The frequency of sublethal damage was examined in two ophiuroid species, Palaeocoma milleri and ?Ophioderma tenuibrachiata (Ophiodermatidae), from a shallow-water Jurassic “starfish bed.” None of 60 specimens was regenerating arms, a result that agrees with four previous studies of Paleozoic and early Mesozoic ophiuroids. By contrast, 66.1 percent of a living Ophioderma brevispinum population from Belize were regenerating one or more arms. For living populations of Ophiothrix oerstedi, the natural injury frequency was high at sites where the field mortality of tethered individuals was high. All predators that have been observed feeding on ophiuroids cause sublethal injuries, which would appear as regenerating arms in the fossil record. These results support the hypothesis that predation pressure on ancient ophiuroid populations was low and increased after the Jurassic.

Endothermic tetrapods differ dramatically from ectothermic tetrapods in having a great capacity to sustain vigorous locomotion. I suggest that this difference reflects alternative adaptive responses to a mechanical constraint that was an inherent consequence of the vertebrate transition from aquatic to terrestrial modes of locomotion and respiration. The earliest tetrapods may not have been able to walk and breathe at the same time. Their sprawling gait and lateral vertebral bending would have required unilateral contractions of the thoracic musculature that may have interfered with the bilateral movements necessary for breathing. Modern lizards, whose locomotor and respiratory anatomy resembles that of the early tetrapods, provide support for this hypothesis because their breathing is greatly reduced during locomotor activity. Tetrapod lineages that gave rise to modern ectotherms apparently retained the constraint, becoming either highly specialized for burst activity based on anaerobic metabolism or specialized in passive mechanisms of defense against predators. The lineages from which birds and mammals are derived have undergone morphological changes that enable simultaneous running and breathing. In modern tetrapods upright posture is correlated with endothermic metabolism. This correlation may have arisen to circumvent ancestral constraints on locomotor stamina.

Before one can study evolutionary rates one must reject the null model of symmetric random walk. for which the requisite quantity does not exist. As random walks reliably simulate all the features we find so compelling in the fossil record—jumps, trends, and irregular cycles—rejection of this irritating hypothesis is much more difficult than one might hope. This paper reviews principal theorems from the mathematical literature of random walk and shows how they may be applied to empirical data by scaling net changes according to the square root of elapsed time. The notorious pair of “opposite” findings, equilibrium and anagenesis, may be construed as deviations from random walk in opposite directions. Malmgren's data on Globorotalia tumida, previously interpreted as an example of punctuated anagenesis, are consistent with a random walk showing neither punctuation nor anagenesis, but instead varying in speed over four subsequences.

Cretaceous floras in Alaska, when compared to those at mid-latitudes, generally indicate later appearances in Alaska of major clades and major leaf morphologies. Compared to mid-latitude floras, Alaskan Late Cretaceous floras contain few major clades. The Alaskan clades diversified but at a low taxonomic level. Migrational pathways into high latitudes were probably along streams. Similar patterns characterized the Alaskan Tertiary, although some southward migrations of lineages occurred during the Neogene.

Review of other Arctic paleontological data from Ellesmere Island, previously used to suggest that the Arctic was a major center of origin during the Late Cretaceous, indicates that the ages of supposedly substantiating dinoflagellate floras were misinterpreted. When the dinoflagellate data are interpreted according to standard methodology, first occurrences of genera and species groups on Ellesmere are, like the Alaskan occurrences, later than first occurrences at middle latitudes.

A computer model of background and mass extinctions in a taxonomic hierarchy has been used to study the effects of different extinction patterns in a search for clues as to the causes of actual extinction events. Model taxa at four levels were built up from speciation events in adaptive space according to rules of origination which seem plausible biologically. The frequency distribution of species among the three higher taxonomic levels in the model is similar to that in living marine taxa which have good fossil records. Three mass extinction patterns were imposed on the model after species diversity had attained equilibrium (i.e., when speciation = background extinction): random; bloc (contiguous niches were cleared); and clade (all members of selected higher taxa were removed). Effects on the taxonomic profile varied with pattern. Four of the five historical mass extinctions resemble the effects of the random pattern. End-Permian families were harder hit than those in the random model, but this may be a result of an extremely high species extinction level. It is concluded that the effect of extinctions on the taxonomic hierarchy provides a tool to help in understanding extinction causes.

Periodicity has recently been reported in the extinction rates of fossil marine families since the Permian. The analysis used appears particularly sensitive to parameter estimation techniques, particularly in the definition of mass extinctions. It also fails to incorporate autocorrelation in the fossil record into its null hypothesis and rests on an inappropriate a posteriori comparison to the null hypothesis. An alternative analysis, examining the time-lags between periods of high extinction rates, produces no evidence of a cycle.

In both jaw geometry and molar morphology, eutherian carnivores (order Carnivora) as a whole display greater diversity (plasticity in evolution from the primitive type) than marsupial carnivores (order Dasyurida). This is related to the difference in tooth replacement between the two taxa. In Carnivora, the permanent carnassial is preceded by a deciduous carnassial; the permanent tooth can erupt in its (geometrically) permanent position, and the post-carnassial molars are free to evolve for specialized functions or be reduced. In Dasyurida, there is relative molar progression, each erupting molar in turn functioning as a carnassial, and subsequently being pushed forwards in the jaw by the next erupting molar. Thus, all molars have carnassiform morphology, and none are free to develop for other functions. The greater plasticity of Carnivora has led to their adaptive zone being broader (as a group they are relatively more eurytopic than Dasyurida), which in turn has led to greater taxonomic diversity within Carnivora than Dasyurida. The resulting pattern from a macroevolutionary point of view is that, even in the absence of direct competition, Carnivora have had greater evolutionary “success” than Dasyurida.

Extinctions at the top of the Sunwaptan Stage (=“Ptychaspid Biomere”) near the Cambrian-Ordovician boundary eliminated about half of North American trilobite families. The families that extend from the shelf into the upper slope show significantly higher survival than those confined to the shelf. Biofacies and lithofacies distribution patterns indicate that the extinctions cannot be attributed to a shelfwide physical environmental perturbation, such as a fall in water temperature or the spread of anoxic waters. We develop a simple biogeographic model which suggests that diversity of a faunal province is influenced profoundly by changes in the number of component biofacies. This model is tested with an analysis of biofacies distribution patterns across the upper boundary of the Sunwaptan Stage. The extinctions correspond closely to lithofacies shifts in the outer shelf that indicate the initiation of major paleogeographic changes, possibly in response to a sea-level rise. The effects of these changes cascade across the entire shelf by the shoreward migration of off-shelf and shelf-margin taxa. Biofacies become reduced in number through telescoping and their environmental ranges expand during the extinction interval, suggesting an increase in the proportion of eurytopic taxa. Selective survival of wide-ranging eurytopes may have influenced the dynamics of faunal replacement by lowering speciation rates of shelf taxa. Consequently, the proportion of shelf endemics will decline and biofacies will be dominated by immigrant taxa. There are sufficient similarities in extinction patterns across the upper boundary of the Sunwaptan Stage and those at other Upper Cambrian stage boundaries to suggest that the biogeographic model developed here may have broader application.

Two alternative hypotheses have been advanced to explain the demise of about half of the mammalian genera exceeding 5 kg in body mass in the later Pleistocene. One hypothesis invokes climatic change and resulting habitat transformations. This fails to predict the increased likelihood of extinctions with increasing body size, greater severity in both North and South America than in Eurasia or Australia, lack of simultaneous extinctions in Africa and tropical Asia, and the absence of extinctions at the end of previous glacial periods. The other hypothesis invokes human predation as the primary cause. This fails to explain the simultaneous extinctions of a number of mammalian and avian species not obviously vulnerable to human overkill. I propose a “keystone herbivore” hypothesis, based on the ecology of extant African species of megaherbivore, (i.e., animals exceeding 1,000 kg in body mass). Due to their invulnerability to non-human predation on adults, these species attain saturation densities at which they may radically transform vegetation structure and composition. African elephant can change closed woodland or thicket into open grassy savanna, and create open gaps colonized by rapidly-regenerating trees in forests. Grazing white rhinoceros and hippopotamus transform tall grasslands into lawns of more nutritious short grasses. The elimination of megaherbivores elsewhere in the world by human hunters at the end of the Pleistocene would have promoted reverse changes in vegetation. The conversion of the open parklike woodlands and mosaic grasslands typical of much of North America during the Pleistocene to the more uniform forests and prairie grasslands we find today could be a consequence. Such habitat changes would have been detrimental to the distribution and abundance of smaller herbivores dependent upon the nutrient-rich and spatially diverse vegetation created by megaherbivore impact. At the same time these species would have become more vulnerable to human predation. The elimination of megaherbivore influence is the major factor differentiating habitat changes at the end of the terminal Pleistocene glaciation from those occurring at previous glacial-interglacial transitions.

Few paleontological studies of species distribution in time and space have adequately considered the effects of sample size. Most species occur very infrequently, and therefore sample size effects may be large relative to the faunal patterns reported. Examination of 10 carefully compiled large data sets (each more than 1,000 occurrences) reveals that the species-occurrence frequency distribution of each fits the log series distribution well and therefore sample size effects can be predicted. Results show that, if the materials used in assembling a large data set are resampled, as many as 25% of the species will not be found a second time even if both samples are of the same size. If the two samples are of unequal size, then the larger sample may have as many as 70% unique species and the smaller sample no unique species. The implications of these values are important to studies of species richness, origination, and extinction patterns, and biogeographic phenomena such as endemism or province boundaries. I provide graphs showing the predicted sample size effects for a range of data set size, species richness, and relative data size. For data sets that do not fit the log series distribution well, I provide example calculations and equations which are usable without a large computer. If these graphs or equations are not used, then I suggest that species which occur infrequently be eliminated from consideration. Studies in which sample size effects are not considered should include sample size information in sufficient detail that other workers might make their own evaluation of observed faunal patterns.

Primary vascular architecture of members of the Paleozoic Aneurophytales (Progymnosper-mopsida) is described. This architecture is somewhat more complex but fundamentally similar (homologous) to that of members of the Trimerophytina, putative ancestors of aneurophytes. It is suggested that the presence of complex stelar morphology in aneurophytes was epiphenomenal, a passive result of changes in growth and development in a trimerophyte-like ancestor. Specifically, I suggest that the evolutionary transformation in primary vascular architecture from haplostele to ribbed protostele was a direct consequence of changes that affected the vertical spacing and degree of organization of lateral appendages in early vascular plants. This view is in sharp contrast to adaptationist explanations of change in stelar morphology expressed by other authors and provides an example of non-adaptive change in evolution.

Stanley's (1979) method of estimating taxonomic longevity from Lyellian curves differs from Kurtén's (1960) because of different underlying assumptions. Kurtén's model supposes that taxon richness and longevity are stochastically invariate over the period used for the Lyellian estimate. Both Kurtén and Stanley seek to calculate the average longevity of a taxon, when the temporal stratigraphic ranges are known after and before a given time datum. Under the exponential decay model used by Kurtén, mean taxonomic longevity is indeed approximately 2.89 half-lives, as he maintained. Stanley's estimate is based on the unrealistic assumptions of uniform longevity and evenly-spaced origins of fossil taxa. This leads to an estimate of longevity as exactly two half-lives.

The mean taxon duration, , and the 50 percent point of the Lyellian curve, T50, are directly proportional to one another: . However, there is a disagreement in the literature over the correct value of the proportionality constant, C. Various authors have claimed that C ≈ 1.44, C = 2.00 and C ≈ 2.89. I critically examine the assumptions underlying these three choices of C and argue that C ≈ 1.44, which is based on an exponential model of survivorship, is more widely applicable than the other values of C.

Deciduousness in mesic, broad-leaved plants occurred in disturbed, middle-latitude environments during the Late Cretaceous. Only in polar environments in the Late Cretaceous was the deciduous element dominant, although of low diversity. The terminal Cretaceous event resulted in wide-spread selection for plants of deciduous habit and diversification of deciduous taxa, thus leaving a lasting imprint on Northern Hemisphere vegetation. Various environmental factors have played important roles in subsequent diversification of mesic, broad-leaved deciduous taxa and in origination and decline of broad-leaved deciduous forests. Low diversity and rarity of mesic deciduous plants in the post-Cretaceous of the Southern Hemisphere indicate that the inferred “impact winter” of the terminal Cretaceous event had little effect on Southern Hemisphere vegetation and climate.

Six drainage basins at the margins of Trinity Lake were analyzed to determine the relations of source vegetation (largely coniferous forest) to plant debris in deltaic deposits that represent high-energy depositional environments. Thirty-one samples containing an estimated 1,043,000 identifiable plant fragments were subjected to a multivariate statistical (correspondence) analysis; in the resulting ordination, samples from the more mesic side of the lake clustered separately from samples from the drier side of the lake. The distribution of a species in the source vegetation is generally paralleled by the distribution of the same species in the samples, and all major forest trees are present in the samples. However, relative abundances in the source vegetation have no direct relation to relative abundances in the samples. Plants growing far away from depositional sites are poorly represented, even if these plants produce organs suited to long-distance transport; this occurs by dilution by material derived from plants in proximity to depositional sites and suggests that megafossil assemblages that contain putative mixtures of high-altitude “temperate” and low-altitude “thermophilic” taxa represent true biotic associations. The information gained from the Trinity analysis is compared to information gained from analysis of plant debris in low-energy depositional environments; each environment contains different kinds of information that is significant in paleoecological reconstructions of regional vegetation. Whereas high-energy environments contain the best taxonomic representation of source vegetation, low-energy environments retain information on spatial distributions of taxa within source vegetation. High-energy environments typically also contain the best representation of different organs of a given taxon.