“There are still many dinosaur people who will say that, ‘Yes, there was an impact, but there were hardly any dinosaurs left by then.’ It's possible, but my first class prejudice is not to accept coincidence on that scale” (S. Gould quoted in Glenn 1994: p. 266, referring to the K/T mass extinction).

Symbioses are often regarded as an important means for the creation of evolutionary novelty as well as a trigger for the abrupt appearance of higher taxa. The fossil record of foraminifer-algal symbiosis suggests that the appearance of this ecological association contributed to the radiation of Paleogene planktic foraminifera. Isotopic evidence shows that photosymbiosis evolved in synchrony with a major diversification of trochospiral planktic foraminifera about 3.5 m.y. after the end-Cretaceous extinction. In modern planktic foraminifera, photosymbiotic species tend to have more cosmopolitan distributions than asymbiotic foraminifera and a greater ability to withstand periods of nutrient stress. The simultaneous taxonomic radiation and acquisition of photosymbiosis are evidence that the ecological strategy permitted Paleocene foraminifera to expand their niche in pelagic environments by diversifying into low-nutrient surface waters.

A comparison of the species longevities of Neogene and Paleogene symbiotic clades suggests that photosymbiosis does not regulate the characteristic rate of taxonomic turnover in clades after they appear. Species longevities are much shorter in Paleocene and Eocene photosymbiotic morphospecies than they are among photosymbiotic Neogene clades; apparently photosymbiosis does not exert a significant control over long-term evolutionary rates. In addition, the absence of a characteristic morphology associated with photosymbiosis in Cenozoic planktic foraminifera suggests that morphology, as with rate of evolutionary turnover, is linked to symbiosis only because of common inheritance instead of a functional relationship. Although the coincidence between the acquisition of photosymbiosis and generic diversification does suggest a linkage between this ecology and the appearance of foraminiferal higher taxa, there is little indication at the present that symbioses control long-term morphological or ecological patterns within these groups after their appearance. Photosymbiosis, and other evolutionary innovations, may be more a catalyst for the differentiation of major groups than a predictable governor on evolutionary rates.

The incompleteness of the fossil record hinders the inference of evolutionary rates and patterns. Here, we derive relationships among true taxonomic durations, preservation probability, and observed taxonomic ranges. We use these relationships to estimate original distributions of taxonomic durations, preservation probability, and completeness (proportion of taxa preserved), given only the observed ranges. No data on occurrences within the ranges of taxa are required. When preservation is random and the original distribution of durations is exponential, the inference of durations, preservability, and completeness is exact. However, reasonable approximations are possible given non-exponential duration distributions and temporal and taxonomic variation in preservability. Thus, the approaches we describe have great potential in studies of taphonomy, evolutionary rates and patterns, and genealogy.

Analyses of Upper Cambrian-Lower Ordovician trilobite species, Paleozoic crinoid genera, Jurassic bivalve species, and Cenozoic mammal species yield the following results: (1) The preservation probability inferred from stratigraphic ranges alone agrees with that inferred from the analysis of stratigraphic gaps when data on the latter are available. (2) Whereas median durations based on simple tabulations of observed ranges are biased by stratigraphic resolution, our estimates of median duration, extinction rate, and completeness are not biased. (3) The shorter geologic ranges of mammalian species relative to those of bivalves cannot be attributed to a difference in preservation potential. However, we cannot rule out the contribution of taxonomic practice to this difference. (4) In the groups studied, completeness (proportion of species [trilobites, bivalves, mammals] or genera [crinoids] preserved) ranges from 60% to 90%. The higher estimates of completeness at smaller geographic scales support previous suggestions that the incompleteness of the fossil record reflects loss of fossiliferous rock more than failure of species to enter the fossil record in the first place.

Truth, goes an old proverb, is the daughter of time. Fifty years ago, G. G. Simpson (1944) brought paleontology into the Neodarwinian fold, arguing that evolutionary tempo can be documented in the geological record and used to inform debate about evolutionary mode. Today, increasingly sophisticated paleontological investigations of rate—be it diversification, extinction, migration, morphological change, or divergence in macromolecular sequence—require calibration of the geological time scale with a precision far greater than Simpson could have anticipated. Expanding research on the relationships between environmental history and evolution also requires unprecedented resolution in correlation and geochronometry.

Fitting the generalized inverse Gaussian-Poisson distribution (GIGP) to observed frequency distributions of taxa from the Late Triassic Molteno Formation of South Africa has yielded estimates of the corresponding preserved biodiversities. Three extrapolations have been made on the basis of the uniquely rich megaflora/insect coassemblages from 100 taphocoenoses: insect species—335 observed, 7740 preserved; vegetative species—206 observed, 667 preserved; gymnosperm ovulate orders—16 observed, 84 preserved. The reliability of the results varies according to the abundance and observed diversity of the taxa. These results, with further estimations in a companion paper of existed diversity (regional, continental and global), hint at Late Triassic floral and faunal richness akin to today. This conflicts with the traditionally held model of an increasing cone of biodiversity through time and suggests a phase of explosive evolution in the Triassic hitherto unsuspected. Application of the GIGP to other well-documented collections from other periods might reveal a pattern of diversity trends offering fundamentally new insights into the evolving terrestrial biosphere.

Three homogeneous models of species origination and extinction are used to assess the probability that ancestor-descendant pairs are preserved in the fossil record. In the model of cladogenetic budding, a species can persist after it branches and can therefore have multiple direct descendants. In the bifurcation model, a species branches to give rise to two distinct direct descendants, itself terminating in the process. In the model of phyletic transformation, a species gives rise to a single direct descendant without branching, itself terminating in the process. Assuming homogeneous preservation, even under pessimistic assumptions regarding the completeness of the fossil record, the probability of finding fossil ancestor-descendant pairs is not negligible. Even if all species of Phanerozoic marine invertebrates in the paleontologically important taxa had the same probability of preservation, on the order of 1%-10% or more of the known fossil species would be directly ancestral to other known fossil species. However, this is likely to be an underestimate, since the probability of finding ancestor-descendant pairs is enhanced by taxonomic, temporal, and spatial heterogeneities in preservation probability. Moreover, indirect genealogical relationships substantially increase the probability of finding ancestor-descendant pairs. The model of budding, the only one in which an ancestor can persist after a branching event, predicts that half or more of extant species have ancestors that are also extant. Thus, the question of how to recognize ancestor-descendant pairs must be carefully considered.

The Brontotheriidae (Perissodactyla, Mammalia) are often used as an illustration of vertebrate macroevolutionary trends because their morphological evolution includes significant size increases accompanied by the disproportionate lengthening of bony frontonasal horns. The positive phylogenetic allometry for horn length vs. skull length is among the strongest known of such relationships in vertebrate phylogeny. Hypotheses explaining the change from small, incipient horns in Eocene ancestors to longer horns in Oligocene descendants have included two heterochronic mechanisms, hypermorphosis (extrapolation) and predisplacement (earlier onset time of horn growth). These proposed peramorphic mechanisms derive from interpretation of adult intergeneric allometries in logarithmic data spaces. Analysis of the raw (unlogged) data shows that the simple allometric model previously used is not an appropriate model for this specific problem. The heterochronic interpretations derived from them are therefore unsupported (but not disproven) by the allometries. A more appropriate allometric model for the data (full model) does not support any heterochronic interpretation. Previously unaccounted for in the heterochronic hypotheses is a complication due to body-size scaling effects on life history stage lengths. Neontological scaling patterns suggest that brontothere size increases were probably accompanied by increasing life spans and longer developmental stages. This effect broadens the types of heterochronies that may be postulated. Semiquantitative analyses comparing brontotheres with similarly sized extant ungulates show the hypothesized effect of larger size on brontothere life history stages. A scaled descendant ontogeny introduces the problem of relative vs. absolute time frames within which to view ontogenetic onset times. Thus, predisplacements, postdisplacements, or nondisplacements may be viewed as relative or absolute with respect to ancestral ontogenies. This raises a fundamental question about how development scales, which in turn affects how heterochronies are interpreted. A scaling effect suggests that brontothere horns are more likely postdisplaced in the traditional absolute time sense. Paradoxically then, while the descendant adult horn is peramorphic, its onset time may have shifted in a paedomorphic direction. Data for two Oligocene juvenile brontotheres suggest that most horn growth occurred late in their longer (i.e., descendant) ontogenies (hypermorphosis), and that the horns probably grew at faster rates (acceleration) than in Eocene taxa.

The use of clade-shape statistics, particularly center of gravity, on paraphyletic groups has been questioned since the introduction of these descriptive statistics. In addition, previous studies have found that early-arising groups of organisms are bottom-heavy in center of gravity relative to later-arising groups, leading to macroevolutionary hypotheses about the nature of diversification. Paraphyletic groups have been asserted to be inherently bottom-heavy because of preconceived ideas as to how paraphyletic group formation affects center of gravity. In turn, early-arising groups of organisms have been asserted to be bottom-heavy because they also tend to be paraphyletic, thus calling into question the biological significance of the bottom-heaviness of early-arising groups.

In this study, both computer simulations and the evolutionary history of families of mammals show that paraphyletic groups are inherently top-heavy. Simulated monophyletic clades and monophyletic families of mammals have centers of gravity near their expected positions at the midpoint of clade duration, while paraphyletic groups are significantly top-heavy.

Early-arising families of mammals are found to be inherently top-heavy, rather than bottom-heavy as found by earlier studies. This new result is likely to be due to the use of updated stratigraphic range data and different taxonomic assignments rather than to bias due to inclusion of paraphyletic groups or bias due to unequal time-unit lengths in the Cenozoic time scale.

One of the most intriguing questions in community ecology remains unanswered: Are ecological communities open assemblages with each species reacting individually to environmental change, or are they integrated units consisting of multispecies assemblages acting in concert? I address this question for marine organisms by examining the taxonomic composition and diversity of Indo-Pacific reef coral communities that have undergone repeated global change between 125 and 30 Ka (thousand years before present).

Investigation of community constancy through time relies on two critical questions: (1) Are there significant differences in taxonomic composition among communities from different times? and if not, (2) Are the observed patterns in temporal similarity significantly different from expected patterns resulting from a random sampling of the available within-habitat species pool?

Constancy in taxonomic composition and species richness of Pleistocene reef coral assemblages is maintained through a 95-k.y. interval in the raised reef terraces of the Huon Peninsula, Papua New Guinea. Fossil reef coral assemblages show limited membership in species composition despite repeated exposure to marked fluctuations in sea level (up to 120 m) and sea-surface temperatures (up to 6°). During the 95-k.y. interval, the reefs experienced nine cycles of perturbation and subsequent reassembly with similar species composition. Spatial differences in reef coral species composition were greater among the three study sites than among reefs of different ages. Thus local environmental parameters associated with riverine and terrestrial sources had a greater influence on reef coral composition than global climate and sea level changes.

The ecological dynamics of reef communities from Papua New Guinea are in marked contrast to those of Quaternary terrestrial and level bottom marine communities which appear to show unlimited community membership on both larger and smaller time scales. Differences in community assembly among ecosystems mean either that coral reefs are fundamentally different or that different ecological patterns and processes are occurring at different temporal scales.

Dinoflagellates are a major component of the marine microplankton and, from fossil evidence, appear to have been so for the past 200 million years. In contrast, the pre-Triassic record contains only equivocal occurrences of dinoflagellates, despite the fact that comparative ultrastructural and molecular phylogenetic evidence indicates a Precambrian origin for the lineage. Thus, it has often been assumed that the dearth of Paleozoic fossil dinoflagellates was due to a lack of preservation or recognition and that the relatively sudden appearance of dinoflagellates in the Mesozoic is an artifact of the record. However, new evidence from a detailed analysis of the fossil record and from the biogeochemical record indicates that dinoflagellates did indeed undergo a major evolutionary radiation in the early Mesozoic.

Dorsal sails supported by hyperelongate neural spines of dorsal vertebrae were evolved by various tetrapods, but most work on their function has centered on the pelycosaur Dimetrodon, in which the sail has generally been interpreted as a thermoregulatory structure that would permit rapid warming in the morning and cooling during the hot midday. The pelycosaur Edaphosaurus differed from other sailed tetrapods in that the neural spines supporting the sail had laterally directed tubercles or cross-bars. Past interpretations of Edaphosaurus suggested that the cross-bars were embedded in a thick fat-storage structure or extended from a thin sail to enhance its utility for intraspecific display. However, wind tunnel modeling of air flow over a thin sail with laterally projecting cross-bars supports a thermoregulatory interpretation of the sail of Edaphosaurus. The cross-bars would produce a turbulent flow, which would increase the effectiveness of convective cooling. Measurements of heat flow in an instrumented model show that cross-bars increase heat loss from the sail. The cross-bars may have enabled Edaphosaurus to thermoregulate effectively with a smaller and lower dorsal sail than would have been required without them.

Hierarchies in natural science are ranked and nested structures such that units at each rank include parts that are units at lower ranks. Hierarchies are able to render complexity tractable, by homogenizing units into collectives and by ordering collectives in ranks of increasing inclusiveness. Hierarchies contrast with positional structures, such as phylogenetic trees, for in trees all positions are occupied by the same sort of entity—there are no ranked collectives—and positions are specified by the order of appearance or precedence of the entities. In hierarchies, interactions within ranks are most important; in trees, sequences of events along branches are of primary concern. As a result hierarchies do, and trees do not, display emergent properties.

The value of the hierarchical structure can be lost when ranks are misspecified. A common error is the use of only a fraction of entities that actually occur in a rank, as when genes are considered as a rank below cells, disregarding the remaining cell contents and rendering the nature of cellular organization moot. Misspecification is also common when attributes or processes are used in ranks without indications of the physical entities to which they refer, thus losing track of the proper composition and ranking of the collectives.

The number of regenerated arms was counted on specimens of two distinct phenotypes of the stalked crinoid Endoxocrinus parrae (Gervais) from a wide bathymetric range in the Caribbean (178-723 m). In one phenotype, the sample was divided into two groups, one from shallower (< 500 m) depths, the other from deeper (≥ 500 m); in the other phenotype the group divided at 550 m. In both phenotypes, the frequency of regenerated arms is significantly higher in specimens from shallower water than in those from deeper water. If the regenerated arms in Endoxocrinus parrae were the result of sublethal predation, as previously suggested, then predation intensity is higher in shallow water than deep water. These results are consistent with the idea of the late Mesozoic marine revolution—that there has been stronger predation on various invertebrates in shallow-water environments since the late Mesozoic. The stalked crinoids may have been unable to cope with increased predation in shelf environments, and they migrated to offshore environments.

In this study I take advantage of an unusual system of fossil lakes in eastern North America to estimate the time for speciation of endemic semionotid fishes. Twenty-one species are all found in sedimentary cycle P4, the deposits of a single Early Jurassic lake, in the Towaco Formation of the Newark Basin in New Jersey. To determine the degree of endemism in the fauna from this fossil lake and estimate time for speciation, I surveyed more than 2000 museum specimens from 45 named localities in the Newark Basin and related basins of the Late Triassic to Early Jurassic Newark Supergroup. Six species not found in deposits equal in age to P4 or older are considered to be endemics, eight species occurring in older deposits presumably colonized Lake P4, and evidence for whether the remaining seven species were endemics or colonists is equivocal. The time for the formation, decline, and evaporation of Lake P4, in which P4 sediments were deposited, has been estimated at 21,000-24,000 years. Because all endemic Semionotus first occur in the first third of lake history, the estimated time for speciation of endemics is six species in 5000-8000 years. This rate is remarkably similar to that estimated for the five cichlids in Lake Nabugabo that diverged from Lake Victoria cichlids in about 4000 years.

The rate and pattern of phenotypic evolution of the endemic land-snail Mandarina chichijimana in the oceanic Bonin Islands through 40,000 years were examined by using radiocarbon-dated fossil specimens. There are drastic variations in rates and patterns of changes detected. Some characters show irregular fluctuation within a restricted range. Other characters show a rapid shift from stasis in one state to stasis in an alternative state. Because of the isolation, the limited distributions, and the presence of transitional forms, these changes are regarded as genuine evolutionary transformations within a lineage. These findings suggest that phyletic evolution is essentially irregular and punctuated.

Steneofiber, an early Miocene European beaver, showed evidence of a K-strategy model of reproduction and important morphological modifications for better adaptation to a semiaquatic way of life. At the same time, a North American branch of Castoridae developed not only a parental care system but also a series of cranial and postcranial osteological adaptations to a burrowing way of life. As the North American and the European Castoridae evolved independently from each other for at least fifteen m.y., these behavioral trends seem to have been inherent in the family for a long time and have apparently promoted, up to the present time, the spread of semiaquatic forms on the two continents; on the contrary, the burrowing branch of the Castoridae rapidly vanished.

Ptychopariid trilobites from the Marjumiid biomere of Laurentia underwent a statistically significant morphological diversification that is concordant with proposed adaptive radiations of trilobites in each of the Cambrian biomeres. An analysis of a subset consisting of the biomere's most characteristic taxa, the Asaphiscacea, Raymondinacea, and Marjumiacea, also illustrates this morphological diversification. In detail, the total data set and subset show a limited range of morphologies near the base of the biomere and a large increase in range in the upper portion of the biomere.

Regional assemblages from the Appalachians, Great Basin, and Texas were also studied to determine if they too show the larger-scale macroevolutionary patterns of trilobites from Laurentia as a whole. The regional assemblages illustrate similar, but not identical, morphological diversifications, which are also similar to the overall Laurentian pattern. Subsets of the characteristic taxa also show this diversification. These results suggest that regional assemblages can be used to investigate these larger-scale macroevolutionary patterns.

Causal mechanisms for the diversification patterns are not clear. Potential mechanisms include: (1) endemic evolution of new morphologies in Laurentia; (2) migration of new morphologies, including intra- and inter-continental migrations; and (3) environmental controls over the distribution of morphologies. Likely causes for the morphological diversification and its similarity among regions probably include aspects of all three mechanisms.

We report quantitative paleoecologic data on the large mammal assemblage preserved in lower Pleistocene deposits at Venta Micena (Orce, Granada, southeastern Spain). Taphonomic studies show that bones were collected mainly by hyaenids, which transported and deposited them near shallow dens. Differential fragmentation of major long bones was produced by hyaenas as a function of their density and marrow content. Strong selection of prey by carnivores—which preferentially killed juveniles, females, and individuals with diminished locomotor capabilities among ungulate prey species of larger body size—is indicated by (1) the abundance of remains of juvenile ungulates in relation to the average weight of adult individuals in each species, (2) attritional mortality profiles for ungulate species deduced from crown height measurements, (3) the presence of many metapodials with different osteopathologies in their epiphyses, such as arthrosis, and (4) a biased intersexual ratio of large bovids. Comparison of the frequencies with which modern African carnivores kill and scavenge ungulates from various size classes with the abundance of these size categories in the assemblage suggests that the Venta Micena hyaena (Pachycrocuta brevirostris) was a bone-cracking scavenger that fed largely on carcasses of ungulates preyed upon and partially consumed by fresh meat-eating carnivores such us saber-toothed felids (Homotherium latidens and Megantereon whitei) and wild dogs (Canis falconeri).

Principal components analysis of Upper Carboniferous (Pennsylvanian) ammonoids (all 117 genera), using 21 variables to measure shell geometry, sculpture and suture complexity, shows that following a sharp decline (∼30%) in generic diversity after the mid-Carboniferous boundary, seven morphotypes persisted throughout the Pennsylvanian (ca. 30 m.y.). Six of these were polyphyletically adopted at different times, while the seventh was monopolized by the prolecanitids, a group whose evolution accelerated during the Pennsylvanian and later gave rise to Mesozoic ammonoids. Innovations in suture geometry distinguished at least 17 of 39 (44%) Pennsylvanian ammonoid families. Average suture complexity increased almost threefold; this was achieved by various methods (lobe serration, insertion of umbilical elements, prong subdivision, lobe trifurcation, and secondary bifurcation), which were recurrent and crossed morphotype boundaries. The Pennsylvanian record supports suggestions that Paleozoic ammonoids were confined to a certain suite of basic shell geometries, showing preference for a limited number of sites in the spectrum of available morphospace. However, these morphic constraints did not, with one possible exception (the prolecanitids), control the emergence of increasing sutural complexity during the Pennsylvanian, which occurred among different lineages in all seven morphotypes.

Investigation of the evolution of calcareous nannoplankton is hindered by the extremely small size (5-10 μm) of their fossils. We introduce new technology, a scanning electron microscope connected to an image analysis system (SEM-IAS), which allows this field to be explored as never before. This system enables a host of morphocharacters to be measured and included in studies of phylogeny and evolutionary dynamics. We have applied the SEM-IAS to study the evolution of Paleocene coccolith genera Cruciplacolithus, Chiasmolithus, and Sullivania. A variety of detailed measurements have been made on over 4000 coccoliths from Deep Sea Drilling Project Site 384 in the temperate North Atlantic and Ocean Drilling Program Site 690 in the Weddell Sea off Antarctica. Our results indicate no simple relationships between morphocharacters, the shapes of all three genera are both complex and highly variable. Although most morphocharacters possess little phylogenetic significance, the areas of different shield cycles show gradual divergence between Chiasmolithus and Sullivania through the Paleocene. Change of most other morphocharacters occurs at variable rates and reversals in trends are common. Minimal correlation exists between the trends and oscillatory shape changes observed at the two sites. We conclude that these trends and oscillations represent local, transitory ecophenotypic variation of the complex form. There is little stasis in the ten-million-year record studied.