Problems of stratigraphic completeness and poor temporal resolution make analysis of faunal change in terrestrial sequences difficult. The fluvial Neogene Siwalik formations of India and Pakistan are an exception. They contain a long vertebrate record and have good chronostratigraphic control, making it possible to assess the influence of biotic interchange on Siwalik fossil communities. In Pakistan, the interval between 18 and 7 Ma has been most intensively studied and changes in diversity and relative abundance of ruminant artiodactyls and muroid rodents are documented with temporal resolution of 200,000 years. Within this interval, diversity varies considerably, including an abrupt rise in species number between 15 and 13 Ma, followed by a decline in ruminant diversity after 12 Ma and a decline in muroid diversity in two steps at 13 and 10 Ma. Significant changes in relative abundance of taxa include an increase in bovids between 16.5 and 15 Ma, a decrease in tragulids after 9 Ma, and a very abrupt increase in murids at 12 Ma. Megacricetodontine rodents also decrease significantly at 12 Ma, and smaller declines are recorded among myocricetodontine and copemyine rodents after 16 Ma. An increase of dendromurine rodents at 15.5 Ma is also observed. There is also a trend of progressive size increase among giraffoids and bovids throughout the sequence.

We have also investigated relationships between biotic interchange and diversity, body size, and relative abundance, concluding that (1) the rapid increase in ruminant and muroid diversity was largely due to immigration, whereas in situ speciation had only a secondary role; (2) during intervals of increasing diversity, resident lineages did not have higher than average rates of in situ speciation; (3) during intervals with rising diversity, greater extinction did not accompany increased immigration; (4) during intervals with falling diversity, there may have been greater extinction in recently invading lineages; and (5) change in diversity was independent of changes in relative abundance and body size.

The origin of ammonite sutures is one of the most interesting open problems in paleontology. Present theories of suture formation deal with function rather than morphogenesis. Here we present a study showing that sutures are scale-invariant. In each of ten different ammonite genera, the ontogenetic sequence of the suture can be characterized by the same fractal dimension. We propose a morphogenetic theory for ammonite sutures that is based on the similarity between sutures and the Saffman-Taylor instability in both fractal characters and physical mechanism.

Throughout the late Quaternary, the Sahul (Pleistocene Australia–New Guinea) vertebrate fauna was dominated by a diversity of large mammals, birds, and reptiles, commonly referred to as megafauna. Since ca. 450–400Ka, approximately 88 species disappeared in Sahul, including kangaroos exceeding 200kg in size, wombat-like animals the size of hippopotamuses, flightless birds, and giant monitor lizards that were likely venomous. Ongoing debates over the primary cause of these extinctions have typically favored climate change or human activities. Improving our understanding of the population biology of extinct megafauna as more refined paleoenvironmental data sets become available will assist in identifying their potential vulnerabilities. Here, we apply a multiproxy approach to analyze fossil teeth from deposits dated to the middle and late Pleistocene at Cuddie Springs in southeastern Australia, assessing relative aridity via oxygen isotopes as well as vegetation and megafaunal diets using both carbon isotopes and dental microwear texture analyses. We report that the Cuddie Springs middle Pleistocene fauna was largely dominated by browsers, including consumers of C4 shrubs, but that by late Pleistocene times the C4 dietary component was markedly reduced. Our results suggest dietary restriction in more arid conditions. These dietary shifts are consistent with other independently derived isotopic data from eggshells and wombat teeth that also suggest a reduction in C4 vegetation after ~45 Ka in southeastern Australia, coincident with increasing aridification through the middle to late Pleistocene. Understanding the ecology of extinct species is important in clarifying the primary drivers of faunal extinction in Sahul. The results presented here highlight the potential impacts of aridification on marsupial megafauna. The trend to increasingly arid conditions through the middle to late Pleistocene (as identified in other paleoenvironmental records and now also observed, in part, in the Cuddie Springs sequence) may have stressed the most vulnerable animals, perhaps accelerating the decline of late Pleistocene megafauna in Australia.

Paleoecologists studying Paleozoic reef-builders have interpreted their growth forms as responses to conditions of depth and turbulence in reef complexes. Comparison of the shapes of Paleozoic stromatoporoids and corals with the growth forms of modern scleractinians has been used to reconstruct Paleozoic conditions. A review of shape zonation on modern reefs indicates that no general pattern is applicable to all reefs and variations in shape are the result of the interaction of many environmental factors with the genetically dictated growth pattern of the coral. In most zones of a reef a wide range of shapes co-exist. The growth forms of corals on modern reefs are not a simple vegetative response to the many environmental parameters that have been shown to influence form, but are constrained by phylogenetic and developmental influences as well as functional ones.

Interpretations of the environments of western Canadian and other mid-Paleozoic reefs have been based on the growth forms of stromatoporoids. The environmental significance of the shapes has been deduced from comparison with the shapes of modern scleractinians, functional morphology, nature of the enclosing sediment, position of growth, position within the reef, and diversity gradients. The validity of these criteria is open to question and considerable doubt remains concerning the significance of the growth forms. The shapes of reef animals are not specific guides to environments of modern reefs and should not be expected to be guides for ancient ones.

The same three subtypes of derived multiserial Hunter-Schreger bands are found in the incisor enamel of African phiomorph rodents from the late Eocene-early Oligocene and the oldest South American Caviomorpha from the Deseadan (late Oligocene). The synapomorphies contained therein, especially arrangement and orientation of interprismatic matrix, make an African origin of the Caviomorpha very probable. A North American origin of the Caviomorpha is thus rejected, as only primitive pauciserial Hunter-Schreger bands have been observed in possible ischyromyoid caviomorph ancestors. A multiserial Schmelzmuster apparently never evolved in the North American rodent fauna.

Few would argue with the assertion that within the practice of comparative morphology, the comparison of shapes is fundamental to any line of synthesis in paleontology. Yet the common act of such a comparison involves a great range of judgments concerning the homology, correspondence and divergence of form of various parts of any two related shapes. Considerations of similarity must include the scalar effects of size and material, the conversion of proportions as descriptive geometric dimensions to those useful numerical values that will be represented as ratios of measured distance (relative or compared against a standard), and, by no means insignificant, the judgment about the design or functional geometry implicit in the static as well as dynamic systems being measured. This review is concerned with these considerations and with quantitative comparisons of biological shape wherein some parts of specimens obviously have changed and others parts have not.

Fossil marine lineages are generally expected to exhibit long-term trends of increasing body size because of inherent fitness advantages or secular changes in environmental conditions. Because empirical documentation of this trend during the Paleozoic has been lacking for most taxonomic groups, the magnitude, timing, and taxonomic breadth of the trend have remained elusive. This study uses the largest existing database of fossil invertebrate sizes from four faunally important phyla to document ecosystem-wide size trends in well-preserved biotas from deep-subtidal, soft-substrate assemblages during the Cambrian through Devonian. Size of type specimens was measured along standard body axes from monographic plates and converted to body volume by using a broadly applicable empirical regression. Results demonstrate that mean body size (herein volume) of individual genera doubles during this interval, especially from the Late Ordovician through Early Devonian. The timing is gradual in spite of major radiations and extinctions, and the increase is primarily attributable to a net increase in the three-dimensionality of genera. The overall increase is not caused by replacement among clades because increases are widespread among arthropods, brachiopods, and echinoderms, at the phylum and class levels; in contrast, mollusks do not display a net size change at either taxonomic level. The increase is also more pronounced in microbivores than in carnivores. Combined with known environmental changes during this interval, and especially records of carbon dioxide, these trends provide support for the claim that primary productivity increased during the early to mid Paleozoic.

In a hyperbaric chamber, a living mature specimen of Nautilus pompilius withstood a hydrostatic pressure of 8.05 MPa (80.5 kg/cm2) equivalent to 785 m deep in the sea. Thereafter it was killed instantly by implosion of the shell. Before implosion, the animal reacted physiologically to increasing pressure. Therefore, the depth of 785 m can be assigned the depth limit of N. pompilius. The result bears on critical interpretations on the paleoecology and paleobiology of extinct nautiloids and ammonoids with similar shells.

Temporal patterns in species occupancy and geographic range size are a major topic in evolutionary ecology research. Here we investigate these patterns in Pliocene to Recent large mammal species and genera in Western Eurasia. By using an extensively sampled fossil record including some 700 fossil localities, we found occupancy and range size trajectories over time to be predominantly peaked among both species and genera, meaning that occupancy and range size reached their maxima midway along taxon existence. These metrics are strongly correlated with each other and to body size, after phylogeny is accounted for by using two different phylogenetic topologies for both species and genera. Phylogenetic signal is strong in body size, and weaker but significant in both occupancy and range size mean values among genera, indicating that these variables are heritable. The intensity of phylogenetic signal is much weaker and often not significant at the species level. This suggests that within genera, occupancy and range size are somewhat variable. However, sister taxa inherit geographic position (the center of their geographic distribution). Taken together, the latter two results indicate that sister species occupy similar positions on the earth's surface, and that the expansion of the geographic range during the existence of a given genus is driven by range expansion of one or more of the species it includes, rather than simply being the summation of these species ranges.

A new account of the mechanical action of the heterocercal tail in fishes is given, developed from study of the swimming of sharks. The heterocercal tail is capable of delivering a thrust that can be oriented in a wide range of angles in the vertical plane. The orientation results from a balance of forces acting in the tail. Normally the heterocercal tail delivers neither an epibatic nor a hypobatic thrust, but rather one directly through the center of gravity of the fish. On the basis of the new account, predictions concerning the shape and proportions of the heterocercal tail are made and tested.

Ecotypic correlations between stable isotopic signals and skeletal size indicate that some Late Cretaceous serial planktic foraminifera were strongly photosymbiotic. In contrast, coeval trochospiral planktic foraminifera do not exhibit the isotope/size signatures that typify strongly photosymbiotic species. Comparison to Cenozoic taxa demonstrates that photosymbiosis has recurred throughout planktic foraminiferal history and has evolved independently in superfamilies characterized by very different gross skeletal morphologies. The historical contingency of that evolution is illustrated by the consequences of the Cretaceous/Paleogene mass extinction, which terminated the Cretaceous lineages of photosymbiotic planktic foraminifera but did not permanently extinguish photosymbiont reliance by planktic foraminifera.

The Westermann Morphospace method displays fundamental morphotypes and hypothesized life modes of measured ammonoid fossils in a ternary diagram. It quantitatively describes shell shape, without assumption of theoretical coiling laws, in a single, easy-to-read diagram. This allows direct comparison between data sets presented in Westermann Morphospace, making it an ideal tool to communicate morphology. By linking measured shells to hypothesized life modes, the diagram estimates ecospace occupation of the water column. Application of this new method is demonstrated with Mesozoic data sets from monographs. Temporal variation, intraspecies variation, and ontogenetic variation are considered. This method can address hypothetical ecospace occupation in collections with tight stratigraphic, lithologic, and abundance control, even when taxonomy is in dispute.

Nipponites, a Late Cretaceous nostoceratid ammonite, shows a peculiar meandering shell growth in the middle-late stage. Assuming neutral buoyancy, and a constant aperture angle relative to the sea bottom, meandering growth of this ammonite was modeled by computer simulation. In this model, the meandering shell growth is controlled by regulation of life orientation. The remarkable similarity in the coiling modes and rib obliquity patterns between the computer-simulated and actual specimens strongly suggests a free living mode of life in Nipponites with an approximately neutral buoyancy. The simulation also suggests that morphological saltation from a simple helicoid form like Eubostrychoceras japonicum to a meandering shell form like Nipponites occurred abruptly without any intermediate form by minor change of the upper and lower limits of growth direction.

If last appearances of marine animal genera are taken as reasonable proxies for true extinctions, then there is appreciable global extinction in every stage of the Phanerozoic. If, instead, backsmearing of extinctions by incomplete sampling is explicitly taken into consideration, a different view of extinction emerges, in which the pattern of extinction is much more volatile and in which quiescent time spans—with little or no global extinction for several million years—are punctuated by major extinction events that are even more extreme than is generally thought. Independent support for this alternative view comes from analysis of genus occurrence data in the Paleobiology Database, which agrees with previous estimates of sampling probability and implies that offsets between extinction and last appearance of one or more stages are quite probable.

Deep-sea submersible observations made in the Bahamas revealed interactions between the stalked crinoid Endoxocrinus parrae and the cidaroid sea urchin Calocidaris micans. The in situ observations include occurrence of cidaroids within “meadows” of sea lilies, close proximity of cidaroids to several upended isocrinids, a cidaroid perched over the distal end of the stalk of an upended isocrinid, and disarticulated crinoid cirri and columnals directly underneath a specimen of C. micans. Guts of two C. micans collected from the crinoid meadow contain up to 70% crinoid material. Two of three large museum specimens of another cidaroid species, Histocidaris nuttingi, contain 14–99% crinoid material.

A comparison of cidaroid gut contents with local sediment revealed significant differences: sediment-derived material consists of single crinoid ossicles often abraded and lacking soft tissue, whereas crinoid columnals, cirrals, brachials, and pinnulars found in the cidaroids are often articulated, linked by soft tissue, and unabraded. Furthermore, articulated, multi-element fragments often show a mode of fracture characteristic of fresh crinoid material. Taken together, these data suggest that cidaroids prey on live isocrinids.

We argue that isocrinid stalk-shedding, whose purpose has remained a puzzle, and the recently documented rapid crawling of isocrinids are used in escaping benthic predators: isocrinids sacrifice and shed the distal stalk portion when attacked by cidaroids and crawl away, reducing the chance of a subsequent encounter. If such predation occurred throughout the Mesozoic and Cenozoic (possibly since the mid-Paleozoic), several evolutionary trends among crinoids might represent strategies to escape predation by slow-moving benthic predators.

Growth of the colony is a basic element of morphological evolution and life history in cheilostome bryozoans. Here we consider the occurrence of different modes of growth in encrusting cheilostomes through geologic time and in well-studied living associations. We assess patterns of zooid formation by direct examination of skeletal characters in species from nearly all diverse fossil assemblages reported from North America and quantify within-assemblage diversities and abundance rankings for fossil encrusting species with different modes of growth. These data document macroevolutionary trends showing a transition from dominance of an apparently primitive mode of budding in the Early Cretaceous to derived modes through the Tertiary. The trends are characterized by their long duration and apparent convergence among systematic subgroups within the Cheilostomata. We then consider the validity of our observations as adaptive trends. Patterns of ecological dominance among living and fossil species indicate that different patterns of zooid formation are important determinants of success of colonies as reflected by their abundance, competitive ability, survivorship, and recovery from injury or predation. The consistency of the long-term trends and evidence for the existence of ecological mechanisms in fossil assemblages suggest a major evolutionary role for biotic interactions.

Sabertooth members of the Felidae, Nimravidae, and Barbourofelidae are well-known for their elongated saber-shaped canines. However, within these groups, there is a wide range of independently derived tooth shapes and lengths, including dirk-tooth and scimitar-tooth morphs. In conjunction with the saberteeth, forelimbs were also used to subdue prey. Thus, there may be a functional link between canine shape and forelimb morphology. Because there are no living sabertooth forms for comparison, extant felids make a good proxy for examining the morphology of these extinct organisms. Here, I examine the forelimb morphology of different sabertooth groups from across North America; I address whether forelimb morphologies are associated with tooth morphologies, and whether these associated tooth and forelimb morphologies are convergent among different families. To answer these questions, I analyzed six functional indices of the forelimbs and two canine characters for 13 species of sabertooth predators and 15 extant felid species. Results indicate that sabertooth morphs with longer, thinner canines show more robust limb proportions. These patterns were convergent among sabertooth felids, nimravids, and barbourofelids, and indicate a positive functional relationship between saber elongation and increased forelimb robustness. This suggests that sabertooth carnivorans demonstrated niche partitioning of predation strategies according to canine shape and corresponding forelimb morphology.

The effect of preservational quality on paleoecologic studies is evaluated quantitatively by using data from 83 fossil collections. These collections are from a restricted Cretaceous time interval (Haustator bilira Assemblage Zone) of Maestrichtian Age and are from the Eastern Gulf Coastal Plain Province. In all, 32,335 specimens were identified, resulting in recognition of 643 different taxa. Each collection was categorized into one of six preservational types, ranging from those in which both aragonite and calcite shells are well preserved to those having only calcite shells preserved.

Statistical comparisons reveal that preservation affects the faunal makeup of these collections. Specifically, collections in which both aragonite and calcite are well preserved have more taxa than collections of poorer preservational quality and contain faunal elements not found in other collections.

These two effects can confound paleoecologic studies of endemism, eurytopy vs. stenotopy, species longevity and other studies of the distribution of organisms in space and time. These effects are especially significant for studies based on presence/absence data, such as published faunal lists and selectively collected samples. In such studies, collections of good preservational quality may be interpreted to represent strata of high diversity, taxa having the more durable hard parts will appear to be widespread and long ranging, and taxa that are preserved only in collections of the best preservational quality will appear stenotopic, endemic, and rare.

The proposition is presented that the large thecae of many Paleozoic crinoids housed gonads, unlike modern crinoids that have the gonads on the arms or pinnules. Early in their history, inadunate crinoid gonads migrated into a voluminous anal sac, effectively separating them from other vital organs. Excision of the sac by predatory fishes and cephalopods would have been less traumatic than an attack on the theca, and the sac could be more readily regenerated. The pores and slits between plates on inadunate sacs are interpreted as gonopores. Some anal sacs may also have served as brood chambers. The traditional explanation of the sac as a special respiratory structure is discounted.

A general model of taxonomic diversity, incorporating diversity-dependent rates of origination and extinction, is constructed to examine the dynamic responses of diversity to perturbation. The model predicts that the trajectories of diversification increase and decrease are substantially different. The trajectories of diversity during disequilibrium conditions are displayed in phase diagrams to permit a simple graphical analysis of stability. A positive displacement of diversity from equilibrium results in a rapid decline in diversity and may involve an initial overshoot of the equilibrium condition. A negative displacement of equal magnitude results in a gradual increase in diversity. The model is expressed as a nonlinear difference equation to incorporate intrinsically a delay time due to the characteristic noninstantaneous response of origination and extinction. The model initially assumes a parabolic curve expressing total taxon origination rate as a function of diversity. A second model, constructed assuming a sigmoidal total taxon origination rate derived from considerations of allopatric speciation, enhances the asymmetry of the diversity response. The delayed recovery of the Triassic fauna is shown to be characteristic of return to equilibrium from an undersaturated condition, whereas the more rapid “catastrophic” decline in the Late Permian fauna is shown to be characteristic of return to equilibrium from the oversaturated condition. It is proposed, although not assumed, that perturbation may include a degree of selectivity related to the dispersal abilities of organisms, thereby enhancing the observed asymmetry.