The recurring debate over the causes of the massive extinctions of such groups as the dinosaurs, ammonites, and calcareous nannoplankton, and the crash of the distinctive Aquilapollenites pollen province, used by biostratigraphers to mark the close of the Cretaceous, has been considerably enlivened with the resurgence of hypotheses suggesting catastrophic events. The impact of an asteroid, explosion of a supernova, sudden changes in oceanic circulation and composition, or atmospheric perturbations, to mention a few, have been put forward as malefactors. But, just how sound is the evidence of a biotic catastrophe?

Life history theory has undergone considerable scrutiny since Stearns (1976) pointed out that neither the deterministic nor the stochastic theories, then current, provided an adequate fit for much of the empirical data he reviewed. Today, opinions on the future of life history studies may vary according to one's view of the mode of operation of evolution itself, the gradualist recommending detailed intraspecific studies and selection experiments, and the punctuationist aiming toward models involving laboratory speciation experiments (Stearns 1980).

It is somewhat dismaying, if not surprising, that so many trained biologists know that dinosaurs may have been “hot-blooded,” yet are completely unaware of even the existence of the mammal-like reptiles, the Therapsida. The reasons for the dearth of widespread knowledge of the therapsids are probably fairly mundane: the mammal-like reptiles are less spectacular in appearance than dinosaurs, and good therapsid fossil localities are restricted primarily to the southern hemisphere. As a result, therapsids seldom become the subjects of museum displays or classroom student presentations. Moreover, biology textbooks, whether at the high school or college level, almost invariably devote more space for recounting the “dinosaur story” than to discussing the therapsid reptiles (1). Consequently, although application of biological systems data to the fossil record has become increasingly popular and useful in the last decade, many neontologists who might potentially make substantial contributions to our knowledge of therapsid biology remain oblivious to the significance of these animals. This is particularly unfortunate—therapsids are, of course, the direct predecessors of mammals, and, as such, the more we understand the mammal-like reptiles the more likely we are to understand the origins and functions of our own anatomical, physiological, and behavioral systems.

Chemical analyses of fossil plants and their associated sediments are currently providing the paleobotanist with biochemical information relevant to the reconstruction of taxonomic relationships. The isolation and chemical identification of various plant pigments from fossils, such as flavonoids and carotenoids (compounds that give flowers their characteristic colors), steroids, fatty acids, and a host of plant phenolic acids, provide the opportunity to characterize the specific paleophytochemical profiles of fossil species.

No one needs reminding that we are well into a revolutionary phase in the study of evolution, systematics, and the interrelationships of organisms. To belabor the metaphor a little, to the thesis of Darwinian evolution and Mayrian systematics has been added a new cladistic antithesis which says that the search for ancestors is a fool's errand, that all we can do is determine sister group relationships of monophyletic taxa based on the analysis of derived characters. Consequently, our attention should be focused upon patterns which can be delineated, discussed, and modified in the light of new data, rather than upon processes which may only be the subject of untestable hypotheses. It is a change in approach that is not easy to accept for, in a sense, it runs counter to what we have all been taught, and it is particularly difficult for the paleontologist to accept because a major feature of the approach is a concentration upon living rather than on fossil forms. In fact, fossils are, in general, either difficult to use or irrelevant, or both, in terms of new attempts to set out the relationships of the major groups of organisms. The subject of this brief notice is a critically important new addition to the literature on this growing, dare I say evolving, subject.

Birds have traditionally been termed the best known group of vertebrates. This cliché, however, relates to the fact that living species are well described, even to the subspecies level. Birds are well known because they are diurnal (therefore easily observed) and because of their aesthetic appeal—birds are beautiful. Because of this appeal, birds have been subject to persistent scrutiny by amateur and professional naturalists alike, and their study has consequently contributed to the development of not only evolutionary thought, but also such diverse fields as ecology, behavior and even comparative physiology. However, while these disciplines have advanced, our understanding of bird phylogeny and evolution has simply not kept pace and the relationships of the higher categories of birds are still very poorly understood.

Modern paleoanthropology is broadly interdisciplinary, integrating the results of studies in hominid (or more generally primate) paleontology, morphology and systematics with archeology, stratigraphy, chronometry, general paleontology, taphonomy and ecology, among other fields. (I here employ the term “hominid” to include all advanced hominoids of Miocene to Pleistocene age, following Delson and Andrews, 1975; similarly “hominine” (or “human”) refers to members of the subfamily Homininae of this usage, especially Australopithecus and Homo. Many other authors restrict hominine/human to Homo alone, employing hominid where I use hominine.) This integrative approach has been both spectacular and successful in eastern Africa (see Laporte 1980), due to the influence of F. C. Howell, the Leakeys and their colleagues, but it has also been responsible for recent advances in other temporal and spatial intervals in human evolution. In this review, I will concentrate on the morpho-evolutionary aspects of recent paleoanthropological studies, indicating major sources and new developments. Most fossils not otherwise referenced are discussed, albeit often with a different interpretation, in Wolpoff's (1980a) text.

The review of current developments in paleobotany by Knoll and Rothwell (1981) prompts some supplementary observations on the state of marine paleobotany and, more generally, the problem of investigating groups with a poor fossil record. The marine angiosperms and the larger noncalcareous algae are such groups, being represented by very few fossils widely scattered in time and space (den Hartog 1970; Parker and Dawson 1965). Tropical freshwater macrophytes are likewise poorly known as fossils (Sculthorpe 1967).

A current question being debated with considerable intensity is whether or not certain geographic areas act as centers of evolutionary radiation and supply species to other areas that are less active or less effective in an evolutionary sense. Darwin (1859) was the first to write about centers of origin which he called “single centers of creation.” He argued that each species was first produced within a single region and that it subsequently migrated from that area as far as its powers of migration and subsistence under past and present conditions permitted. Adams (1902), in discussing the influence of the southeastern United States as a center of distribution for the flora and fauna of North America, provided a series of criteria for the determination of “centers of dispersal.” His first, and evidently most important criterion was the location of “the greatest differentiation of a type.”

In the past twenty years, both knowledge of fossil plants and ways of looking at the paleobotanical record have expanded significantly. Studies of Precambrian microfossils have provided insight on early photoautotrophs, while fundamental changes in perceptions of Silurian and Devonian plant remains have clarified our understanding of the colonization of land, as well as the subsequent evolution of complex stems, leaves, and the seed habit. A recurring question concerns the phylogenetic relationships of gymnosperms: is the gymnospermy found in various living and extinct taxa the result of evolutionary convergence or of common descent? Rapidly accumulating data on the reproductive and developmental biology of Paleozoic seed ferns is reopening debate on this issue. The mystery of angiosperm origins remains “abominable”, but the past two decades of research have seen convincing documentation of the initial radiation and rise to taxonomic and ecological dominance of the flowering plants.

While phylogenetic and systematic botany remain at the core of paleobotanical research, increased attention is being devoted to studies of ontogeny and reproductive biology, paleoecology, taphonomy, paleophytochemistry, paleoclimatology, and paleobiogeography. Studies of evolutionary rates and diversity are in their infancy, but initial results permit an optimistic appraisal of the contributions that paleobotanists can make to evolutionary paleontology.

A diffusion model of the distribution of a phenotypic character in a group of species is developed and analyzed. The model incorporates the combined effects of phyletic evolution, speciation and extinction. Directed speciation is modeled by assuming there is some bias to phenotypic changes during speciation. Species selection is modeled by assuming there is some dependence of either speciation or extinction rates on the phenotypic character. Three examples are analyzed to illustrate the use of the model. A model of completely random changes due to both phyletic evolution and speciation shows how between-species differences are established. A model of directed speciation due to multiplicative changes during speciation shows how a simple assumption about the speciation process can produce macroevolutionary trends. A model of species selection due to differences in extinction rates shows how the efficacy of species selection depends on the between-species variance produced both by speciation and by phyletic evolution.

Writers as disparate in professional interest as those describing speciation in Drosophila, predicting weather, or supporting creationism have all recently focused on the “sudden” appearance of taxa in the geologic record. In the process, each has cited the punctuated equilibrium argument. Owing to the enormously wide attention which this issue has received since its introduction almost a decade ago, it seems worthwhile to try to place the paleontological and biological evidence in a 1981 perspective. The focus I have chosen is to try to analyze the issue, much as in recent columns in Current Happenings on competitive exclusion, and on larval dispersal and biogeography, in which are put forth alternative explanations for a set of data on a general problem.

Micropaleontology is a peculiar subject: it is not easily defined, it focuses on geologic problems, and it ignores fundamental paleontologic and evolutionary questions it could best attack. As a result of its historic development, micropaleontology is directed to the solution of stratigraphic, paleoceanographic and paleoclimatologic problems, but it has seldom addressed paleobiologic or evolutionary ideas. It is a tradition rather than a discipline. The term “micropaleontology” and all it signifies should be abandoned, for it obscures natural relationships, attracts people with geologic rather than biologic approaches, isolates its practitioners in a blanket of systematics, biostratigraphies, and terminologies, and, as a result, discourages outsiders with other viewpoints or contributions from utilizing its fine fossil record. The growth of the field has been exponential in people-power and literature but not in the development of fundamentally new ideas. Micropaleontology has therefore contributed little to recent paleobiologic or evolutionary hypotheses, in spite of the possession by the many organisms relegated to it of biological properties and fossil records which have much potential for the generation and testing of such hypotheses. Microfossil studies have served geology powerfully and they should continue in that role, but they should also be used to fulfill their promise in the interpretation of paleobiogeography, paleoecology, morphology, evolutionary processes and the origin of new groups and ground plans.

Data on numbers of marine families within 91 metazoan classes known from the Phanerozoic fossil record are analyzed. The distribution of the 2800 fossil families among the classes is very uneven, with most belonging to a small minority of classes. Similarly, the stratigraphic distribution of the classes is very uneven, with most first appearing early in the Paleozoic and with many of the smaller classes becoming extinct before the end of that era. However, despite this unevenness, a Q-mode factor analysis indicates that the structure of these data is rather simple. Only three factors are needed to account for more than 90% of the data. These factors are interpreted as reflecting the three great “evolutionary faunas” of the Phanerozoic marine record: a trilobite-dominated Cambrian fauna, a brachiopod-dominated later Paleozoic fauna, and a mollusc-dominated Mesozoic-Cenozoic, or “modern,” fauna. Lesser factors relate to slow taxonomic turnover within the major faunas through time and to unique aspects of particular taxa and times.

Each of the three major faunas seems to have its own characteristic diversity so that its expansion or contraction appears as being intimately associated with a particular phase in the history of total marine diversity. The Cambrian fauna expands rapidly during the Early Cambrian radiations and maintains dominance during the Middle to Late Cambrian “equilibrium.” The Paleozoic fauna then ascends to dominance during the Ordovician radiations, which increase diversity dramatically; this new fauna then maintains dominance throughout the long interval of apparent equilibrium that lasts until the end of the Paleozoic Era. The modern fauna, which slowly increases in importance during the Paleozoic Era, quickly rises to dominance with the Late Permian extinctions and maintains that status during the general rise in diversity to the apparent maximum in the Neogene. The increase in diversity associated with the expansion of each new fauna appears to coincide with an approximately exponential decline of the previously dominant fauna, suggesting possible displacement of each evolutionary fauna by its successor.

Almost at the end of his chapter on Mutation, G. G. Simpson in 1953 in The Major Features of Evolution noted that “There is also increasing evidence that mutation rate is itself, to some degree, a genetically controlled character.” If for mutation one uses the broad definition of the origin of new hereditary types, then the glimmerings to which Simpson referred now have become a documented fact at the molecular level.

A simple theoretical argument shows that the evolutionary process will look gradual if it is considered on too fine or too coarse a time scale. There exists an intermediate time scale in which the distribution of evolutionary rates will appear as bimodal.

Ricklefs (1980) suggested the use of neontological data to distinguish between puncuated equilibrium and gradualism as modes of evolution. This paper investigates his model and finds it contains oversimplifications that make any test difficult. We modify his model slightly and use it as a limited test of punctuated equilibrium by large morphological shifts at speciation. This test is applied to a data set of 110 species from two families of bats, the Emballonuridae and the Molossidae. We find no evidence of consistently large morphological shifts at the formation of subspecies, species or genera.

Almost every living and fossil group of gymnosperms has been proposed as a possible ancestor of angiosperms. A common problem with many of these proposals is their reliance on hypothetical intermediate forms. Another common problem is finding correctly-oriented organs homologous to all the important reproductive structures of angiosperms.

These problems are least troublesome for a glossopterid origin of angiosperms. Recently discovered ovule-bearing organs of these plants may represent evolutionary intermediates, or analogous plants, between glossopterids and angiosperms. According to recent reinterpretations of glossopterid ovule-bearing organs, they have structures in an orientation which may be homologous with both the outer ovular integument and the carpel of angiosperms. Considering the reproductive and vegetative features of glossopterids, the hypothesis that they may be part of a stock ancestral to angiosperms should be seriously considered.

A theoretical approach to the analysis of historical factors (Raup 1972) in evolutionary morphology is presented which addresses transformational hypotheses about structural systems. This (structural) approach to testing historical hypotheses about phylogenetic constraints on form and function and structural and functional versatility involves (1) the reconstruction of nested sets of structural features in monophyletic taxa, (2) the use of general or emergent organizational properties of structural and functional systems (as opposed to uniquely derived morphological features), and (3) the comparative examination of the consequences for structural and functional diversity of these general features in related monophyletic taxa.

Three examples of emergent organizational properties are considered: structural complexity, repetition of parts, and the decoupling of primitively constrained systems. Two classes of hypotheses about the evolution of design are proposed. Transformational hypotheses concern historical pathways of change in form as a consequence of general organizational features which are primitive for a lineage. Relational hypotheses involve correlations between structure-function networks primitive for a clade and morphological diversity both between and within terminal taxa. To the extent that transformational and relational hypotheses about form are corroborated, they provide evidence of underlying regularity in the transformation of organic design that may be a consequence of the hierarchical organization of structural and functional patterns in organisms.

The classic biometrical study of phyletic evolution in Kosmoceras (Brinkmann 1929) is evaluated using unpublished raw data provided by Professor Brinkmann. Most morphological characters show statistically significant changes over time yet it is difficult to provide an unequivocal biological interpretation for these changes. In a few cases, runs tests indicate that evolution was nonrandom in the sense that fewer reversals in the direction of evolution occurred than would be predicted from a null hypothesis based on a random walk. These cases suggest persistence of natural selection regimes for fairly long periods of time. In other cases, and with other kinds of testing, the random walk model cannot be rejected although failure to reject the hypothesis does not justify its acceptance! Thus, the contribution of random factors (either genetic drift or selection in a randomly changing environment) cannot be assessed with confidence. It is problematical also whether the Kosmoceras series represent significant evolution by phyletic gradualism or just the natural temporal variation that characterizes stasis (sensu Eldredge and Gould 1972).