Understanding the origin of modern communities is a fundamental goal of ecology, but reconstructing communities with durations of 103–106 years requires data from the fossil record. Early Pliocene to latest Pleistocene faunas and sediments in the Meade Basin and modern soils and rodents from the same area are used to examine the role of environmental change in the emergence of the modern community. Paleoenvironmental proxies measured on modern surface soils and paleosols are described, and faunal dynamics of fossil rodents are discussed. Mean annual precipitation (MAP) was estimated from elemental concentrations and magnetic properties, and warm-season temperature and δ18O of soil water was estimated using carbonate isotope paleothermometry on pedogenic nodules. MAP and temperature estimates from paleosols exhibit no short-term variability, no long-term trends, and generally bracket modern values. Estimated soil water δ18O values increased through time, suggesting aridification played a role in the evolution of the regional grassland ecosystem. Carbon isotope analyses of biomarkers are used to examine the abundance of C4 grasses, which suggest more C4 biomass and more variability in C4 biomass than carbonate proxies. Rodent species richness remained constant due to balanced rates of extinction and immigration, both of which show episodic spikes consistent with a balance between forcing mechanisms that result in equilibrium on long time scales. Overall, these results suggest that different mechanisms of faunal change may be acting at different time scales, although the stratigraphic resolution of paleoenvironmental proxies needs to be increased, and body size and dietary distributions of rodents need to be determined before which processes of change are most important can be decided.

Coral reefs have experienced a profound shift in community structure in recent decades, a pattern that contrasts with the apparent constancy of Caribbean reef zonation over the past 2 million years. The abrupt decline in branching Acropora palmata and massive frame-builders like Montastrea annularis in the Caribbean is troubling, and similar patterns have been reported from virtually every ocean. As we ponder the future of coral reefs, we must be mindful that our best monitoring records span perhaps half a century – and those are exceedingly rare. “Pristine” reefs may not have existed since Columbus sailed for the new world, and anthropogenic impacts probably extend even farther back in time.

Despite the vagaries of evolutionary change, taphonomy and time averaging, the geologic record still represents a unique source of important information about the processes that have controlled community structure and reef building in the absence of human influences. The creation of rigid and elevated structures requires calcification rates that are capable of filling the accommodation space created by rising sea level. This has been complicated over the past three to four decades as accelerated sea-level rise has been joined by a suite of stresses that probably slow accretion. Explaining the recent reef decline and posing realistic models of future change will require an understanding of carbonate cycling in the past, the processes that have been involved and a quantitative assessment of how anthropogenic stresses are affecting both.

At the least a look back in time may help to constrain the thresholds at which change might be expected to occur in the future. At best, the context gained from examining the “recent” geological past may provide insights into which possible solutions are most consistent with observed patterns at larger spatial and temporal scales.

PALEONTOLOGICAL collecting, transport of fossil materials, and the ownership of paleontology collections are governed and affected by a wide range of laws and regulations, from land law to bequests. Compliance with all applicable laws can be confusing, especially when a collector has to negotiate Federal, state, local, tribal and international requirements.

Unlike archaeology, paleontology does not have a body of laws specific to fossil protection. Most legal problems in paleontology arise from land access and permission to collect on public lands, theft and trespass concerns, public trust violations, land title and rights, and related issues. In the United States, there are no definitive overarching statutes governing fossil resources per se as separate from other land resources.

Ecology, the study of interactions among organisms and their surroundings, can be approached on multiple scales ranging from the organism to the biosphere (Fig. 1), with unique processes governing interactions and dynamics at each scale. Individual organisms interact with their environment in many ways, including feeding, movement, and respiration. Populations are groups of individuals of a single species living in a local area, and population ecology relates to the dynamics of population size, density, and demographic structure. Communities consist of the populations living and interacting in an area; community ecologists study interactions within communities and their effects on the abundance, diversity, and distribution of species and populations. Ecosystems consist of communities of organisms plus their chemical and physical environment, and ecosystems are typically studied in terms of the movement of energy and nutrients among organisms and the environment. The biosphere encompasses all ecosystems (Fig. 1).

Fossil diatom assemblages are useful for reconstructing past environmental changes in riverine systems. However, few studies have attempted to utilize paleolimnological techniques in these settings. Analysis of sediments from riverine environments can provide key information predating the impact of human development, which cannot be acquired by other means. Paleolimnological techniques can be used to determine the natural variability in these systems and to estimate the magnitude and rates of change that the environment may have undergone as a result of anthropogenic or climatic factors, and to provide realistic goals for management of negatively-impacted systems.

Reconstructing past riverine settings requires an understanding of the factors that control the spatial distribution of diatoms in riverine settings; this paper discusses the impact of resources, stressors, and disturbance events, which are the primary controls on the distribution of benthic diatoms in modern riverine environments. A selection of case studies that utilize paleolimnological techniques to infer past stream hydrology are also discussed; these examples encompass the use of fossil diatom assemblages from sediments recovered from lowland floodplain and meandering river systems, estuarine environments, fluvial lakes, arctic deltaic environments, and terminal lakes.

The great abundance and diversity of diatoms in lacustrine sediments and their ability to adjust to rapid changes in physical, chemical, and biological conditions makes them ideal for the study of lake history. Continuous diatom records from long-lived lakes have the potential to answer questions of basin history, climate variability, ecological change, and evolution. Isolated Tertiary outcrops provide a more limited record of environmental conditions, but as the ability to correlate individual exposures improves through the use of techniques such as tephrochronology, it is becoming possible to evaluate the timing of environmental or evolutionary changes on a regional basis.

Duncan (1957) and Osburn (1957) provided excellent literature surveys on the paleoecology and ecology of bryozoans; this report is intended as an updating of Duncan's work. Publications on modern bryozoans are not included here except for certain papers directed toward paleontologic problems. Since Duncan, and Osburn, ecological and paleoecological summaries have been published by Hyman (1959), Cheetham (1963), Ryland (1970) and Cuffey (1970). Schopf (1969) surveyed bryozoan paleoecology from the viewpoint of colony growth habits and Heckel (1974) and Cuffey (1977) summarized knowledge of bryozoan occurrences in reefs. Most authors have emphasized cheilostomes; information on stenolaemates is limited.

The 520 million year evolutionary history of the Cephalopoda is punctuated by a number of severe crises during each of which this class came very close to extinction. These are fully documented only for the externally shelled, or ectocochlian, cephalopods to which my remarks are, therefore, restricted. The word crisis should be defined narrowly in the sense in which it is used in medicine, business, and the social sciences: “a condition…. felt to endanger the continuity of the individual or his group “(Webster's Third International Dictionary). Within species, genus, and family groups evolutionary crises are, of course, commonplace, and even orders may disappear without threatening the extinction of an entire class. It is only when all, or almost all, taxa of family-group and lower hierarchic level disappear more or less simultaneously, or within a geologically very short period of time, that we may speak of a crisis, a situation that threatens the very survival of a class, or higher taxon, of organisms. It is the purpose of this presentation to study in some detail this kind of situation as it has affected the evolutionary history of the Cephalopoda.

Most major topics that bear on the lophophorate condition have been ably treated in preceding contributions for either the Bryozoa or Brachiopoda. Accordingly I shall attempt a comparative approach, first characterizing the lophophorates as a whole and then contrasting the groups with an eye towards the evolutionary implications of resemblances and differences. To set a practical target I shall attempt contrasts between the feeding systems, because they seem to be particularly important to the present habits, habitats and distribution patterns of these groups. From this approach, questions naturally arise as to the evolutionary history of the lophophorates and in particular of extinct types of Brachiopoda for which modern analogues are unknown; these problems form potential research areas of special interest. To conserve space I have tried where possible to cite only more recent and/or general works that themselves contain ample references. I have assumed that by this point in the volume the reader will be acquainted with the gross morphology of bryozoans and brachiopods and with the major descriptive terms applied thereto. Because phoronids are not specifically covered in other contributions, I have included a wider range of phoronid references including some historically important works.

As demonstrated by Silurian Konservat Lagerstätten from North America, not all Lagerstätten represent living associations but are biased taphonomically, and the conditions necessary for exceptional preservation are environmentally, temporally, and areally diverse.

The early Silurian (late Llandovery-early Wenlock; Brandon Bridge strata) Lagerstätte from Waukesha, Wisconsin, was deposited under peritidal conditions in a thin, narrow zone adjacent to a karst-formed paleoscarp during transgression. Anoxic conditions resulting from restricted circulation and eutrophication are indicated by sediment lamination, shell decalcification, absence of sessile benthos, coiling of worms, absence of Chondrites (ubiquitous elsewhere), and presence of Pacytheca alga. Although anoxia, which was neither widespread nor long-lived, excluded most benthonic organisms, arthropods are abundant and diverse. These are mainly exuviae as suggested by consistent lack of specific body parts, extreme compaction, monotaxic size-sorted assemblages, absence of trackways and escape traces, and absence of enrollment in response to anoxia. This then is not a living association, but a taphonomic accumulation of mostly arthropod exuviae that were concentrated hydrodynamically.

Arthropods (mainly eurypterids and phyllocariids) dominate late Silurian (Ludlow-Pridoli; various units) Lagerstätten that were deposited in hypersaline peritidal lagoons surrounding the Michigan Basin in the U.S. and Canada. Although less diverse, these biotas were more widely distributed and of longer duration than the Waukesha Lagerstätte. Hypersalinity inhibited bacterial decomposition and lowered oxygen solubility, further excluding benthos by creating interstitial anoxia. These compose another example of taphonomically biased Lagerstätten, consisting chiefly of arthropod exuviae.

The late Silurian (Ludlow, Racine Dolomite) Lecthaylus Lagerstätte was deposited in deeper water on the shelf or slope of the Michigan Basin in northeastern Illinois. The limited biota, dominated by a single worm taxon (Lecthaylus) includes phyllocariids, graptolites and inarticulate brachiopods. Worms are outstretched and grouped in an orientation that suggests in situ burial. Laminated strata are succeeded by bioturbated sediment in cyclic repetition, indicating recolonization by wormlike burrowers (Lecthaylus?) following rapid sediment influx and burial of the biota under interstitial anoxic conditions. This is probably an autochthonous biota; sessile benthonic organisms may be absent as a result of soft substrate consistency or high sedimentation rate.

These Silurian Lagerstätten show that anoxia required for early diagenetic mineralization and exceptional preservation may be established in different amounts of time and in various ways (stagnant sediment trap, hypersalinity, obrution) and settings from peritidal to shelf/slope. Identification of these variations is important for prediction of additional Lagerstätten sites. Although arthropods in exuviae-dominated Lagerstätten may accurately reflect their true taxonomic diversity, they are probably present in greater numbers and in higher dominance relative to other taxa than in living associations.

Caribbean cheilostomes are a highly diverse component of the tropical American marine benthos with an excellent fossil record. Many workers have tended to lump taxa into morphologically variable, geographically widespread species originating in the Miocene, but recent morphometric and genetic analyses have revealed large suites of cryptic species, barely distinguishable morphologically, within several important genera. Most species in such suites have narrow geographic and stratigraphic ranges. In Stylopoma, for example, canonical discriminant and cluster analyses based on skeletal morphology yielded 19 late Neogene to Holocene species, most of which had been previously classified as S. spongites. Seven species were available for genetic analysis, of which six have been confirmed to differ by protein electrophoresis, either by fixed allele differences or significant genetic distances in sympatry. A combination of cladistic and stratophenetic analysis suggests that the most widely distributed and long-lasting species, which originated early in the Miocene, was ancestor to most or all of the other tropical American Stylopoma species. Despite extensive sampling, five species are narrowly distributed, with all known fossil and viving specimens separated by less than 1000 km, and all but three of the 18 descendant species have been restricted throughout their history to relatively limited parts of the tropical western Atlantic. These patterns are consistent with allopatric speciation of peripheral isolates, only a few of which have achieved wide distributions. Cladogenesis was highly episodic, reaching a peak in Late Miocene time, well before final closure of the Panamanian portal, but after formation of the sill that disrupted oceanic circulation patterns throughout the region.

Although most occurrences of Ediacaran fossils are from shallow-shelf deposits, taxonomically-similar assemblages have recently been described from a 2.5 km-thick succession of dark mudstones and turbiditic sandstones in the Windermere Supergroup of the Mackenzie Mountains, northwestern Canada. The paleogeographic position (20-40 km seaward of the shelf edge), abundant evidence of mass flow, and the complete absence of in situ shallow-water features imply that deposition took place on a slope considerably below storm wave-base. Ediacaran fossils were not observed in axial trough deposits (lower parts of the Twitya and Sheepbed formations), but megafossils occur sporadically in lower to middle slope deposits higher in the same formations. Megafossils and trace fossils are present in upper slope settings (Blueflower Formation) at the top of the Ediacaran succession. The megafossil assemblage varies stratigraphically, but in all formations is dominated by discoid forms (e.g. Cyclomedusa, Ediacaria, Nimbia); frondose forms and vendomiids are very rare.

Megafossils are preserved mainly as positive features on the soles of thin turbidite beds. Most fossiliferous beds begin with the rippled layer of the turbidite (Tc), but a few begin with the graded (Ta) or parallel-laminated (Tb) layer. Consistent orientation and high relief of individuals, evidence of mutual deformation during growth of adjacent organisms, and other taphonomic features imply that virtually all of the taxa represent benthic polypoid and frond-like organisms (not jellyfish). Slump structures occur commonly in the sandstone fill of fossils, suggesting that many of the organisms were buried alive by the turbidite and later decomposed. Other individuals, even on the same bedding plane, exhibit graded to laminated fill identical to that of the overlying turbidite bed, indicating that the depressions on the sea bottom produced by these individuals were empty at the time of turbidite deposition. Escape structures are absent, suggesting that the Ediacaran organisms were not capable of burrowing up through even thin layers of sand.

Ediacaran megafossils are invariably preserved on black, wrinkled surfaces similar to those elsewhere interpreted as microbial mats. Molding of delicate features (including tentacles), preservation of open molds as negative epireliefs, and sedimentological evidence of considerable cohesion of these surfaces relative to the underlying turbiditic muds (Td,e) supports this interpretation, and suggests that microbial mats were as important in the preservation of these deep-water Ediacara faunas as they were in their shallow-water equivalents. The presence of the wrinkled mats and their associated Ediacaran fossils almost exclusively in the pyritic intervals of the succession suggests that both may have lived under exaerobic conditions in this deep-water setting.

After two centuries of scientific endeavor, scientists have concluded that the age of the Earth is 4.54 billion years. This value, which is based on the relationships between lead isotopes in meteorites and in the Earth, has an uncertainty of less than 1 percent and is consistent with numerous radiometric age measurements on ancient rocks found on the Earth and Moon as well as on meteorites. In addition, the antiquity of the Earth is consistent with evidence indicating that the Milky Way Galaxy and the universe are of the order of 14-16 billion years (abbreviated Ga) in age.

Much effort has been expended in determining the geological utility of conodont elements; little has been spent on determining their usefulness to the conodont animal. Most conodonts had an apparatus made up of a number of morphologically distinct, complex elements. Such apparatuses were borne by members of the Ozarkodinida, Prioniodinida, and Prioniodontida, together accommodating ~75 percent of known conodont genera.

The ozarkodinid apparatus consisted of an anterior battery of S and M elements behind which lay opposed pairs of Pb and Pa elements. Debate over its function has centered on two main hypotheses. These have considered the apparatus either as a filter feeding system, or as teeth. Ontogenetic analysis reveals that ozarkodinid apparatus growth was incompatible with a filtering function. The rate of increase in size of the S and M elements (the postulated filtering system) was insufficient to have met the increasing food requirements of the growing animal.

Like the apparatus of ozarkodinids, that of prioniodinids was differentiated into an anterior S and M element series and posterior, paired Pa and Pb elements. Despite these similarities in element arrangement, the prioniodinid apparatus does not exhibit the same degree of morphological differentiation as that of ozarkodinids. The Pa and Pb elements were probably involved in swallowing rather than cutting and grinding food.

The prioniodontid apparatus is poorly known but it is clear that although the morphology of elements is comparable to ozarkodinids, their arrangement in the apparatus was markedly different. Until the architecture of the apparatus has been determined, it's mode of function can only be guessed at. Preliminary knowledge of the apparatus, however, suggests that it operated differently to those of ozarkodinids and prioniodinids.

Understanding of the function of conodont elements requires that their morphology is studied within the context of an integrated multielement apparatus. There is substantial variation in apparatus composition and differentiation, and element morphology between clades. This variation undoubtedly reflects, to a large extent, differences in apparatus adaptability and versatility, functional flexibility, and food specificity; all factors that in other groups have had a major influence on evolutionary patterns.

In the Proterozoic Clemente Formation at Cerro Rajon, south of Caborca, Sonora, we have collected sandstone beds that contain many small, sediment-filled structures. Each structure is a thin-walled, elongate sack, about 1.5 cm tall, oriented perpendicular to bedding. The sacklike structures are laterally flattened and roughly elliptical in transverse section, with the major axis of the ellipse measuring several mm and the minor axis 2-3 mm. The walls are not mineralized and consist of a thin layer of cryptocrystalline clay. One or both walls of each specimen is undulatory with a wavelength of 3-4 mm. The sacks are closed at the bottom, but appear to be open at the top, like an uninflated toy balloon. On the bottom surface of the sandstone bed, beneath each vertical sack structure, is a prolate ellipsoid-shaped sole mark. The long axis of each ellipsoid sole mark is parallel to the long axis of the associated sack structure, and the sole marks are oriented sub-parallel to one another on the surface of the bed. We tentatively interpret these structures to be the holdfasts of gregarious, attached, benthic organisms oriented sub-parallel to one another on the sea floor.

A preliminary study of carbon and oxygen isotope stratigraphy was carried out on the 2 km-thick Proterozoic through Lower Cambrian section at Cerro Rajon. Samples were collected every 50 m, and analyses were done in the laboratory of J.M. Hayes at Indiana University, whose assistance is gratefully acknowledged. The isotope record shows a primary signature for most of the section. Although the wide spacing of sample collection does not permit an unequivocal intercontinental correlation, a prominent negative δ13C excursion near the base of the Papalote Formation may correlate with similar excursions at the Vendian-Cambrian boundary on several continents. This would place the base of the Cambrian of the Caborca area several hundred meters lower than previously thought, but still several hundred meters above the possible body fossils of the Clemente Formation.