The last two decades have seen the status of deposits containing soft bodied Cambrian fossils rise from geological curios into one of the foundations of modern thinking on early metazoan evolution and ecology. Some thirty of these soft bodied assemblages or Lagerstätten, resembling the Burgess Shale fauna are now known. One of these is the Lower Cambrian Emu Bay Shale fauna from Kangaroo Island, South Australia.

The Emu Bay Shale has been mapped in two localities approx. 8 km (5 miles) apart on the northern coast of Kangaroo Island, at Emu Bay and at Big Gully. Previous investigations into the numerically abundant Lagerstätten fauna at Big Gully have highlighted its unusually pauperate diversity, with only some seven species described. The preservation is also unusual, comprising replacement by iron stained calcite. The fauna is confined to a 10 m thick basal siltstone. The age of the deposit is believed to be mid to upper Botomian and is thus marginally older than Early Cambrian soft bodied assemblages found on the North American continent and predating the better known Middle Cambrian Burgess Shale.

In late 1991, a study of the Emu Bay Shale was undertaken to document the palaeontology and palaeoecology of the fauna. Preliminary findings, whilst increasing the number of species, confirm the pauperate diversity of the fauna. The new forms include several specimens of anomalocarid appendages. These not only represent the first occurrence of this form in Australia, but also the first occurrence outside the Burgess Shale of anomalocarid appendages with 11 segments, as compared with the more common and widespread 14 segment appendages. This connection may be important in the light of recent palaeoreconstructions which show the west coast of Canada and eastern Australia in close proximity during the early Cambrian. Also the spatial arrangement of the appendages indicates that anomalocarids may have shoaled and hunted in groups. They appear to have fed on the sea bottom, possibly using their appendages to probe the muddy bottom for shallowly buried prey as well as for capturing and transporting prey to the mouth.

The assemblage appears to be dominated by the preservation of hard or permineralized body parts. However, abundant calcified ribbon-like structures concentrated on some bedding planes have yet to be classified. Several exceptionally preserved specimens of Myoscolex appear to have a series of metamerically repeated ‘paddle-like’ appendages, similar to some forms from the Burgess Shale, thus casting doubt on an annelid affinity.

The assemblage appears representative of a deep water, low oxygen environment prone to periodic anoxia, possibly similar to the accretionary environment of the Burgess Shale.

The Emu Bay Shale at Emu Bay exhibits a shelly assemblage, mostly comprised of disarticulated Hsuaspis exuvia with occasional small Redlichia exuvia and hyolithids. No calcite replacement is evident. The location represents current swept, probably shallow water environment.

Paleontological studies can bring to light two important aspects of the speciation process: long term patterns of morphological change, and the paleoenvironmental context of such changes. We examined the temporal patterns of morphological change and their geographic and paleoenvironmental context in species of Prunum (Marginellidae; Gastropoda) from the Neogene of the northern Dominican Republic. We document a speciation event from P. coniforme (Sowerby 1849) to P. christineladdae (Maury 1917) which is unusual in both its temporal expression, and in the relative clarity of the ecological setting for speciation.

We believe that the changes in morphology from P. coniforme to P. christineladdae represent a speciation event. The two species are distinguished by several shell features, including overall shape, spire height, relative height of the top of the lip, and apertural denticulations. The nature and magnitude of these differences, compared with morphological differences among extant species of Prunum, indicate that separate species designations are warranted for P. coniforme and P. christineladdae. A sequence of stratigraphic and morphological intermediates between these species provides strong stratophenetic evidence for speciation.

The stratigraphic interval characterized by intermediate morphologies includes approximately 22 m of section. Sedimentation rates yield estimates of approximately 73,000–275,000 years for our interval of morphologic change. This transitional interval represents between 0.6–2.5 % of the total duration of the ancestral species.

The patterns of morphological change exhibited by the two species generally fit the predictions of punctuated equilibrium; change from ancestor to descendent is relatively rapid, outside the transitional interval species exhibit no directional morphologic trends, and the ancestral species persists after speciation.

Our data reveal some information on the mode of speciation. Prunum species from our study area exhibit well-defined depth ranges. P. christineladdae occurs only in deep water deposits, whereas P. coniforme is common in shallow water deposits. Based on distributional data, we suggest that depth, or one or more of its associated variables, was critical to the isolation and evolution of P. christineladdae.

Mass extinctions profoundly affect patterns of diversification and skeletal innovation in the succeeding radiation. For instance, promising adaptations may be removed permitting traits of the few survivors to proliferate. Consequently, patterns of survivorship could control directions of radiation following the extinction event. Alternatively, selection during radiation may be quite different from extinction conditions. The founders may be quickly superseded by taxa with wholely new innovations that are built upon, but are distinct from, the founding morphologies.

Planktic foraminifera nearly became extinct at the end of the Cretaceous. Of the two or three lineages that survived, perhaps only one founded the bulk of the Paleocene radiation of Globigerinacea. In addition, there was little habitat diversification within the surviving lineages. Nearly all the morphological and ecological innovations occur in a single clade that diverged rapidly from the ancestral stock.

Neither of the best known surviving lineages diversified much after the Cretaceous. Hedbergella monmouthensis is the ancestor of Danian Globanomalina archaeocompressa. The two taxa are nearly identical in both morphology and in isotopic signature. Significantly, the globanomalinids displayed very little diversification, like their Cretaceous ancestors before them. Instead, species were replaced one after another in an anagenetic trend and consistently occupied a moderately deep-water habitat. Similarly, triserial Guembelitria gave rise to only a modest radiation of biserial species in the earliest Danian primarilly within near surface water habitats.

Cladistic analysis suggests that the major part of the Cenozoic radiation was founded by one or two Cretaceous taxa. Most Danian trochospiral species abruptly radiated into two main stocks in the earliest Danian. All of them are probably derived from Hedbergella, but they rapidly became morphologically differentiated from this Cretaceous survivor. Alternatively, many of the features of the Danian species may have been inherited from another Cretaceous survivor–possibly a species of Rugoglobigerina–as suggested by comparative studies of early ontogeny. In either case, the group split rapidly into two main lineages. One, rooted in non-spinose ‘Morozovella’ taurica, led to the major diversification of the muricate-walled morozovellids. Isotopic data suggest this lineage spread from a moderately deep water habitat into the near-surface waters where the major diversification occurred. The other lineage developed spinose wall texture and gave rise to the diverse subbotinid radiation. Stable isotopic data suggests the subbotinids grew consistently in the coldest and presumably deepest waters. Their spinose wall texture suggests they were at least partly carnivorous, by analogy with living spinose taxa.

These patterns of morphological and ecological diversification suggest that the immediate survivors did not radiate markedly but retained the evolutionary rates and habitats of their Cretaceous ancestors. Most of the radiation occurred in a clade whose innovations evolved during the Danian, rather than simply retooling traits of their founder. Likewise, the radiation occurred principally in surface and deep water habitats, both largely vacated by the extinction event. The intermediate depth habitats were continuously occupied by the persistent hedbergellid-globanomalinid lineage. Their habitat was not invaded by other radiating clades. Evidently, survival alone does not confer the capacity for subsequent diversification upon a founding species. Innovation seems to be the key to dominance rather than mere persistence through an episode of heightened extinction.

Previous underwater observations have demonstrated that detached stalk pieces with a few noditaxes are often found in the habitats of modern isocrinid crinoids. They sometimes stand on the substrate by grasping hard objects by cirri. According to the growth of the stalk, the distal parts are repeatedly detached from the main body and discarded on the sea floor. There has been no information about the “fate” of such isolated stalk pieces. Abundance of stalk pieces of crinoids in the geologic column must be considered with reference to the modern analogue.

We have collected by dredging specimens of modern stalked crinoid Metacrinus rotundus Carpenter from the depths of 135-150 m in Suruga Bay, central Japan. Specimens were transferred to a large temperature controlled aquarium (13°) within several hours after capture. While keeping the animals, a few specimens have autotomized the distal stalk, and isolated pieces with a few noditaxes were left in the aquarium. They have kept the same postures and still attached to pebbles by cirri for approximately one year. No further disarticulation nor regeneration occurred to the stalk pieces.

Section of the stalk piece stained by hematocyanin showed that the nuclei were well colored and the fragmental stalk was considered as living. This result strongly suggests a possibility that such fragmental stalks can live for a long time in the natural environment. Abundant occurrence of stalk elements from the geologic record have been attributed to a taphonomic process; selective accumulation of a part of the body after death, but the present results imply that these stalk pieces could live alone for a long time on the sea floor.

Variation in terrestrial productivity and biomass impacts evolution through linkages between productivity and biodiversity and through the types of resources available for consumption by herbivores. Geographic variation in terrestrial plant carbon is known on a global scale for extant biomes and is strongly correlated with precipitation, temperature, and the area of wetlands. Although estimates of extant terrestrial plant carbon density are still somewhat uncertain, the highest densities clearly occur in tropical and temperate rainforests, and the lowest occur in deserts, semideserts, and arctic/alpine tundra. Patterns of variation in ancient terrestrial plant carbon can be estimated through the correlation between biome/climate and carbon density, provided individual biomes show little change through time in primary productivity or density of plant carbon.

Density of terrestrial plant carbon has been estimated on a global scale for the latest Cretaceous, late Paleocene/Eocene, middle-late Eocene, early Miocene, and Holocene/Recent using the biomal reconstructions of Wolfe (1984), Upchurch (this symposium), and others. Latest Cretaceous (Maastrichtian) estimates indicate a relatively low value of 700-800 gigatons, which may underestimate carbon due to the presence of extensive latest Cretaceous coastal wetlands. However, much of this figure is readliy explainable by extensive deserts in Asia and little evidence for areally extensive tropical rainforest.

Major increase in terrestrial plant carbon occurred during the Paleocene/earliest Eocene in conjunction with a major areal increase in rainforest. During the early Miocene terrestrial global carbon was approximately 1200-1300 gigatons. This figure decreased by about half between the early Miocene and Holocene/Recent. The decrease in terrestrial carbon density resulted from a decrease in area of tropical and subtropical forests and increase in area of deserts, grasslands, and mediterranean woodlands/chapparal.

The Pennington Formation (Chesterian, Mississippian) of northeastern Alabama is a regressive, distal lobe of the Pennington/Lee clastic wedge, located on the western flank of the Appalachians in the Tennessee structural salient. The clastic units of the Pennington include sandstone, siltstone, mudstone, clay shale and coal and are genetically related to the effects of progradation. The presence of limestones and dolostones within the southwestwardly prograding and thinning Pennington is due to the lateral equivalency and interfingering relationships of the Pennington with the upper part of the adjacent Bangor Limestone shelf.

A highly diverse ostracode fauna as been collected from outcrops along the Pennington-Bangor transition in northeastern Alabama. The most common assemblage of ostracodes is dominated by kirkbyaceans and includes species of Amphissites, Polytylites, Kirkbyella, Kirkbya and Reviya. Bairdiaceans are noteably absent from this assemblage. The Kirkbyacean Assemblage is only found in middle to outer shelf palaeoenvironments where clastic input is high, but where salinity conditions are thought to have been typically marine. In middle to outer shelf limestone-producing palaeoenvironments, a Bairdiacean Assemblage is dominant, although kirkbyaceans are still present.

A Sansabellid Assemblage, consisting of kloedenellaceans such as Sansabella, Geisina, Geffenina, Nufferella and Glyptopleura appears to be produced under rapidly changing nearshore, inner shelf conditions, where terrigenous input was often high and palaeosalinities may have been variable or less than normal marine. The Sansabellid Assemblage contains occasional kirkbyaceans, however bairdiaceans are noteably absent. Intermediate assemblages contain elements of the three main assemblages and reflect the transition from the inner to outer shelf.

In summary, the ostracode assemblages of the Pennington-Bangor transition in northeast Alabama provide indicators of palaeoenvironmental change during the southwestward progradation of the Pennington deltaic wedge onto the Bangor Limestone shelf. The prime factors resulting in palaeoecological response appear to have been variations in terrigenous input and palaeosalinity.

High quality (>2% TOC) Upper Devonian source rocks are developed in several sequence types. The commonest type, accounting for 70% of the studied examples is the transgressive sequence with a basal hiatus. Others include shallowing upward sequences (12%), lacustrine sequences in fault-controlled basins (7%), distal slope sequences (7%), and evaporite capped sequences (4%).

Starting from the synthesis of Johnson, Klapper, and Sandberg (1985) it has been possible to demonstrate correlativity of Upper Devonian transgressive episodes globally. The marked association of epeiric sea Upper Devonian source rocks with transgressions heightens interest in their causation. Could they have been produced by glacio-eustatic sea-level change as Stanley (1984; 1988) implies? Quantitative paleoclimate modeling and isotopic paleotemperatures for the Upper Devonian suggest not. Modeling using CCM1 at NCAR, including five year seasonal cycles, suggests the absence of any large southern hemisphere ice volume. Because much of the Upper Devonian land mass was either in equatorial or high latitude regions, there was little development of monsoonal climates. Midlatitude cyclonic activity was also much less than at present, meaning less polar transport of moisture and drier polar areas. Precipitation maxima largely coincided with topographic elevations. In contrast to the Late Ordovician to earliest Silurian, there was no Upper Devonian perennial snow cover even over the high latitude southern land mass. This was in spite of winter land temperatures as low as -40°. in eastern Gondwana. In that area and elsewhere, there was thin winter snow cover which melted in late spring resulting in no build-up of snow cover to produce glaciation. This was mainly the consequence of low winter precipitation in Gondwana. High latitude sea surface temperatures were certainly cold enough to displace or exclude some organisms. However, in low latitude areas where Upper Devonian extinctions also took place, modeled sea surface temperatures range between 27° and 34°. Such areas would have been refuges for any organisms displaced by cold, high latitude waters. The higher temperature values of low latitudes are convergent with the isotopic paleotemperatures determined by Brand (1989) using well preserved Upper Devonian brachiopods. Brand's determinations suggest temperatures even reaching lethal values for many plankton (37°). The extinction of reefs by the close of Frasnian time could have been partly a result of such elevated temperatures. Stacked extinctions of conodonts (Ziegler and Lane, 1987) and acritarchs may have been a further result. The loss of reefs, an important consumer of plankton, may have permitted a relative increase in plankton abundance crossing from more oceanic areas into epeiric seas, possibly contributing to high quality source rock deposition.

Phenacodus vortmani and P. primaevus, members of the mammalian radiation (Tiffanian - Bridgerian) in western North America, were digitigrade five-toed ungulates who were good runners compared to their contemporaries. P. vortmani was smaller and more slender (presacral vertebral column = 463 mm) while P. primaevus was larger and more robust (presacral vertebral column = 814 mm).

The presacral vertebral column in these phenacodontids consists of 7 cervical, 15 thoracic, and 6 lumbar vertebrae, with the sectional length proportions being very similar in P. vortmani and P. primaevus.

Morphologies and relationships of the vertebral structure in the cervical section allow both dorsoventral and mediolateral movements in both animals. Structures in the cranial thoracic section allow some mediolateral movement but restrict dorsoventral motion, adding stability and allowing forward transfer of momentum generated in the hind limb and caudal vertebral column. Structures in the caudal thoracic and especially the lumbar sections allow greater dorsoventral movements which enabled both phenacodontids to increase stride length beyond that accomplished by the limbs alone. In the smaller P. primaevus. the orientation of the zygapophyses emphasizes dorsoventral movements and restricts mediolateral movements compared to that in P. vortmani. providing the larger animal with greater efficiency in the flexion and extension of the posterior vertebral column during running.

Patterns of epibiont coverage are potentially useful tools in the determination of modern and ancient sedimentation rates as well as life habits of host organisms. A study was conducted to characterize patterns of epibiont settlement in various tropical environments and substrate types. Settling plates of clean aragonite shell were placed in six carbonate environments (beach, grass bed, bioturbated sand flat, back reef, forereef, and muddy bay) on St. Croix to document successional trends and timing of infestation by preservable, calcareous epibionts. Coralline algae were first to settle on freshly exposed substrate (within one week), followed by the foraminiferan Planorbulina and serpulid/spirorbid worm tubes. This successional order of epibiont encrustation is proposed as a measure of the length of time a shell has been exposed.

The results of this experiment were compared to epibiont patterns on naturally occurring substrates from the same environments. Because the study areas were from essentially the same reef-lagoon system, all sites were exposed to a common pool of encrusting organisms. Of primary interest were differences in encrustation on 1) varying host species, 2) rough- vs. smooth-shell surfaces, 3) infaunal vs. epifaunal shells, 4) substrates of different size, and 5) gastropods vs. bivalves. In addition, the preservability of these patterns was examined on mollusks sampled within Holocene reef cores from St. Croix.

Few preferences of epibionts for given shell-host species were noted. However, in lagoon grass-bed areas, epifaunal gastropods consistently showed greater coverage by late-stage encrusters than did infaunal bivalves. Within any environment, epibionts preferentially settled on rough substrates over smooth (e.g. heavily ribbed Codakia were more encrusted than smooth Tellina). Also, bivalve interiors were less encrusted than exteriors. While neither the interior nor exterior of these infaunal bivalves is likely to be encrusted during life, the interior of both species remained less encrusted, perhaps controlled by the smooth nature of the shell interior.

Differences in both the abundance and diversity of epibiont faunas were noted between substrates of different size. Epibiont faunas from mollusk shells smaller than 8 cm had fewer epibiont species than did coral substrates at least 15 cm across. The foram Gypsina, a white sheet-like encruster, and several species of bryozoa, all late-stage encrusters, were more successful on larger substrates from the same environments. This may be controlled by the successional patterns described above. Larger substrates were presumably exposed longer and thus acquired a higher diversity of encrusting species, thereby allowing some encrusters to spread over more area. Size differences exerted more control on epibiont coverage than did substrate type (i.e. coral vs. mollusk). The primary control of epibiont coverage, therefore, was the length of time a shell was exposed. Substrate-selective patterns were not as great as those occurring between environments.

Shells recovered from reef cores looked very much like those described from the reef surface. The occurrence of mollusk remains throughout the cores, along with a 5700±70 ybp radiocarbon date from a Chione valve from the bottom of one core, indicates that these are not simply recent shells that have fallen into the reef interior. Therefore, epibiont coverage has high potential for being preserved on shells caught up in the accreting reef.

Evolutionary patterns can be considered in terms of two interacting continuums (a) the magnitude of environmental fluctuations of physical variables especially climatic, and (b) the availability of metabolic energy beyond basic needs for maintenance and survival (Parsons, 1991) so giving four extreme combinations:

(1) widely fluctuating environments, low metabolic energy availability. This situation is a feature of species borders where the energetic costs of environmental perturbations restrict normal physiological processes so that ecological range expansions are precluded. Provided extinctions do not occur, species would alter their ranges to track longer term climatic changes as described in the historical and fossil records.

(2) widely fluctuating environments, high metabolic energy availability. This combination favors opportunists and colonists. Furthermore, following a relaxation of stress intensity after a mass extinction there could be a burst of speciation in such generalist species.

(3) stable environments, low metabolic energy availabilty. This combination represents deep sea and cave environments where low metabolic rate is an adaptation to accomodate stresses such as anoxia and low resource availability. Consequently the capacity for evolutionary change is low in these habitats which tend to contain relict species.

(4) stable environments, high metabolic energy availability. On energetic grounds speciation is theoretically possible, but high vulnerability to any stressful perturbation would be restrictive in practice since some stress is the norm in natural populations.

The potential for evolutionary change and speciation is low in these four extremes, however in intermediate habitats the potential is higher as implied in (2) when stress intensity is relaxed. The intermediate habitats would be characterized by moderately fluctuating environments where the metabolic cost of stress would not preclude adaptive change. Furthermore, the stress levels in such habitats should lead to sufficient underlying genetic variability to be permissive of adaptive responses to environmental change (Parsons, 1991). This paradigm may apply to speciation in tropical rain forests. A fossil analogy would be marine invertebrates in frequently disturbed onshore habitats.

Martin Rudwick's 1972 book “The Meaning of Fossils” was structured around five events in the history of paleontology, set in 1565, 1666, 1796, 1829, and 1857. Each event was tied to developments in paleontology, geology and biology in the surrounding decades. The central conceptual issues in those five episodes—the origin of fossils, geochronology, extinction, gradualism or catastrophism, and the origin of species—are all still with us. Rudwick's history ended with the 1870s, and the gap between then and now is almost as great as that between his two most widely separated episodes. My own experience in paleontology spans one-third of that gap; I shall talk about the meaning of fossils today, in the context of recent developments in paleontology (mostly of vertebrates) and biology, and how those affect our understanding of fossils. My main headings are: techniques and methods (of preparation and interpretation of fossils), the completeness of the fossil record (how we assess that, and how our assessment is changed by new finds and by new interpretations), the rise of molecular biology and its impact on paleontology, and some aspects of the relation between evolutionary theory and paleontology.

Articulate brachiopods underwent a major taxonomic and morphologic diversification during the Ordovician, yet remarkably little is known about the environmental, ecologic, and biogeographic contexts surrounding this event. An exception is Lockley's (1983) synthesis of brachiopod-dominated paleocommunities from the Welsh Basin. His study focused on a small geographic area dominated by siliciclastic sediments that was positioned at high paleo-latitudes during the Ordovician. North America, in contrast, was positioned at the equator and was the site of extensive carbonate platform development. A factor analysis of 165 North American assemblages was undertaken for comparison to Lockley's summary. The comparison suggests that the radiation of articulate brachiopods varied latitudinally, with different superfamilies radiating and achieving dominance in different biogeographic provinces. This pattern is also expressed by the relative abundance relationships among dominant genera making up the biofacies and therefore suggests that adaptation to local environmental parameters may have been an important governing factor.

The analysis of North American assemblages indicates that the composition of brachiopod biofacies changed dramatically as the Ordovician radiation unfolded. Ibexian and early Whiterockian shelf environments were dominated by orthaceans with porambonitaceans important in nearshore Ibexian environments. In the late Whiterockian a major turnover in biofacies composition occurred that marked the appearance and/or diversification of several new articulate superfamilies. Late Whiterockian through Cincinnatian offshore environments were characterized by plectambonitaceans and enteletaceans with strophomenaceans also moderately important. Nearshore environments were dominated by strophomenaceans, orthaceans, and rhynchonellaceans. Atrypaceans appeared nearshore in the Mohawkian but shifted their center of dominance offshore by the Cincinnatian. Deep basin environments were rarely inhabited by articulate brachiopods and were dominated throughout the Ordovician by inarticulates (lingulaceans). There was no major change in composition of the deep-water inarticulate biofacies that paralleled the turnover seen among articulates on the platforms.

The Welsh Basin biofacies described by Lockley are broadly similar to the North American biofacies. Orthaceans characterized Arenigian (late Ibexian and early Whiterockian) shelf environments. Orthaceans and strophomenaceans dominated Llanvirnian through Caradocian (early Whiterockian - early Cincinnatian) nearshore environments and plectambonitaceans and enteletaceans dominated offshore environments. Inarticulates were dominant in deep basin environments throughout the Ordovician. In contrast to North America, rhynchonellaceans and porambonitaceans, although present in the Welsh Basin, apparently never formed a distinct biofacies. In the case of the porambonitaceans, this may reflect poor sampling of Lower Ordovician strata. Enteletaceans, on the other hand, appeared earlier (Arenig) in the Welsh Basin than in North America and eventually diversified to become dominant in a broader range of environments that included the nearshore.

The Sirius Passet Fauna of North Greenland is one of the oldest Cambrian lagerstätten from the North American continent. It is known from a single locality in Peary Land (83°N, 40°W), on the shores of the Arctic Ocean, where outer shelf mudstones from the lower part of the Buen Formation (Early Cambrian) yield a rich assemblage of mainly poorly skeletised organisms with preserved soft parts. The steeply-dipping fossiliferous mudstones occur in close proximity to horizontally-bedded platform carbonates of the underlying Portfjeld Formation (Early Cambrian) in a structurally complex terrane. The boundary between the fossiliferous mudstones and the platform carbonates apparently defines the original northern margin of the carbonate platform and is not, as previously suggested, a structural feature, although some minor tectonic modification can not be excluded. Thus, the fossiliferous mudstones were apparently deposited in a transitional slope setting basinward of the shelf edge.

As currently known, the Sirius Passet Fauna comprises about 40 species, based on a collection of almost 5,000 slabs collected during brief visits to the isolated locality in 1989 and 1991. Arthropods dominate, with bivalved bradoriids and the trilobite Buenellus higginsi Blaker, 1988 being the numerically most abundant taxa. Weakly skeletised Naraoia-like and Sidneyia-like arthropods often preserve limbs and gills, as do bivalved arthropods similar to Waptia. Choia is the most common of several sponges. Worms include both priapulids and polychaetes, with a large palaeoscolecidan being conspicuous.

Fully articulated specimens of halkieriid worms, clad in an armour of hundreds of individual sclerites, are most notable amongst several problematic taxa. Rare specimens of possible onychophorans are also present, while brachiopods, hyoliths and other shelly fossils are rare or absent.

The Sirius Passet Fauna seems to show little taxonomic similarity to the Middle Cambrian Burgess Shale of western Canada or the Chengjiang Fauna from the Lower Cambrian of China at the generic level. Together with the latter fauna, however, it confirms both the general picture of Cambrian life presented by the Burgess Shale, and the existence of this great diversity of weakly skeletised arthropods already in the Early Cambrian.

Assessment of changes in terrestrial ecosystems since Cretaceous time, until recently, has had to rely on paleobotany (including paleopalynology) and vertebrate paleontology to provide data for analysis. Insects contribute a major portion of the terrestrial diversity in any ecosystem, but their fossil record and state of preservation had discouraged paleoecological study beyond the Pleistocene. With the discovery of prolific Upper Cretaceous amber deposits in Russia and Canada, and the investigation of Tertiary amber deposits from the Baltic, the Dominican Republic, Mexico and the USA, the prospect of clarifying changes in insect diversity and ecology over time becomes real. Methods are reported which allow the description of species richness and relative abundance of arthropod taxa from an Upper Cretaceous (Campanian: 75 MYA) amber deposit in Alberta, Canada. Diversity and abundance are described at the Order level for hexapods, and for the Acarina and Araneae. Taxa present, in order of abundance, are Homoptera (66 specimens/kg of amber), Diptera (28/kg), Acarina (21/kg), Hymenoptera (13/kg), Araneae (12/kg), Psocoptera (4/kg), Coleoptera (2/kg), Blattodea (1/kg), Thysanoptera (1/kg), Trichoptera (0.6/kg). Other orders present are Lepidoptera, Collembola, Dermaptera, Mantodea, and Ephemeroptera. In total, of 35 identified families, 8 are extinct. There are about 20 genera identified, of which only 1 is extant. All identified species are extinct. Estimated species richness is about 100 species of arthropods. In comparison, virtually all Families reported from Baltic amber (Oligocene) are still extant, as are the majority of genera. Morphology and feeding structures are well within the variation seen in modern insects. This suggests that throughout the Tertiary, Entomologists would feel quite at home with the insect fauna, and during the Upper Cretaceous, they would have little difficulty identifying insects at least to the family level. It is hypothesized that the taxonomic structure of modern insect communities was well established before the end of the Cretaceous, and that the structure and interrelationships of insect guilds were also very similar to those of today.

A fundamental assumption of paleoecology is that spatial variability in species distributions and associations reflect underlying spatial variability in physical environmental parameters. For example, gradients in species composition are usually interpreted as relating to gradients in variables such as water depth, temperature, or soil moisture. Numerous examples support the idea that when an environmental gradient is known to exist, there is a corresponding non-random community gradient. We suggest, however, that the reverse may not necessarily be true; i.e., a community gradient may exist even in the absence of an underlying physical gradient.

We have developed a series of models for the spatial distribution of organisms on landscapes (spatially heterogenous areas ranging in size from hectares to many square kilometers). In these models, a landscape is represented by a two-dimensional lattice, where each node of the lattice is a habitat site. Each habitat site is randomly assigned to one of a set of multiple habitat types (generally 3-6). A map of the lattice would thus show a random distribution of habitat types.

Habitat sites are competed for by sessile organisms that complete their life cycle in one time step (e.g., annual plants). “Seeds” are spread to a site from its eight next nearest neighbors. Each species' seeds successfully germinate on only a subset of the available habitat types (its “niche”), with one or more types being optimal (highest probability of germination). These subsets can overlap, so that different species can potentially occupy the same site. The probability of a given species taking over a site depends on the number of neighboring sites it occupies and whether the site is optimal. A site can be taken over by a suboptimal species if it locally more abundant.

Each organism's niche directly controls its ability to spread (“percolate”) through the landscape. Under the next-nearest neighbor rule, a species must be able to live on >40% of all possible sites in order to spread. Competition, by reducing the number of available sites, may prevent a species from reaching all habitable sites, even those that are optimal.

In one model, five habitat types are randomly distributed on a 201 × 201 matrix. Five species, each of which has an optimal habitat corresponding to one of the five habitats but can live on two additional habitats, are randomly introduced at one edge of the map and are allowed to spread. When the resulting distribution maps are examined, preferred species associations and gradients are observed, although there is no underlying habitat gradient. Instead, the observed patterns result from a combination of biotic interactions and historical contingencies, such as founder effects.

This and related models show how random processes can produce biotic patterns in the absence of environmental patterns. They provide appropriate neutral models for the interpretation of paleoenvironmental patterns based solely on species distributions.

The phylogenetic relationships of the echinoderms remains controversial due to the traditional use of morphological characters which do not reflect convergent evolution. While biochemical techniques and DNA analysis may be used in addition to morphological characters for analysis of living echinoderms, these tools cannot be extended to fossils. Shell matrix proteins - of echinoderms may be trapped and preserved for millions of years in fossil genera.

Analysis of shell matrix protein from Astropectin irregularis, Luidia clathrata and Mellita tenuis, reveal the presence of at least three major proteins of approximate molecular weights 230, 83 and 17 kDa common to all species. Astropectin irregularis showed four additional major bands of molecular weights 150, 90, 52 and 35 kDa along with at least 12 minor bands. Luidia clathrata showed five additional major bands of molecular weights 99, 60, 40, 24 and 21 kDa and at least 13 other minor bands. Mellita tenuis showed three additional bands of molecular weights 115, 96, and 24 kDa along with at least 4 minor bands.

As the three common proteins have been found in both seastars (A. irregularis and L. clathrata) and echinoids (Mellita tenuis), further analysis of these shell matrix proteins may be used to elucidate phylogenetic relationships within the Echinodermata. In addition homoplasies may be identified and phylogenetically reassessed.

Downcore changes in carbonate content can be produced by varying rates of taphonomy, physical and biological reworking or changes in rates of carbonate addition. Only the latter can be used to investigate changes in carbonate productivity in the living community. Only the latter indicate unequivocal changes in community structure. The stratigraphic, taphonomic and biologic records from two cores in Copano Bay, Texas were analyzed to determine (1) whether variations in shell content with depth were caused by variations in carbonate preservation, carbonate production or sedimentation rate and (2) the extent to which characteristics of fossil assemblages such as species composition, numerical abundance, biomass, and trophic and habitat structure, identified similar or different trends. Below the top few cm of the sedimentary column, variations in carbonate content with depth could be attributed to variations in carbonate production. Most biological attributes varied similarly with depth and, hence, time on both long (≥ 100 yr) and short (~ 10 yr) temporal scales. These variations could not be explained by any taphonomic process, sediment reworking and burial, or sedimentation rate. Despite a vigorous taphonomic milieu, explaining the shell content of Copano Bay sediments requires the preservation of nearly all carbonate produced. Doing so requires the preservation of most of the relatively large-shelled biota (large species and adults) which retain important evidence of changes in the community's history in this area. The results reemphasize the importance of large individuals and biomass in paleontologic reconstruction and suggest that changes in community productivity, which in paleontologic usage, must be carbonate productivity, are preserved in the fossil record in some assemblages. Taphofacies analyses might be used to identify such assemblages.

Recent breakthroughs in magnetostratigraphy and 40Ar/39Ar dating have shown that the boundary between the Chadronian and Orellan land mammal “ages” (long thought to be mid-Oligocene) correlates with the Eocene-Oligocene boundary (about 33.9 Ma). This boundary gives an exceptionally dense, detailed record of faunal, floral, and climatic changes, well constrained by magnetostratigraphy and radiometric dating.

Evidence from paleosols and land floras (Retallack, 1992) document a striking cooling and drying event across this boundary, with a woodland vegetation (greater than 1000 mm annual precipitation) replaced by a wooded grassland (500 mm annual precipitation). According to Wolfe (1992), mean annual temperature declined almost 13°, and the annual range of temperature increased dramatically from 5° to about 25°. Sedimentological evidence from eastern Wyoming (Evanoff et al., 1992) show an abrupt transition from moist floodplains to semi-arid landscapes with abundant wind-blown volcaniclastic dust. Most of these events took place over a few thousand years. This is certainly one of the most severe climatic events in the Cenozoic.

Late Eocene land snails (Evanoff et al., 1992) are large-shelled subtropical taxa now typical of central Mexico, indicating a mean annual range of temperature of 16.5° and annual precipitation of about 450 mm. In the early Oligocene, these were replaced by drought-tolerant small-shelled taxa indicative of a warm-temperate open woodland with a pronounced dry season. Reptiles and amphibians (Hutchison, 1992) show a trend toward cooling and drying, with aquatic forms (crocodilians, freshwater turtles, and salamanders) replaced by land tortoises; size reduction in turtles also indicates increased aridity. Mammals show only minor changes across this boundary. A few archaic groups which may have depended on woodland browsing (such as the rhino-like brontotheres, the camel-like oromerycids, and several archaic rodent groups) are the only taxa to go extinct. Minor speciation events occur in horses, the deer-like leptomerycids, and camels. The oreodont Miniochoerus shows a gradual dwarfing of about 30% over about 100,000 years. Most other species show no significant changes across this climatic crisis, although some change in relative abundance. Most mammals show stasis spanning millions of years before and after this transition, and some of the land snails are virtually indistinguishable from modern taxa.

Traditional Neo-Darwinian theory would predict that animals should evolve rapidly in response to such strong climatic selection. Instead, most animals respond by going extinct and being replaced by unrelated forms, or do not change at all. A few show punctuated speciation events at the boundary, and only one shows prolonged gradual dwarfing. This suggests that animals are not infinitely flexible “balls” on an adaptive landscape, but have some kind of internal homeostasis that prevents gradual change in response to selection. Extinction, emigration, or punctuated speciation events seem to be the preferred response.

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 past year, a strong consensus in the geological community has developed in favor of comet or asteroid impact as the ultimate cause of the K-T mass extinction, although many paleontologists remain doubtful. The discovery of tektites and craters with argon-argon ages matching the K-T boundary has finally removed the “smoking gun” problem. It is important, therefore, to evaluate large-body impact as a possible cause of other Phanerozoic extinctions, and to do so as carefully as possible before enthusiasm for the K-T success overwhelms objectivity in this research area.

Approximately 60% of all species extinctions in the Phanerozoic occurred in “pulsed” extinctions, defined as ecologically and geographically pervasive episodes in which the number of species going extinct in a geologically short interval far exceeds any reasonable estimate based on chance coincidence of independent events. In addition to the well-known mass extinctions, pulsed extinctions often mark system, series, and stage boundaries, and probably some zonal boundaries.

To be plausible, any proposed cause of pulsed extinctions must be (1) geographically pervasive (regional or global), (2) effective in diverse habitats, and (3) relatively quick-acting (to inhibit survival of species by migration or adaptation). The stresses causing the extinctions must be sufficiently severe and rare to be beyond the reach of natural selection, so that species do not have prior opportunity to evolve defenses.

These requirements severely limit the possibilities to phenomena that occur on time scales of one million to tens of millions of years, far longer than the tens or hundreds of years available for study by traditional actualistic approaches. In view of the Phanerozoic record, it is not surprising that the earth has not experienced a pulsed extinction in historic times (excluding human influences). This suggests that extinction is one case where the present is a not the key to the past, and a full exploration of the problem will require a substantial re-ordering of thinking.

Furthermore, because pulsed extinctions involve geographically widespread species (as well as restricted taxa), and because extinction of widespread species may be qualitatively different from that of local endemics, the common extrapolation from studies of extinction in local populations is risky.

Of the many phenomena suggested as causes of pulsed extinction, large-body impact is the one that most nearly satisfies the requirements, and is therefore the least unlikely of the candidates. Temporal distribution is especially critical. Currently accepted flux estimates for comet and asteroid impacts are in the appropriate frequency range to explain the extinction record, but testing the hypothesis will depend on better radiometric dating of the 100+ craters and other confirmed impact events.