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?

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.

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.”

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.

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.

Factor analysis of morphometric data from fossil and recent Archaeogastropoda reveals that there has been a progressive reduction in the variety of archaeogastropod shell shapes through time. High and low spired genera have slowly disappeared while equidimensional forms, which have always been the most common, have become even more abundant. The taxonomic manifestation of this trend has long been appreciated and involves: 1) the extinction of most of the Pleurotomariacea, the Euomphalacea, Trochonematacea, and several other superfamilies, which collectively comprise most of the variation in shape among early archaeogastropods, and 2) the proliferation of the primarily equidimensional Trochacea and Neritacea. I suggest that this macroevolutionary trend may be explained by the general process I refer to as “stabilizing species selection.” More specifically, I suggest that the mechanism of stabilizing species selection in the case presented here may have been differential rates of origination.

I believe that the innovative concept of species selection has been burdened by the adherence of its advocates to the idea that differential extinction is its primary mechanism. This preference for differential extinction is rooted in our emphasis upon differential mortality in microevolution and is not based upon data of macroevolutionary change. I argue that differential origination may be as important as differential extinction in directing macroevolutionary change and that demographical and autecological properties of species may be its agents. Recognition of the importance of differential origination will have an important impact upon our concept of the relationship between adaptation and the evolutionary process.

The pattern of arm branching and arm morphology in the camerate crinoid family Melocrinitidae became more complex during an evolutionary sequence which extended from Late Ordovician to Late Devonian. The fully evolved melocrinitid arm pattern bears an amazing resemblance to the theoretically ideal lay-out for harvesting roads on a banana plantation. This may not be coincidental since the problems faced by a banana plantation manager are much the same as those of a crinoid: the harvesting of an evenly distributed micro-particulate resource from an area and its delivery to a central point for processing. The analogy suggests a detailed explanation of the melocrinitid morphology and evolution. It also raises the question: why did the pattern not become dominant among crinoids if it was so efficient? It may have been unlikely to evolve; it may reflect an unusual food supply. I prefer an explanation in which the plantation pattern demands a rigidity of the crinoid crown which is characteristic of camerates but is uncommon among other crinoids: the latter have adopted a strategy of feeding which emphasizes flexibility in anatomy and behavior. The banana plantation pattern is equally rare among other organisms. Thus an “ideal” may not be common in a group of organisms for cost-benefit reasons. This does not mean that the adaptationist's approach is improper, or that random, historical, or constructional constraints routinely overwhelm adaptation. Rather, it means that cost-benefit analysis should take a larger part in functional studies, as it does in natural selection, and that theoretical ideals should be viewed with caution.

Among the various forms developed by marine colonial filter feeders, erect colonial fans have evolved in representatives of several phyla. Branches are relatively narrow, evenly spaced from one another, proliferate by bifurcation, and in most colonies continue from their point of origin to the distal margin of the colony. Their narrowness and uniform placement is apparently related to filling an area with multiple tentacle bells of similar size. The major architectural problem for such a colonial suspension feeder seems to be construction of a sheet composed of narrow branches such that water may be filtered as it flows through the sheet, between branches.

The simplest form of the filtration sheets is a uniformly expanding wedge, in which new branches originate at regular intervals from the point of origin of the wedge. Variation in rate of addition of new branches results in more complex forms, such as paraboloids, flaring fans, spirals, and highly folded sheets.

In cheilostome bryozoans with rigidly arborescent growth habits, resistance to breakage under forces generated by flowing water or collision with moving objects depends on the strength and design of supporting skeletal parts. To investigate the abilities of modern and Tertiary cheilostomes to resist breakage, we measured bending strength in fresh, preserved, and fossil material; measured drag on actual and model colonies; and calculated stress within colonies and breaking values under concentrated and uniform loads. Among nine modern, five Oligocene, and four Paleocene species, inferred live bending strength (24–85 MNm−2) and stiffness (42–65 GNm−2) appear to be species-specific properties overlapping those of similar mineral-organic composite skeletons of Mollusca. Unlike those of Mollusca, cheilostome skeletons appear isotropic in bending, with strength not clearly related to microstructure or composition. Bending strength and morphologic disposition of skeletal material combine to produce a wide range of abilities to resist breaking. At early growth stages, almost all species appear highly resistant; at later ones, some break at velocities <0.2 m sec−1 or concentrated loads <2 g, whereas others remain unbroken at velocities >2 m sec−1 or concentrated loads >100 g. A negative correlation between strength and resistance indicates that design is the more important factor in the abilities of these bryozoans to withstand forces of these kinds. An apparent trend toward more resistant designs from Paleocene to modern species is related chiefly to increasing rates at which branches thicken toward the colony base. The consequent change in design may even have permitted modern species to use weaker skeletal material while increasing their overall resistance.

Two kinds of adaptation aid infaunal bivalve mollusks in sustaining their life positions against potentially disruptive water movements: (1) ability to retard scour of surrounding sediment and (2) ability to reburrow rapidly if exhumed.

The shell of the venerid Anomalocardia brasiliana is ornamented with concentric ridges that are asymmetrical in cross-section; experiments show that these ridges aid the animal in burrowing by gripping the sediment during backward rotation of the shell. The shell of the less deeply burrowing venerid Chione cancellata also bears concentric ridges, but these are symmetrical and experiments show that they hinder burrowing; other experiments demonstrate that these ridges reduce scour of sand from around a partly exposed animal. The single cardiid species Trachycardium egmontianum possesses adaptations comparable to those of the two venerid species, in the form of spines of two varieties; experiments show that the flared anterior spines facilitate burrowing and the cupped posterior spines reduce scour.

Conspicuous ornamentation of the kinds considered here was rare throughout the Paleozoic. Its evolutionary deployment occurred primarily during the post-Paleozoic adaptive diversification of infaunal bivalves, which was triggered by the evolution of efficient burrowing mechanisms. The general premium on maintaining infaunal life positions was accentuated for bivalves after the Paleozoic by the origins of important modern predatory taxa.

We have investigated whether changes in marine faunal diversity during the Pleistocene would have been affected by changes in sea level. Our estimate of changes in area of shallow marine seas between low stand and high stand of sea level (approximately 200 m) leads to a prediction of approximately a 25% change in species diversity, 10% change in generic diversity and less than a 5% change in familial diversity. This agrees with the observation that large scale generic or familial changes have not been widely noted for the Pleistocene. As in other intervals of geologic time, changes in the sizes of faunal provinces owing to changes in sea level are less likely to be the significant factor in changing marine diversity than are changes in the number of faunal provinces.

Living echinoids provide a structural analogue to the rigid thecae of many extinct echinoderms and are here used to examine some consequences of the increased rigidity and decreased number of plates which occurred in several lineages of echinoderms. A special feature of the echinoids is the large spines which protect the echinoid tests from failure under impact. The spines absorb energy or spread loads because the spines break or the tissue connecting the spine to the test is stretched or torn. Spines that absorb impacts might be superfluous in echinoderms encased in a rigid test or theca if they have flexible stems or are in low energy habitats, but spines should be useful to stemless thecate echinoderms on hard substrata. In the absence of spines, a flexible theca of overlapping plates might be superior to a rigid theca. Greater rigidity does not necessarily provide greater protection.

Tracts of podial pores are sites of weakness in all tests examined [Eucidaris tribuloides (Lamarck), Echinometra viridis Agassiz, Diadema antillarum Philippi, Lytechinus variegatus (Lamarck), Tripneustes ventricosus (Lamarck)]. Therefore arrangement of pores affects strength of rigid thecae. Sutures are stronger than plates in most species examined, but cracks cross sutures, and tests of E. tribuloides frequently break along sutures. It is not yet proven that sutures increase toughness of rigid tests by relieving stress on plates or stopping cracks. If resisting failure under impact is important, then preconditions for acquiring rigidity are life in a low energy habitat or accessory structures which absorb or spread impacts.