliotidae), a widely distributed group in modern oceans that displays a broad range of body sizes and contains fossil representatives from the late Cretaceous (60–75 Ma). Geographic analysis of maximum shell length in living abalones showed that small-bodied species, while most common in the Tropics, have a cosmopolitan distribution, whereas large-bodied species occur exclusively in cold-water ecosystems dominated by kelps and other macroalgae. The phylogeography of body size evolution in extant abalones was assessed by constructing a molecular phylogeny in a mix of large and small species obtained from different regions of the world. This analysis demonstrates that small body size is the plesiomorphic state and largeness has likely arisen at least twice. Finally, we compiled data on shell length from the fossil record to determine how (slowly or suddenly) and when large body size arose in the abalones. These data indicate that large body size appears suddenly at the Miocene/Pliocene boundary. Our findings support the view that fleshy-algal dominated ecosystems radiated rapidly in the coastal oceans with the onset of the most recent glacial age. We conclude with a discussion of the broader implications of this change.