The Permian/Triassic mass extinction, the most devastating biotic crisis of the Phanerozoic, has aroused considerable scientific interest. However, because research has focused primarily on understanding the magnitude of diversity reduction and causal mechanisms, the nature and timing of biotic recovery in the Early Triassic are still poorly understood. Marine limestones in the Lower Triassic Moenkopi Formation, which disconformably overlies the Upper Permian of southeastern Nevada and southern Utah, provide a rare opportunity to study the aftermath of the mass extinction in shallow water carbonate environments.

Two contemporaneous members of the Moenkopi record the first marine incursion from the northwest in the Early Triassic (Smithian), the very sparsely fossiliferous marginal marine Schnabkaib Member in Nevada and southwest Utah, and the Sinbad Limestone in central-southern Utah, a marine unit dominated by amalgamated and condensed fossil-rich beds. The Virgin Limestone member was deposited during a subsequent (Spathian) Early Triassic sea level rise, about 4-5 Ma following the Permian/Triassic boundary, and includes nearshore and inner shelf limestones characterized by fossiliferous storm beds.

Because the fossiliferous limestones of the Smithian Sinbad and the Spathian Virgin were deposited in similar shallow subtidal settings, they provide an opportunity to compare and contrast the status of biotic rebound at different points along an Early Triassic “time transect.” Analysis of bulk samples reveals that the older Sinbad and younger Virgin are similar in each possessing 2-3 different benthic marine paleocommunities of low within-habitat species richness. There are, however, several important differences between the Sinbad and Virgin faunas. The richly fossiliferous Sinbad assemblages are primarily molluscan, composed of approximately 2-8 species of bivalves, which may or may not be accompanied by ammonoids and 0-11 species of gastropods. Small spines, possibly belonging to an echinoid, are numerous in some samples. Although bivalves are also abundant in Virgin Limestone assemblages, fossils of other higher taxa are well-represented, including abundant crinoid ossicles, common brachiopods, echinoid spines and plates, and rare ammonoids and gastropods. Sinbad faunas also appear to lack epibionts and borers, while they are present but not abundant in the Virgin.

The addition from Sinbad to Virgin times of groups other than molluscs, with different life habits and strategies, most likely led to an increase in spatial partitioning and resource utilization, in particular the development of epifaunal tiering with the appearance of stalked crinoids in the Virgin. This pattern of earliest Triassic community dominance by molluscs followed by later more “Paleozoic-like” communities has been observed in other regions. Earliest Triassic paucity of epibionts and borers indicates significant reduction in the biotic component of taphonomic processes, including taphonomic feedback, when compared with other time intervals. Data from these Early Triassic assemblages thus indicate the initiation of both an evolutionary and an ecological rebound between Sinbad (Smithian) and Virgin (Spathian) times.

At Miguasha, Québec (earlier referred to as Scaumenac Bay), the Escuminac Formation, lowermost Upper Devonian, yields an abundant and diverse fish fauna and flora. Both vertebrates and plant fossils from the locality are reknowned throughout the world. The excellent preservation, including that of endocranial anatomy, enabled Jarvik to describe and illustrate fine anatomical details of the osteolepiform Eusthenopteron. That gives the wrong impression that Miguasha is throughout the Escuminac Formation an outstanding Conservat Fossil-Lagerstätte.

The cliffs at Miguasha bear fishes throughout the approximately 120 m thick Escuminac Formation. The lithology of the sediments changes throughout the sequence. Close to the base of the formation, acanthodians and anaspid-like agnathans occur in laminites, sometimes hundreds on one horizon. In these laminites, soft tissue preservation may occur (anapsid-like agnathans), and diagenetic transformations of acanthodians into organic substance led to misinterprations and recognition of the “larval chordate Scaumenella.” Most common within the sequence are limy concretions with different fish fossils, most commonly Bothriolepis. Three-dimensionally preserved fishes occur within the sandstone-siltstones and sometimes within the concretions. In all these cases, dermal bone is preserved, and in few cases chondral bone too, as in Eusthenopteron. One can characterize these fossiliferous sections of the Escuminac Formation as Concentration Fossil-Lagerstätte, whereas the laminites are Conservat Fossil-Lagerstätten.

The depositional environment was previously interpreted as an intermontaneous basin, based on tectonic and paleogeographic position. More recent paleogeographic reconstructions show a connection with Scottish deposits and to marine deposits in the present day North Sea. The lack of invertebrates and of marine plant remains, and the occurrence of vertebrates in other localities were used as additional indicators for freshwater deposition.

The sedimentological features are ambiguous, the turbidites, such as those found at Miguasha, can occur in marine or large freshwater bodies. Conchostracans occur, sometimes in the thousands on a single plane, in the basal part of the Escuminac Formation. They occur today in freshwater or brackish environments; the same species as the one in the Escuminac Formation is reported from lower Upper Devonian marine deposits in the Baltic (Koknese, Latvia). A detailed comparison of the fish fauna with other lower Upper Devonian fish faunas indicates a coastal marine environment. That is supported by rare trace fossils and by different chemical analyses of the sediments and 87S/86S analysis of Bothriolepis bones.

In conclusion, earlier interpretations of the paleogeographic position of the Escuminac Formation at Miguasha and chemical and faunal indicators contradict each other in the interpretation of the paleoenvironment of the formation.

In 1913, in the concluding remarks to his two volume compendium, Principles of Stratigraphy, Amadeus Grabau wrote, “When the science of Stratigraphy has developed so that its basis is no longer purely or chiefly paleontological, and when the sciences of Lithogenisis and Orogenesis … are given their due share in the comprehensive investigation of the history of the earth, then we may hope that Paleogeography, the youthful daughter science of Stratigraphy will have attained unto that stature that will make it the crowning attraction to the student of earth history.” It has taken nearly 80 years for Grabau's vision to be realized. The fruits of the plate tectonic revolution combined with our new understanding of global eustasy and event stratigraphy, make it now possible to map the changing geography of the earth's surface with unparalleled detail and accuracy.

In this poster session, we present 28 paleogeographic maps illustrating the changing configuration of mountains, land, shallow seas, and deep ocean basins during the Phanerozoic. The plate boundaries (spreading ridges, subduction zones, and transform faults) that were active during each time interval are also shown. For the Mesozoic and Cenozoic these plate boundaries are based on a synthesis of linear magnetic anomaly data and fracture zone locations compiled by PALEOMAP Project (International Lithosphere Program). The Mesozoic and Cenozoic orientation of the continents relative to the Earth's axis of rotation has been determined using a combination of paleomagnetic data and hot spot tracks. The location of Paleozoic plate boundaries, though speculative, is based evidence of past subduction and inferred sea floor spreading. The relative longitudinal positions of the continents and the width of the intervening Paleozoic oceans have been adjusted to best explain changing biogeographic and paleoclimatic patterns.

The land, sea and mountain distributions portrayed on these 28 paleogeographic reconstructions have been used as input for a series of computer simulations of paleoclimate. The paleoclimatic model, which was developed by C.R. Scotese and M. I. Ross, uses the latitudinal distribution of land and sea, as well as the orientation of ancient mountain belts to predict the distr ibution of high and low pressure cells, prevailing wind direction, relative wetness/dryness, as well as zones of coastal upwelling. This model, which takes a simple parametric approach, makes predictions which are similar to the more robust General Circulation Model (GCM), but requires far less computer resources.

Sequence Stratigraphic Analysis is claimed to be a “new globally valid system of stratigraphy … a precise methodology to subdivide, correlate and map sedimentary rocks” (Vail et al., 1991, p. 622). Sequence stratigraphic units, such as depositional sequences, depositional systems tracts, and parasequences, are time-equivalent rocks of specific durations controlled by cyclical changes in sediment supply related to eustasy. These units are bounded by regionally extensive unconformities with erosion beneath and onlapping strata above, or by physical surfaces separating either different patterns of stratal geometry or shoaling-up facies units. According to this school, precise correlations are based upon inferred time relations within depositional models.

Several key concepts of sequence stratigraphy have their origins in early geological studies. For many years geologists have separated time-equivalent strata by regional unconformities related to changes in climate or sea level, e.g., J. Woodward, 1695 and T. C. Chamberline, 1909. Stratal surfaces, such as bentonites and limestone markers, have been used in place of fossils for time correlations since the first wells were drilled. Stratigraphic models have strongly influenced how we correlate strata since the time of William Smith.

Two developments are, indeed, new and have sparked the current resurgence in stratigraphic research. One is the seismic technology to test the physical continuity of strata on a regional scale (50-100 km), and to test the stratal geometry of genetically related depositional packages. The second is the chart of global coastal onlap events and eustasy (Haq et al., 1988).

Some key research problems are: (1) how to identify unique, time-significant stratal surfaces; (2) how to test their physical continuity; (3) how to test the time relations within depositional models; and (4) how to identify the unique, time-significant global events recorded in the stratigraphic record. These stratigraphic concepts can be tested by graphic correlation, which is a powerful technique of high precision, quantitative stratigraphy. Its application in Cretaceous sections of the Gulf Coast and Oman, and in the Plio-Pliestocene of the Gulf Coast aids the distinction between synchronous surfaces and diachronous boundaries.

The trace fossil Oldhamia reflects systematic strip mining of an infaunal, worm-like sediment feeder. It is known from many parts of the world in Cambrian complexes, whose flysch-like and accreted character suggests deposition on a deep continental slope. In similar rocks of the North Carolina Slate Belt. Oldhamia is associated with rare specimens of the Ediacara-type body fossil Pteridinium, as well as tool marks of a problematic stiff organism reminiscent of graptolite stipes (Vendospica).

This occurrence (1) extends the stratigraphic range of Oldhamia into the Late Proterozoic. It also reminds us that, by that time, worm-like, endobenthic bilaterians (2) had become behaviorally specialized and (3) had colonized shelf and deep-sea bottoms well before the Cambrian evolutionary explosion. (4) Since bioturbators were small and did burrow strictly along bedding planes, their mixing effect was as yet negligible. (5) The new tool-mark fossils tell us that complex, organic-walled and perhaps colonial organisms were around in addition to sand-corals (Psammocorallia), possibly sponges and the probably plasmodial Vendobionta.

Global diversity often is treated as a barometer of evolutionary success of clades without reference to their occurrence in ecological or biogeographical space. But global diversity is a composite of various spatial scales: alpha diversity, the number of taxa co-occurring in local communities; beta diversity, the distinction in taxonomic composition among local communities; and gamma diversity, the distinction, or degree of endemism, among geographic provinces, It has been argued by some workers that global diversity correlates strongly with alpha (and beta) diversity but by others that provinciality is the principal control of global patterns. The distinction is important, implicating either ecological processes (“adaptation”) or physical geography (“contingency”) as the major factor in expansion of clades.

We have examined the ecological half of this problem with a data base comprising 505 fossil assemblages sampled from Paleozoic strata of Laurentian North America. On the basis of associated sedimentary characteristics, each assemblage has been assigned to one of six environmental categories, ranging from onshore peritidal situations to offshore basinal conditions. For each taxonomic order and class, average numbers of genera in each category have been determined for each of 18 time units. These average alpha diversities have been contoured on time-environment diagrams and compared to patterns of global diversity.

Three major generalizations are derived from these diagrams:

1. Major groups tend to be environmentally conservative, maintaining their life zones of maximum and minimum alpha diversity over vast stretches of time.

2. Onshore-offshore shifts are most common during early expansion or late contraction of groups, when their global diversity is rapidly waxing or (more slowly) waning.

3. Maxima and minima in global diversity within the groups through time, with few exceptions, are reflected in alpha diversity as fluctuations within the environments of maximum richness and/or as variations in the range of environments occupied.

The last observation indicates a tight link between local ecology and global diversity, although the direction of causation is not unambiguous: alpha diversity could be reflecting only the global pool from which species can be recruited into local communities. However, in view of the onshore-offshore shifts during early and late histories of clades we conclude that local ecology is the dominant factor in controlling global diversity, and provinciality is secondary.

Recently a general cladistic framework for early avian evolution has emerged. Postcranial modifications in the wrist joint and elsewhere firmly establish birds as a diversified subgroup of maniraptoran theropods. And the best known Mesozoic avians–Archaeopteryx and Late Cretaceous Hesperornis and Ichthyornis –have been positioned as successive sister taxa to living birds. Within this framework, however, several basic phylogenetic questions need to be addressed: (1) Which maniraptorans are most closely related to birds? (2) How was the modern avian skeleton built during the first third of avian history, between Archaeopteryx and Late Cretaceous Hesperornis and Ichthyornis? (3) And what are the relationships between the major groups of living birds?

Avian origins. Synapomorphies listed by Ostrom and others to unite birds and other theropods typically apply to all maniraptorans or higher-level theropod clades, leaving unsettled the question of which maniraptorans constitute the immediate outgroups to birds. Deinonychosauria is confirmed as the sister-group to Aves, based principally on synapomorphies of the pectoral and pelvic girdles. In contrast to some previous suggestions, this study supports monophyly of Deinonychosauria (uniting dromaeosaurids and troodontids), with a single origin of the hyper-extendable, raptorial digit II of the pes.

Sinornis and the evolution of powered flight and perching. Archaeopteryx lacks the profound modifications of the avian skeleton that characterize Ichthyornis and modern birds. Recent discovery of Lower Cretaceous birds has brought to light important intermediate stages in the transformation of the avian skeleton. Sparrow-sized Sinornis, discovered in Lower Cretaceous lake deposits in China, exhibits features that are associated with sustained powered flight; the laterally directed glenoid and V-shaped ulnare suggest that the wing was capable of tight flexion during flight. Features unrelated to the flight apparatus, in contrast, have not been altered; the skull is toothed, the manal digits are flexible and clawed, and gastralia are present beneath the rib cage.

Higher-level relationships among living birds. The deep branching history of living birds occurred before the end of the Cretaceous and can be reconstructed from anatomical and genetic evidence in living birds. DNA sequences have been obtained from the mitochondrial cytochrome b gene in a variety of living birds. These data are consistent with a basal split between palaeognaths and neognaths and support the basal position of galliforms and anseriforms among neognaths. Piciforms appear to be closely related to passeriforms, and Corvida does not appear to be monophyletic, in contrast to recent DNA-DNA hybridization results.

With its vast well and seismic data base, coupled with expanded sedimentary and biostratigraphic cycles that apparently were driven by glacial eustacy, the Gulf Coast offshore region provides a unique opportunity to develop and test sequence models. Virtually every major oil company and a number of academic institutions are currently engaged in some form of sequence analysis.

Regional studies incorporating biostratigraphic analyses of more than 120 wells integrated with a seismic grid exceeding 24,000 line smiles, have shown the Gulf Coast to be an unstable prograding margin, and that characteristic seismic criteria developed for stable progradational margin models do not always apply. Biostratigraphic approaches consistent with the procedures and objectives of sequence analysis thus play a preeminent role in providing a chronostratigraphic framework, and in utilizing biotic patterns to aid in the delineation of systems tracts.

For the pre- Wisconsin Plio-Pleistocene, 15 biostratigraphically and seismically resolvable and regionally mappable sequences are documented. Those for the past one million years approximate 100,000 year cycles. All of the sequences are calibrated by highest occurrence datums (HOD) which almost invariably occur within condensed sections developed either during maximum flooding events or on lowstand slope fans. This association with condensed sections begs the question whether or not these HOD are true extinctions, and whether or not sediment accumulation rates, or similar techniques, derived from them, can reliably be used to establish the position and absolute age of sequence bounding unconformities.

Seismic and well data suggest that sequence bounding surfaces in this province are usually subtle, and that the hiatus they may represent is, except in extreme cases, beyond the resolution of the biostratigraphic framework. Sequence boundary placement can be routinely interpreted through integration of bioistratigraphic data, including condensed sections, wireline log patterns, and seismic character. In slope paleo-environments, condensed sections commonly are temporally equivalent to both the trasgressive and highstand systems tracts on the shelf, and their upper surface may coincide with the sequence boundary. In paleo-shelf settings, condensed sections frequently are restricted to the transgressive systems tract, and their contained HOD may be suppressed by succeeding highstand deposits. In such cases, sequence boundaries are best placed by wireline log and seismic criteria.

Pitfalls and limitations to the proposed biostratigraphic approach to sequence stratigraphy are discussed and illustrated.

A new method for the preparation of bone samples for δ18O-PO4 analysis has been developed. The phosphate from bone samples is separated and purified using ion exchange chromatography, and then precipitated as silver phosphate using the Firsching method. O2 is then extracted by reaction with bromine pentafluoride and converted to CO2 for isotopic analysis. Advantages of the silver phosphate technique over the bismuth phosphate technique are (1) the simplicity of the method, (2) silver phosphate is not hygroscopic so atmospheric water is not an oxygen contaminate, and (3) very small samples (2 mg to 10 mg) can be analyzed with an increase of precision compared to previous techniques. Iron and silica oxides added to Ag3PO4 standards produce no offset, which suggests that this new technique is not sensitive to interferences from cements commonly found in fossil bone material. Analyses have been performed on standards ranging in size from 30 mg to 2 mg with a σ1 of ± 0.05 per mil.

The δ18O-PO4 compositional pattern of the bones of modern vertebrates have been analyzed to provide a base for the interpretation of the δ18O-PO4 pattern of fossil vertebrates. The average %PO4 in modern mammals and reptiles is approximately 15% with a σ1 of 2-3 %. The average %PO4 of fossil reptiles range from 10 to 25% with σ1 variations of up to 10%. The %PO4 variation can be related to cementation of void spaces in the bone material. XRD analysis reveals that calcite, dolomite, ankerite, and silica cements are commonly present. FTIR (Fourier Transform Infrared Spectroscopy) yields low indices calculated according to the formula of Shemesh, 1990 [GCA 54(9):2433]. Thin sections of the fossil bone material show detailed structures. All this evidence suggests that the fossil bone δ18O-PO4 composition is pristine and not altered by diagenesis. The total δ18O-PO4 σ1 variation of 10 or more skeletal elements analyzed for each individual specimen varies from 0.1 per mil for a domestic cow (Bos) to 0.8 per mil for a Komodo dragon (Varanus). Variations in between appear to be related to thermal physiology and variations in drinking water δ18O due to seasonality or migration.

Benthic foraminifera recovered from sediments in the waters surrounding San Juan Island, Washington, were examined to assess taphonomic damage and to compare magnitude of the taphonomic agents of abrasion, solution and microboring to studies done in tropical environments. Abrasion experiments of 24, 72, 120 and 240 hour duration were run on Elphidiella and Islandiella, two benthic foraminifera common in the Puget Sound region. Results show that styles of taphonomic damage observed in field sediment samples, including impact pitting, scratching, caving and exfoliation, were produced on experimentally manipulated groups in as few as 24 hours. Elphidiella appears slightly more resistant to abrasive reduction compared to Islandiella, which produced a wide range of abrasive features within 3 days.

A control group of Elphidiella and Islandiella was placed in a mesh bag for 240 hours to assess taphonomic alteration by solution, boring and encrustation, removed from the effects of abrasion. These specimens showed no significant solution reduction, but within 3 days were covered with algal filaments and diatoms. Taphonomic damage observed in field specimens can be divided into destructive and constructive agents. Destructive features include breakage, pitting, boring, scratching, and exfoliation. Constructive features include pyritization and encrustation by diatoms and other algae. Although several naturally occurring abrasion features were produced in the experimental abrasion runs, the magnitude of taphonomic damage seen in field specimens was not achieved experimentally. Features of extreme taphonomic damage include complete removal of the outer chamber walls, as well as removal of all but the umbilical regions of planispiral forms. Solution and predation are largely responsible for such severely damaged tests.

The claim that rudist bivalves competitively displaced corals from reef frameworks in the Cretaceous combines two assertions: (1) that rudist formations commonly developed as reefs; and (2) that the autecology of rudists was convergent with that of hermatypic corals. We dispute both assertions, and thus reject the hypothesis of competitive displacement. We argue instead that mobile sediments, rather than frameworks, dominated the margins of most of the extensive carbonate platforms of the period, and that it was on these non-reefal biotopes that the rudists flourished.

Definitions of reefs tend to combine two major elements: (1) a robust biogenic framework (with accompanying sedimentary and diagenetic components); and (2) topographical relief. Such definitions are clearly rooted in Recent coral reefs, in which endosymbiotic zooxanthellae permit the extensive growth of colonial coral frameworks in shallow but relatively nutrient-poor waters and topography is largely the legacy of Pleistocene changes in sea-level. In rudist formations, in contrast, individual rudist aggregations are volumetrically limited, relative to sediment, often loosely constructed, and evidently showed little relief. Tabular and small lenticular units predominate.

Differences in structure and palaeoenvironmental situation between rudist and coralgal associations are the effect of the different autecologies of the constituent organisms. While the clonal growth of corals predisposed them to framework development, the aclonal development of rudists was better suited to the opportunistic occupation of a variety of temporarily available substrata. Moreover, the tolerances and growth responses of rudists to such factors as water turbidity, nutrients and current regime were quite different from those of hermatypic corals. Despite repeated assertions in the literature that rudists possessed zooxanthellae, only a few species show any evidence for such a symbiosis and other evidence suggests that most lacked them.

Rudist/coral competition is therefore doubtful, even though members of both groups co-occur in many areas. The relative demise and migration into deeper water of coral frameworks in the Cretaceous was thus probably independently caused.

A handful of mass extinctions, scattered through the Phanerozoic, forever changed the course of life on Earth, eliminating large numbers of clades from the evolutionary race and allowing the survivors to diversify following the extinction. These ecological-evolutionary upheavals extirpated whole communities and eliminated otherwise successful clades from the evolutionary race. While the mechanism(s) responsible for most mass extinctions remain to be identified, their impact on the biosphere is self-evident. Thus, recognition of a previously overlooked, severe extinction early in the Phanerozoic provides important new insights and perspectives on the history of life

In the course of research on the biogeographic distribution of Early Cambrian metazoan taxa, I compiled a database on the geographic and stratigraphic distribution of metazoan genera. The data are derived from the primary literature on the paleogeographic and stratigraphic distributions and systematics of Early Cambrian fossils. The Russian zonation scheme for the Siberian Platform (incorporating four stages, in ascending order: Tommotian, Atabanian, Botomian, and Toyonian) was employed for biostratigraphic correlations. Correlations of other regions to the Siberian stages were based upon work by F. Debrenne and her colleagues on archaeocyathans and upon M. D. Brasier's correlations from small shelly fossils. While there is no accepted global correlation scheme for Lower Cambrian strata, this approach yields results that are useful at the four-stage level of resolution. The data base currently includes more than 850 genera.

Examination of the aggregate data reveals a substantial reduction (>60%) in the global total of genera extant in the Toyonian, in comparison to the Botomian stage. The extinction rate of genera at the end of the Botomian exceeds 80 percent. By comparison, the end-Permian extinction eliminated slightly more than 60 percent of the extant genera.

In addition to the general reduction in generic diversity, Brasier (1982) has documented a fall in sea level and reduction in the shelf area. Associated with this regression was a loss of reef-forming archaeocyathan genera. While a small number of archaeocyathan genera persisted into the Toyonian (and a few genera have been reported from Late Cambrian strata in Antarctica), the bulk of archaeocyath diversity was lost in the Botomian. The losses in diversity, extermination of reef-forming organisms, and high turnover in conjunction with a marine regression matches the pattern observed at most other mass extinctions.

It is remarkable that this relatively severe extinction has gone mostly unnoticed by paleobiologists. Much of the data is relatively new, a product of intense international study of early metazoan faunas. Most likely, the mass of data produced by Lower Cambrian specialists over the past ten years has yet to reach the treatises and monographs where it can be easily summarized. Also, resolution of patterns within the Early Cambrian has waited on the development of correlations and a satisfactory zonation. Indeed, detailed study of the Botomian extinction will await more accurate correlations.

Phylogenetic analysis of a data matrix of 86 skeletal characteristics, and of the first 400 bases of the 5’ end of the large subunit ribosomal RNA gene produce congruent cladograms for 11 extant echinoids. Based on these cladistic analyses the great majority of morphologic and molecular apomorphies can be placed in one of 18 independent geological time intervals. When the cladogram is calibrated using the fossil record of post-Paleozoic echinoids, rates of molecular change in 28S rRNA can be calculated and compared with estimated rates of morphological evolution.

Morphological and molecular apomorphies acquired in each time interval both correlate moderately strongly with time elapsed, but less strongly with one another. As expected, morphological rates vary considerably over time and between sister groups, but so too do molecular rates. When averaged over all echinoids studied, the number of morphological apomorphies accrued yields a slightly higher Spearman Rank correlation coefficient with time elapsed than does the number of molecular apomorphies accrued. This is because there is a three-fold difference in the rate of molecular change amongst the echinoid lineages studied.

The deep-sea floor is traditionally perceived as a remote and deliberate environment; a habitat where a gentle rain of detrital food particles and sluggish bottom currents force biological processes to proceed at slow, steady rates. In this view, benthic community structure is controlled by equilibrium processes, such as extreme levels of habitat partitioning (e.g., “grain matching”) made possible by remarkable ecosystem stability. A number of recent discoveries indicate, however, that the deep-sea floor may be neither remote nor deliberate. Pulses of food and kinetic energy rapidly reach the seafloor from the dynamic upper ocean, and endogenous disturbances may be surprisingly frequent and intense. The biological processes driven by these events can be highly variable in space and time, exhibiting disequilibrium dynamics. I briefly review three types of events (large food falls, pulses of phytodetritus, and biogenic mound building) that “punctuate” the apparent “equilibrium” of the deep-sea floor, and describe how these events may change patterns of macrofaunal feeding, growth, recruitment and/or competitive exclusion. I then discuss how these changes may affect processes of paleoecological significance, including (1) the dispersal and evolution of chemosynthetic communities, (2) mechanisms and rates of trace production/destruction, and (3) maintenance of macrofaunal diversity at the ocean floor.

Silurian organisms preserved in southeastern Alaska (Alexander terrane) inhabited marine environments within an island-arc complex during a phase of waning volcanism and are fossilized in a diversity of shallow-marine platform and deep-water deposits. These fossils exhibit a distinctive suite of characteristics and share fundamental similarities with biotas of Paleozoic-Mesozoic age that are preserved in other accreted island terranes of North America. These special attributes reflect the colonization, evolution, and diversification of marine organisms adjacent to subconical/conical volcanic edifices characterized by relatively high rates of subsidence, steep submarine slopes, tectonic instability, and biogeographic isolation. Recognition of these diagnostic features enables many ancient island faunas to be distinguished from those that lived on the craton and enhances differentiation of island biotas from pelagic assemblages that accumulated as oozes in deep ocean basins.

Although island faunas exhibit a high degree of variability in taxonomic diversity, levels of endemism, and provincial affinities, many share a significant number of similarities. Several of these shared attributes reflect organismal evolution in biogeographic isolation at island sites separated from continental and other source regions by considerable geographic distances or at locations unfavorably situated with respect to oceanic currents transporting teleplanic larvae. Comparison of Silurian island-arc faunas from Alaska with coeval assemblages from different tectonic settings and with modern volcanic islands shows that oceanic island biotas commonly are characterized by: (1) initially impoverished, normal marine faunas of low diversity and abundance that are preserved in exceptionally thick platform sequences; (2) sequential development of organic structures from fringing to barrier reefs on the outer shelf during thermal subsidence and lateral expansion of the carbonate platform; (3) restricted faunas devoid of normal marine shelly benthos and tolerant of quiet-water conditions, muddy substrates, and fluctuations in salinity, temperature, and oxygen concentrations in back-reef lagoons; (4) extensive taphonomic redistribution of organisms along bathymetric gradients and downslope preservation in debris flows, slumps, and turbidites of mixed fossil assemblages derived from shelf and shelf-margin habitats; (5) rapid lateral and vertical changes in biofacies, reflecting complex depositional systems in fault-block basins; (6) insular biotas with relatively high levels of endemism; (7) complex paleobiogeographic affinities expressed in assemblages that comprise mixtures of taxa from different faunal regions; and (8) relict biotas that may represent the protracted survival of some organisms in island refugia.

Because many accreted islands are poorly preserved and highly deformed, recognizing these distinctive features in oceanic island faunas enhances identification of allochthonous volcanic arcs, seamounts, atolls, and hot-spot islands in the ancient geologic record. Using fossils to identify islands in accreted terranes is especially important when island origins of strata are suspected but difficult to prove because calc-alkaline volcano-plutonic rocks or derivative volcanogenic and quartz-poor siliciclastic deposits are absent or not exposed. Hence, relying on fossils to recognize oceanic islands that survived destructive tectonic processes offers an expanded list of geologic criteria to aid in reconstructing plate boundaries marking ancient zones of convergence and to use in unraveling the tectonic history of ocean basins recorded in suspect terranes.

Iterative patterns of morphological evolution present a unique opportunity to explore the causal mechanisms of evolution. We report here on an iterative morphological trend within a clade of prosobranch gastropods.

We studied the Melanopsis impressa lineage from Middle to Late Miocene marginal lake sediments of the Pannonian basin (central and eastern Europe). The descendants of M. impressa evolved a type of whorl shouldering in at least two different instances. The first instance occurs in the Late Miocene Pannonian Stage, when the smooth and conical M. impressa gives rise to M. fossilis, a species characterized by strong shouldering. The disappearance of M. fossilis coincides with a major contraction in the areal extent of the lake and with a shift from brackish to fresh water at the end of the Pannonian Stage. Melanopsis impressa may have survived this event in marginal drainage environments; during the subsequent Pontian Stage, M. impressa or a close relative gives rise to a second shouldered descendant (M. petrovici-M. cylindrica complex).

The constructional aspects of shouldering are different in each case. In the first instance, shouldering is characterized by a broad and rounded ridge in the middle of the adapical half of the body whorl, usually associated with a depressed area adapically. In contrast, shouldering in the second instance is a simple, rounded or angled spiral prominence on the adapical half of the whorl.

Repeated development of a character in a single lineage might suggest that the parallelism is due to an intrinsically defined pathway. The different constructional aspects of shouldering in our examples, however, suggest that it was the selective regime that was repetitive. The brackish paratethyan sea of the Pannonian Stage and the smaller, freshwater lake of the subsequent Pontian Stage differed in many respects, but hydrodynamic or predatory selection pressures may have evoked similar morphological responses.

In addition to the breakup of Pangea, other major events occurring in the ancient Pacific during late Paleozoic and early Mesozoic time were the development and dispersal of exotic terranes which now characterize large portions of the eastern and western Pacific margins. While the terrane concept made sense out of the geologic crazy quiltwork pattern of these regions, considerable uncertainties still exist concerning terrane origins and their paleogeographic histories. Did terranes of the eastern and western pacific merely border Pangea or did they once exist within far-flung reaches of the ancient Pacific Ocean? Paleontology is now exploring and seeking answers to such issues based on benthic invertebrate fossils.

Like examples in the western Pacific rim of Asia, the American Cordillera contains volcanic terranes with fossil content and history quite different from coeval rocks of the adjacent craton. Some terranes may have developed close to ancient North America, but others show evidence of having existed in settings far-removed from the craton. Over time, some terranes could have experienced considerable geographic displacement via tectonic processes (faulting, rift volcanism, seafloor spreading).

Many terranes experienced protracted volcanic episodes of oceanic history during Permian and Triassic time. Terrane amalgamations occurred during Triassic and Jurassic time, and later in the Mesozoic were followed by accretion to the North American Craton. Some terranes such as Quesnellia, Cache Creek, Stikine, Wallowa, Eastern Klamath, and Wrangellia yield excellent benthic marine fossils—many of tropical Tethyan derivation, but other fossil assemblages are of mixed paleogeographic affiliations. Two island arc terranes, Stikinia and Wallowa, contribute to evolutionary and biogeographic issues with Triassic and Jurassic, tropical to temperate marine fossils. These include calcareous algae, sponges and corals occurring in reef sequences which can be related to better known examples from Asia and the former Tethys region. Continuing paleontological investigations into fossils from exotic terranes of the Cordilleran region, offer promise in the resolution of late Paleozoic and early Mesozoic circum-Pacific events and in the attainment of unified views of global paleogeography.

Taxonomic databases are important tools in the study of faunal diversity and evolution. The usefulness of the inferences drawn from these databases is diminished when the role of environment is not considered. Analysis of the foraminiferal database at the genus and family levels is used to demonstrate the effect of water depth on presumed changes in taxonomic diversity and evolutionary turnover rates.

This paleoenvironmental effect is particularly noticeable when foraminiferal faunas of the late Paleozoic and the Mesozoic and Cenozoic intervals are compared. The late Paleozoic fauna is dominated by the Fusulinina and shallow-water (0–200 m) Textularuna. Standing diversity fluctuates greatly, and evolutionary turnover is high. This reflects short-term fluctuations in sea level which led to the rapid formation and destruction of narrow ecological niches. Evolutionary turnover appears to be related to reef growth during this time. This trend may also reflect an increased number of k-selected specialists which serve as proxy indicators for a slow-circulating oligotrophic ocean system. Shallow-water taxa may also be predisposed to extinction due to their reliance on symbiotic algae. The extinction event at the end of the Permian resulted in the loss of almost 70% of the standing generic diversity. This included the complete loss of the Fusulinina as well as a number of shallow-water textularids. Cohort survivorship curves are steep and taxon ages short during this time.

The diversity increase over the past 245 million years has largely been due to the addition of deep-water (200-10,000 m) taxa. This was particularly true during the Late Cretaceous and early Eocene, and may reflect the relatively high eustatic sea level during those intervals. The relationship between reef development and evolutionary turnover rates is less clear during this time interval. Although the extinction event that marked the end of the Cretaceous resulted in a greater loss in absolute taxonomic diversity than occurred at the end of the Permian, the relative loss in generic diversity was only about 21% due to the large number of deep-water taxa. When the entire fauna is considered, cohort survivorship curves are less steep and taxon ages are longer than in the late Paleozoic, but when only the shallow-water taxa are considered, the results are similar to those for the late Paleozoic.

Skeletal fish remains, including several vertebrae (Teleostei incertae sedis), were recovered from the core catcher section (subbottom depth, 10.5 m) of a piston core taken in the Gulf of California (28° 00.34’ N, 111° 31.32’ W; 460 m water depth). Bottom water temperatures in this area are typically less than 10°. Bone material retained original crystal morphology as well as a chemical composition consistent with hydroxyapatite. Insoluble collagen from one small bone fragment, extracted by decalcification in EDTA, was AMS radiocarbon dated at 28,070 ± 310 years b.p. (TO#2190).

Proteins from ancient fish bone fragments were partitioned by sequential extraction into two soluble fractions, non-mineral-associated and mineral-associated, and an insoluble fraction. The amino acid compositions of these extracts were compared to modern fish bone extracts. Soluble fossil fish bone extracts were enriched in collagen, consistent with peptide bond cleavage in this molecule and retention of degradation products by the mineral matrix, as observed previously in other ancient bones.

Three non-collagenous bone cell-produced proteins, osteocalcin, osteonectin, and bone sialoprotein, were identified immunochemically by ELISA (enzyme-linked immunosorbent assay) in the mineral-associated fraction from these ancient fish bones. The serum protein albumin was also identified immunochemically, suggesting that hydroxyapatite binding may enhance preservation of biomolecules in the fossil record. DNA, another molecule that binds to hydroxyapatite, was also observed in the mineral-associated ancient fish extract. The DNA showed signs of both in situ cleavage and complexing to an autofluorescent component that has been observed in other ancient specimens. Thus, the continuous presence of water does not by itself preclude preservation of non-collagenous proteins, insoluble collagen, or DNA in bone for tens of thousands of years. Anoxia and low temperatures afforded by burial in this basin slow molecular decay.

Small animals are underrepresented in the vertebrate terrestrial fossil record primarily due to differential preservation of skeletal material. Oceanic sediments provide an underexploited source of small vertebrate remains containing molecular as well as morphological information with chronometric and systematic utility.

Among multicellular organisms, the fossil record of vascular plants is, perhaps, uniquely informative about pattern and process leading to the establishment of major groups. Although classifications above the family level remain highly debatable, especially with regard to level, important insight has been gained into external morphology and internal anatomy of the earliest members of the clade, as well as into general patterns of diversification and change in form through time. Despite these advantages, cladistic methods have brought into sharp focus significant problems with important characters at high taxonomic levels. Putative synapomorphies used to diagnose major groups often have conflicting phylogenetic implications which, according to the cladistic paradigm, must be interpreted as homoplasy. From a biological standpoint, however, unrecognized instances of homoplasy in the character set often seem unlikely due to the complexity of the features involved, and the lack of plausible mechanisms producing multiple parallelisms or reversals by means of “known” processes such as adaptation, homeosis, heterochrony, or functional constraint. Added to this are conceptual and practical problems concerning morphological gaps (and what might bridge them) between recognized groups. One of the most interesting challenges to current approaches are enigmatic fossils early in the history of apparent clades exhibiting unprecedented variability in expression of supposedly diagnostic features. As a result, terminology originally developed to circumscribe alternative morphological states within clades completely breaks down. Perhaps, what's needed here is a more dynamic model of evolutionary change linking hypotheses of synapomorphy with specific changes in the structuring “rules” (or capacities) of development.

Among characters used to diagnose major groups of vascular plants, differences in stelar architecture remain among the most important. Comparative evidence suggests that early vascular plants have essentially the same relatively well-understood developmental mechanisms as living plants; vascular tissues differentiate according to hormone (primarily auxin) gradient signals, that are the more-or-less the passive consequence of shoot geometry during growth. Because early plants have an extremely simple organography (dichotomizing stems with no leaves), an unparalleled opportunity exists to understand historical changes leading to establishment of major stelar morphs in the fossil record terms of changed dynamics of continuous serial development at the shoot apex. A computer simulation of vascular tissue patterning under hormone influence will be presented, and suggestions offered regarding the relative plausibility of alternate routes of evolutionary change between major groups.