Morphological adaptations may indicate increased specialization (narrowing of ecological niche) or expansion of the suite of lifestyles available to an organism (increasing niche breadth). Hypsodonty in mammals generally has been interpreted as a specialization into a grazing niche from a browsing niche. Here I examine the feeding strategy of the extinct hypsodont camel Hemiauchenia through an analysis of stable carbon isotope values from its tooth enamel, which was used to clarify its feeding strategy and to resolve conflicting interpretations of dental versus muzzle attributes. The paleodiet of Hemiauchenia is then used to test whether hypsodonty correlates to grazing within fossil Lamini. This study focuses on fossils from Florida, which is geographically ideal because unlike other regions of the country almost all extant plants on which animals browse use the C3 photosynthetic pathway. In contrast, most of the grasses and sedges utilized by grazers use the C4 photosynthetic pathway. If Hemiauchenia was an obligate grazer, the stable carbon isotope values of tooth enamel should reflect primarily a diet of C4 grass and sedge (>−1.3%). If Hemiauchenia was mainly a browser, the isotopic value should be considerably more negative reflecting ingestion primarily of C3 browse (<−7.9%). The mean δ13C values for Hemiauchenia during each time interval average more negative than −8.0%, indicating a dominantly C3 browse diet, and there is no evidence for abandonment of the browsing niche from the Hemphillian through the Rancholabrean North American Land Mammal Ages. However, an increase in the range of isotopic values indicates a diet with a higher proportion of C4 grasses and sedges through time. This study therefore suggests that Hemiauchenia was a hypsodont intermediate feeder with preference for browse during the past 5 million years. Hypsodonty is not strictly associated with obligate grazing; instead it may, in this case, represent an adaptation to widen niche breadth that allowed grazing as well as browsing.

The Mesozoic marine revolution focuses on increased predation by durophagous (shell-crushing) predators and the concomitant evolution of prey organisms that occurred in the Mesozoic. Evidence of this predator/prey revolution is found in the appearance and increase of new types of predators that can crush hard shells of prey organisms, and is also found in the morphological changes of prey organisms, such as the appearance of a protective shell morphology of gastropods. We present new data based on the occurrence of shell fragments that indicate a slower increase in durophagous predation than has been considered previously.

The results of an experiment on shell abrasion, in which shells were tumbled in barrels with sediments, indicate that incomplete bivalves and gastropods with angular margins from shallow-marine deposits can be considered as good evidence of durophagous predation. Such angular shell fragments are virtually absent from Japanese Mesozoic shell beds, whereas they are occasionally or commonly found in the Paleogene and are usually abundant in Neogene shell beds. The dominant occurrence of fossil shell fragments in the Cenozoic, as well as the data from shell abrasion experiments using tumbling barrels, indicates that wave agitation or currents do not produce shell fragments with angular margins. Such angular shell fragments are interpreted as the result of durophagous predation that has increased during Cenozoic time, and can be a useful tool in estimating durophagous predation in the fossil record. Revised data on the number of durophagous predator taxa (crustaceans and teleostean fishes) also support this conclusion.

Accurate estimates of body mass in fossil taxa are fundamental to paleobiological reconstruction. Predictive equations derived from correlation with craniodental and body mass data in extant taxa are the most commonly used, but they can be unreliable for species whose morphology departs widely from that of living relatives. Estimates based on proximal limb-bone circumference data are more accurate but are inapplicable where postcranial remains are unknown. In this study we assess the efficacy of predicting body mass in Australian fossil marsupials by using an alternative correlate, endocranial volume. Body mass estimates for a species with highly unusual craniodental anatomy, the Pleistocene marsupial lion (Thylacoleo carnifex), fall within the range determined on the basis of proximal limb-bone circumference data, whereas estimates based on dental data are highly dubious. For all marsupial taxa considered, allometric relationships have small confidence intervals, and percent prediction errors are comparable to those of the best predictors using craniodental data. Although application is limited in some respects, this method may provide a useful means of estimating body mass for species with atypical craniodental or postcranial morphologies and taxa unrepresented by postcranial remains. A trend toward increased encephalization may constrain the method's predictive power with respect to many, but not all, placental clades.

Regardless of the macroevolutionary issues at stake, most students of biodiversity would agree that there is value in calibrating global biodiversity trends through critical intervals. To cite one obvious example, given the overwhelming interest in mass extinctions, we would certainly like to know the extent to which diversity declined during these events. Just as significantly, if we are to argue that any mass extinction was truly a global phenomenon, we must demonstrate definitively that its biotic effects reached around the world. Clearly, “standard” global compendia (e.g., Sepkoski 1992, 2002) are insufficient for the latter objective, because they contain no geographic or environmental information. At the least, a database that compares biodiversity transitions among different regions or paleoenvironments is required. Such analyses have the added benefit of providing opportunities to evaluate geographic and environmental selectivity in extinctions, an important facet of any attempt to understand what caused them (e.g., Raup and Jablonski 1993; Jablonski and Raup 1995).

Global biodiversity dynamics result in large-scale patterns of change in the variety of life on earth. One deceptively simple measure of global biodiversity is the total count of species or supraspecific taxa that have been described from each subinterval of the Phanerozoic record. These tallies usually are obtained from data compilations based on extensive literature searches supplemented with examination of collections in museums (Sepkoski 1993; Alroy et al. 2001). Such measures of global biodiversity dynamics are probably not meaningless, but it is difficult to understand what they mean. The number of taxa alive on Earth at any one time is a function of innumerable ecological factors acting at the full range of temporal and spatial scales (Willis and Whittaker 2002). Changes in global richness might result from increasing local richness as local communities become more complex (Valentine 1969; Bambach 1977). At the regional scale, changing oceanographic conditions, climate, and the relative positions of continents and shallow seas might alter global taxonomic diversity by changing the size and arrangement of biogeographic units (Valentine 1970). Therefore, the best hope for understanding global diversity patterns is to collect information on local assemblages. These hierarchically organized data can then be integrated to test alternate hypothetical mechanisms of change. Data compiled as the endpoints of stratigraphic or geographic ranges are useless for this purpose. This has been known at least since Bambach (1977) explored patterns of change in alpha diversity of level-bottom marine communities.

Ediacaran fossils at Mistaken Point, southeastern Newfoundland (terminal Neoproterozoic; 565–575 Ma) represent the oldest known animal communities. In contrast to most Phanerozoic fossil assemblages, in which postmortem transportation, bioturbation, and the accumulation of hardparts obscure community relationships, all fossils in the Mistaken Point assemblages were sessile, soft-bodied organisms that show no evidence of mobility in life or transportation after death. Mistaken Point assemblages are spectacularly preserved on large bedding planes as in situ census populations of hundreds to thousands of fossils, recording the living soft-bodied benthic community at the moment it was smothered by volcanic ash. This unique preservation style allows ecological tests routinely conducted in modern communities (e.g., species richness, abundance, “biomass,” diversity, and evenness, as well as statistical tests of nearest-neighbor interactions) to be applied to the fossil communities. Observed patterns of community variability are consistent with the theory that Mistaken Point fossil surfaces are “snapshots” recording different stages of ecological succession, progressing from communities of low-level feeders (e.g., pectinates and spindles) to frond-dominated communities with complex tiering and spatial structure. The presence of diverse slope communities at Mistaken Point suggests that the deep sea was colonized rapidly during the evolution of complex organisms. Species richness, abundance, and diversity values, as well as levels of intraspecific interaction, all fall within the typical range observed in modern slope communities. These structural similarities imply that ecological processes present in Ediacaran communities at Mistaken Point were strikingly similar to the processes that operate in modern deep-sea animal communities.

Among polygynous mammals, a heightened risk of mortality is linked to the intensity of intragender competition and life-history stages, such as sexual maturity, where inexperienced individuals are vulnerable to the aggressive behaviors of dominant individuals. In this respect, the age- and sex-specific mortality patterns found in fossil assemblages could be informative of sociality in extinct species. This possibility was explored by comparing the age- and sex-specific demography of attritional rhinoceros assemblages, Teleoceras proterum (n = 2) and Aphelops malacorhinus (n = 1), from pond and fluvial sedimentary facies of the late Miocene of Florida, with modern skeletal assemblages of extant rhinos and other large mammals.

Subadult and young adult males (between 15–40% of potential life span) numerically dominate the Teleoceras assemblages, indicating a disproportionately high frequency of localized young male mortality. The estimated age-specific mortality rates indicate elevated mortality risks among males at an age equivalent to the years encompassing male physiological and social maturity in modern rhinos, a pattern that suggests a high frequency of socially mediated mortality. Age-specific mortality rate curves of modern black rhino populations are essentially identical. A high frequency of intraspecific fight-related mortality characterizes modern rhinos and strongly suggests that elevated Teleoceras mortality was influenced by intragender competition. Although Teleoceras is widely believed to have been the analog of extant Hippopotamus, mortality rates of young males are not elevated in a modern Hippopotamus population. The Aphelops assemblage is not significantly male-biased and does not indicate elevated mortality rates of young males, suggesting that aspects of Aphelops sociality differed from modern rhinos. Although the nature of Aphelops sociality is not clear, aggression toward young males may have been less extreme or less frequent in Aphelops populations.

The vertebrae of sauropod dinosaurs are characterized by complex architecture involving laminae, fossae, and internal chambers of various shapes and sizes. These structures are interpreted as osteological correlates of a system of air sacs and pneumatic diverticula similar to that of birds. In extant birds, diverticula of the cervical air sacs pneumatize the cervical and anterior thoracic vertebrae. Diverticula of the abdominal air sacs pneumatize the posterior thoracic vertebrae and synsacrum later in ontogeny. This ontogenetic sequence in birds parallels the evolution of vertebral pneumaticity in sauropods. In basal sauropods, only the presacral vertebrae were pneumatized, presumably by diverticula of cervical air sacs similar to those of birds. The sacrum was also pneumatized in most neosauropods, and pneumatization of the proximal caudal vertebrae was achieved independently in Diplodocidae and Titanosauria. Pneumatization of the sacral and caudal vertebrae in neosauropods may indicate the presence of abdominal air sacs. Air sacs and skeletal pneumaticity probably facilitated the evolution of extremely long necks in some sauropod lineages by overcoming respiratory dead space and reducing mass. In addition, pulmonary air sacs may have conveyed to sauropods some of the respiratory and thermoregulatory advantages enjoyed by birds, a possibility that is consistent with the observed rapid growth rates of sauropods.

Accurate reconstruction of the biomass, structure, and productivity of ancient forests from their fossilized remnants remains an interesting challenge in paleoecology. In well-preserved Tertiary fossil Metasequoia forests of Canada's Arctic, in situ stumps and fragments of stems, treetops, and branches contain substantial information about tree dimensions that can be used to determine tree height, stand biomass, and other characteristics such as canopy depth and structure, and the history of stand development. To validate a method for reconstructing the biomass of the Eocene floodplain Metasequoia forests of Axel Heiberg Island, we measured stump diameters and spacing, and stem, branch, and treetop characteristics in living Metasequoia glyptostroboides and Chamaecyparis thyoides stands in ways that simulate the limited measurements that can be made in well-preserved fossil forests in Canada and probably elsewhere. We used those limited measurements to estimate tree height and volume, branch and foliar dry weights, and tree biomass. The estimates derived from the limited data set are usually within 15% of the estimates derived from the methods currently used in forest ecology for determining those metrics in modern forests. Under appropriate conditions, the biomass of ancient forests can be estimated with reasonable confidence.

Very different questions are involved when we attempt to assess modern versus ancient global biodiversity. Because of the megabiases of taphonomy, eustasy, and tectonics, our estimates of paleobiodiversity can never be absolute; whether or not we can accurately estimate total diversity in the modern world is an open question, but we certainly cannot in the fossil record. The issues are whether we have any way of studying relative change in biodiversity through time, and how best this might be accomplished. That is, can we meaningfully estimate the shape of a global temporal diversity curve?

Long-term diversity equilibria, ecological incumbency, and widespread recurrent fossil assemblages have each been cited as evidence that local processes, such as competition, played an important role in structuring communities over geologic time. We analyze the relationship between local and regional diversity in tropical marine communities spanning approximately 13 Myr of the Late Ordovician to test for the role of local processes in structuring local communities. We find a significant and strong positive relationship between local and regional diversity, indicating that local communities were not saturated with species and that local processes did not exert a dominant influence on local diversity. Rather, local diversity was influenced more by regional oceanographic processes that governed the size of the regional species pool. This evidence for unsaturated communities is consistent with the Walker and Valentine hierarchically structured niche model of global diversification. These results come at the beginning of the 200-Myr Paleozoic plateau in both local and global diversity and therefore raise the question whether local communities were ever saturated with species during the Paleozoic. Similar studies need to be conducted during other times in the Paleozoic to determine if this is indeed the case.

Skeletal remains of Eocene Archaeoceti provide the only direct and unequivocal evidence of the evolutionary transition of whales from land to sea. Archaeocete skeletons complete enough to be informative about locomotion are rare (principally Rodhocetus and Dorudon), and these deserve to be studied in comparison to the full spectrum of semiaquatic mammals. A principal components analysis of 14 trunk and limb measurements for 50 species of living semiaquatic mammals reduces the observed variation to three informative axes. The first principal axis (PC-I) represents overall size (water mice and shrews have the lowest scores on this axis and the hippopotamus has the highest); the second axis (PC-II) represents a spectrum of aquatic adaptation (seals have the lowest scores and tapirs have the highest); and the third principal axis (PC-III) represents a spectrum ranging from hindlimb- to forelimb-dominated locomotion (sea otters have the lowest scores and the platypus the highest).

Dorudon fits poorly into a morphospace defined solely by living semiaquatic mammals; thus a second 53-species set was analyzed, adding an anthracothere to represent an artiodactyl ancestral morphology and two species of archaeocetes to represent successive stages of early whale evolution. This addition has little effect on the first two principal axes but changes the third substantially. PC-III now represents a contrast of lumbus- (and presumably tail-) dominated versus hindlimb-dominated locomotion (Dorudon has the lowest score and Rodhocetus the highest, whereas the otter shrew has the lowest score among living mammals and the desman the highest). Mammals that are more aquatic have a shorter ilium and femur combined with longer manual and pedal phalanges, whereas the reverse is true for more terrestrial taxa. Lumbus- and tail-dominated swimmers tend to have a longer lumbus combined with shorter pedal elements, whereas the reverse is true for hindlimb-dominated swimmers. Trunk and limb proportions of early middle Eocene Rodhocetus are most similar to those of the living, highly aquatic, foot-powered desmans. Trunk and limb proportions of late middle Eocene Dorudon indicate that it was a lumbus-and-tail-powered swimmer specialized in the direction of modern whales. Thus it appears that the land-to-sea transition in whale evolution involved at least two distinct phases of locomotor specialization: (1) hindlimb domination for drag-based pelvic paddling in protocetids (Rodhocetus), with tail elongation for stability, followed by (2) lumbus domination for lift-based caudal undulation and oscillation in basilosaurids (Dorudon). Rates of evolution in both phases of this change of adaptive zone are about an order of magnitude higher than background rates for the timescale involved.

For decades, paleobiologists have treated global diversity estimation as a straightforward problem (Miller 2000): count up the known higher taxa in each geological time interval, make a diversity curve, and go straight ahead to analyzing and interpreting the trends. However, global diversity curves recently have come under attack from all sides. Some researchers argue that although traditional curves are strongly affected by sampling biases (e.g., Smith 2001; Peters and Foote 2002), these biases can be corrected by assembling large, locality-level databases with detailed contextual information (Alroy et al. 2001). Others point to the large gap between true total global richness and the meager head counts the fossil record has to offer, and conclude that workers should focus exclusively on local and regional diversity (Jackson and Johnson 2001). Here I argue that although further fieldwork surely is needed, understanding global diversity in the short term remains a tractable goal—as long as we move quickly to build a discipline-wide, globally extensive paleontological database.

Abundant fossil plant remains are preserved in the high-latitude middle Eocene deposits of the Buchanan Lake Formation on Axel Heiberg Island, Nunavut Territory, Canada. Intact leaf litter, logs, and stumps preserved in situ as mummified remains offer an opportunity to determine the structure, biomass, and productivity of two Taxodiaceae-dominated forests that grew north of the Arctic Circle (paleolatitude 75–80°N). We excavated fossil tree trunks and treetops to develop equations that describe the height, structure, and mass of the aboveground components of Eocene-age Metasequoia trees. We combined those data with surveys of in situ stumps to determine the structure, biomass, and productivity of two fossil forests, “N” and “HR.” We calculated a canopy height of 40 ± 3 m for the N forest and 25 m ± 2 m for the HR forest. Buried knots in dissected logs and abundant branch-free bole wood indicate that these were tall, closed-canopy forests. Stem tapers indicate that the overstory was of uniform height. Stem volume equaled 2095 m3 ha−1 and stem biomass was 628 Mg ha−1 in the N forest. Volume and biomass in the HR forest were much smaller, 211 m3 ha−1 and 63.3 Mg ha−1, respectively. We estimated understory tree biomass to be 40 Mg ha−1 in the N forest and 3.5 Mg ha−1 in the HR forest. Recovery of seven fossil treetops with exposed branch stubs enabled us to make estimates of branchwood and foliar biomass using allometric equations derived from modern, plantation-grown Metasequoia glyptostroboides. Estimated stand-level branch biomass was 13 and 6.7 Mg ha−1 in the N and HR forests, respectively. Standing foliar biomass was estimated to be 3.2 and 2.1 Mg ha−1 in the N and HR forests, respectively. Using annual ring widths, the reconstructed parabolic stems, and wood density of modern Metasequoia, we calculated annual wood production to be 2.3 Mg ha−1 yr−1 for the N forest and 0.55 Mg ha−1 yr−1 for the HR forest Assuming that the ancient Metasequoia were deciduous like their living relatives, annual aboveground net primary productivity was 5.5 Mg ha−1 yr−1 for the N forest and 2.8 Mg ha−1 yr−1 for the HR forest. Our estimated biomass and productivity values for N are similar to those of modern old-growth forests of the Pacific Northwest of the United States and old-growth coastal Cordillera forests of southern Chile.

The asphalt deposits of Rancho La Brea are well known for preserving a prolific and diverse Late Pleistocene fauna. However, little taphonomic research has been done on these collections. To better understand the formation of this impressive assemblage, a taphonomic study of the bones of the large mammals from one asphalt deposit, Pit 91, was carried out, and results are presented here. The predominance of carnivore specimens in the Rancho La Brea deposits has long been explained by a scenario in which a prey animal was trapped in asphalt and attracted large numbers of carnivores who became trapped in turn. Hypotheses generated from this scenario were tested by collecting taphonomic data on over 18,000 specimens. Weathering data indicate that elements were deposited fairly rapidly. However, patterns of skeletal part representation for the seven most common species demonstrate that complete skeletons are not present. Water transport is ruled out as the primary process responsible for removing skeletal elements based on abrasion data. Instead, the feeding activity of carnivores (ravaging) appears to have been an important factor in the formation of the assemblage.

The negative consequences of anthropogenic activities such as agriculture and urbanization (e.g., deforestation, greenhouse gas emissions, and pollution) have become exacerbated by rapid rates of human population increase (see Pimm et al. 2001). Subsequent habitat loss and modification has accelerated rates of extinction, creating a biodiversity crises which arguably is one of the most pressing problems of the twenty-first century. Although causative agents are unclear, the fossil record suggests that biotas undergo periods of massive extinction as well as considerable diversification (Alroy et al. 2001; Jackson and Johnson 2001) at the global scale, even in the absence of human activities. As such, quantifying the spatial and temporal dynamics of biodiversity in past and contemporary times, and understanding their mechanistic bases represent disciplinary emphases of evolutionary and environmental biology. Equally important, such understanding is a critical step in informing regional as well as global management strategies and conservation efforts. Nonetheless, considerable controversy or uncertainty exists surrounding the patterns, underlying mechanisms, and strategies of conservation (Willig 2000; Andelman and Willig 2002). The past may provide important insights into a number of relevant issues regarding contemporary biodiversity (and vice versa), but only recently has the dialogue between neontologists and paleontologists charted productive areas of collaboration. Indeed, a growing body of work has questioned the meaning of global measures of biodiversity (past or present) and has suggested that only detailed studies at local sites provide resolution to important issues about biodiversity. This is due, in part, to considerable sampling problems associated with broad-scale estimation, including the averaging of local and regional patterns.

Bivalves and gastropods, prominent members of the Modern Evolutionary Fauna, are traditionally noted for sharing remarkably similar global diversity trajectories and environmental distributions throughout the Phanerozoic. By comparing their fossil occurrences at several scales within a finely resolved geographic, environmental, and temporal framework, it is possible to evaluate whether such similarities are caused primarily by intrinsic macroevolutionary factors or extrinsic ecological factors. Using a database of 7779 global gastropod and bivalve genus occurrences, we investigate the geographical and environmental attributes of bivalves and gastropods during the Ordovician Period at scales ranging from global, to a comparison among five paleocontinents, to an intracontinental comparison of four regions within Laurentia. Although both classes shared statistically indistinguishable global diversity trajectories and broadly similar environmental distributions during the Ordovician, their environmental distributions differed in several significant features. Furthermore, the diversity trajectories and environmental distributions of these classes differed significantly among paleocontinents and among regions within Laurentia. Bivalves were consistently most diverse in deeper water, siliciclastic-rich settings in higher-latitude paleocontinents whereas gastropods were consistently most diverse in shallower, carbonate-rich settings in more-equatorial paleocontinents. Notably, these environmental differences were robust to changing physical parameters within paleocontinents, with each class consistently tracking its preferred environmental setting. These results suggest that environmental factors played significant, albeit distinct, roles in the Ordovician diversifications of gastropods and bivalves. However, their similar global diversity trajectories suggest that shared, intrinsic macroevolutionary attributes also may have played an important role in the evolution of these classes during the Ordovician Radiation.