Paedomorphosis has played an important evolutionary role in several vertebrate lineages, yet there are few studies in which fossils have been used to document this evolutionary pattern directly. The unusually good fossil record of lungfishes offers an excellent opportunity to do this. An approach to recognizing paedomorphic character complexes in fossil lineages is formalized, and the interdependence of ontogenetic and phylogenetic studies is reemphasized. Concordant evolutionary changes in seven characters representing a variety of organ systems are discussed. For example, in Devonian lungfishes, the tail is heterocercal, endochondrally ossified bones are present, and the fin rays are similar to those of other Osteichthyes. Recent lungfishes have protocercal tails, suppression of endochondral ossification, and greatly reduced fin rays. The data suggest that paedomorphosis played a pervasive role in the evolution of lungfishes and give further evidence for the evolutionary importance of heterochrony.

Some statistical methods are described for the detection and estimation of variability in the rate of evolution, from biometrical data on single characters in fossil lineages. The methods were applied to some published examples of protistan and mammalian lineages, extending between 0.8 and 6.4 Myr in duration. Of six cases examined, only one failed to show evidence for significant variation in the rate of evolution, and only four deviated significantly from a random walk pattern, despite significant net evolutionary change in all cases but one.

Formulae are developed for the fraction of the population that must be eliminated by selection in each generation in order to account for a given rate of evolution in a metrical trait. A combination of directional and stabilizing selection is assumed. The effects of competition based on phenotypic value are also considered. The formulae are applied to data on evolutionary rates and their variances. It is concluded that most selective elimination is due to stabilizing selection, and that even very rapid evolutionary change in a single character usually involves low levels of additional elimination. It is suggested that long-sustained evolutionary trends are unlikely to be caused either by gradual change of the optimum under stabilizing selection or by the effects of competitive selection in favor of extreme individuals. It is possible that genetic correlations between traits under selection may limit the response of a single trait to directional selection and hence produce very gradual change.

Several important questions in evolutionary biology and paleobiology involve sources of variation in extinction rates. In all cases of which we are aware, extinction rates have been estimated from data in which the probability that an observation (e.g., a fossil taxon) will occur is related both to extinction rates and to what we term encounter probabilities. Any statistical method for analyzing fossil data should at a minimum permit separate inferences on these two components. We develop a method for estimating taxonomic extinction rates from stratigraphic range data and for testing hypotheses about variability in these rates. We use this method to estimate extinction rates and to test the hypothesis of constant extinction rates for several sets of stratigraphic range data. The results of our tests support the hypothesis that extinction rates varied over the geologic time periods examined. We also present a test that can be used to identify periods of high or low extinction probabilities and provide an example using Phanerozoic invertebrate data. Extinction rates should be analyzed using stochastic models, in which it is recognized that stratigraphic samples are random variates and that sampling is imperfect.

Taphonomic analysis of several late Pleistocene mastodon (Mammut americanum) skeletons excavated in southern Michigan provides compelling evidence of mastodon butchery by Paleo-Indians. The occurrence of butchery and details of butchering technique are inferred primarily from patterns of bone modification. An important aspect of butchering practice was production and use of tools fashioned from bones of the animal being butchered. Evidence for butchery and bone tool use includes matching marks on the conarticular surfaces of disarticulated pairs of bones; cutmarks on bones; green bone fracturing; use wear, secondary flaking, and impact features on bone fragments; and burned bone. Interpretation of these features is facilitated by information on patterns of bone distribution and disarticulation preserved in a primary depositional context. Preliminary comparisons among nine sites indicate that putative butchering sites differ consistently and in a variety of ways from sites that appear to record no human involvement. Although based on a small sample of sites, the apparent frequency of butchered individuals relative to those that were not butchered is unexpectedly high. These findings provide new evidence of a well-developed “bone technology” employed by the late Pleistocene human inhabitants of eastern North America. In addition, these data offer circumstantial support for the hypothesis that human hunting was an important factor in the late Pleistocene extinction of mastodons.

Scanning electron microscope (SEM) examination of bone surfaces from the Pleasant Lake mastodon, excavated in southern Michigan, documents features indicative of butchery. These features are identified by comparison with modern bones modified by human and natural processes. We report new studies of (1) marks made by bone tools during removal of meat from and disarticulation of carcasses and (2) use wear developed on bone tools. We also apply previously developed criteria for recognizing stone tool cutmarks and stages in the burning of bone. The Pleasant Lake site, dated to between 10,395 ± 100 and 12,845 ± 165 b.p., provides compelling evidence of mastodon butchery and bone tool use. Another site, near New Hudson, Michigan, provides replication of much of this evidence. Together these sites offer new examples of patterns of bone modification and extend the geographic and temporal representation of the much discussed, but still controversial, late Pleistocene bone technology.

The sequences of skeletal disarticulation in a broad range of African mammals in a tropical savanna environment suggest that in general the process is very consistent. There is some variation among species, but this cannot yet be convincingly related to higher taxonomic categories or to body size. Disarticulation begins shortly after death, proceeds more or less continuously, and is almost complete after 5 yr. Because of the overall predictability of disarticulation, the stage of disarticulation reached by comparable fossil skeletons provides useful information about their taphonomic history prior to burial.