Amino acid analyses of undecalcified samples of fossil crocodile and rhinoceros enamel and dentin from mature teeth revealed that the total protein content of these mineralized fossil tissues varied from ~0.01–0.007% by weight. Except in one instance, amino acid analyses of the enamel proteins revealed them to be free of collagen and to have an amino acid composition similar to the proteins obtained from the enamel of mature modern vertebrates. Molecular sieving of the acid soluble enamel proteins demonstrated that the components consisted principally of small peptides and free amino acids, as in the enamel of modern vertebrates.

Based on the presence of hydroxyproline (hyp) and hydroxylysine (hyl), collagen was detected in undecalcified mature dentin of fossil rhinoceros, but not in undecalcified crocodile dentin. It was only by sequential extraction procedures that the presence of collagen in the dentin of fossil crocodile was established, emphasizing the utility and importance of analyzing the soluble components in specific extracts of the fossil. Based on these data and the concentrations of hyp and hyl in the material solubilized by the various solvents, the dentin of fossil rhinoceros contained considerably more collagen per weight and as a percentage of the total protein in the dentin than did the dentin of fossil crocodile.

As with modern dentin, EDTA and dilute acid solubilize the noncollagenous proteins and peptides found in fossil enamel and dentin, some of which contain O-phosphoserine [Ser(P)], an amino acid unique to mineralized connective tissues. Similar to recent reported findings from fossil bone, less of the original content of the noncollagenous proteins, including those phosphorylated, is degraded and removed from the enamel and dentin during fossilization than the percentage of dentinal collagen and the nonphosphorylated domains of the enamel proteins which are removed. This selective resistance to degradation and removal of the noncollagenous proteins, including phosphoproteins, may reflect the strong interaction of these proteins with the mineral phase of fossilized tissues. The amount and close packing of the inorganic crystals may also inhibit the interaction of the proteins in the interior of the enamel and dentin with the geochemical environment.

Distributions of brachiopods from low-latitude paleogeographic settings, primarily in the Tethyan Ocean of southern Europe, with additional data from North America allow some observations on the bathymetric distribution of early Mesozoic brachiopod orders. Norian and latest Triassic (Rhaetian) brachiopod biofacies are dominated in shallowest waters by short-looped terebratulids (Terebratulidina) while spire-bearing athyrids (Athyrida) are common components of deeper-water environments in the latest Triassic. In the late Early Jurassic (Pliensbachian), shallow-water brachiopod faunas are dominated by rhynchonellids, short-looped terebratulids are commoner in relatively deeper shelf waters, and spiriferids and long-looped terebratulids (Terebratellidina) are abundant in deeper-water shelf environments.

Following the end-Triassic extinction event there appears to be niche-replacement in deep-water shelf environments of Late Triassic athyrids by spiriferids and long-looped terebratulids in the Early Jurassic. Rhynchonellids appear to have diversified into shallowest water environments; specialized short-looped terebratulids may have occupied deeper-water niches that resulted ultimately in the success of the enigmatic Pygopidae later in the Jurassic and Cretaceous.

A modern Lesser Flamingo (Phoeniconaias minor) assemblage was collected along the shoreline of Lake Emakat, a saline-alkaline lake in northern Tanzania. Taphonomic analysis found the assemblage to be heavily weathered. This is likely due to the bone's heightened exposure to solar radiation and corrosive soil and water chemistries, as is expected to occur in such depositional environments.

Analysis found that deep, wide, longitudinal cracks penetrate the medullar cavities of both weathered and unweathered long bones. The cause and taphonomic consequence of these cracks are addressed here, using data from Lake Emakat and from controlled studies. Results support repeated (episodic) submersion, followed by drying, as the causal mechanism behind these wet-dry cracks. Mineral salt uptake by bone may explain the early appearance and prevalence of these cracks in saline-alkaline lake settings, as compared to other depositional settings.

The rate of weathering and incidence of wet-dry cracking varies significantly across limb elements. This difference correlates to element specific resistance properties to external loading forces. Heavy weathering weakens the structural integrity of bone and can accelerate its fragmentation. This can lead to bird bone loss in nearshore and ephemeral wetland settings, which may then affect resulting skeletal part, diversity, and richness profiles. Heavy weathering can therefore obscure important taphonomic and paleoecological information.

The weathering data collected here are then applied to a fossil bird assemblage from the FLK Complex, (late Pliocene), Olduvai Gorge, in Tanzania. Results provide evidence for the effect of weathering on paleoecological and behavioral interpretations. Weathering should be considered when analyzing fossil bird assemblages.

We explore the relationships among the geographic ranges of genera, the ranges and positions of their constituent species, and the number of species they contain, considering variation among coeval genera and changes within genera over time. Measuring range size as the maximal distance, or extent, between occurrences within a taxon, we find that the range of the most widespread species is a good predictor of the range of the genus, and that the number of species is a better predictor still. This analysis is complicated by a forced correlation: the range of a genus must be at least as large as that of each of its constituent species. We therefore focus on a second measure of range, the mean squared distance, or dispersion, of occurrences from the geographic centroid, which, by analogy to the analysis of variance, allows the total dispersion of a genus to be compared to the mean within-species dispersion and the dispersion among species centroids. We find that among-species dispersion is the principal determinant of genus dispersion. Within-species dispersion also plays a major role. The role of species richness is relatively small. Our results are not artifacts of temporal variation in the geographic breadth of sampled data. The relationship between changes in genus dispersion and changes in within- and among-species dispersion shows a symmetry, being similar in cases when the genus range is expanding and when it is contracting. We also show that genera with greater dispersion have greater extinction resistance, but that within- and among-species dispersion are not demonstrable predictors of survival once the dispersion of the genus is accounted for. Thus it is the range of the genus, rather than how it is attained, that is most relevant to its fate. Species richness is also a clear predictor of survival, beyond its effects on geographic range.

Studies of extinction in the fossil record commonly involve comparisons of taxonomic extinction rates, often expressed as the percentage of taxa (e.g., families or genera) going extinct in a time interval. Such extinction rates may be influenced by factors that do not reflect the intrinsic severity of an extinction trigger. Two identical triggering events (e.g., bolide impacts, sea level changes, volcanic eruptions) could lead to different taxonomic extinction rates depending on factors specific to the time interval in which they occur, such as the susceptibility of the fauna or flora to extinction, the stability of food webs, the positions of the continents, and so on. Thus, it is possible for an extinction event with a higher taxonomic extinction rate to be caused by an intrinsically less severe trigger, compared to an event with a lower taxonomic extinction rate.

Here, we isolate the effects of taxonomic susceptibility on extinction rates. Specifically, we quantify the extent to which the taxonomic extinction rate in a substage is elevated or depressed by the vulnerability to extinction of classes extant in that substage. Using a logistic regression model, we estimate that the taxonomic susceptibility of marine fauna to extinction has generally declined through the Phanerozoic, and we adjust the observed extinction rate in each substage to estimate the intrinsic extinction severity more accurately. We find that mass extinctions do not generally occur during intervals of unusually high susceptibility, although susceptibility sometimes increases in post-extinction recovery intervals. Furthermore, the susceptibility of specific animal classes to extinction is generally similar in times of background and mass extinction, providing no evidence for differing regimes of extinction selectivity. Finally, we find an inverse correlation between extinction rate within substages and the evenness of diversity of major taxonomic groups, but further analyses indicate that low evenness itself does not cause high rates of extinction.

Genera by their very nature are expected to be monotypic and geographically and environmentally restricted at their origin, and most genera do not endure past their stage of first appearance. At the same time, those genera that do endure have a capacity to expand greatly in geographic range, environmental breadth, and species richness. Here we ask what it is that allows some genera and not others to survive past their inception. Using occurrence data from the Paleobiology Database, we find that initial geographic range has the strongest effect on survival, followed by environmental breadth, with the effect of species richness weaker on average. The effect of geographic range is strongest if measured as the distances spanned by the occurrences of a genus rather than the number of distinct areas in which a genus lives. We document substantial secular variation in selectivity of early survival. The most striking aspect of this variation is that survival is only weakly selective among genera that first appear during the Mesozoic. By following genera beyond their stage of first appearance, we find that selectivity with respect to all factors becomes systematically stronger as cohorts age and genera become more differentiated in range, breadth, and richness. This may help account for a previously identified statistical effect of genus age on the chances of survival.

Taxon-age distributions were compiled for families of marine animals surviving or becoming extinct in each stage of the Phanerozoic. I demonstrate, through the use of a modified bootstrap analysis, that there is no difference between the longevity of families becoming extinct during times of background extinction and times of mass extinction. In both mass and background extinction intervals the mean age of families that become extinct is 2 standard deviations below the geometric mean taxon age of families available for extinction. Young families are more susceptible to extinction, perhaps as the result of lower species richness or of occupying a smaller geographic range. There is no tendency during mass extinctions toward loss of families with different taxon ages other than those that become extinct during background times. Thus, in terms of family survival, mass extinction appears to be an exaggeration of processes of background extinction.

The organic matrix components of a fossil ammonoid shell from the Upper Cretaceous, can be separated into sub-fractions which are generally comparable to those found in extant Nautilus, using ion exchange chromatography. This suggests that at least portions of these components are sufficiently well preserved to interact characteristically with the ion exchange resin. Amino acid compositions of these sub-fractions, however, do not resemble Nautilus organic matrix sub-fractions, indicating that considerable diagenetic alteration of this material has taken place.

Oysters, whose inner shell layer contains chambers, vesicles, and sometimes chalky deposits, often have extraordinarily thick shells of large size, prompting the idea that there is something unusual about the process of shell fPormation in these and similarly structured bivalves with the oyster syndrome. I propose the hypothesis that calcifying microbes, especially sulfate-reducing bacteria growing on organic substrates in fluid-filled shell-wall chambers, are responsible for shell calcification away from the shell-secreting mantle of the host bivalve. Other phenomena, including the formation of cameral deposits in fossil cephalopods, the cementation of molluscs and barnacles to hard substrata, the formation of a calcified intriticalx on the shell's exterior, and cementation of objects by gastropods on the shell for camouflage, may also involve calcifying bacteria. Several lines of inquiry are suggested to test these hypotheses.

Toothed cetacean (Odontoceti) lineages in the Miocene and Pliocene evolved rostra that are proportionally more elongate than any other aquatic mammal or reptile, living or extinct. Their similarities in cranial proportions to billfish may suggest a convergent feeding style, where the rostrum is swept through the water to hit and stun prey. Here we calculated second moment of area from rostral cross sections of these fossil odontocete taxa, as well as from extant ecological analogues, to infer variation in feeding behavior. Our results show that the extremely long rostra of extinct toothed whales vary considerably in functionally relevant measures of shape and likely exhibited a diversity of feeding behaviors, ranging from those similar to modern odontocetes to those convergent with billfish. Eustatic sea-level and temperature maxima of the Miocene likely led to changes in prey characteristics or abundance that enabled the repeated evolution of this extreme morphotype, which later went extinct during late Pliocene climatic deterioration.

Subcolony boundaries within Paleozoic bryozoan colonies, not otherwise easily observable, can be located precisely by computer mapping of variables derived from Fourier series. The monticule-centered subcolonies were maintained by morphogenetic gradients that controlled zooecial size and form, zooidal degeneration (producing brown bodies), and the spacing of monticules with respect to each other. These gradients were probably determined by the release of a budding inhibitor from polymorphic zooids within the monticule. In colonies with active monticular budding the morphogenetic gradients represent ontogenetic series, as the zooids that arose in the monticule gradually migrated outward along modified spiral pathways. Polymorphism, including reproductive functions, is probably reflected in the spatial order of zooids away from a monticule. In subcolonies with monticular budding, polymorphs represent different stages in the life history of a single zooid, with gradual transitions in zooecial form between castes.

The structural similarity between monticules and oghurd dunes supports the idea that they also functioned as excurrent water outlets, possibly with reproductive polymorphs clustered near the outflow. The variability of monticular size and spacing in some colonies indicates that hydrodynamic efficiency was compromised by the need for developmental plasticity. The development of active budding within monticules is considered an ecophenotypic response to the external environment, suggesting that all monticules within the Stenolaemata were potential budding sites. Monticules were successful adaptations in bryozoans because they performed a multiplicity of functions. While regulating the morphogenesis of the colony, they simultaneously served the metabolic functions of waste removal, feeding and reproduction.

Shotwell's method of paleoecological reconstruction attempts to define community membership of mammals represented within paleontological assemblages. Analysis of the measure of community membership upon which the method is based (relative skeletal completeness) shows this measure to be a function of sample size. A method for controlling for the effects of sample size upon measures of relative skeletal completeness is needed. A method is suggested which employs ratios of numbers of individuals to numbers of specimens, and a specific correction of Shotwell's method is proposed.

The floral community along South Africa's southwest coast today is dominated by shrubby strandveld, renosterveld, and coastal fynbos vegetation. The grass family (Poaceae), represented primarily by C3 taxa, is scarce by comparison. Nevertheless, grass has a long history along this coast, as indicated by the presence of ∼5-million-year-old C3 grass pollen and phytoliths in sediments at the fossil locality of Langebaanweg E Quarry. Because the pollen and phytoliths of other plant families, including fynbos, have also been found, it has been difficult to determine whether grass was scarce or abundant in this environment. In order to shed light on this issue, I analyzed the dental mesowear of the E Quarry bovids. Results indicate that only one (Simatherium demissum) of seven analyzed species was a grazer. These compare well with the results of a microwear texture analysis, which indicate that none of the seven analyzed species were obligate grazers. These two studies point strongly toward a heavily wooded environment and not one that was dominated by grass. Although a conventional dental microwear analysis did identify three out of seven E Quarry bovid species as grazers (Bed3aN Damalacra, Kobus subdolus, and S. demissum), only S. demissum probably actually was a grazer. I suggest that the grazer signal exhibited by the other two bovid samples indicate that these species were taking advantage of a spike in grass abundance, probably during the winter growth season.

Facets of the Silurian receptaculitid Ischadites barrandei are arranged in circlets about a nucleus. They form a set of spirals, originally eight in number, but increasing by the intercalation of new facets (initiating new spirals) in later circlets. We have simulated the surficial geometry of this alga by assuming, as much evidence indicates, that facets are limited in final size and that new spirals must therefore be intercalated in order to cover the surface with a fully tesselated pattern. We use only five parameters in our simulation: nature of the surface (radius of a sphere), tightness of the spirals (assumed to be logarithmic) and rate of increase in facet width (three parameters of an equation fitted to actual data). The program draws facets in circlets and intercalates new ones whenever the sum of facet diameters is at least a facet less than the circumference of the circlet. By holding all but one parameter constant, we can test the influence of single factors upon the pattern of intercalation. We compare these figures with actual patterns of intercalation for eight specimens. Variation in tightness of the spiral seems to affect the pattern most radically—tight spirals intercalate fewer facets because new circlets stay near the pole of the sphere. The morphology of intercalation supports the interpretation of Rietschel (1969, contra Nitecki, 1972 and Byrnes, 1968) that the nuclear circlets are the oldest part of the plant and that new circlets are generated at the opposite pole. Our simulation represents a basic pattern in nature, not a specific feature of receptaculitids. All structures that fill space with spirals and impose limits upon the size of individual units must add new spirals. Bryozoans subject to similar constraints but growing in a completely different way (peripheral growth in radial rows) display the same final pattern.

As paleontological studies are generally distorted by gaps and biases in the fossil record, it is important to assess its completeness. Here we address the fossil record of Parareptilia, a Permian–Triassic amniote clade, applying two measures of specimen completeness: the skeletal completeness metric (SCM) and the character completeness metric (CCM). The SCM quantifies how much of the skeletal material of a taxon is preserved, whereas the CCM measures the amount of phylogenetic information available. The latter was implemented using two different approaches. In this study, we compare three completeness metrics. Two CCM implementations show a strong correlation with each other, but only the second implementation of the CCM correlates significantly with the SCM, possibly due to character selection in phylogenetic data sets. There is no correlation between diversity of parareptiles and their completeness, implying that the observed fluctuations in diversity are not driven by the completeness of the fossils. The mean completeness of parareptiles through time is consistently high compared with previously studied tetrapod clades, suggesting that most parareptile taxa are based on reasonably complete specimens. Clade-specific differences reveal no link between body size and completeness. However, the analyses confirm the impact of ecology, with aquatic mesosaurids being better preserved than terrestrial taxa.

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.

Nautilus pompilius at Fiji lives abundantly to about 600 m depth while the shell implodes between 730–900 m when sunk in a cage. From this, and the average parameters of the septum, its tensile strength is calculated to 110–140 MPa. This is markedly higher than the latest value from direct tensile tests (78 MPa). In recent pressure tests by Saunders and Wehman with dry shells from the Philippines, implosion occurred at pressure equivalents to 310–680 m depth, without significant correlation with septal thickness. We attribute this excessive range and non-correlation to structural damage by postnecrotic processes. The recalculated tensile strength from their original data is 56–137 MPa; the higher values are compatible with our values for septal nacre of Nautilus and Spirula (c. 155 MPa). Septal curvature and thickness in orthocones thus remain useful guides to bathymetry.

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.

Survival of North American shelf trilobite families during a mass extinction across the upper boundary of the Upper Cambrian Sunwaptan Stage (=“Ptychaspid Biomere”) cannot be predicted from patterns of turnover among their component species: on the shelf, stratigraphic ranges of species belonging to surviving families do not differ significantly from those of eliminated families. Thus, the sorting of families during the extinctions cannot be explained by simple upward causation from the individual level. However, families that ranged from shelf to slope environments before the extinctions (most of which are pandemic) fared significantly better than those confined to shelf settings (which tend to be endemic to North America), indicating that family survival was influenced by geographic and environmental distribution, a property emergent above the individual level. One factor implicated in clade survival during normal background times, high species richness, did not influence the outcome of mass extinction. The results affirm the importance of a hierarchical approach to the interpretation of macroevolutionary patterns and provide some support to the suggestion that sorting processes operating during mass extinctions differ from those of background times.