The growth rates of ammonites and extinct nautiloids have been estimated in two ways: through analyses of shell growth lines and by analyzing the patterns of oxygen isotopic values from successive septa. In both types of studies, it has been assumed that the amount of time between successive chamber formation events is approximately constant. This assumption has never been tested with living cephalopods, however. To examine this, 10 immature Nautilus pompilius and two immature N. macromphalus were maintained in a surface aquarium for a period of 1 yr and periodically radiographed. The radiographs allowed direct observation of chamber formation events and apertural shell growth. During this observational period 61 separate chamber formation events were observed in the nautiluses. The time between separate chamber formation events increased in successively produced chambers, and varied from a minimum of 2–3 wk in a specimen of 45-mm shell diameter to a maximum of 13–15 wk in a specimen of 132-mm shell diameter. Unlike interval of chamber formation, which increased during ontogeny, rate of apertural shell growth showed no observable rate increase or decrease during ontogeny prior to maturity. With the onset of maturity, as marked by the shell characteristics defined by Collins et al. (1980), apertural shell growth rates dropped markedly, and ceased coincident with the removal of the last volumes of cameral liquid in the last formed, approximated chamber. Both rate of apertural shell growth and septal spacing were affected by degree of shell breakage.

Morphological analysis of four higher taxa of fossil marine invertebrates shows that, over the history of paleontology, there is no general tendency for morphologically extreme or modal species and genera to be described preferentially early or late. Reconstructing the expected evolutionary sequences of morphological disparity that would have been estimated at various times during the past century and a half reveals features that are sensitive to sampling (for example, peak trilobite disparity in the Ordovician, peak of post-Paleozoic crinoid disparity in the Triassic, and peak blastoid disparity in the Permian), as well as more robust features (for example, increase in trilobite disparity from the Cambrian to the Ordovician, continued increase in trilobite disparity despite a drop in taxonomic diversity after the Early Ordovician, decrease in blastoid disparity from the Devonian to the Carboniferous, and increase in crinoid disparity from the Jurassic to the Cretaceous followed by decline during the Cretaceous). Although we still have much to learn about the evolution of form, in many respects our view of the history of biological diversity is mature.

Quantitative systems for describing naticid borehole position in bivalve and gastropod prey are presented. Pleistocene nassariid prey were bored at 53% of the distance up the shell and 8° to the right of the columella. A similar stereotyped position was found for Recent prey. The longitudinal shell axis and the aperture of the gastropod shell are proposed as primary cues in orienting prey for boring.

Evolutionary stasis has often been explained by stabilizing selection, intrinsic constraints, or, more recently, by spatially patterned population dynamics. To distinguish which of these mechanisms explains a given case of stasis in the fossil record, stasis must first be rigorously documented in a high-resolution stratigraphic time series of fossil specimens. Furthermore, past studies of evolutionary mode in fossil mammalian lineages have often been limited to univariate traits (e.g., molar crown area). It is reasonable to assume that tooth shape, a multivariate trait, reflects important additional aspects of tooth form and function. Here we present the results of a geometric morphometric analysis of the lower dentition of the Paleocene-Eocene condylarth species Ectocion osbornianus collected from the Bighorn and Clarks Fork Basins of northwestern Wyoming. Tooth margin shape, cusp configuration, and shearing crest shape were digitized for the last lower premolar, p4, and for two lower molars, m1 and m3. Multivariate statistical tests of evolutionary mode were used to analyze the change in shape variance over time in addition to the magnitude and direction of shape change. Test results characterize the shape time series as consisting of counteracting changes with less change than expected under a random walk (i.e., stasis). The temporal structure of shape variance implies that the sampled E. osbornianus most likely represent a single population, which is not concordant with the population dynamic mechanism of stasis. Stabilizing selection and/or intrinsic constraints remain as the mechanisms that could explain stasis in the lower dental shape of E. osbornianus despite the variable environmental conditions of the Paleocene–Eocene.

The end-Permian mass extinction, the largest extinction of the Phanerozoic, led to a severe reduction in both taxonomic richness and ecological complexity of marine communities, eventually culminating in a dramatic ecological restructuring of communities. During the Early Triassic recovery interval, disaster taxa proliferated and numerically dominated many marine benthic invertebrate assemblages. These disaster taxa include the bivalve genera Claraia, Unionites, Eumorphotis, and Promyalina, and the inarticulate brachiopod Lingularia. The exact nature and extent of their dominance remains uncertain. Here, a quantitative analysis of the dominance of these taxa within the fossil communities of Panthalassa and Tethys benthic realms is undertaken for the stages of the Early Triassic to examine temporal and regional changes in disaster-taxon dominance as recovery progresses. Community dominance and disaster-taxon abundance is markedly different between Panthalassic and Tethyan communities. In Panthalassa, community evenness is low in the Induan stage but increases significantly in the Smithian and Spathian. This is coincident with a significant decrease in the relative abundance and occurrence frequency of the disaster taxa, most notably of the low-oxygen-affinity taxa Claraia and Lingularia. While the disaster taxa are present in post-Induan assemblages, other taxa, including two articulate brachiopod genera, outrank the disaster taxa in relative abundance. In the Tethys, assemblages are generally more even than contemporaneous Panthalassic assemblages. We observe an averaged trend toward more even communities with fewer disaster taxa in both Panthalassic and Tethyan assemblages over time.

Scleractinian corals have two fundamentally different life strategies, which can be inferred from morphological criteria in fossil material. In the non-photosymbiotic group nutrition comes exclusively from heterotrophic feeding, whereas the photosymbiotic group achieves a good part of its nutrition from algae hosted in the coral’s tissue. These ecologic differences arose early in the evolutionary history of corals but with repeated evolutionary losses and presumably also gains of symbiosis since then. We assessed the biodiversity dynamics and environmental occupancy of both ecologic groups to identify times when the evolutionary losses of symbiosis as inferred from molecular analyses might have occurred and if these can be linked to environmental change. Two episodes are likely: The first was in the mid-Cretaceous when non-symbiotic corals experienced an origination pulse and started to become more common in deeper, non-reef habitats and on siliciclastic substrates initiating a long-term offshore trend in occupancy. The second was around the Cretaceous/Paleogene boundary with another origination pulse and increased occupancy of deep-water settings in the non-symbiotic group. Environmental factors such as rapid global warming associated with mid-Cretaceous anoxic events and increased nutrient concentrations in Late Cretaceous–Cenozoic deeper waters are plausible mechanisms for the shift. Turnover rates and durations are not significantly different between the two ecologic groups when compared over the entire history of scleractinians. However, the deep-water shift of non-symbiotic corals was accompanied by reduced extinction rates, supporting the view that environmental occupancy is a prominent driver of evolutionary rates.

Comparisons between modern death assemblages and their source communities have demonstrated fidelity to species diversity across a variety of environments and taxonomic groups. However, differential species preservation and collection (including body-size bias) in both modern and fossil death assemblages may still skew the representation of other important ecological characteristics. Here, we move beyond live-dead taxonomic fidelity and focus on the recovery of functional ecology (how species interact with their ecosystem) at the community level for a diverse non-volant mammal community (87 species; Amboseli, Kenya). We use published literature to characterize species, using four functional traits and their associated categorical attributes (i) dietary mode (11 attributes; e.g., browser, grazer), (ii) preferred feeding habitat (16 attributes; e.g., grassland, woodland), (iii) preferred sheltering habitat (17 attributes; e.g., grassland, underground cavity), and (iv) activity time (7 attributes; e.g., diurnal, nocturnal, nocturnally dominated crepuscular). For each functional ecological trait we compare the death assemblage's recovered richness and abundance structure of constituent functional attributes with those of the source community, using Jaccard similarity, Spearman's rho, and the Probability of Interspecific Encounter (evenness). We use Monte Carlo simulations to evaluate whether these empirical comparisons are significantly different from expectations calculated from randomized sampling of species from the source community. Results indicate that although the Amboseli death assemblage is significantly overrepresented by large-bodied species relative to the Amboseli source community, it captures many functional dimensions of the ecosystem within expectations of a randomized collection of species. Additional resampling simulations and logistic regressions further illustrate that the size bias inherent to the Amboseli death assemblage is not a major driver of deviations between the functional ecological properties of the death assemblage and its source community. Finally, the Amboseli death assemblage also enhances our understanding of the mammal community by adding nine species and two functional attributes previously unknown from the ecosystem.

Evidence that can be used to interpret the life habits of extinct organisms usually takes three forms: functional analysis, analogy with living organisms, and geological evidence. Independent quantitative tests for habit are rarely available. A theory of optimum eye design originally derived for living aquatic arthropods provides quantitative data that are used to test previous suppositions about the life habits of two Ordovician pelagic trilobites: that the telephinid trilobite Carolinites was epipelagic while the cyclopygid Pricyclopyge was mesopelagic. Optimum compound eye design theory uses measured lens diameters and interommatidial angles to determine the “eye parameter” (p), which can be used to gauge approximate optimum level of illumination for the eyes of these trilobites. The eye parameter provides an independent test for their relative paleobathymetry. Values of the eye parameter measured in the dorso-ventral direction across two eyes of Carolinites killaryensis utahensis were found to have medians of 2.13 and 3.24. Values measured in the antero-posterior direction have medians of 3.17 and 4.86 for the two eyes. Values measured in the dorso-ventral direction across two eyes of Pricyclopyge binodosa have medians of 4.23 and 4.98, while values measured in the antero-posterior direction have medians of 7.06 and 8.31. Eye parameters are higher in Pricyclopyge than in Carolinites, the difference statistically significant at p = 0.05. The eyes of Pricyclopyge are optimally designed for lower levels of illumination than are those of Carolinites. This accords with the previous interpretations of the former trilobite as mesopelagic and the latter as epipelagic.

Larger body size has long been assumed to correlate with greater risk of extinction, helping to shape body-size distributions across the tree of life, but a lack of comprehensive size data for fossil taxa has left this hypothesis untested for most higher taxa across the vast majority of evolutionary time. Here we assess the relationship between body size and extinction using a data set comprising the body sizes, stratigraphic ranges, and occurrence patterns of 9408 genera of fossil marine animals spanning eight Linnaean classes across the past 485 Myr. We find that preferential extinction of smaller-bodied genera within classes is substantially more common than expected due to chance and that there is little evidence for preferential extinction of larger-bodied genera. Using a capture–mark–recapture analysis, we find that this size bias of extinction persists even after accounting for a pervasive bias against the sampling of smaller-bodied genera within classes. The size bias in extinction also persists after including geographic range as an additional predictor of extinction, indicating that correlation between body size and geographic range does not provide a simple explanation for the association between size and extinction. Regardless of the underlying causes, the preferential extinction of smaller-bodied genera across many higher taxa and most of geologic time indicates that the selective loss of large-bodied animals is the exception, rather than the rule, in the evolution of marine animals.

The earliest Paleocene record of calcareous nannoplankton presents a unique opportunity to understand the evolutionary recovery of life from mass extinction. Nannoplankton were devastated at the Cretaceous/Paleogene boundary and their subsequent recovery can be studied in great detail because of their abundance in sediments, continuous stratigraphic occurrence, and near global distribution. Here we determine when and where new species of nannoplankton originated and how they dispersed following the Cretaceous/Paleogene mass extinction. Initially, we focus our efforts on North Pacific and South Atlantic deep sea sites with orbital age control to compare the precise timing and dynamics of the recovery between the locations. We then broaden our investigation to six sites from different basins and a variety of environments to study global patterns of the initial recovery. Our results show that many taxa in key Paleogene lineages originated in the North Pacific Ocean and that assemblages comprised primarily of new Paleogene taxa were not observed at other sites for several hundred thousand years. Survivors that were adapted to eutrophic post extinction conditions rapidly expanded in Southern Hemisphere sites where they dominated assemblages for most of the initial recovery. We therefore hypothesize that groups of survivors formed regionally incumbent assemblages in the Southern Hemisphere that limited diversification and dispersal of new Paleogene taxa. The end of survivor dominance correlates to the recovery of the biologic pump and subsequent decrease in surface ocean nutrient concentration 300–400 Kyr after the boundary. Only after survivors were removed did new Paleogene nannoplankton assemblages become abundant globally. Our results indicate that competition from regionally incumbent survivors was as an important control on the K/Pg recovery of nannoplankton.

Much of what is known about the long-term history of biodiversity and rates of taxonomic evolution in the fossil record derives from literature-based compilations of fossil stratigraphic ranges. It has been suggested that taxonomic and stratigraphic errors in these compilations are randomly distributed and, therefore, introduce no significant bias to macroevolutionary patterns. Here we compare a new, comprehensive global database of Ordovician and Early Silurian crinoids to Sepkoski's global genus compendium.

Approximately 44% of the crinoid genera resolved to substage in Sepkoski's compendium are taxonomically inaccurate (i.e., invalid, nomina dubia, or column genera) or have incorrect first and/or last occurrences. Errors in Sepkoski's compendium result from incomplete coverage of existing taxonomic work and incorrect stratigraphic correlations that, in some cases, are propagated throughout the taxonomic literature. Stratigraphic range errors are nonrandomly distributed among substages in Sepkoski's compendium. The result is underestimated richness in the Early Silurian and significantly overestimated rates of extinction in the Late Ordovician. There is no similar bias in Sepkoski's substage origination rates for crinoids.

At the stage-level of temporal resolution, Sepkoski's crinoid data are more accurate. In this case, only 32% of the compendium's crinoid genera contain some stratigraphic or taxonomic inaccuracy. However, errors still result in incorrect macroevolutionary patterns, particularly with respect to rate of origination in the Ashgill, which is significantly underestimated in Sepkoski's compendium. Genera described since the completion of Sepkoski's compendium have had relatively little effect on estimated rates of evolution at both stage and substage resolution.

These results suggest that macroevolutionary patterns among some taxa in Sepkoski's compilation may be significantly influenced by nonrandomly distributed taxonomic inaccuracies and stratigraphic range errors. In the case of the apparent end-Ordovician mass extinction among crinoids, the revised history reveals a dramatically reduced role for extinction at the substage-level of temporal resolution. At the stage level, Sepkoski's original compilation strongly exaggerates the excess of extinction over origination in the Ashgill. Although biases inherent in the stratigraphic record remain unaccounted for, removing taxonomic and stratigraphic errors in Sepkoski's compendium substantially changes our understanding of the nature of large-scale biotic change for an important Paleozoic taxon during the end-Ordovician.

In cheilostome bryozoans with rigidly arborescent growth habits, resistance to breakage under forces generated by flowing water or collision with moving objects depends on the strength and design of supporting skeletal parts. To investigate the abilities of modern and Tertiary cheilostomes to resist breakage, we measured bending strength in fresh, preserved, and fossil material; measured drag on actual and model colonies; and calculated stress within colonies and breaking values under concentrated and uniform loads. Among nine modern, five Oligocene, and four Paleocene species, inferred live bending strength (24–85 MNm−2) and stiffness (42–65 GNm−2) appear to be species-specific properties overlapping those of similar mineral-organic composite skeletons of Mollusca. Unlike those of Mollusca, cheilostome skeletons appear isotropic in bending, with strength not clearly related to microstructure or composition. Bending strength and morphologic disposition of skeletal material combine to produce a wide range of abilities to resist breaking. At early growth stages, almost all species appear highly resistant; at later ones, some break at velocities <0.2 m sec−1 or concentrated loads <2 g, whereas others remain unbroken at velocities >2 m sec−1 or concentrated loads >100 g. A negative correlation between strength and resistance indicates that design is the more important factor in the abilities of these bryozoans to withstand forces of these kinds. An apparent trend toward more resistant designs from Paleocene to modern species is related chiefly to increasing rates at which branches thicken toward the colony base. The consequent change in design may even have permitted modern species to use weaker skeletal material while increasing their overall resistance.

The cranial structure of anteosaurid and many tapinocephalid dinocephalians became modified in a manner consistent with Geist's hypothesis that they used their heads for pushing and ramming during intraspecific combat. These modifications are most pronounced in certain tapinocephalids by the evolution of a strong dorsal head shield supported by a massive arch network suitable for receiving and supporting blows delivered to the dorsal surface of the head. The position of the occipital condyle reduced the torque created by such blows at the craniocervical joint. Evidence also indicates that the head was reoriented into a position suitable for butting. The cranial architecture displayed by dinocephalians suspected of headbutting differs from that of living mammalian rammers. The differences can be directly attributed to the modification, in the former, of a reptilian skull with its relatively unexpanded braincase into a ramming instrument.

The known Cretaceous formicoids are better interpreted from morphological evidence as forming a single subfamily, the Sphecomyrminae, and even a single genus, Sphecomyrma, rather than multiple families and genera. The females appear to have been differentiated as queen and worker castes belonging to the same colonial species instead of winged and wingless solitary females belonging to different species. The former conclusion is supported by the fact that the abdomens of workers of modern ant species and extinct Miocene ant species are smaller relative to the rest of the body than is the case for modern wingless solitary wasps. The wingless Cretaceous formicoids conform to the proportions of ant workers rather than to those of wasps (Figs. 1–2) and hence are reasonably interpreted to have lived in colonies.

The Cretaceous formicoids are nevertheless anatomically primitive with reference to modern ants and share some key traits with nonsocial aculeate wasps. They were distributed widely over Laurasia and appear to have been much less abundant than modern ants.

Particle size reduction is a primary means of improving efficiency in herbivores. The mode of food particle size reduction is one of the main differences between herbivorous birds (gizzard) and mammals (teeth). For a quantitative comparison of the efficiency of food comminution, we investigated mean fecal particle sizes (MPS) in 14 herbivorous bird species and compared these with a data set of 111 non-ruminant herbivorous mammal species. In general MPS increased with body mass, but there was no significant difference between birds and mammals, suggesting a comparable efficiency of food processing by gizzards and chewing teeth. The results lead to the intriguing question of why gizzard systems have evolved comparatively rarely among amniote herbivores. Advantages linked to one of the two food comminution systems must, however, be sought in different effects other than size reduction itself. In paleoecological scenarios, the evolution of “dental batteries,” for example in ornithopod dinosaurs, should be considered an advantage compared to absence of mastication, but not compared to gizzard-based herbivory.

In North America, hipparion horses consisted of four distinct genera, Hipparion, Neohipparion, Nannippus, and Cormohipparion, known from the medial Miocene to the late Pliocene, ca. 15.5–2 ma ago. The speciation mode is determined for 10 of the 16 valid hipparion species; 50% (5) seem to have resulted from anagenesis and 50% (5) from cladogenesis. Roughly contemporaneous species of the four hipparion genera seem to proceed through similar evolutionary stages of cranial and dental characters. The mean hipparion species longevity is 3.3 ma (N = 16); the mean generic longevity is 8.4 ma (N = 4). Only two species become extinct in less than 2 ma; extinction occurs at a rate of ca. 470 μmacarthurs for species with durations between 2 and 5 ma. For selected dental characters, mean evolutionary rates (for the 16 species) were between .08 darwins (d) and .03 d with crown height evolving most rapidly. Despite the commonly held notion that fossil horses evolved rapidly, these data suggest normal or average (horotelic) evolution for hipparions, which is not surprising because they were already established in the grazing adaptive zone during their history.

The foraging paradigm of trace fossil theory has historically accorded random behavior to non-food-limited deposit-feeders and non-random behavior to food-limited feeders. A series of randomness measures derived from empirical modeling, simulation modeling, stochastic modeling and probability theory applied to foraging patterns observed in deep-sea bottom photographs from the Arctic and Antarctic yielded a behavioral continuum of increasing non-randomness. A linear regression of trace positions along the continuum to bathymetric data did not substantiate the optimal foraging efficiency-depth dependence model of trace fossil theory, except that all traces exhibited a greater optimization than that of simulated random foraging. It is hypothesized that optimization as evidenced by non-random foraging strategies represents maximization of the cost/benefit ratio of resource exploitation to risk of predation and that individual foraging patterns reflect an exploration response to the morphometry of a patchily distributed food resource. Differential predation and competition may account for the co-occurrence of random and non-random strategies within the same bathymetric zone.

A late Miocene population of Neohipparion cf. leptode from the Love Bone Bed of Florida was found to have 13 discrete annual age classes based on eruption sequences and tooth wear. The large sample size of individuals (minimum number = 229) allowed the estimation of standard population parameters, including age-specific mortality rates. The average age of death for a newborn was 3.5 years, but those individuals that survived the 64% juvenile mortality occurring during the first two years lived an average of 8.0 years. The potential longevity of this species of Neohipparion had not increased beyond that of known samples of Merychippus, despite increased crown height. The paleoenvironment of the collecting site was a wooded grassland savanna with annual wet and dry seasons. The Neohipparion population migrated into the area during the dry season but left in the wet season to give birth away from the collecting site.

Experienced workers in a field are unlikely to change their assessment of basic philosophical issues. Einstein for example never accepted the indeterminacy required by the Heisenberg uncertainty principle, despite the urgings of Max Born and virtually all others. Similarly even earlier, some older workers had refused to accept the young Einstein's theories. Now if issues in physics are not open and shut, they are even less so in paleontology. Possibly it is useful to probe the underlying basic philosophical background to our discipline. The purpose of the present article is to indicate that the inductive, deterministic approaches which have been used almost exclusively in paleontology have stringent limitations. For some types of problems, deductive stochastic processes are more interesting. If we can make the distinction of ‘few’ versus ‘many,’ then it is quite easy to consider deterministic explanations for the individual cases (the movement of individual molecules) but to reserve stochastic explanations for the ensembles of events (the movement of molecules too numerous to count).

A rate of extinction must specify both the amount of taxonomic change and the duration of that change. A consistent means of temporal measurement must be used to establish the duration. Terms used to describe the extinction, like catastrophic and gradual, should be quantitatively defined in relation to this framework.

Resolving rates of extinction in the stratigraphic record is limited by (1) the precision of chronostratigraphic correlations between individual sections and (2) the temporal completeness of litho- and biostratigraphic records in those sections. In this study, temporal completeness is estimated in eight of the best-known fluvial and pelagic sections spanning the K-T boundary. Temporal standardization is provided by correlations to the geomagnetic polarity time scale. A review of the literature documents lithologic criteria that might be used to infer the presence of a hiatus of some length at the biostratigraphically recognized K-T boundary. Rather than rejecting the presence of such gaps, this study argues that a hiatus of some length does exist and tries to estimate both a maximum limit for its duration and the probability that it represents a given duration below that limit.

Pelagic sections are probably more complete than fluvial ones. The section at Caravaca, Spain, can be expected to be the most complete, probably preserving sediment during each 10,000-yr interval of Chron 29R. The section in the San Juan Basin, New Mexico, is expected to be the most complete fluvial section, probably preserving sediment during each 100,000-yr interval of 29R.

Results indicate that our best-known marine and terrestrial sections spanning the K-T boundary should not be expected to document biologically catastrophic rates of extinction. A sufficiently precise means of global correlation that is independent of biostratigraphy and causal hypotheses is still unavailable, and it is very unlikely that the sections examined are complete at the 100-yr or biologically catastrophic level of precision. So, although catastrophic amounts of extinction might have occurred during the K-T transition, it seems unlikely that we can distinguish episodes of extinction lasting 100 yr or less from episodes lasting as long as 100,000 yr. Consequently, acceptance of catastrophic hypotheses based on these stratigraphic records seems improbably optimistic at this time.