Immature specimens of the Late Cretaceous pterosaur Pteranodon were identified using three size-independent criteria: (1) fusion of various cranial and postcranial elements; (2) degree of epiphyseal ossification; and (3) bone grain or degree of ossification of limb-bone shafts. Immature individuals make up 15% of available specimens of Pteranodon and do not differ significantly in size from mature individuals. This and the extensive fusion of the mature skeleton suggest that Pteranodon had determinate growth. The bone of limb-bone shafts of immature individuals is fibro-lamellar bone, which suggests that they grew rapidly to adult size. The size-independent criteria can also be used to identify immature and mature individuals of other pterosaur taxa, and other large pterodactyloids also probably exhibited rapid determinate growth.

One of the striking yet scarcely documented episodes of clade replacement in the post-Paleozoic fossil record is the decline of cyclostome Bryozoa and the corresponding, rapid diversification of cheilostome Bryozoa. These clades are closely associated morphologically and phylogenetically, and their ecological similarities have previously led to the inference that competition was a primary cause of the overt pattern of replacement. Alternatively, previous compilations of bryozoan families and genera have implied that extinctions at the Cretaceous/Tertiary boundary differentially affected cyclostomes, and thus were also an important factor in the transition.

We first evaluated the ecological context for competition between the two clades, then updated and reexamined the history of absolute family diversity for bryozoans in consecutive geologic stages from Jurassic to Recent. The resulting trends echo the patterns shown in earlier family level compilations, but indicate a slight shift in the frequency of cheilostome family originations from Late Cretaceous to early Paleogene. The relative fall in cyclostome family diversity at the Cretaceous/Tertiary boundary is significantly less than shown in earlier genus level compilations. We then assessed these various compilations of absolute diversity by analyzing species counts and percentages in 728 fossil assemblages, primarily from North America and Europe, over the same time interval. Cyclostome species overwhelmingly dominate assemblages from Jurassic through Cenomanian, then decline significantly in average percentage dominance through the Campanian. Cheilostomes are predominant in Campanian and later assemblages. Cyclostome species percentages do decrease overall through the Tertiary, but this decrease is small and non-uniform, varying around 30%, with a sharp drop in the Late Neogene. Our within-assemblage results indicate that as cheilostomes radiate, their mean species diversity, maximum diversity, and variance all increase, thereby accounting for much of the decline in average percentage of cyclostomes within assemblages. While this result does not exclude a role for competition, an hypothesis of relative decline in cyclostome species richness based on competitive extinction alone seems unlikely. Further, despite decreases in absolute species counts following end-Cretaceous extinctions, within-assemblage percentages of cheilostome or cyclostome species show only slight change relative to one another. Comparison of these and earlier diversity compilations indicates that the dynamics of bryozoan clade replacement may be perceived differently at different ecologic scales or taxonomic ranks.

Predatory marine snails and their prey provide a unique look at many aspects of predation events, allowing behavioral inference and studies of coevolution. This study examines differential predation patterns, rates, and success of two co-occurring gastropod predator families which drill two co-occurring species of Turritella (Turritellidae: Gastropoda) in the Gulf of California. Both naticid and muricid predators, identified by the shapes of their respective boreholes, attacked the thinner-shelled Turritella leucostoma more frequently than the thicker-shelled Turritella gonostoma. Both species were drilled more frequently and more successfully by naticid, as compared to muricid, predators. Naticids drilled prey in the 40- to 70-mm size class most frequently. Prey over 100 mm in length were relatively safe from all drilling predators. Predator size (estimated by borehole diameter) in naticids was correlated with prey size in both species, but for a given-sized prey, predators on T. gonostoma were proportionally larger. There was no size correlation for muricid predators. Unsuccessful attempts (incomplete drilling) were started on the suture more often than were completed holes, for both predator families on both prey species. Naticids began drilling T. leucostoma on the suture significantly less than expected by chance. We looked for possible changes over evolutionary time by analyzing prey shells from Pleistocene and Recent storm deposits. We found no evidence of change in any aspect of implied predatory behavior over the past 100 k.y.

After having been very abundant in the Early Maastrichtian Globotruncana gansseri zone, Inoceramus remains disappear from five stratigraphic sections in the Basque region of France and Spain in the lower Abathomphalus mayaroensis zone, ~2.5 m.y. before the Cretaceous–Tertiary boundary. Several lines of evidence demonstrate that these shell fragments are preserved in place and accurately record the pattern of the decline and disappearance of the group. The dominant taphonomic process seems to have been passive disaggregation of the shell as shell proteins decayed. The resulting shell fragments were dispersed only locally by burrowing organisms. Shell fragments decline in abundance over tens of meters of section and there are subtle differences between sections which suggests Inoceramus was eliminated by gradual changes in ecological conditions that affected the basin roughly simultaneously but with some geographic variability.

The incidences of selected features of dicotyledonous wood that are believed to be of ecologic and/or phylogenetic significance (distinct growth rings, narrow and wide vessel diameter, high and low vessel frequencies, scalariform perforations, tangential vessel arrangement, ring porosity, and helical wall thickenings) were plotted through time (Cretaceous–Recent). There are marked differences between the Cretaceous and Tertiary in the frequency of all wood anatomical features. Incidences of features that are associated with markedly seasonal climates in extant floras do not approach modern levels until the Neogene. Correlations of wood anatomical features with ecology do not appear to have been constant through time, because in the Cretaceous different features provide conflicting information about the climate. Throughout the Tertiary the southern hemisphere/tropical and the northern hemisphere/temperate regions differed in the incidences of ecologically significant features and these differences are similar to those in the Recent flora. Possibilities for reliably using dicotyledonous wood for climatic reconstructions appear restricted to the Tertiary and Quaternary. However, at present the fossil wood record for most epochs and regions is too limited to permit detailed reconstructions of their past climate.

The biomass of marine consumers increased during the Phanerozoic. This is indicated by the increase in both fleshiness and average size of individuals of dominant organisms, coupled with the conservative estimate that dominant organisms in the Cenozoic are at least as abundant as those in the Paleozoic. As faunal dominants replaced one another during the Phanerozoic the general level of metabolic activity increased due to both increase in basal metabolism and increase in more energetic modes of life. This demonstrates that the expenditure of energy by marine consumers has increased with time as well. There is a time lag in the expansion of more energetic life habits from environmental settings known to have high food supply into regions expected to have lower rates of food supply (e.g., bivalves into offshore carbonate environments or deep burrowing deposit feeders into the full range of shelf environments), and a time lag in diversification of energetic modes of life (e.g., predation or deep burrowing deposit feeding) for long intervals after they first appeared. This suggests that the supply of food increased across the whole spectrum of marine habitats during the Phanerozoic. The great diversification of specialized predators especially suggests that biomass increase took place all the way down the food chain to the level of primary production. The development of plant life on land and the impact of land vegetation on stimulating productivity in coastal marine settings, coupled with the transfer of organic material and nutrients from coastal regions to the open ocean, and the increase through time in diversity and abundance of oceanic phytoplankton all point to increased productivity in the oceans through the Phanerozoic.

A series of experiments was carried out to investigate the nature and controls (oxygen, microbial populations, agitation) on the degradation of soft tissues. Decay was monitored in terms of morphological change, weight loss, and change in chemical composition in the polychaete Nereis virens. Polychaetes include a range of tissue types of differing chemical composition and preservation potential: muscle, cuticle, setae, and jaws. Regardless of conditions, all the muscle had broken down and fluid loss through the ruptured cuticle had reduced the carcass to two dimensions within 8 days at 20°C. In most cases some cuticle, in addition to the jaws and setae, remained after 30 days. Where oxygen was completely eliminated, the rate of decay of the more volatile issues was significantly reduced. The degree of both osmotic uptake of water by the carcass and changes in water pH differed depending on whether the system was open or closed to oxygen diffusion. Autolytic and chemical processes are not sufficient to fully degrade the carcass in the absence of bacteria. Where internal bacteria are present, the presence or absence of water column bacteria made little difference to decay rate. Initial degradation (in the first 3 days) affects mainly the lipid fraction and the collagen of the cuticle. Later decay reduces the nonsoluble protein and increases the relative proportion of refractory structural components (tanned chitin and collagen) to more than 95% by day 30. Thus, only the sclerotized tissues are likely to survive beyond 30 days in the absence of early diagenetic mineralization. The sequence of degradation predicted from the relative decay resistance of macromolecules in the sedimentary record (protein → carbohydrate → lipid) is not, therefore, a consistent indicator of the preservation potential of structural tissues which incorporate them.

The experiments reveal five stages in the decay of polychaete carcasses; whole/shriveled, flaccid, unsupported gut, cuticle sac, jaws and setae. All are represented in the fossil record. This allows an estimation of how far decay proceeded before it was halted by the fossilization process. The most complete preservations occur in the Cambrian where the Burgess Shale preserves evidence of muscle tissues. Traces of the gut and cuticle are more widely preserved, as at Mazon Creek, Grès à Voltzia, Solnhofen, and Hakel. Preservation varies within Konservat-Lagerstätten. The most common whole body preservation includes only the more recalcitrant tissues, jaws (where present) and setae, with an impression of the body outline. The stage of decay can be used as a taphonomic threshold, to provide an indication of how significantly the diversity of an exceptionally preserved biota is likely to have been reduced by taphonomic loss.

Analysis of molluscan collections from a 3+ m.y. interval around the Cretaceous–Tertiary (K–T) interval in east Texas suggests that molluscs suffered an extinction at or near the K–T boundary, followed by a prolonged period of stress which lasted through the P0 and P1a planktic foraminiferal zones. The stressed period was characterized by low species richness, low abundances of individuals, high species turnover and a dominance of deposit feeders. Species richness and the relative abundance of deposit feeders generally track the 13C depletion curve suggesting that the stress was caused by a lack of primary production. A stable, relatively diverse, suspension feeding molluscan community was reestablished less than two million years after the K–T boundary. The total number of species within the habitat did not recover to Cretaceous levels within the study interval.

We examined the radiocarbon age, taphonomic condition and stratigraphic position of shells of the venerid bivalve Chione spp. from the tidal flats of Bahia la Choya, Sonora, Mexico. Shells in Bahia la Choya are time-averaged. Thirty shells yielded radiocarbon dates from modern (A.D. 1950 or younger) to 3569 years before present. The median calendar age of inner flat shells is 483 years; the median age of tidal channel shells is 427 years. We interpret such long shell survival to be the result of frequent shallow burial. Such burial retards bioerosion of shells.

The taphonomic condition of shells varied with environment. Shells from the surface of the inner flats were better preserved than shells from the tidal channel. Shells are more likely to be physically worn and biologically degraded in the waters of the channel than on the quieter and more frequently exposed inner tidal flat. Taphonomic condition is an unreliable indicator of a shell's time-since-death. Poorly-preserved shells on the inner flats tended to be old, but in general shell condition was much more variable than shell age. A shell's condition is more likely the result of its total residence time on the surface than its time-since-death (surface time plus burial time).

Two composite short (44 cm and 50 cm) cores revealed varying degrees of stratigraphic disorder (the departure from perfect correlation between relative stratigraphic position and relative age). One of eight shells in the inner flats core was disordered; four of nine shells in the tidal channel were disordered. The actual age range of surface shells approximates the age range of shells in cores. Stratigraphic disorder is a consequence of both time-averaging and physical and biogenic mixing.

Time-averaging controls the degree of precision possible in paleoecological studies. Environmental changes and ecological phenomena occurring within a span of 3500 years would not be recognized in deposits like those of Bahia la Choya. Time-averaging and stratigraphic disorder also constrain the temporal resolution possible in microstratigraphic studies of evolution. The extent of time-averaging and stratigraphic disorder will dictate an appropriate sample interval. In order to prevent temporal overlap between successive samples in deposits like Bahia la Choya, sample spacing should not be less than approximately 0.5 m.

Climatic change has long been regarded as an important factor in evolutionary history. In particular, periods of enhanced extinction in marine taxa (especially those from warmer waters) have frequently been linked to decreases in seawater temperature. Studies of the physiology of marine invertebrates and fish alive today have revealed well-developed abilities to cope with temperature change, and there would thus appear to be a dichotomy between the rates of temperature change associated with extinction in geological history and the very much faster rates (by several orders of magnitude) with which many marine organisms can cope today. Nevertheless, evidence from ecology and biogeography indicates that temperature, or some temperature-associated factor, does play a significant role in determining the limits to performance, and hence distribution. The resolution of the dichotomy between the evidence from paleontology and physiology may come through a consideration of the role of the previous evolutionary history of the fauna, the influence of sudden temperature events, or the impact of climatic change on individual competitive ability, community structure, and ecosystem functioning. Studies of the energetics of marine invertebrates in relation to temperature and the evolutionary history of polar faunas indicate that we should beware of anthropocentric judgements in attempting to understand the role of climatic change in evolutionary history, and be critical in distinguishing the role of temperature per se from temperature-associated ecological factors. Present evidence suggests that climatic change in the sea, at least at the rates currently believed to be typical, is unlikely to cause extinction by direct physiological impact. It is more likely that extinction is caused by ecological factors; temperature change is thus only one of several factors that may promote those ecological changes that are currently the best candidates for the proximate cause of extinction in the sea.