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.

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.

Latex casting of macroinvertebrate fossils, when filling natural molds, produces a positive, or cast, reproduction of the organism. The use of latex molds to cast fossils in plaster or plastic materials will be discussed elsewhere in this volume. The purpose of this paper is to describe the preparation of latex casts for study and photography. The procedure for preparing a latex mold is essentially the same. Latex casts, carefully made, reproduce surficial detail with remarkable fidelity and a photograph of a whitened, stained-latex cast is often times indistingushable from a photograph of a well- preserved whitened body fossil.

If one were to ask a group of paleontologists “How do dinosaurs fit into the history of life on Earth?” the answers would all be different. The question is so big that it surpasses the vision of a single person, and the answers would be as diverse as those of the blind men describing an elephant from its parts. The answer which follows is also from someone who cannot see the whole “elephant.” It is so simple that it is surely grossly inadequate, like lamely describing the hypnotically beautiful appearance of the Earth from space as spherical.

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.

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.

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.

Climactichnites Logan, 1860, is known only from its large trail up to 20 cm in width, a trace superficially resembling a rope ladder. Prominent lateral ridges are parallel throughout the length of the trail; they may be smooth and hemispherical in cross-section or crenulated, much like a pie crust. Between these ridges is a series of raised dune-like bars and furrows dug into the substrate. The bars and furrows show considerable individual variation between trails and also variation along a trail. Ovoid impressions are known which occur at the start of trails. The posterior of these impressions is well rounded; the anterior is triangular, and for a short distance from the impression, the trail is developed on only one side. One exceptionally preserved impression shows curved, closely spaced, fine lines parallel to the posterior.

The trails are found only in sandstone, and where they are present, they are abundant. Slightly equivocable evidence indicates a Dresbachian (early Late Cambrian) age for the occurrences in New York, Missouri, and Wisconsin; trails in Ontario and Quebec are less certainly dated. Desiccation cracks and air escape hole suggest that the trail was fully exposed to the atmosphere.

From this data, a large number of sketches were made to reconstruct an animal able to make such a trail. Each attempt produced new speculation on the morphology. In the final rendition, the animal is bilaterally symmetrical, broad and low. The integument is tough, and the sole bears a subcentral mouth anteriorward. Lateral flaps scraped and compressed damp sand to make the parallel ridges. The anterior was strongly musculated and thin. This anterior flap grasped the sediment, alternating on either side of the animal to pull the form forward when the lateral flaps were relaxed. Curved rows of cilia on the posterior moved loose sand into dunes between the furrows formed by the anterior flaps.

This reconstruction is like that of no other animal known in the Vendian or the Phanerozoic.

The sauropod dinosaurs, those long-necked, long-tailed giants, burst onto the world scene in the Lower Jurassic period and lived on until the end of the Age of Reptiles at the close of the Cretaceous. From the shapes of their teeth it is clear that they were herbivorous, and what an enormous amount of plant material they must have continuously consumed to fuel their gigantic bulk. Colbert (1962) estimated the weight of an adult Apatosaurus (Brontosaurus) at 34 metric tons, and that of Brachiosaurus at 78 metric tons. Dale Russell (see Russell, Beland and McIntosh, 1980) regards these estimates as too high by perhaps a factor of two, but in any case their masses were immense. The sauropods were quadrupedal, and their limbs were oriented in a columnar position as in large mammals, and unlike those of other dinosaurs. From this fact and a bone histology more nearly like that of mammals than typical reptiles, Bakker (1975) and de Ricqlès (1968, 1980) have independently suggested that the sauropods may have been warm-blooded (endothermic). Many dinosaur experts concede that this may have been true of some of the smaller, faster-moving carnivores, but the majority seem unconvinced of endothermy in the sauropods. Instead, it seems more appropriate to regard them as inertial homeotherms: that is, their large mass ensured a fairly constant body temperature, as in large mammals. However, as in mammals, the story is probably more complex than a single fact or factor can explain (Thomas and Olson, 1980; Weaver, 1983).

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.

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.

Critics of the concept of organic change through time have demanded proof not only of “transitional forms” but of specific transitions among higher taxonomic groups. Transitional forms among species and between a species of one genus and a species of another genus have been criticized because most demonstrated ancestor-descendant transitions are considered to occur within one “kind” of organism; the “kind” concept is bereft of biological meaning.

Natural selection acts upon organisms at all stages of ontogeny, and especially at larval-juvenile stages. Large shifts in the morphology of one or more features are common in groups of organisms that evolve by heterochrony. Because heterochrony involves a change in timing of the appearance or development of a particular feature, recognition of heterochrony requires a confident knowledge of ontogeny. The resulting increase in complexity (e.g. recapitulation) or decrease in complexity (e.g. paedomorphosis), well documented among living organisms, commonly excludes morphologic intermediates. Paedomorphosis is especially important in the evolution of progressively simplifying lineages and has been well documented from living plants and animals and fossil representatives of echinoderms (blastoids, crinoids), conodonts, arthropods, mollusks and vertebrates. Heterochrony characterizes the evolution of most metazoan organisms, occurs at all taxonomic levels and was probably responsible for major innovations by which higher taxonomic groups are recognized.

The thermal physiology of extinct reptiles has been a hotly debated topic for the last two decades, with no direct evidence available to help solve the debate. Oxygen isotopes are fractionated with respect to temperature between an animal's body water and bone phosphate, thus providing avenues for deriving the first direct evidence of dinosaur thermal physiology.

Multiple samples from both cortical and cancellous areas from individual bones were sampled in order to determine the heterogeneity of δ18O values within single bones. Bones from both the body core (ribs and vertebrae) and the extremities (limbs and caudal vertebrae) of known individual dinosaurs were sampled in this method. This allows for a comparison of isotopic heterogeneity from bones of all body regions. In ectothermic heterotherms or mass homeotherms the δ18O values from the extremities are expected to generally be heavier than those from ribs or dorsal vertebrae. It is also expected that there would be a greater degree of heterogeneity of δ18O values from bones in the extremities than those in the body core for these individuals. This relationship would result from the greater degree of heat loss from the extremities than body cores due to greater surface areas and distance from the heart. This relationship has been seen in analyses on bones from the modern Varanus komodoensis. On the other hand, true endothermic homeotherms should show a very narrow range of hetergeneity of δ18O values both within individual bones and between bones within single individuals as seen in modern mammals.

Dinosaurs analyzed indicate isotopic heterogeneities within individual bones intermediate between modern mammals and Varanus, with the Tyrannosaurus showing the greatest isotopic variability. However, this isotopic heterogeneity is relatively small and is not significantly different for bones from the body core and extremities. This indicates that heterogeneity of the δ18O values is most likely the result of variations in drinking water δ18O values throughout an individual's lifetime rather than daily or seasonal variations in body temperatures.

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.

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.

Holocene patch-reefs occur throughout the shallow marine platform, to the lee of the barrier reef in northern and southern Belize, Central America. Patch reefs on the northern shelf that occur within an areally extensive patch reef complex (Mexico Rocks) indicate that differences exist between reefs here and well-studied patch reefs on the southern shelf that have been used by workers as a general model for patch reef development throughout Belize. This model proposes that patch reefs on the Belizean shelf are dominated by typical Atlantic-Caribbean, biotically-zoned coral assemblages of Acropora palmata and A. cervicornis that kept up or caught up with Holocene sea level rise during the last 8000 years to form large “keep up” or in some instances “catch up” reefs.

In contrast to those in the south, the northern patch reefs are not biotically zoned, are dominated by Montastrea annularis rather than Acropora spp., and are much younger (400 years old) than those in the south. In addition, northern shelf patch reefs developed predominantly by lateral growth in a milieu of static sea level and are herein called “accretion” type reefs. These differences in biotic and sedimentologic parameters between reefs on the northern and southern shelves imply fundamentally different ecologic and sea level history controls on patch reef formation from north to south. A leading contributor to the variation among the reefs along the Belizean shelf may be species-specific growth rates of the coral species that initiate each patch reef, and response to sea level fluctuation versus stasis through time.