For a survivorship curve to show a meaningful pattern, it is essential that a suitably homogeneous group is selected for analysis. If taxa have originated at different times in the geological record and have consequently experienced different extinction probabilities during the times that they existed, they do not constitute such a homogeneous group. A correction factor for variations in real-time extinction rates must be employed, as is described here. By application of the “corrected survivorship score,” it is shown that the Paleogene planktonic foraminifera exhibit a very strong survivorship pattern, namely an extinction probability that progressively increases with taxonomic longevity. That is to say, when extinction occurred, it was preferentially selective of older taxa. This is manifested as convexity in the survivorship curves. However, the pattern is degraded by variations in the real-time extinction rate, which causes straightening of the survivorship curves if they are calculated in the usual uncorrected way. If the law of constant extinction is to be tested for a given group, it is necessary either that stochastically constant real-time extinction rates are demonstrated or that variations in the extinction rate are corrected for in the manner described. As a separate issue, it is also essential that biologically meaningful taxa are analyzed. The convexity of planktonic foraminiferal survivorship curves is probably an artifact of the way evolving lineages have been subdivided in the application of typological taxonomy. Consequently, we are still a long way from being able to use survivorship analysis of planktonic foraminiferal data for adequately testing evolutionary models such as the Red Queen's hypothesis.

The shovel-tusked gomphotheres are normally portrayed scooping up water plants with their shovellike mandibular tusks. This portrayal is based on speculation about the possible functions of the lower tusks and misinterpretation of mandibular-tusk wear patterns that goes back to the 1920s and 1930s. In addition, most literature concerning shovel-tusker feeding behavior ignores the possibility that the upper tusks may have had a role in feeding, as they do in modern African elephants. Because wear patterns on tusks provide direct evidence as to how tusks were used during feeding, I examined and interpreted patterns on the lower and upper tusks of shovel-tusked gomphotheres on the basis of theoretical models of tusk wear to determine how the tusks were used in feeding.

This examination led to the following conclusions. (1) The genus Amebelodon was characterized by feeding opportunism, gathering food with both its lower and upper tusks in a variety of ways. (2) There is evidence for similar flexibility within the genus Serbelodon. (3) Wear patterns on mandibular tusks of Platybelodon grangeri and Torynobelodon barnumbrowni indicate that these taxa did not practice mandibular shoveling but used these tusks to cut tough vegetation in a specialized fashion. (4) The flaplike trunks (probosces) generally attributed to shovel-tusked gomphotheres in restorations are shown almost certainly to be erroneous; morphological and functional evidence suggests that these animals had trunks similar to those of modern elephants. (5) Strong tusk sexual dimorphism is unknown in the shovel-tusked gomphotheres except for Platybelodon and should not be found in any taxa that relied on their tusks for procuring food. New restorations of both Amebelodon and Platybelodon are provided that are more consistent with the actual evidence bearing on their feeding behavior.

Although much natural historical evidence has been adduced in support of the occurrence of several mass extinctions during the Phanerozoic, unambiguous statistical confirmation of the mass extinction phenomenon has remained elusive. Using bootstrapping techniques that have not previously been applied to the study of mass extinction, we have amassed strong or very strong statistical evidence for mass extinctions (see text for definitions) during the Late Ordovician, Late Permian, and Late Cretaceous. Bootstrapping therefore verifies three of the mass extinction events that were proposed by Raup and Sepkoski (1982). A small amount of bootstrapping evidence is also presented for mass extinctions in the Induan (Triassic) and Coniacean (Cretaceous) Stages, but high overall turnover rates (including high origination) in the Induan and uncertain estimates of the temporal duration of the Coniacean force us to conclude that the evidence is not compelling.

We also present the results of more liberal X2 tests of the differences between expected and observed numbers of familial extinctions for stratigraphic stages. In addition to verifying the mass extinctions identified using bootstrapping, these analyses suggest that several stages that could not be verified as mass extinction stages using bootstrapping (including the last three in the Devonian, and the Norian Stage of the Triassic) should still be regarded as candidates for mass extinction. Further analysis will be required to test these stages in more detail.

The function of serrated teeth is analyzed by experimental comparison with the action of artificially made steel blades. Serrated blades cut compliant materials with a grip-and-rip mechanism, whereas smooth, sharp blades cut by concentrating a large downward force on a tiny area.

Tyrannosaurid teeth from the Cretaceous Judith River Formation bear rows of serrations that have thick, rounded enamel caps, gripping slots between neighboring serrations, thick enamel bodies inside the teeth underneath the gripping slots, and a root beneath each serration. In contrast, the carnivorous dinosaur Troodon has teeth with exposed pointed serrations, thin enamel, and possibly serration roots.

Serrations on the teeth of Troodon and the fossil shark Carcharodon, cut compliant materials in the same way as a serrated hacksaw blade. In contrast, the cutting action of tyrannosaurid teeth most closely resembles that of a dull smooth blade. The spaces between the serrations act as minute frictional vises that grip and hold meat fibers; chambers between neighboring serrations receive and retain small fragments of meat, and inevitably would have acted as havens where bacteria could be stored. These spaces may therefore have led to infections in wounds, analogous to those inflicted by the living Komodo dragon or ora. By analogy, the hunting and feeding behavior of tyrannosaurs may have resembled that of the ora.

Serrations and slots are widely distributed among cutting devices in the natural world, and many of these deserve further study. For example, the carnassial teeth of mammalian carnivores cut by a combination of static force at the cutting edge, a crushing or scissoring action at the advancing junction between upper and lower teeth, and by lateral gripping and compression in a slot, like that seen on a much smaller scale in tyrannosaurid serrations. Mammalian teeth operate well only when deployed with sophisticated control over jaw movement, however, and the fine neural control necessary to operate them may have formed the basis for the later development of intelligence in mammals.

Previously, being interested in mammals was largely a matter of being interested in teeth, whereas being interested in reptiles was largely a matter of being interested in everything but teeth. I suggest that the teeth of at least some reptiles are as rich in information as the teeth of any mammals.

Dental measurements are commonly used in the diagnosis of fossil elephant species, yet elephant teeth develop slowly, within a highly dynamic context that enhances opportunities for physical deformation (or its subtler manifestation, quantitative phenotypic variation). This paper examines intraspecific variation in elephant teeth and compares it with variability in other mammals (83 species in 7 orders). I conclude that (1) male elephants tend to have slightly larger cheek teeth than females, though the difference is not marked; (2) of the full complement of six cheek teeth per jaw quadrant, no single tooth consistently varies less than the others (so on this basis, for taxonomic decisions no tooth is preferable to the customarily used M3 = tooth VI); (3) single-population samples vary less than more inclusive, geographically heterogeneous samples of elephant teeth; (4) although differential wear and eruption are important sources of variation in dental measurements, complete elephant teeth are consistently more variable in length and width than the cheek teeth of other mammals; (5) variability in dental dimensions of recognized fossil species of elephants is in general not grossly inconsistent with variability noted in modern elephants, but there are some exceptions. With the information and guidelines presented here, consideration of variability, and assessment of the statistical power permitted by available samples, can enhance confidence and precision in the delimitation of species and provide a firmer basis for macroevolutionary inferences.

This study assesses swimming potential in a variety of ammonoid shell shapes on the basis of coefficients of drag (Cd) and the power needed to maintain a constant velocity. Reynolds numbers (Re) relevant to swimming ammonoids, and lower than those previously studied, were examined. Power consumption was scaled to a range of sizes and swimming velocities. Estimates of power available derived from studies of oxygen consumption in modern cephalopods and fish were used to calculate maximum sustainable swimming velocities (MSV).

Laterally compressed, small thickness ratio (t. r.) ammonoids, previously assumed to be the most efficient swimmers, do not experience the lowest drag or power consumption at all sizes and velocities. At low values of size and velocity associated with Reynolds numbers below 104, less compressed forms have smaller drag coefficients and reduced power requirements. At hatching a roughly spherical shell shape would have minimized drag in ammonoids; with increasing size, hydrodynamic optima shift toward compressed morphologies.

The high energetic cost of ammonoid locomotion may have limited dispersal and excluded ammonoids from high current velocity environments.

Polymorphism is being actively investigated by ostracode specialists because the phenomenon is widespread and may be a key to understanding speciation patterns and evolutionary processes. However, the methods for recognizing the phenomenon and the cause or causes of polymorphism are still under debate. This study presents an example of genetically controlled ostracode dimorphism in which the relationship between the two forms can be explained in terms of heterochrony. The living males as well as the females of Loxoconcha uranouchiensis in Aburatsubo Cove, central Japan, are found to be dimorphic in size, shape, and surface ornamentation of the carapace. The dimorphic forms appear concurrently in the same microhabitat, suggesting that the dimorphism is genetically rather than environmentally controlled. Although the large and the small forms are indistinguishable in their early stages, morphological differences gradually appear and become complete after the final molting, which is the seventh molting for both forms. The characters determined by the number of moltings, such as the numbers of reticules, bristles, and pores, are identical between adults of the two forms. In contrast, for characters affected by the growth condition of the epidermal-cell system, such as carapace shape and fine surface ornamentation, the small-form adult is similar to the penultimate instar of the large form. Taking the large form as a standard, the small form is paedomorphic. These two forms are reproductively isolated and should be considered different species.