Time is so fundamental to the everyday thinking of paleobiologists and geologists that it is seldom given close critical attention. Many of the currently debated issues in evolutionary history—catastrophic extinctions and punctuated vs. gradual morphological change, for instance—include assumptions about time and rate which are seldom made explicit. Methods now exist for calibrating evolutionary patterns through estimates of time components in the fossil and sedimentological records. There is a growing realization that increased precision in defining time frameworks can greatly clarify evolutionary problems. This has helped to stimulate renewed interest in the traditional topic of time and how it is represented in the biological and geological record.

In earlier and simpler times in North American geology, there was an extraordinarily large amount of unexplored ground per available geologist to study it. State and territorial geological surveys, which undertook the first comprehensive mapping programs in the nineteenth century, were at first able to make only the grossest descriptions of outcrops in order to complete their assignments to map an area. In these pioneer surveys, black shales stood out as very easily identifiable strata; characteristically colored, fine grained, with distinctive lamination, and well known to lack fossils found so commonly in adjacent strata. “Black shale, undivided” is a very familiar legend in older outcrop descriptions; the lack of comparability of black shales to other strata effectively prevented their division, for both conceptual and technical reasons. This is one of the many paradoxes we can recognize in relation to black shales; they are as difficult to interpret as they are easy to recognize.

The most popular theoretical propositions are often those which spell the final doom to a notion that has already fallen into disrepute. This is as true today as it was when August Weismann (1892) published his seminal volume, Der Keimplasma, which far more than Cuvier's vituperative attacks, put the ideas of Lamarck to final rest.

Historical biogeographers are divided over the major process whereby extant species, or their ancestors, arrived in their present geographical locations. One faction promotes the idea of discrete “centers” of evolutionary radiation, from which species have been supplied to other areas by long-distance dispersal. A second faction advances the notion of widespread ancestral biotas, which have been fractionated into descendant biotas over time (vicariance). A seemingly endless polemic has elevated these rather simple alternatives to causes célèbres, and many workers have responded by dismissing virtually the entire vicariance literature (see Pielou 1981). We believe that the important distinction between vicariance and center-of-origin/long-distance-dispersal can be made clear to those interested in questions of paleobiogeography. In our opinion, the recent contribution by Briggs (1981) in this journal did not do so, and we now take the opportunity to try.

Stratigraphic range data are used to derive time scales on which taxonomic survivorship curves for genera and families are as nearly as possible independent of their times of origin. These time scales correct for temporal variations in overall extinction rates caused by major extinctions and the pull of the Recent. Survivorship curves for genera and families on their respective time scales are well fit by Pareto distributions differing only in their scale parameter.

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.

Bases of attachment of Archimedes colonies are very rare, but many colonies show evidence of origination from a pre-existing set of branches. The evidence consists of spiralled supports (axial screws) originating from fragments of pre-existing sets of branches, proximal taper of colonies or axial screws to a diameter smaller than that of bases of attachment, early stages of new colonies originating from the whorl margins of older colonies, and sets of laterally fused colonies. In the most favorable environments Archimedes populations were dominated by a few genets that consisted of hundreds to perhaps thousands of genetically identical colonies.

The ability to reproduce by colony fragmentation was probably an important cause of Archimedes' abundance in the Chesterian seas of eastern North America, especially where it occurred in dense populations in the lee of submarine carbonate shoals. Colony fragmentation, the importance of which is becoming increasingly recognized in modern corals and bryozoans, was also of importance in Paleozoic seas.

Evolutionary changes in herbivore abundance, diversity, and ability to excavate calcareous substrata occurred independently in three major herbivore groups: mollusks, urchins, and fish. These changes in herbivory have escalated dramatically since the mid-Mesozoic Era to the extent that herbivory today is more intense than at any time in the past.

Today, calcareous red algal crusts (i.e., corallines) are a conspicuous and frequently dominant element of shallow marine communities. Corallines and their (assumed) parent taxon, solenopores, probably always required grazing to remain free of epiphytes. The large scale evolutionary trend toward increased grazing intensity may have given the corallines a distinct advantage over the more herbivore-susceptible solenopores. Four anatomical characters unique to corallines may have facilitated their rapid expansion into shallow reef environments and subsequently (more than 100 million years later) allowed them to withstand the more intense levels of grazing that evolved in those environments. Today corallines are the only algal form to thrive under, and often even require, intensive herbivory. The extinction of solenopores and the adaptive radiation of corallines parallel a gradient of escalating herbivory over time.

Herbivores capable of excavating calcareous substrate are also frequently capable of denuding, and preventing the establishment of, stands of large leathery (kelp-like) macrophytes. It is possible that large-scale increases in herbivory have caused large-scale reduction of algal biomass in benthic communities. The presence of algal forests especially in the Paleozoic and early Mesozoic Eras may be a new variable to consider in reconstructing paleoenvironments.

656 mandibles and isolated teeth of the bovid Pachytragus solignaci Robinson from two localities in the Miocene Beglia Formation, Gafsa, Tunisia, have been individually aged on the basis of ontogenetic development and state of dental wear. The sample probably represents normal but seasonally restricted mortality. Life table analysis indicates an annual mortality rate of 25–30%, increasing in old animals. Dental dimensions are affected by stabilizing selection which sets in as the tooth comes into function, earlier mortality being nonselective in that respect.

The age (mortality) profiles of ungulate species in a fossil fauna are useful for reconstructing modes of death and of bone accumulation. Crown height measurements probably provide the most practical means of obtaining age profiles in most fossil samples. Reliable, interpretable profiles will result when individual age is estimated from crown height using a mathematical model first suggested by C. A. Spinage and when the individual ages are grouped into relatively broad age classes. One potential objection to the model is that it requires tedious calculation and there is a strong possibility of calculation error when many crown heights are involved. This problem may be circumvented by the use of an interactive BASIC program appended to this paper. The user supplies the raw crown heights in a fossil sample, together with estimates of initial unworn crown height, ages of dental shedding and eruption, and maximum possible individual age. The program then tabulates the number of individuals in successive 10%-of-potential-lifespan intervals.

The hypothesis that there is a characteristic rate of exponential radiation for the Insecta is tested for forty-nine of the most diverse family-level taxa in the Coleoptera, Diptera, and Hymenoptera. Data used are estimates of Recent species diversity and age of first appearance in the fossil record, as in the original statement of the hypothesis by Stanley (1979). There is no evidence of a characteristic radiation rate for the insects. A more exact method is proposed for identifying clades that are radiating exponentially. When applied to Stanley's data for the mammalian family Bovidae, it indicates that the Bovidae are not radiating exponentially at a characteristic rate. Future research might emphasize the reliable identification of clades that are radiating exponentially, prior to drawing conclusions about rates that might characterize higher taxa.