C. M. Yonge's idea that differences in habitat distribution and species diversity between archaeogastropods and caenogastropods are caused by differences in their respective abilities to obtain oxygen in turbid water is tested experimentally for the first time. Of 11 species of marine prosobranchs studied—six archaeogastropods and five caenogastropods—three archaeogastropods and two caenogastropods show significant reductions of respiration in response to turbidity, as shown using one-way analysis of covariance (ANCOVA). Two-way nested ANCOVA, which goes beyond one-way ANCOVA by incorporating all data into a single analysis, was also unable to detect any significant difference between archaeogastropods and caenogastropods in their respiratory responses to turbidity. Though the number of species studied was limited, the data and statistical tests suggest that there may be no biologically important systematic difference between archaeogastropods and caenogastropods in their respiratory responses to turbid conditions. Results of this study cast doubt on the validity of Yonge's hypothesis and suggest the need for new research into the controls of gastropod distribution and species diversity.

A computer model is presented which is capable of calculating both the photosynthetic efficiency (I) of any specified plant shape and the stress related to the total moment arm (M) imposed on vertical branching patterns. Computer simulations indicate that a flattened plant thallus and an erect branching growth habit are two plant shapes capable of optimizing photosynthetic efficiency during indeterminate growth. These two morphologies have geometric analogues in the dorsiventral thalli of some bryophytes and in the vertical axes of mosses and tracheophytes, respectively.

Extension of the model to complex, three-dimensional branching patterns indicates that I and I/M are maximized when branching is overtopped (treelike, with lateral branches on a main axis) and when lateral branching systems are planated (frondlike). Geometric alterations of branching patterns that result in optimization of I and I/M can be simulated by computer and are shown to be similar to morphologic alterations attending the early evolution of vascular land plants. It is suggested that a number of major evolutionary trends seen in Upper Silurian to Upper Devonian times can be expressed in terms of optimizing the display of photosynthetic tissues (I) or the balance between photosynthetic efficiency and incurred moment arms (I/M).

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.

A three-phase kinetic model with time-specific perturbations is used to describe large-scale patterns in the diversification of Phanerozoic marine families. The basic model assumes that the Cambrian, Paleozoic, and Modern evolutionary faunas each diversified logistically as a consequence of early exponential growth and of later slowing of growth as the ecosystems became filled; it also assumes interaction among the evolutionary faunas such that expansion of the combined diversities of all three faunas above any single fauna's equilibrium caused that fauna's diversity to begin to decline. This basic model adequately describes the diversification of the evolutionary faunas through the Paleozoic Era as well as the asymmetrical rise and fall of background extinction rates through the entire Phanerozoic. Declines in diversity and changes in faunal dominance associated with mass extinctions can be accommodated in the model with short-term accelerations in extinction rates or declines in equilibria. Such accelerations, or perturbations, cause diversity to decline exponentially and then to rebound sigmoidally following release. The amount of decline is dependent on the magnitude and duration of the perturbation, the timing of the perturbation with respect to the diversification of the system, and the system's initial per-taxon rates of diversification and turnover. When applied to the three-phase model, such perturbations describe the changes in diversity and faunal dominance during and after major mass extinctions, the long-term rise in total diversity following the Late Permian and Norian mass extinctions, and the peculiar diversification and then decline of the remnants of the Paleozoic fauna during the Mesozoic and Cenozoic Eras. The good fit of this model to data on Phanerozoic familial diversity suggests that many of the large-scale patterns of diversification seen in the marine fossil record of animal families are simple consequences of nonlinear interrelationships among a small number of parameters that are intrinsic to the evolutionary faunas and are largely (but not completely) invariant through time.

The mineralized hard parts of Nautilus, including the mandibles, statoconia, and uroliths, are more complex with respect to ultrastructure, mineralogy, trace element, and isotopic composition than was previously recognized. X-ray diffraction and amino acid composition analyses of the organic structural hard parts (siphuncle tube, shell wall and septum organic matrix, mandibles, and muscle tendon sheath) show that two different chitin-protein complexes are utilized by Nautilus. The mandible mineral hard parts are particularly complex, with five different minerals present in various locations. A comparison of the statoconia of Nautilus species with the statoliths of dibranchian cephalopods reveals an evolutionary trend in which carbonate is substituted for phosphate. This study also shows that Nautilus uses a number of different crystal-forming processes for constructing its hard parts. The data presented here provide a broad spectrum of information, which, when applied to the fossil counterparts, can be utilized for improving our understanding of ancient nautiloid biology.

Bottom site remote camera photosequences at depths of 73–538 m on forereef slopes in Palau show that Nautilus belauensis is a highly mobile, chemosensitive, epibenthic scavenger and opportunistic predator. The overall depth range of this species is ca. 70–500 m, but photosequences indicate a preferred range of 150–300 m. Nautilus is active both nocturnally and diurnally, locating bait sites within 1–2 h. Associated macrofauna includes caridean shrimps, crabs, and eels; teleosts are rare below 100 m, but sharks are recorded in most photosequences below 250 m. Summarily, Nautilus exhibits a combination of characters that typify deep-sea strategy, including reproductive tactics, growth rate, and population dynamics. This and other evidence suggest that fossil Nautilidae may have been deep-water forms, in contrast to the typically shallower water ammonoids, and that Nautilus is a normal component of the deep forereef rather than a late Cretaceous refugee from shallow water.

Three features that provide information on the paleobiologic significance of fossulae in North American Late Ordovician solitary rugose corals are (1) irregularities in shape and position of the outer wall, (2) discontiguous septal growth lamellae, and (3) foreign objects incorporated into interseptal chambers within the corallum. Outer wall irregularities indicate that portions of a polyp could detach from the calice and could contract and expand radially by a significant amount and for prolonged periods of time during ontogeny, especially in the vicinity of the alar and cardinal fossulae. Discontiguous lamellae indicate that the polyp could detach from septa and contract laterally, especially in the cardinal fossula. This began with the onset of maturity and probably reflects reproductive activity. Ostracodes are the most common foreign objects in these coralla and are usually situated within or near the cardinal and alar fossulae. In the most likely hypothesis accounting for their presence, a live ostracode entered the calice when one side of the polyp temporarily detached from the corallum and contracted radially. It became trapped upon expansion and reattachment of the soft parts. The polyp moved upward in its corallum by detachment and uplift of the aboral surface. In a less likely hypothesis, the ostracode was captured by the coral for food and came to rest on the floor of the central cavity. It was incorporated into an interseptal chamber when the polyp moved upward in its corallum by atrophy of the aboral surface and formation of a new base above the object. In either hypothesis, portions of the polyp in the cardinal and alar fossulae probably functioned throughout ontogeny for water circulation in the central cavity, and for the intake of food and/or ejection of undigested material through the mouth. Taxonomic, stratigraphic, and paleobiogeographic variability in frequencies of the three features may indicate differences in the necessity and/or ability of polyps to perform these functions involving the fossulae. This could be a reflection of environmental and/or genetic factors.

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.

A survey of the primary xylem anatomy and dimensions of axes (=“stems”) of Upper Devonian plant petrifaction/compression fossils reveals the following: among genera, the primary xylem strand (1) increasingly deviates from a cylindrical geometry (=haplostele) as both the axis diameter and the nonxylem (“ground”) tissue volume increase and (2) increases in geologically younger specimens. (3) The perimeter length to area ratio of the primary xylem strand (or the primary xylem surface area to volume ratio) is dependent upon axis diameter or the area of the ground tissue. This ratio (4) decreases in evolutionary lineages that involve the appearance of larger plants that maintain a haplostelar anatomy (e.g., the evolution of trimerophytes from a rhyniophyte ancestor) or increases in evolutionary lineages involving the appearance of nonhaplostele anatomy (e.g., the evolution of progymnosperms and pteridophytes from trimerophyte ancestors) and (5) the relative amount of primary xylem to ground tissue increases in stratigraphically younger specimens. These trends are interpreted within the context of (1) correlations between the diameter of axes and the complexity of the primary xylem anatomy reported for some extant pteridophytes and (2) changes associated with the evolution of new primary xylem configurations and organographic relationships. Based on the appearance of new ontogenetic patterns and concomitant changes in the anatomy of the primary xylem strand associated with the evolution of derived plant groups, a stria extrapolation of a size to complexity correlation based on ontogenetic studies to the phyletic level is considered suspect.