The Paleozoic and post-Paleozoic radiations of crinoids present an opportunity to explore genomic and ecological explanations for patterns of morphologic diversification. Analysis of discrete-character data that cover the principal features of the crinoid skeleton shows that both Paleozoic and post-Paleozoic increases in morphological disparity were abrupt; this is consistent with rapid exploitation of open ecological opportunities in both cases. For the post-Paleozoic, this result is sensitive to some aspects of data analysis and sampling, so it cannot be regarded as unequivocal. The deceleration in morphological diversification within each radiation is consistent with an observed decline in rates of taxonomic origination as well as with the attainment of functional or structural limits. Despite these similarities in the two radiations, Paleozoic crinoids exploited a wider range of morphological designs than did their post-Paleozoic successors. Post-Paleozoic crinoids exploited a wide range of ecological strategies despite being stereotyped in many aspects of form. This difference between the radiations is consistent with an increase in the rigidity of genetic and developmental systems. The range of post-Paleozoic designs is not in essence a subset of the Paleozoic spectrum. The two radiations resulted in morphological distributions that are largely nonoverlapping, perhaps reflecting a different range of ecological strategies.

Patterns of bipolar or antitropical distributions occur in a diverse array of marine invertebrate, vertebrate, and plant groups in the eastern Pacific Ocean. Available geologic and paleontological evidence does not support vicariance as a process in the creation of these distributions but instead favors biotic interchange between hemispheres. Moreover, the timing of these events suggests several breaches (both northward and southward) of the tropics rather than a single event. The fossil record is extremely important in delimiting potential hypotheses and allowing correlation with vicariance events. The congruence of some interchanges with major regional tectonic activity and others with Pleistocene glaciations is not surprising and argues for a plurality of mechanisms. Extinction of endemic taxa following interchange among marine invertebrates is rare, and none of the antitropical distributions reviewed here suggests that the arrival of a taxon in the adjoining hemisphere resulted in the extinction of an endemic taxon. Instead, interchange and endemic taxa coexist. In contrast to the extinction patterns, the patterns of radiations are extremely diverse with some immigrant taxa undergoing remarkable radiations, whereas other taxa are represented by single species. Temperate nearshore rocky communities in both the northern and southern hemispheres appear to be mosaics of species that share common ancestry (because of interchange), are cosmopolitan, and have independent origins within the region. Although some communities appear to be organized around products of interchange (e.g., kelp forests of California and Chile), only the taxa have immigrated; linkages and interactions between species are independent and locally derived.

Modern marine plankton communities include a broad diversity of metazoans that are suspension-feeding or micropredatory as adults. Many benthic marine species have larval stages that reside, and often feed, in the plankton for brief to very long periods of time, and most marine benthic communities include large numbers of suspension-feeders. This has not always been the case. Cambrian benthic communities included relatively few suspension-feeders. Similarly, there were few metazoan clades represented in the plankton, either as adult suspension-feeders or as larvae. Review of the fossil record suggests that the diversification of the plankton and suspension-feeding marine animals began in the Late Cambrian and continued into the Ordovician. These changes were accompanied by, and probably influenced, concurrent major changes in the marine realm, including an increase in tiering within benthic communities, the replacement of the Cambrian fauna by the Paleozoic fauna, and a general taxonomic diversification. The ultimate cause of these changes is uncertain, but it appears likely that the plankton was and is a refuge from predation and bioturbation for adults and larvae alike. The expansion in plankton biomass thus provided increased ecological opportunities for suspension-feeders in the plankton and benthos.

The degree of perceived taxonomic change in various lineages may be directly related to their general morphologic complexity: more complex forms appear to change more rapidly. “Rates of evolution” as customarily reported by paleontologists may therefore be a poor indication of evolutionary changes in the underlying genome. Two approaches were used to examine this problem. (1) We have estimated the degree of morphologic complexity by using the number of descriptive terms per genus, and per family, for 12 major groups of animals. Three general levels of complexity occur: (i) gastropods, bivalves and ectoprocts have relatively few terms; (ii) echinoids, foraminiferans, ostracodes, nautiloids, corals, trilobites, and brachiopods have an intermediate number of terms; (iii) mammals and ammonoids appear to have a relatively large number of terms. These 3 levels of complexity also increase in rate of taxonomic turnover; i.e., an increasing rate of evolution. (2) Using a cluster analysis based on morphologic similarity, we grouped 200 lineages of a computer-generated phylogenetic sequence according to 4 phenetic bases: 3, 5, 10 and 20 morphologic traits. Groups based on a few characters are longer lived and are commonly polyphyletic in comparison with groups based on many characters. In both the real world and the computer simulation, the bias of differential morphologic complexity may account for the observation that “only complicated animals evolve.” Most paleontologic studies of the “rate of evolution” may tell us more about morphologic complexity than about evolutionary rates of genomes.

Late Cretaceous dinosaur eggshells from southern France and the Spanish Pyrenees, presumably belonging to the sauropod Hypselosaurus priscus Matheron, are almost exclusively composed of primary calcite. Besides normal development of these eggshells, there appear two kinds of pathologic tendencies: bi- or multi-shells (infrequent), and shells with a reduced thickness (increasing in frequency until, in the uppermost horizon, they represent more than 90% of the sample). The extinction of the species is attributed primarily to the consequences of thinning of the eggshells.

The physiological mechanisms producing pathologic dinosaur eggshells are evaluated in the light of homologous phenomena occurring in living birds and reptiles. On this basis, it is concluded that in the late Maastrichtian populations of “Hypselosaurus,” pathologic eggshells were caused by hormonal imbalances of the vasotocin and of the estrogen levels. On the same basis it is postulated that the teratological shell repetition led to embryo suffocation and that the pathological reduction in shell thickness caused shell breakage and dehydration of the embryo. The lethal results are evident from the frequent absence of “resorption craters” in the mammillary knobs of pathologic shells, a fact which indicates either lack of fertilization of the eggs or the perishing of the embryo prior to the calcification of its skeletal bones. A change in environmental conditions is the ultimate factor which caused hormonal imbalances and extinction. Such a change is indicated by a shift of the mean oxygen isotopic composition (δ18O) of eggshell carbonates from −0.6%o to −5.3%o, and by changes in Sr. Information of palaeo-climate is primarily derived from eggshells of living birds and reptiles. The correlation between temperature and oxygen isotopic composition of waters (and related carbonates) is less distinct than for marine carbonates. δ13C ranges from −16.5 to −4.5 of eggshells of extant species indicate food from “normal” C3 metabolism and from C4 metabolism of plants in a dry climate. “Hypselosaurus” populations probably consumed “normal” C3 plants. Using isotopic calibration of eggshell carbonates for the interpretation of δ13C and δ18O values of dinosaur eggshells, a slight change from higher to lower temperatures or a change from a dry to a more humid climate during the time from Lower (and Middle) to Late Maastrichtian can be assumed. The latter explanation is favored because the exceptionally high Sr in the Early Maastrichtian eggshells could be a potential indicator of co-existing evaporites.

Leaf mass per area (MA) is a central ecological trait that is intercorrelated with leaf life span, photosynthetic rate, nutrient concentration, and palatability to herbivores. These coordinated variables form a globally convergent leaf economics spectrum, which represents a general continuum running from rapid resource acquisition to maximized resource retention. Leaf economics are little studied in ancient ecosystems because they cannot be directly measured from leaf fossils. Here we use a large extant data set (65 sites; 667 species-site pairs) to develop a new, easily measured scaling relationship between petiole width and leaf mass, normalized for leaf area; this enables MA estimation for fossil leaves from petiole width and leaf area, two variables that are commonly measurable in leaf compression floras. The calibration data are restricted to woody angiosperms exclusive of monocots, but a preliminary data set (25 species) suggests that broad-leaved gymnosperms exhibit a similar scaling. Application to two well-studied, classic Eocene floras demonstrates that MA can be quantified in fossil assemblages. First, our results are consistent with predictions from paleobotanical and paleoclimatic studies of these floras. We found exclusively low-MA species from Republic (Washington, U.S.A., 49 Ma), a humid, warm-temperate flora with a strong deciduous component among the angiosperms, and a wide MA range in a seasonally dry, warm-temperate flora from the Green River Formation at Bonanza (Utah, U.S.A., 47 Ma), presumed to comprise a mix of short and long leaf life spans. Second, reconstructed MA in the fossil species is negatively correlated with levels of insect herbivory, whether measured as the proportion of leaves with insect damage, the proportion of leaf area removed by herbivores, or the diversity of insect-damage morphotypes. These correlations are consistent with herbivory observations in extant floras and they reflect fundamental trade-offs in plant-herbivore associations. Our results indicate that several key aspects of plant and plant-animal ecology can now be quantified in the fossil record and demonstrate that herbivory has helped shape the evolution of leaf structure for millions of years.

Previous discussions of mass extinction mechanisms generally focused on circumstances unique to each event. However, some have proposed that extensive volcanism combined with bolide impact may offer a general mechanism of mass extinction. To test this hypothesis we compared generic extinction percentages for 73 stages or substages of the Mesozoic and Cenozoic. We found that the highest frequency of intervals with elevated extinction occurred when continental flood basalt volcanism and bolide impact co-occurred. In contrast, neither volcanism nor impact alone yielded statistically elevated extinction frequencies. Although the magnitude of extinction was uncorrelated with the size of the associated flood basalt or impact structure, crater diameter did correlate with extinction percentage when volcanism and impact coincided. Despite this result, case-by-case analysis showed that the volcanism-impact hypothesis alone cannot explain all intervals of elevated extinction. Continental flood volcanism and impact share important ecological features with other proposed extinction mechanisms. Impacts, like marine anoxic incursions, are pulse disturbances that are sudden and catastrophic, and cause extensive mortality. Volcanism, like climate and sea level change, is a press disturbance that alters community composition by placing multi-generational stress on ecosystems. We propose that the coincidence of press and pulse events, not merely volcanism and impact, is required to produce the greatest episodes of dying in Phanerozoic history.

Paleoecologists have long sought to obtain estimates of the sizes of extinct populations. However, even in ideal cases, accurate counts of individuals have been hampered by the fact that many organisms disarticulate after death and leave their remains in the form of multiple, separated parts. We here analyze the problem of estimating numbers of individuals from collections of parts by developing a general counting theory that elucidates the major contributing variables. We discover that the number of unique individuals of a particular species that are represented in a fossil collection can be described by an intricate set of relationships among (1) the number of body parts that were recovered, (2) the number of body parts that were possessed by organisms belonging to that species, and (3) the number of individuals of that species that served as the source of the parts from which the paleontological sample was obtained (the size of the “sampling domain”). The “minimum number of individuals” and “maximum number of individuals” methods currently used by paleontologists to count individuals emerge as end members in our more general counting theory. The theory shows that the numbers of individuals of a species that are represented in a sample of body parts is fully tractable, at least in a theoretical sense, in terms of the variables just mentioned. The bad news is that the size of the “sampling domain” for a species can never be known exactly, thus placing a very real limit on our ability to count individuals rigorously. The good news is that one can often make a reasonable guess regarding the size of the sampling domain, and can therefore make a more thoroughly informed choice regarding how to estimate numbers of individuals. By isolating the variables involved in determining the numbers of individuals in paleontological samples, we are led to a better appreciation of the limits, and the possibilities, that are inherent in the fossil record.

The borophagine canids were bone-cracking scavengers in the Miocene-Pleistocene of North America. In this they parallel the Recent hyenas. This paper analyzes the borophagine adaptation in relation to that of hyaenids, using Osteoborus cyonoides as an example. The emphasis during canid evolution on the posterior molars, which is a derived condition, created a constraint on the adaptation of borophagines. This constraint meant that the borophagines used P4/4 as bone-cracking teeth, whereas hyaenids use P3/3. The latter adaptation has the advantage of separating the bone-cracking teeth from the meat-cutting portion of the dentition, thereby allowing a dual purpose dentition in hyaenids. In borophagines, no such dual purpose was possible, and it is suggested that they were closer to obligate bone-cracking scavengers than Recent hyaenids. Other than the evolution of a specialized bone-cracking tooth, the borophagines adapted to bone cracking by evolving a vaulted and strengthened skull for the dissipation of the strong forces generated during bone cracking. In this they again parallel the hyaenids. Evolution within borophagines involved an elaboration of patterns already set at the group's inception, creating an evolutionary trend which was mediated by the constraint on the bone-cracking morphology. This trend may be due to selection or sorting, or may, under certain assumptions, be stochastic. Other evolutionary trends may also be epiphenomena of constraints that lock morphological evolution.

As Van Valen has demonstrated, the taxonomic survivorship curve is a valuable means of investigating extinction rates in the fossil record. He suggested that within an adaptive zone, related taxa display stochastically constant and equal extinction rates. Such a condition is evidenced by straight survivorship curves for species and higher taxa. Van Valen's methods of survivorship analysis can be improved upon and several suggestions are presented. With proper manipulation of data, it is possible to pool the information from extinct and living taxa to produce a single survivorship curve and therefore a single estimate of extinction rate. If extinction rate is constant at the species level (producing a straight survivorship curve), higher taxa in the same group should be expected to have convex survivorship curves. The constancy of extinction rates (here termed Van Valen's Law) can and should be tested rigorously. Several methods are available, of which the Total Life method of Epstein is particularly effective.

The rapid ecological expansion of grasses with C4 photosynthesis at the end of the Neogene (8–2 Ma) is well documented in the fossil record of stable carbon isotopes. As one of the most profound vegetation changes to occur in recent geologic time, it paved the way for modern tropical grassland ecosystems. Changes in CO2 levels, seasonality, aridity, herbivory, and fire regime have all been suggested as potential triggers for this broadly synchronous change, long after the evolutionary origin of the C4 pathway in grasses. To date, these hypotheses have suffered from a lack of direct evidence for floral composition and structure during this important transition. This study aimed to remedy the problem by providing the first direct, relatively continuous record of vegetation change for the Great Plains of North America for the critical interval (ca. 12–2 Ma) using plant silica (phytolith) assemblages.

Phytoliths were extracted from late Miocene-Pliocene paleosols in Nebraska and Kansas. Quantitative phytolith analysis of the 14 best-preserved assemblages indicates that habitats varied substantially in openness during the middle to late Miocene but became more uniformly open, corresponding to relatively open grassland or savanna, during the late Miocene and early Pliocene. Phytolith data also point to a marked increase of grass short cells typical of chloridoid and other potentially C4 grasses of the PACMAD clade between 8 and 5 Ma; these data suggest that the proportion of these grasses reached up to ∼50–60% of grasses, resulting in mixed C3-C4 and highly heterogeneous grassland communities by 5.5 Ma. This scenario is consistent with interpretations of isotopic records from paleosol carbonates and ungulate tooth enamel. The rise in abundance of chloridoids, which were present in the central Great Plains since the early Miocene, demonstrates that the “globally” observed lag between C4 grass evolution/taxonomic diversification and ecological expansion occurred at the regional scale. These patterns of vegetation alteration imply that environmental change during the late Miocene-Pliocene played a major role in the C3-C4 shift in the Great Plains. Specifically, the importance of chloridoids as well as a decline in the relative abundance of forest indicator taxa, including palms, point to climatic drying as a key trigger for C4 dominance.

The enigmatic fossil Wiwaxia corrugata is organically preserved in the Burgess Shale (Middle Cambrian, British Columbia) and is therefore extractable by careful acid maceration of the mineralic matrix. High magnification transmitted light microscopy and SEM of macerated Wiwaxia sclerites reveal a substantial amount of previously undescribed structural and microstructural detail. Anatomical and histological comparison with modern organisms indicates that Wiwaxia sclerites are polychaete paleae (flattened setae) and that Wiwaxia was a jawed annelid broadly related to the extant polychaete families Chrysopetalidae and/or Aprhoditidae (Palmyra). Canadia spinosa, an uncontested fossil polychaete from the same beds, shows a paleal microstructure identical to that of Wiwaxia, as well as a closely comparable gross anatomy and taphonomic grade. The unique combination of taxonomically significant characters shared by Wiwaxia and Canadia suggest that they are more closely related to each other than either is to any other fossil or extant polychaete. Thus they constitute a separate superfamily, Canadiacea superfam. nov., in the order Phyllodocida.

The classic biometrical study of phyletic evolution in Kosmoceras (Brinkmann 1929) is evaluated using unpublished raw data provided by Professor Brinkmann. Most morphological characters show statistically significant changes over time yet it is difficult to provide an unequivocal biological interpretation for these changes. In a few cases, runs tests indicate that evolution was nonrandom in the sense that fewer reversals in the direction of evolution occurred than would be predicted from a null hypothesis based on a random walk. These cases suggest persistence of natural selection regimes for fairly long periods of time. In other cases, and with other kinds of testing, the random walk model cannot be rejected although failure to reject the hypothesis does not justify its acceptance! Thus, the contribution of random factors (either genetic drift or selection in a randomly changing environment) cannot be assessed with confidence. It is problematical also whether the Kosmoceras series represent significant evolution by phyletic gradualism or just the natural temporal variation that characterizes stasis (sensu Eldredge and Gould 1972).

Cladograms predict the order in which fossil taxa appeared and, thus, make predictions about general patterns in the stratigraphic record. Inconsistencies between cladistic predictions and the observed stratigraphic record reflect either inadequate sampling of a clade's species, incomplete estimates of stratigraphic ranges, or homoplasy producing an incorrect phylogenetic hypothesis. A method presented in this paper attempts to separate the effects of homoplasy from the effects of inadequate sampling. Sampling densities of individual species are used to calculate confidence intervals on their stratigraphic ranges. The method uses these confidence intervals to test the order of branching predicted by a cladogram. The Lophospiridae (“Archaeogastropoda”) of the Ordovician provide a useful test group because the clade has a good fossil record and it produced species over a long time. Confidence intervals reject several cladistic hypotheses that postulate improbable “ghost lineages.” Other hypotheses are acceptable only with explicit ancestor-descendant relationships. The accepted cladogram is the shortest one that stratigraphic data cannot reject. The results caution against evaluating phylogenetic hypotheses of fossil taxa without considering both stratigraphic data and the possible presence of ancestral species, as both factors can affect interpretations of a clade's evolutionary dynamics and its patterns of morphologic evolution.

The exceedingly rich middle Pleistocene mammalian fauna from the classic Ensenadan Tarija basin in southern Bolivia contains a diversity of medium to large-bodied herbivores consisting of both endemic (†Toxodontia, †Litopterna, Xenarthra) and immigrant (Rodentia, Proboscidea, Perissodactyla, and Artiodactyla) taxa. In order to characterize feeding ecology and niche differences, a suite of morphological characters was measured for each of 13 species of herbivorous mammals from the Pleistocene of Tarija; these were combined with carbon isotopic results from tooth enamel. (The Xenarthra were excluded from this study because they lack tooth enamel.)

Several different bivariate and multivariate combinations of characters can be used to characterize the feeding adaptations, niches, and guild composition of the Tarija mammalian herbivores. During the Pleistocene the browsing guild in the Tarija basin is interpreted to include the tapir (Tapirus tarijensis), extinct llama (Palaeolama weddelli), peccary (Tayassu sp.), and deer (Hippocamelus sp.). The mixed-feeding guild included two horse species (Hippidion principale and Onohippidium devillei), litoptern (Macrauchenia patachonica), and capybara (Neochoerus tarijensis). The grazing guild included the numerically dominant horse (Equus insulatus), two lamine species (Lama angustimaxilla and cf. Vicugna, provicugna), notoungulate (Toxodon platensis), and gomphothere proboscidean (Cuvieronius hyodon). The grazing guild has the widest range of body sizes relative to the two other guilds. Closely related sympatric species within the Equidae and Camelidae differentiate their niches from one another using a combination of body size, feeding ecology, and probably local habitat. Most of the paleoecological reconstructions resulting from this combined morphological and isotopic analysis corroborate previous studies based primarily on morphology; there are, however, some notable surprises.

The fossil record of echinoids is poor because soon after death they break apart into isolated plates. In the present seas regular echinoid species outnumber irregular species; whereas, in the Tertiary only 20% of the known echinoid species are regular. This suggests that regular echinoids are less likely to be preserved than irregular echinoids. The tests of regular echinoids are exposed to scavengers and currents upon their death, but irregular echinoids generally live buried in the sediment and are protected from these destructive forces. Furthermore, the tests of the regular echinoids lack the calcareous supports found in some irregular echinoids. The gut is not filled with sediment and its apical system is generally larger and more fragile. Finally, many regular echinoids live in environments less likely to be preserved in the sedimentary record.

Although the irregular echinoid is more likely to be fossilized, its record is poor during some periods in the past. Although 1,014 irregular echinoid species are known from the Eocene, only 83 species are known from the Paleocene and only 343 are known from the Oligocene. Is this reduction because fewer species lived then or because they have not been preserved?

The evolution of scutes in thyreophoran dinosaurs, based on Scutellosaurus, Scelidosaurus, Stegosaurus, and several ankylosaurs, began with small rounded or ovoid structures that typically had slight, anteroposteriorly oriented keels. These scutes were elaborated in two general and overlapping ways: they could flare laterally and asymmetrically beneath the keels that mark the anteroposterior axis, and they could be hypertrophied in their distal growth to produce plates, spikes, and other kinds of ornamentation. Stegosaurus plates and spikes are thus primarily hypertrophied keels of primitive thyreophoran scutes, sometimes with elaboration of dermal bone around their pustulate bases. Histologically, most thyreophoran scute tissues comprise secondary trabecular medullary bone that is sandwiched between layers of compact primary bone. Some scutes partly or mostly comprise anatomically metaplastic bone, that is, ossified fibrous tissue that shows incremental growth.

The “plumbing” of Stegosaurus plates was not apparently built to support a “radiator” system of internal blood vessels that communicated with the outside of the plates and coursed along their external surfaces to return heated or cooled blood to the body core. Possibly a purely external system supported this function but there is no independent evidence for it. On the other hand, many of the vascular features in stegosaurian plates and spikes reflect bautechnisches artifacts of growth and production of bone. Surface vascular features likely supported bone growth and remodeling, as well as the blood supply to a keratinous covering. When the gross and microstructural features of the plates and spikes are viewed in phylogenetic context, no clear pattern of thermoregulatory function emerges, though an accessory role cannot be eliminated in certain individual species. It seems more likely, as in other groups of dinosaurs, that the variation of dermal armor form in stegosaurs was primarily linked to species individuation and recognition, perhaps secondarily to inter- and intraspecific display, and rarely to facultative thermoregulation.

Fossil bone microanalyses reveal the ontogenetic histories of extinct tetrapods, but incomplete fossil records often result in small sample sets lacking statistical strength. In contrast, a histological sample of 50 tibiae of the hadrosaurid dinosaur Maiasaura peeblesorum allows predictions of annual growth and ecological interpretations based on more histologic data than any previous large sample study. Tibia length correlates well (R2>0.9) with diaphyseal circumference, cortical area, and bone wall thickness, thereby allowing longitudinal predictions of annual body size increases based on growth mark circumference measurements. With an avian level apposition rate of 86.4 μm/day, Maiasaura achieved over half of asymptotic tibia diaphyseal circumference within its first year. Mortality rate for the first year was 89.9% but a seven year period of peak performance followed, when survivorship (mean mortality rate=12.7%) was highest. During the third year of life, Maiasaura attained 36% (x=1260 kg) of asymptotic body mass, growth rate was decelerating (18.2 μm/day), cortical vascular orientation changed, and mortality rate briefly increased. These transitions may indicate onset of sexual maturity and corresponding reallocation of resources to reproduction. Skeletal maturity and senescence occurred after 8 years, at which point the mean mortality rate increased to 44.4%. Compared with Alligator, an extant relative, Maiasaura exhibits rapid cortical increase early in ontogeny, while Alligator cortical growth is much lower and protracted throughout ontogeny. Our life history synthesis of Maiasaura utilizes the largest histological sample size for any extinct tetrapod species thus far, demonstrating how large sample microanalyses strengthen paleobiological interpretations.

The Cretaceous/Tertiary (K/Pg) mass extinction has long been viewed as a pivotal event in mammalian evolutionary history, in which the extinction of non-avian dinosaurs allowed mammals to rapidly expand from small-bodied, generalized insectivores to a wide array of body sizes and ecological specializations. Many studies have used global- or continental-scale taxonomic databases to analyze this event on coarse temporal scales, but few studies have documented morphological diversity of mammalian paleocommunities on fine spatiotemporal scales in order to examine ecomorphological selectivity and ecospace filling across this critical transition. Focusing on well-sampled and temporally well-constrained mammalian faunas across the K/Pg boundary in northeastern Montana, I quantified dental-shape disparity and morphospace occupancy via landmark- and semilandmark-based geometric morphometrics and mean body size, body-size disparity, and body-size structure via body-mass estimates.

My results reveal several key findings: (1) latest Cretaceous mammals, particularly metatherians and multituberculates, had a greater ecomorphological diversity than is generally appreciated, occupying regions of the morphospace that are interpreted as strict carnivory, plant-dominated omnivory, and herbivory; (2) the decline in dental-shape disparity and body-size disparity across the K/Pg boundary shows a pattern of constructive extinction selectivity against larger-bodied dietary specialists, particularly strict carnivores and taxa with plant-based diets, that suggests the kill mechanism was related to depressed primary productivity rather than a globally instantaneous event; (3) the ecomorphological recovery in the earliest Paleocene was fueled by immigrants, namely three multituberculate families (taeniolabidids, microcosmodontids, eucosmodontids) and to a lesser extent archaic ungulates; and (4) despite immediate increases in the taxonomic richness of eutherians, their much-celebrated post-K/Pg ecomorphological expansion had a slower start than is generally perceived and most likely only began 400,000 to 1 million years after the extinction event.

Several metrics, including average difference among species, range of occupied morphological space, and number of character-state combinations, are used to investigate morphological diversification in Paleozoic crinoids. Despite several phases of taxonomic diversification, the maximal level of disparity reached in the Ordovician remained essentially unsurpassed. Although new regions in morphological space were occupied after the Devonian, these were not as extensive as those that had been evacuated prior to the Carboniferous. This discordance between extensive total morphological change and limited net change further supports previous arguments for the importance of morphological constraints in crinoid evolution. Major changes in the occupation of morphological space correspond with changes in taxonomic diversity within certain higher taxa. The extent to which advanced cladids (Poteriocrinina) appear to expand into new morphological space is exaggerated by the large number of very similar species in this group. If fewer species are sampled, by considering only those forms that differ from each other by at least some prescribed amount, poteriocrines appear to be less extreme morphologically. In contrast, other groups that seem to occupy unique regions in morphological space continue to do so even if fewer of them are sampled. Major crinoid clades—Camerata and Cladida+Flexibilia—do not show the same evolutionary pattern as Crinoidea, but instead exhibit a more gradual diversification of morphology. This observation provides additional support for the existence of qualitative differences among taxa of different rank.