A marked retardation of dental ontogeny characterizes the family Elephantidae. As a consequence of this retardation, elephant teeth are subject to the forces of mastication, eruption, and progression while still in a developing and pliant stage. As specimens described here illustrate, the mechanical forces are often sufficient to deform the gross morphology of dentitions. Morphological variation in elephant teeth can be regarded as “fabricational noise”—revealing information about the dynamic context in which the teeth develop. Accordingly, dental variation is less species-specific in elephants than in other mammals. The fossil record may comprise fewer species of elephants than is generally believed, and trends inferred to reflect rapid evolution within this family may in fact reflect phenotypic plasticity.

Sublethal injuries recorded in the shells of five Upper Mississippian ammonoid species from the Imo Formation of northwest Arkansas are manifested as repaired shell breaks, which can be categorized as minor, moderate, massive, deep-acute, or as perforations. Overall, 15% of the ammonoids exhibit some form of repaired break. The injuries are distributed as follows: Anthracoceras discus 9%; Fayettevillea bransoni 13%; Fayettevillea friscoense 21%; Rhadinites miseri 24%; Richardsonites mapesi 38%. These figures are substantially lower than in living Nautilus, in which more than one-half of adult specimens exhibit repaired shell breaks. The different frequencies of injuries may reflect species-selective predation, differential abilities to sustain and to repair shell damage, or they may be due to interspecific differences in physical parameters such as shell thickness and body chamber length. The most likely possible perpetrators of the injuries include sharks, other fishes, and cephalopods.

The tailbend, a downward flexure of the vertebral column, is a prominent feature of post-Triassic ichthyosaurs. However, due to the vagaries of preservation and of preparation, its presence cannot be verified in all skeletons. Computed tomography offers a solution to the problem by identifying the wedge-shaped centra that contribute to the tailbend. Leptopterygius tenuirostris appears to have a tailbend, albeit slightly downturned. There is also evidence that its close relative Eurhinosaurus longirostris had a tailbend, too.

Application of multivariate statistical techniques, especially correspondence analysis, results in the recognition of four major communities for the Creede plant assemblages: fir-spruce forest, fir-pine forest, pine-juniper forest or woodland, and mountain mahogany chaparral. Physiognomy of the Creede assemblages indicates a mean annual temperature of <2.5°C. Paleoaltitudinal estimates based on this temperature estimate are inconsistent with physiographic and structural data of post-depositional uplift, unless the climatic effects of a closed basin are factored in; these effects imply that the Creede paleotemperature (and hence paleoaltitude) is applicable to the caldera rim. A variety of data indicate that summers were dry and most precipitation occurred as snow. The stratigraphic sequence of assemblages indicates that significant precipitational change occurred during deposition of the Creede plant-bearing beds. Chamaebatiaria, a shrub that now inhabits dry, open environments, had an ancestral taxon characteristic of the Creede fir-forest communities and strongly indicates a major shift in habitat for this lineage during the Neogene. A second genus, Luetkea, which is now herbaceous, is represented by a probable woody ancestral taxon that was common in the Creede forest communities. Consideration of the adaptive and morphologic histories of the Creede lineages suggests that physiologic adaptation may precede morphologic change. The Creede forest communities have no modern homologues.

Using queueing theory and the fast Fourier transform, we develop a new approach to analyzing the diversity paths of fossil taxa. The methods employed focus on calculating the probabilities, for each taxonomic group, of arriving at particular values of the diversity at particular times, assuming that diversity paths are random walks. These probabilities, which are represented in probability matrices, allow us to establish a number of null hypotheses that can be used to test for randomness in the diversity paths of the taxonomic groups themselves. As the model employed here is conceptually similar to that employed by Gilinsky and Bambach (1986) in bootstrapping, one consequence of the approach is, in effect, an analytic solution of the bootstrap. A comparison of bootstrapping and analytic results in 15 taxa of marine invertebrates gives nearly identical results. The analytic approach is more general, however, and allows for the calculation of probability matrices under other model assumptions not treated here. We have also applied the probability matrices to a series of tests for nonrandomness as a whole, in contrast to the more usual method of testing particular clade statistics. The familial diversity paths of all 36 extinct orders of marine invertebrates with ten or more families were analyzed. In no case was the null hypothesis of randomness rejected at the 0.05 level. Given the model, and assuming that extinct taxa are representative of all taxa, the familial diversity paths of marine orders appear to behave as random walks.