The Cambrian information revolution describes how biotically driven increases in signals, sensory abilities, behavioral interactions, and landscape spatial complexity drove a rapid increase in animal cognition concurrent with the Cambrian radiation. Here, we compare cognitive complexity in Cambrian and post-Cambrian marine ecosystems, documenting changes in animal cognition after the initial Cambrian increase. In a comparison of Cambrian and post-Cambrian Lagerstätten, we find no strong trend in the proportion of genera possessing two types of macroscopic sense organs (eyes and chemoreceptive organs such as antennae, feelers, or nostrils). There is also no trend in general nervous system complexity. These results suggest that sophisticated information processing was already common in early Phanerozoic ecosystems, comparable with behavioral evidence from the trace fossil record. Most taxa capable of complex information processing in Cambrian ecosystems were panarthropods, whereas mollusks and chordates made up larger proportions afterward. In both the Cambrian and the present day, ecological occupation of diverse habitat tiers and feeding modes is possible with even simple nervous systems, but ecological lifestyles requiring rapid, regular movement are almost exclusively associated within brain-bearing taxa, suggesting a connection with fast information-processing abilities and bodily responses. The overall rise in cognitive sophistication in the Cambrian was likely a unique event in the history of life, although some lineages subsequently developed more elaborate sensory systems and/or larger brains.

The mathematical relationship between species survivorship and duration curves is derived using standard demographic arguments. The result, when applied to the late Cenozoic mammals, suggests that there was an inhomogeneity in the mammalian radiation just before the Wurm, or that the mammalian speciation process has not yet attained the stable-age distribution.

The discrete cosine transform (DCT) is a Fourier-related transform widely used in signal processing and well suited to analyzing open outlines such as ammonite ribs. The method is applied here to depict and decipher the ribbing morphospace of a large group of Lower Jurassic ammonites composed of the Oxynoticeratidae and their close ancestors. Because they are clearly associated with buoyancy and/or swimming ability, the usually clearly involute, comparatively smooth and compressed shells of these ammonites may well be misleading taxonomic markers. In this context, quantitative analysis of the ribbing pattern using the DCT may significantly improve our perception of the ornamental patterns expressed within the group. A set of 251 specimens illustrating the worldwide fauna and selected from more than 80 publications is analyzed. Big differences are found in the evolutionary patterns of the two main lineages of Oxynoticeratidae currently accepted in the literature. A previously unsuspected Mediterranean group comprising principally the genus Parasteroceras is identified from its distinctive ornamentation. The northwest European and Mediterranean genera Eparietites, Oxynoticeras, and Parasteroceras do not feature among the American (East Pacific) faunas. This finding calls into question some generally accepted correlations between European and American stratigraphic frameworks. The study shows that the DCT is a valuable tool for discriminating between species within the huge and often puzzling range of ornamental variation of the main genera (e.g., Gleviceras and Radstockiceras).

This study addresses the question of evolutionary tempo and mode in a sequence of Upper Cretaceous bivalves in the genus Pleuriocardia from the Western Interior Basin of North America. Change between species was probably phyletic (without persistence of ancestors). There is some evidence for weak gradual change within the lineage, but most important change is concentrated in short intervals of time. Detailed examination of the differences among samples reveals pronounced geographic variation, whereas temporal variation within localities is generally minor. The relatively rapid episodes of change fit the model of punctuated equilibrium, but the phyletic nature of species-level change does not.

The value of the debate about the punctuated and gradualistic models has been to force a more criticial examination of fossil sequences, but these sequences should not be forced into narrowly defined categories. A variety of evolutionary patterns may exist in the fossil record, and it is this variation in pattern that will inform us of the underlying processes.

The origin and evolutionary histories of the two most abundant and diverse genera of invertebrates (Prosserella: Brachiopoda and Syringostroma: Stromatoporoidea) in the Detroit River Group and associated rocks in the vicinity of the Michigan Basin appear to support the models of either allopatric speciation and punctuated equilibria (Eldredge and Gould, 1972) or quantum evolution (Simpson, 1944; 1953). Four morphotypes of Prosserella arose almost simultaneously (a “burst”) just below the base of the Detroit River in sandstone deposited near the axis of the Findlay Arch and persisted without evidence of significant progressive evolutionary change (a “trend”) until their almost simultaneous extinction by lineage termination near the top of the Detroit River. Neither ancestors nor descendants of Prosserella have been recognized and even the familial placement of the genus is uncertain. The genus, its species and morphotypes probably arose by means of very profound genetic or chromosomal “revolutions” that probably took place in small allopatric populations; each population quickly increased in abundance and geographic range and persisted without further significant morphologic modification until its extinction.

S. ristigouchense from the Lower Devonian of New Brunswick is the probable ancestor to six (or seven) species of Syringostroma that appear almost simultaneously (another “burst”) in lower Detroit River carbonate rocks deposited near the eastern margin of the Michigan Basin. Two of these new species are known only from reefs of early Detroit River age (a “crash”), four species persist without significant morphological change to at least the end of Detroit River deposition, and one of these was the probable ancestor to yet another newly evolved species that is abundantly represented in the conformably overlying Columbus Limestone.

The “founding fathers” of chronostratigraphy were pre-Darwinian and based their concepts and methods on assemblages of co-occurring taxa of unknown phylogenetic relations (assemblage-zones, concurrent range-zones and Oppel-zones) rather than on the range-zones of successional species in the same phylogenetic lineage (lineage-zones). Assumptions of these early biostratigraphers concerning the temporal relations of taxa are in close accord with the premises of punctuated equilibria and quantum evolution. The development of the chronostratigraphic system during the 19th century attests to the success of these early methods which depend for their precision on the number of taxa used and determination of the significance of morphologic differences among these taxa and their geographic and stratigraphic distributions.

Under favorable circumstances, biogeographic and biostratigraphic data can be combined to identify accurately the time and place of origin of a given taxon, and to reconstruct the pattern of its subsequent radiation. This study considers the dendrasterid sand dollars, which are abundant today along the Pacific Coast of North America. The Neogene sand dollar record in this region is particularly good; in fact, sand dollars have traditionally been used as provincial index fossils.

The dendrasterids originated in central California at the end of the Miocene; the oldest forms are dated at about 6.0–6.5 Ma. They spread south to Baja California during the Pliocene, and then north to Alaska during the Quaternary. This historical pattern is not an artifact of the record; it is consistent with independent paleogeographic evidence. The dendrasterids supplanted an older Mio-Pliocene sand dollar fauna; they are now completely dominant in the temperate coastal waters of the northeastern Pacific. They have reached this position in less than 7 m.y. since their first local appearance. The rapid rise of dendrasterids could be related to their aberrant morphology and behavior; these adaptations allow dendrasterids to suspension-feed, in a manner unique among living echinoids.

Dendrasterids are characterized by “eccentric” test morphologies. Even the oldest species are highly eccentric; transitional forms are unknown. The first dendrasterids appear suddenly in the provincial “Jacalitos Stage,” above an unconformity which represents no more than about 1 m.y. They do not occur in the underlying units, although other fossil sand dollars are abundant. The dendrasterids may have arisen rapidly, through a heterochronic change in the development of older, noneccentric forms. Recent ontogenetic studies have documented the feasibility of this process.

Clymeniid ammonoids appeared during the Late Devonian (Mid-Famennian) and quickly radiated before becoming extinct at the Devonian/Carboniferous boundary. Outwardly indistinguishable from other ammonoids, clymeniids are distinguished internally by their dorsal siphuncle, contrasted to a ventral siphuncle in almost all other ammonoids. Comparisons of a sample of Clymeniida (n = 22 genera), Goniatitida (n = 33), Prolecanitida (n = 12), and Anarcestida (n = 13) indicate that clymeniids fall within the range of other ammonoids in terms of shell geometry and suture complexity, but their siphuncles average two to three times larger and clymeniid shells are approximately 33% thicker than those of other ammonoids. Although a dorsal siphuncle would be about 50% smaller in surface area and volume than if located in a ventral position, the enlarged clymeniid siphuncle partially and, in some cases, fully compensated for this loss. Hydrostatic simulations of 15 clymeniid genera indicate that their thicker (therefore heavier) shells would have resulted in relatively short body chambers (≈280°) and high aperture orientations (≈90°). In static life-position, these orientations would have placed the dorsal clymeniid siphuncle at or near the bottom of the most recently formed chambers, seemingly an ideal location for draining liquid from the chamber. Migration of the siphuncle to the dorsal side of the shell occurs suddenly during early ontogeny (within the first two or three chambers), and mutation of homeotic gene expression is offered as a possible explanation for the sudden shift. A dorsal siphuncle may have resulted in selection for enlarged siphuncles, but this may have incurred loss of strength against hydrostatic pressure (thereby reducing depth limits) and thus rendered the clade more susceptible to the multiple eustatic and anoxic events that marked the end of the Devonian.

A simple theoretical argument shows that the evolutionary process will look gradual if it is considered on too fine or too coarse a time scale. There exists an intermediate time scale in which the distribution of evolutionary rates will appear as bimodal.

A short stratigraphic interval near Bulin in western Hunan (China) yields multiple specimens of the ~514-Myr-old oryctocarine trilobite Oryctocarella duyunensis. Size data obtained from these specimens indicate that, from meraspid degree 1 onward, degrees represent successive instars. Meraspid growth persisted until a terminal stage was reached, providing the first example of determinate growth in trilobites and, notably, in an early Cambrian species. The sample contains three varieties of such terminal stages, recognized as holaspids, with 9, 10, or 11 thoracic segments, respectively. During the meraspid phase, growth rates were not constant in this species. The pattern of growth seen in the Bulin assemblage differs modestly from that reported in the same species from two other localities, attesting to microevolutionary variation in developmental patterns among these collections.

Species selection has received a great deal of theoretical attention but it has rarely been empirically tested. It is important to determine the level of selection that operated during a particular extinction event because it can help distinguish between traits that were actually responsible for extinction and those that were merely correlated with it. Here, we present a test that can help distinguish between organismal and species-level selection, which we demonstrate using the high-resolution fossil record of planktonic foraminifera species recorded in deep-sea sediment cores. Our test examines the fate of survivors and victims during the Cretaceous/Paleogene (K/Pg) mass extinction within single geographic regions, where all individuals experience the same selection pressures. Selection at the organismal level implies that individual members of surviving species are more fit than those of victimized species, and therefore should be more likely to survive in affected areas; conversely, selection at the species level implies individuals will suffer equally within an affected area. We find that survivors of the mass extinction suffered very high extirpation rates in cores where the overall extinction rate was high, indicating that individual members of the surviving species were generally no more fit than individual members of extinct species. Rather, these species were able to survive because they possessed advantageous species-level traits, such as larger geographic ranges and greater abundances than victimized species. This geographic pattern of extirpation suggests that selection operated at the species, rather than organismal, level during the K/Pg mass extinction of planktonic foraminifera.

A current question being debated with considerable intensity is whether or not certain geographic areas act as centers of evolutionary radiation and supply species to other areas that are less active or less effective in an evolutionary sense. Darwin (1859) was the first to write about centers of origin which he called “single centers of creation.” He argued that each species was first produced within a single region and that it subsequently migrated from that area as far as its powers of migration and subsistence under past and present conditions permitted. Adams (1902), in discussing the influence of the southeastern United States as a center of distribution for the flora and fauna of North America, provided a series of criteria for the determination of “centers of dispersal.” His first, and evidently most important criterion was the location of “the greatest differentiation of a type.”

Cheek teeth of some mammalian herbivores exhibit pronounced changes in occlusal size and shape through wear, purportedly caused by strong curvature. Such changes are extreme in the upper cheek teeth of extinct, dentally archaic lagomorphs. Morphologic and taxonomic turnover in lagomorphs suggests that these dentally archaic forms may have been unable to develop hypselodont (ever-growing) cheek teeth. This study investigates how the interaction of tooth shape and wear can cause occlusal size and shape changes, and potentially impose structural constraints on crown height. These constraints may help explain extinction of mammals with teeth like archaic lagomorphs, evolution and diversification of other mammalian herbivores during the late Miocene, and the relative paucity of hypsodont cheek tooth shapes in extant mammals.

I first quantify two-dimensional curvature accounting for shape differences observed in hypsodont teeth, P4s of the archaic lagomorphs Russellagus and Hesperolagomys, which exhibit pronounced change with wear, and Ondatra lower incisors, which show minimal change with wear. Using this quantification, I generate theoretical curvature morphologies and describe a geometric model of tooth wear that generates values for qualitative and quantitative aspects of the occlusal surface at different wear stages. Modeled results of wear surface topography and dimensions closely correspond to observed patterns in Russellagus, Hesperolagomys, and Ondatra. Model results on wear in theoretical tooth morphologies identify two major shape factors influencing wear: orientation of the wear surface (incisor-like or cheek-tooth-like), and tooth curvature (“concentric” or “nonconcentric”). Modeled wear also suggests two geometric constraints on crown height. Teeth with nonconcentric curvatures can have crown height limited by potential tooth area. “Incomplete wear” in any tooth can present severe constraints on increasing crown height, causing structurally untenable morphologies in very tall-crowned to hypselodont teeth.

Electron microprobe analyses of platform (pectiniform Pa) elements of Permian conodonts reveal detailed and systematic chemical element distributions. The crown of the conodont element is more densely mineralized than the basal body and shows evidence of less dense mineralization in areas of rapid growth. Patterns in sodium and sulfur concentrations indicate oral to aboral differentiation within conodont elements. These chemical element patterns support oral exposure during life and functional use as a tooth, and they approximate the erupted and embedded positions of the conodont tooth when the animal was alive. Previously unrecognized spatial distributions of geochemically important chemical elements warrant consideration in future geochemical studies of conodonts.

Paleoecological studies enhance our understanding of biotic responses to climate change because they consider long timescales not accessible through observational and experimental studies. Using predatory drillholes produced on fossil bivalve shells by carnivorous gastropods, we provide an example of how climate change affected predator–prey interactions. We quantitatively examine temporal changes in fossil molluscan assemblages and predation patterns from the Pleistocene Japan Sea, which experienced drastic environmental changes in relation to glacial–interglacial climate cycles. We found significant changes in predation patterns associated with a decline in the abundance of warm-water molluscan species. Climate-mediated fluctuations in the eustatic sea level and resultant weakening of the Tsushima Warm Current caused a decline in a warm-water shell-drilling predator, which moderated the predation pressure and size relationship between the predators and the bivalve prey. Our results indicate that climate-mediated range shifts of species in present-day and future marine ecosystems can likewise increase altered predator–prey interactions.

Changes in the physical environment are major drivers of evolutionary change, either through direct effects on the distribution and abundance of species or more subtle shifts in the outcome of biological interactions. To investigate this phenomenon, we built a fossil data set of drilling gastropod predation on bivalve prey for the last 11 Myr to determine how the regional collapse in Caribbean upwelling and planktonic productivity affected predator–prey interactions. Contrary to theoretical expectations, predation increased nearly twofold after productivity declined, while the ratio of drilling predators to prey remained unchanged. This increase reflects a gradual, several-fold increase in the extent of shallow-water coral reefs and seagrass meadows in response to the drop in productivity that extended over several million years. Drilling predation is uniformly higher in biogenic habitats than in soft sediments. Thus, changes in predation intensity were driven by a shift in dominant habitats rather than a direct effect of decreased productivity. Most previous analyses of predation through time have not accounted for variations in environmental conditions, raising questions about the patterns observed. More fundamentally, however, the consequences of large-scale environmental perturbations may not be instantaneous, especially when changes in habitat and other aspects of local environmental conditions cause cascading series of effects.

We appreciate Dr. Scott's comments about our paper (Malmgren and Kennett 1981), but wish to clarify some aspects which we hope will help provide a better understanding about the Late Neogene evolution of the Globorotalia (Globoconella) group (Kennett and Srinivasan 1983). We also wish to dispute some of Scott's other criticisms. In effect, Scott's arguments have provided no reason to justify abandonment of our initial contention that this lineage represents one of the best documented cases of phyletic gradualism in any group of fossils.

We support Scott's notion that divergence of the lineage took place near the Miocene-Pliocene boundary, but this divergence is not relevant for our evolutionary study. In fact, the Early Pliocene form resembling Globorotalia conoidea was already recognized by one of us (J.P.K.) 10 yr ago (Kennett 1973). It was distinguished as G. cf. conoidea and not G. conoidea as stated by Scott. In our previous papers (Malmgren and Kennett 1981, 1982) we confined our attention to the evolution that occurred in the primary temperate stock (cool subtropical) water mass—the abundant and dominant forms of Globoconella.

The excellent fossil record of conodonts represents an ideal, yet underutilized, resource for resolving fundamental issues of pattern and process in evolutionary theory. However, this potential has not been exploited because the quantitative understanding of the evolution of conodont element morphology is limited. This work applies standardized morphometric protocols to skeletal elements belonging to the conodont Pterospathodus, derived from a densely sampled section from Estonia. It has established a robust quantitative framework for morphological variation in Pterospathodus, permitting statistical analysis of the current qualitative hypotheses of evolutionary pattern within this genus for the first time. Apparent directional trends were statistically compared with patterns expected for directional evolution, an unbiased random walk and stasis, using maximum-likelihood model fitting, rescaled range analysis, and the runs test. Results confirmed the presence of trends in size and shape change through time, providing an example of convincing directional morphological change in a fossil lineage. The morphometric analyses have also allowed quantitative investigation of ontogenetic processes in Pterospathodus, suggesting that allometric repatterning was the proximal mechanism responsible for mediating the observed shifts in morphology through time. The results have demonstrated that conodonts represent an important resource for understanding evolutionary pattern and process in the fossil record.

The Order Spiriferinida spanning the latest Ordovician to Early Jurassic is a small group of brachiopods overshadowed by other taxon-rich clades during the Paleozoic. It diversified significantly after the end-Permian extinction and became one of the four major clades of Triassic brachiopods. However, the phylogeny and recovery dynamics of this clade during the Triassic still remain unknown. Here, we present a higher-level parsimony-based phylogenetic analysis of Mesozoic spiriferinids to reveal their evolutionary relationships. Ecologically related characters are analyzed to indicate the variances in ecomorphospace occupation and disparity of spiriferinids through the Permian–Triassic (P-Tr) transition. For comparison with potential competitors of the spiriferinids, the pre-extinction spiriferids are also included in the analysis. Phylogenetic trees demonstrate that about half of the Mesozoic families appeared during the Anisian, indicating the greatest phylogenetic diversification at that time. Triassic spiriferinids reoccupied a large part of the ecomorphospace released by its competitor spiriferids during the end-Permian extinction; they also fully exploited the cyrtiniform region and developed novel lifestyles. Ecomorphologic disparity of the spiriferinids dropped greatly in the Early Triassic, but it rebounded rapidly and reached the level attained by the pre-extinction spiriferids in the Late Triassic. The replacement in ecomorphospace occupation between spiriferids and spiriferinids during the P-Tr transition clearly indicates that the empty ecomorphospace released by the extinction of Permian spiriferids was one of the important drivers for the diversification of the Triassic spiriferinids. The Spiriferinida took over the empty ecomorphospace and had the opportunity to flourish.

The repeated return of tetrapods to aquatic life provides some of the best-known examples of convergent evolution. One comparison that has received relatively little focus is that of mosasaurids (a group of Late Cretaceous squamates) and archaic cetaceans (the ancestors of modern whales and dolphins), both of which show high levels of craniodental disparity, similar initial trends in locomotory evolution, and global distributions. Here we investigate convergence in skull ecomorphology during the initial aquatic radiations of these groups. A series of functionally informative ratios were calculated from 38 species, with ordination techniques used to reconstruct patterns of functional ecomorphospace occupation. The earliest fully aquatic members of each clade occupied different regions of ecomorphospace, with basilosaurids and early russellosaurines exhibiting marked differences in cranial functional morphology. Subsequent ecomorphological trajectories notably diverge: mosasaurids radiated across ecomorphospace with no clear pattern and numerous reversals, whereas cetaceans notably evolved toward shallower, more elongated snouts, perhaps as an adaptation for capturing smaller prey. Incomplete convergence between the two groups is present among megapredatory and longirostrine forms, suggesting stronger selection on cranial function in these two ecomorphologies. Our study highlights both the similarities and divergences in craniodental evolutionary trajectories between archaic cetaceans and mosasaurids, with convergences transcending their deeply divergent phylogenetic affinities.