The history of vascular land plant diversity from the late Silurian to the Early Carboniferous has two major features: a pronounced diversity peak in the late Siegenian-Emsian (Devonian), approximately 12 million years after the appearance of vascular land plant body fossils; and a diversity low in the late Frasnian-early Famennian (Devonian), which coincides with the Frasnian-Famennian mass extinction of marine invertebrate faunas. Because the diversity of fossil land plants depends in part on sampling intensity, this diversity history requires evaluation. Biogeographic data are useful for assessing diversity histories because they incorporate one of the best measures of sampling intensity, the number of localities known from a time interval, and because the amount of biogeographic differentiation present during an interval may influence global diversity.

The data for this study consist of compression-impression genera from 394 Late Silurian-Devonian and 64 Tournaisian (Early Carboniferous) floral assemblage lists. Most of these assemblage lists represent florules: defined as the compression-impression genera found in a single formation, member, or other narrow stratigraphic horizon at a single outcrop. However the data include some regional lists from China and parts of the former U.S.S.R., because we could not obtain florules for all time intervals from these regions. Regional lists consist of the genera found in one formation from a limited geographic region. All of the Laurussian assemblage lists used in this study (244 Late Silurian -Devonian and 49 Tournaisian lists), including those from the Russian platform, represent florules. Linear regression of both the total diversity and the standing diversity of vascular land plant genera against the number of floral assemblage lists from each interval suggests that the number of floral assemblage lists correlates strongly and significantly with generic diversity (r = 0.88). Thus, the late Siegenian-Emsian diversity peak is probably an artifact of sampling: there are more florules described from the late Siegenian-Emsian than from the Eifelian and Givetian combined. The late Frasnian - early Famennian diversity low may be an artifact of sampling: few reliably-dated assemblages exist for this interval. However, late Frasnian - early Famennian assemblages show no biogeographic differentiation between ‘equatorial’ Laurussian assemblages from the United States and Europe and northern ‘non-equatorial’ assemblages from Arctic Canada and Siberia. This biogeographic differentiation is a persistent feature of floral assemblages from all other Devonian time intervals, and from the Early Carboniferous. Low numbers of florules could cause an apparent loss of biogeographic differentiation for an interval. Conversely, all three phenomena (low diversity, low numbers of florules, and loss of biogeographic differentiation) may indicate that the Frasnian-Famennian mass extinction affected terrestrial land plants.

The diversity history of Late Silurian through Early Carboniferous land plants suggests that three major evolutionary innovations: heterospory, which appeared in the late Emsian; arborescence, which appeared in the Givetian; and seeds, which appeared in the late Famennian had little effect on land plant diversity.

Long-standing interpretations of paleontologic, sedimentologic, and stratigraphic evidence from Permian-Triassic marine sequences in western Wyoming have suggested an interruption in deposition of several million years' duration between the two systems, even though physical evidence of unconformity is subtle and somewhat equivocal. We postulated that an unconformity of this duration should be more pronounced in paralic and non-marine facies in central and southeast Wyoming than in adjacent inner-shelf marine facies in westcentral Wyoming. Therefore, we correlated an erathem boundary-bearing sequence from westcentral Wyoming (where it is faunally controlled) to southeast Wyoming (where it is non-fossiliferous) and studied this sequence for evidence of hiatus. The correlations were made using surface sections, surface gamma-radiation logs, and subsurface log suites.

In southeast Wyoming, the lithostratigraphic equivalent to the systemic boundary in westcentral Wyoming is located within a redbed-evaporite sequence traditionally interpreted as having accumulated in paralic and/or terrestrial depositional environments. Physical evidence of disconformity at this surface in southeast Wyoming is no greater, and is in places less, than at several other horizons within the boundary-bearing sequence. Also, petrologic examination of the terrigenous clastic units below, through, and above the boundary-bearing sequence in central and southeast Wyoming suggests notable stability of the depositional environment. Southeastward stratigraphic thinning of various units within this boundary-bearing sequence is demonstrable; however, compelling evidence of regional truncation is not evident, and the stratigraphic thinning appears to be due to primary depositional processes rather than post-depositional erosion during hiatus.

We interpret slow, episodic, yet generally continuous deposition of evaporite and siliciclastic units in southeast Wyoming across the Permian-Triassic boundary. If true, then conventional biostratigraphic estimates of the duration of a hiatus separating Permian inner and middle-shelf carbonate facies from overlying Triassic siliciclastics in western Wyoming appear to be overly long, and may need re-evaluation.

The northeast-trending Reelfoot basin, extending from northeast Arkansas and westernmost Tennessee into southeastern Missouri, southernmost Illinois, and westernmost Kentucky, is geologically, and socioeconomically, significant because it is co-extensive with the New Madrid Seismic Zone, one of the most seismically active areas of the central and eastern United States. The basin has been periodically active from its inception as a rift basin in the Proterozoic to the present and has accumulated up to at least 5,000 m of sediment, including up to at least 1 km of Cretaceous and Tertiary sedimentary strata near the head of the Mississippi Embayment. Structural and stratigraphic interpretations within the subsurface pre-Mesozoic part of the basin have been based almost entirely on geophysical and physical stratigraphic criteria; these interpretations have been loosely constrained due to an extreme sparsity of drillhole data through the Paleozoic sequence. Recent analysis of Cambrian and Ordovician fossils (conodonts, palynomorphs, brachiopods, and trilobites) from cuttings and core from a very few drillholes allows establishment of the beginnings of a verifiable stratigraphy for this part of the sequence. The paleontological data also provide (1) biofacies evidence for interpretations of the depositional setting during part of the Late Cambrian and Early Ordovician interval and (2) thermal maturation data pertaining to the post-depositional geothermal history of these strata.

Upper Cambrian phosphatic brachiopods and trilobites provide improved correlations between strata in the basin, the Ozark shelf to the northwest, and the Upper Mississippi River Valley. Cold-water-realm palynomorphs and trilobites from siliciclastic rocks of turbiditic origin in the central part of the Reelfoot basin support an interpretation, based on sedimentary structures in a short interval of core, of a deep-water basinal origin for these strata.

Lower Ordovician conodonts provide a biostratigraphy for the carbonate rocks of this part of the sequence; correlations can be made with the shallow-water sequences of the Knox, Prairie du Chien, and Arbuckle Groups, and the Ozark sequence of the adjacent shelf areas to the east, north, and west. The uppermost Lower Ordovician strata in the basin record a short-term incursion of cooler water environments, reflected by the character of both the conodont fauna and the lithofacies. The youngest Paleozoic dates known from the basin south of the Pascola arch are latest Ibexian (Early Ordovician).

Thermal alteration indices of both the Cambrian palynomorphs (organic-walled microphytoplankton) and Ordovician conodonts in the deeper parts of the basin, corroborated by fluid inclusion thermometry, vitrinite reflectance, and other geochemical techniques, are of higher values than predicted using any published estimates of overburden burial. These maturation values most likely reflect burial enhanced by the passage of hydrothermal fluids on a regional scale; they place constraints on interpretations of the tectonothermal evolution of the basin.

The hypothesis that biotic interactions have escalated over geologic time suggests that taxonomic groups such as bivalves, which developed representatives with high-energy life habits, preempted resources and drove “obsolete” low-energy groups, such as articulate brachiopods, into ecological refugia. Articulates had been the dominant benthos in a broad range of Paleozoic habitats. Modern refugia include areas of darkness and low primary productivity, such as fjords, caves, and polar regions. If the escalation hypothesis is true, then the modern articulates concentrated in these habitats should have extremely low energy budgets. The more energetic bivalves should be abundant higher in the photic zone and have higher energy budgets.

The equation Consumption = Growth (metabolizing tissue) + Reproduction + Respiration + Faeces + Excreta (nitrogenous) describes the energy balance in an organism. Energy acquisition is a critical factor for the persistance of individuals and species. Scaling equations relating particle filtration rates (consumption) to tissue mass were developed experimentally for two northern and two southern hemisphere species of brachiopods. Similar equations were developed for a northern and a southern hemisphere mussel species. The scaling equations allow correction for size differences which would otherwise confound physiological comparisons between species. Both northern and southern hemisphere brachiopod species were collected from deep, dark fjords or soft bottom habitats with Paleozoic style faunas. The mussels were collected from the same areas, but occurred higher in the photic zone.

Results indicate that the articulate brachiopods have a significantly lower ability to collect food particles from the water than do the mussels, for animals of similar body mass. These results support the hypothesis that escalated biotic interactions account, in part, for the ecological replacement of the formerly dominant Paleozoic articulate brachiopods by Mesozoic and Recent suspension-feeding bivalves.

The shape of an isometric gastropod shell can be described completely by specifying the pattern of shell secretion around the aperture (relative to aperture size) and the growth rate of the aperture itself. These descriptors provide a “natural” morphometric in that they correspond to the specific biological processes involved in constructing the shell.

Describing shell form in this way allows us to specify what developmental changes must occur during the transition of one shell form to another. In particular, we can distinguish between transitions that can occur through purely heterochronic processes (changes in growth rate) and those that require a change in the specific pattern in which cells of the mantle lay down shell. We can also investigate just what changes occur during the ontogeny of non-isometric shells.

Any change in either the pattern of shell secretion or the growth rate of the animal leads to changes in a number of classical morphometric measures, such as apex angle and whorl expansion rate. Those transformations resulting from changes in growth rate, however, are much more predictable than those resulting from changes in the pattern of shell production. A slight increase in the growth rate of the animal, for instance, produces a correspondingly slight increase in the apex angle and the rate of whorl expansion. By contrast, the consequences of a slight change in the pattern of shell production are highly sensitive to just how that change was achieved.

Data from 8 genera of marine snails show that the variance within each genus, relative to the variance among all genera, is smaller for measures of aperture shape (which can only be altered through a change in the pattern of secretion of shell material) than for characters that can change through heterochronic transformations (such as apex angle). Furthermore, the shell forms of a number of non isometric shells can be described by a constant pattern of shell production and a variable growth rate.

Heterochronic changes thus appear to be the preferred mechanism for changing phenotype in gastropod shells. Those characters that can only be altered by changing the pattern of shell production around the mantle, such as aperture shape, appear to be more conservative than those that can be changed through purely heterochronic transitions. This is consistent with the idea that mutations which alter many characters in a highly correlated manner have a higher probability of being favored by selection than those with relatively unpredictable consequences.

For historical reasons, Darwin insisted on continuity of evolutionary transformation, which he believed would result in the “Origin of Species”. By the title of his book, he stigmatized species as the basic unit of evolution. If evolution is a historically unique process, a species originates only once, and if it goes extinct, it is lost forever. As a consequence, no “natural laws”, or general statements can cover the origin or extinction of particular species taxa; only particular statements are possible. For reasons such as these, some authors have proposed to view species as individuals.

Can higher taxa be conceived of as individuals, too? If so, higher taxa would have to perform as units of evolution as species are believed to do. To deny so would introduce a fundamental ontological difference between “species taxa” and “higher taxa” without epistemological justification. I argue that the “discovery procedure” (Nelson, 1989) for species is the same as for higher taxa, and hence that species are taxa. However, the “discovery procedure” for monophyletic taxa results in an inclusive hierarchy of “groups under groups”, which is incompatible with Darwinian causes of evolution, predicting an exclusive hierarchy of ancestors and descendants. If it is agreed that successful scientific explanation must link hypothetical causes to observed effects in a testable manner, the conclusion must be that macroevolutionary scenarios built on species, or higher taxa, are descriptive rather than explanative. The Darwinian unit of evolution is, in fact, the geographically determined population, not the species (as Darwin himself realized). The alternative is to treat the inclusive hierarchy of species and higher taxa, and the pattern it reveals through time and space, as a reflection of history, which means that causes of this historical process are not only non-Darwinian, but remain a “black box” (Nelson, 1989) until today.

The Hartselle Sandstone of northern Alabama represents a mesotidal strandplain complex of Hombergian (middle Chesterian) age that was reworked by a transgressing sea. Transgressive reworking resulted in complex facies patterns that can best be deciphered by ichnology. Thickly bedded, unbioturbated beach to shoreface sandstone is widespread at the base of the formation. Wavy-bedded back-barrier to shelf sandstone and shale predominate in the middle and upper parts of the formation and contain distinctive assemblages of trace fossils, invertebrates, and plants.

Barriers with a broad, gently sloping beach face and muddy coastal swamps typified the Hartselle strandplain which extended across northern Alabama. Barrier and coastal-swamp deposits lack trace fossils but locally contain an indigenous lycopod flora including stumps and Stigmaria root systems.

Back-barrier tidal flats and lagoon deposits have trace-fossil assemblages dominated by bivalve traces that probably represent brackish environments. Marginal-marine sandstone contains chiefly monospecific assemblages and is reworked by bivalves and unknown organisms; Lockeia, Uchirites, and Rosselia are dominant at different sites. The Lockeia assemblage includes bedding surfaces with crowded bivalve resting traces. The abundance, density, and small size of monospecific burrows suggests estuarine conditions with high food supply and rapid larval colonization. The Uchirites assemblage is characterized by bivalve trails, representing probably brackish substrates with a high sedimentation rate.

Shelf sandstone and shale include bivalve resting traces and trails (Lockeia ispp., Uchirites isp. aff. U. triangularis, Walcottia rugosa, and W. imbricata), asteroid and ophiuroid resting traces (Asteriacites stelliforme and Pentichnus pratti), trilobite resting traces and trackways (Rusophycus ispp. and Petalichnus isp.), and dwelling burrows, feeding burrows, trails, and trackways of unknown organisms (Chondrites-like burrows, Phycodes isp., Haplotichnus isp., Rosselia isp., Planolites montanus, Nereites missouriensis, Tasmanadia twelvetreesi, imbricate burrows, and wavelike burrows). Some shelf areas even supported diverse calcified faunas containing crinoids, fenestrate bryozoans, and articulate brachiopods.

The Hartselle Sandstone is a facies mosaic that records indundation of an extensive strandplain complex and a distinctive stratigraphic succession of lithofacies and biofacies. Hartselle ichnofacies have unique aspects, but are similar to those of other marginal-marine Carboniferous strata in eastern North America. The paleoecologic complexity of the Hartselle Sandstone helps to establish the dynamic range of Carboniferous ecosystems, which have yet to be fully explored.

Geologists have long been plagued by the lack of evidence for the origin of ancient micrite deposits: any paleontological evidence is typically obscured or lacking altogether. The role of modern marine picoplankton gives insight into the origin of one mode of lime mud formation and may aid in the interpretation of ancient marine deposits.

Whitings, patches of floating lime mud in supersaturated seawater on carbonate platforms, obtained from the Bahama Bank were analyzed utilizing biochemical techniques and Transmission Electron Microscopy. All Whitings indicated a close association between picoplankton cellular material and calcium carbonate crystals. Culture experiments indicated the presence of at least ten different picoplankton species in Whitings water. Two major genera found were the blue-green algae, Synechococcus and Synechocystis. Field and laboratory experimental data indicated that these cells and cellular organics play a major role in Whitings formation. The cells may undergo epicellular precipitation of calcium carbonate induced by photosynthesis. Environmental conditions necessary for this process have been delineated through field data and laboratory experiments.

While picoplankton organics are rarely preserved over geologic time, the product of their life habit, namely lime mud, is preserved as micrite. Thick occurrences of micrite deposited in marine environments are widespread throughout the geologic record, ranging in age from Precambrian to Recent. Although rare, fossilized blue-green algae have been observed in Archean rocks and may be the only evidence that implicates these organisms in lime mud formation. The Whitings phenomenon serves as an excellent example in which a specific type of organism may be a prolific contributor to the rock record, and yet leaves no direct paleontological evidence of its involvement.

The oldest-known dinosaurs (Herrerasaurus, Pisanosaurus) occur within the Ischigualasto Formation. Recent work in the formation has brought to light significant new material, including the complete skeleton of a new primitive dinosaur. We sketch below the paleoenvironment and faunal succession during the range of these early dinosaurs, and review some of the taphonomic factors that shaped their fossil record.

The Ischigualasto Formation (Carnian?) is included within the Agua de la Peña Group, a series of continental Triassic deposits exposed in the Ischigualasto-Ville Union Basin of northwest Argentina. Ischigualasto sediments rest unconformably upon the carbonaceous fluvial/lacustrine Los Rastros Formation; this contact is characterized locally by marked angular discordance. The upper contact is gradational into red-beds of the Los Colorados Formation. Medium- to coarse-grained conglomeratic sandstones, siltstones, and silty mudstones dominate the section. Sand bodies are characterized by medium- to large-scale trough cross-stratification and broad lenticular/narrow sheet geometries, and are interpreted as deposits of shallow, low-sinuosity streams. Siltstones and mudstones show pervasive evidence of soil development, including root traces, nodular caliche horizons, and pedogenic slickensides. Deposits attributable to lacustrine/paludal sedimentation are scarce, and freshwater vertebrates and invertebrates are extremely rare. These data suggest an upland depositional setting on a low-relief alluvial plain with seasonal climate.

The Ischigualasto vertebrate fauna includes archosaurs, rhynchosaurs, traversodontid and carnivorous cynodonts, and temnospondyl amphibians. Rhynchosaurs dominate (relative specimen abundance) in the lower half of the section, but are absent from the upper half. Traversodontid cynodonts occur throughout the formation, but are much more abundant up-section. Archosaurs, carnivorous cynodonts, and particularly temnospondyls are rare throughout, with dinosaurs limited to the lower half. No major stratigraphic or sedimentologic changes occur up-section, and there is no evidence for significant shifts in physical or chemical taphonomic processes. Thus, trends in relative taxon abundance likely record a true biotic signal (e.g., local extinction, immigration) rather than a taphonomically-driven preservational bias.

Fossils are preserved as isolated carcasses or disarticulated elements, most often in fine-grained overbank facies. Bone beds and microsites are conspicuously absent. Temnospondyl remains were found within a local carbonaceous lens developed upon a sand body, suggesting autochthonous burial in an abandoned-channel setting. Isolated skulls, particularly those of the traversodontid Exaeretodon, are extremely common. Fifteen isolated crania of this cynodont were mapped in a single stratum with limited areal exposure. Abundant preservation of isolated therapsid crania has also been reported in the Beaufort Series (Permo-Triassic) of the Karoo Basin, South Africa (Smith, 1980). Post-disarticulation hydrodynamic sorting (enhanced by scavenging?) of an areally dispersed mass-mortality assemblage may explain this unusual occurrence.

The oldest angiosperm leaves from Patagonia were reported from Baquero Formation (Barremian-Aptian) in a mesofitic flora of more than one hundred gymnosperm and fern species. The next younger records are from the Chubut Group, a thick assemblage of pyroclastic sediments, with sand and conglomerate facies and frequent paleosols. In the Sierra de San Bernardo area sediments are mainly tufaceous and fluvial, deposited under an arid climate in shallow lakes and swamps of the alluvial plains. The sea was hundreds of kilometers to the West. Four Formations were described: Matasiete (Aptian), Castillo and Bajo Barreal (Senonian) and Laguna Palacios (Campanian-Maastrichtian). We explored in the Senonian Formations, and studied a few outcrops that can be sorted as:

a) Monospecific, with only Onychiopsis sp., in palustral sediments. b) Strongly dominated by Eauisetum sp, and few remains of two dicot species with large, entire margined, low rank leaves, in palustral sediments. c) Strongly dominated by two species of angiosperms with small leaves, associated with remains of conifers in tufaceous beds deposited in the alluvial plain. d) Dominated by a few species of dicots, with medium size, entire margined leaves. Also with about 10 species of ferns, gymnosperms and lobate angiosperms. They are in alluvial plains sediments. e) More balanced associations, with several abundant species, including angiosperms with lobate and leaves. They are in fluvial sediments.

Although angiosperm radiation and taphonomy undoubtedly accounts for differences of plant composition between outcrops, it seems apparent that the record of early angiosperms in Chubut Group is represented by remains of many different plant associations, with few species, adapted to different environments, that probably coexisted, and developed under an arid climate, far from the sea.

The objective of this project is to understand the long-term relationships, if any, if within-clade bivalve shell morphology to variations in shell growth rate and possible underlying environmental factors. As a preliminary approach to this problem, a study was undertaken to record the history of shell morphology, on the Florida peninsula, of the venerid bivalve Chione cancellata L. (Lower Pliocene - Recent). Samples were obtained from the following formations: Lower Pinecrest (3.5-3.0 mya), Caloosahatchee Fm. (2.5-1.8 mya), Upper Pinecrest Beds (2.4-1.8 mya), Bermont Fm. (1.6-1.1 mya), Anastasia Fm. (0.05 mya), and Recent. The total data set comprised ten samples.

Eleven morphometric measurements were selected on their predicted sensitivity to growth rate-caused variations in valve convexity. Comparisons of sample data sets were performed using principal components and canonical variates analyses. Only left-handed valves were analyzed. The results of both the principal component and canonical variates analyses indicate that a disproportionately large amount of the variance in the composite data set is accounted for by one morphometric dimension. This dimension is essentially a summary of contrast between anterior hinge morphology and posterior adductor muscle morphology. The samples form three major clusters; (1) Bermont Fm., Anastasia Fm. and Recent samples, (2) Caloosahatchee Fm. and U. Pinecrest samples, and (3) L. Pinecrest samples. There is some overlap of extremes between clusters (2) and (3), but otherwise the clusters are distinct. The result is a gradual but significant change of morphology during a 3.5 m.y. time span.

The next step in the project is to seek an explanation for the above observations. The provinciality of the phenomenon will be tested more extensively with the inclusion of Neogene and Recent samples from the Southern Caribbean and the Atlantic Coastal Plain. Also, considering the dynamism of Florida's oceanographic conditions (temperature, productivity and circulation) during the last 3.5 m.y., correlation of oceanographic conditions with C. cancellata's growth rate and morphology will be examined. The proposed method is a systematic sampling of stable oxygen and carbon isotopes from valves within the samples analyzed.

Medicine and paleontology have been intertwined from the start. Gideon Algernon Mantell, a family physician from Sussex, and his wife, while on patient care “rounds,” found the first English dinosaur. Nineteen years later in 1841, Sir Richard Owen established the neologism, dinosaur, to categorize these animals. It is not accidental that the first Dean of Kansas University School of Medicine was also the founder of the University's Museum of Natural History. Rheumatology and paleontology paths have also crossed in the form of Thinocetus arthritus, so named because the ligamentous fusion in a specimen mistaken for arthritis.

Technology and understanding of disease processes have advanced sufficiently to allow hypotheses to be critically examined. The underlying assumptions are that:

1. Disease manifestations are relatively stable through time.

2. Tissue is preserved in a state amenable to analysis.

3. Pathology can be distinguished from diagenesis (pseudopathology).

4. Analysis of pathology as a skeletal phenomenon provides more insight than examination of isolated bones.

5. Analysis of pathology as a population phenomenon provides more insight than examination of isolated skeletons.

Exemplifying the intertwining nature of the fields is the presence of spine and sacroiliac involvement and the nature and distribution of erosive lesions in the great apes (Gorilla and Pan (chimpanzee), the lesser ape (Hylobates) and Old World monkeys (Theropithecus, Papio, Cercopithecus, Macaca, Presbytis, Colobus, and Erythrocebus). This allowed definitive diagnosis of spondyloarthropathy. Reproducibility of diseases across species lines has been established for spondyloarthropathy (gorilla, chimp, monkey), not only for gross or radiologic appearance of individual bones, but also for skeletal distribution. More recently, similar observations have been made for Smilodon and Mammuthus. Reactive arthritis, related to infectious agent diarrhea or sexually transmitted, is a consideration. Infectious agent diarrhea is common in Old World primates. This natural disease state provides a unique model system for in depth analysis of the contribution of genetic and environmental factors to disease pathophysiology.

Paleobiogeography will play an important role in furthering our understanding of global change, particularly with respect to providing constraints on past climates. As a result of this there is increasing emphasis within the paleontological community on the past spatial distributions of faunas, extinctions, and originations. Thus there is an increasing interest in reconstructions of the past distributions of continents, so that maps and paleo-latitudes of faunas, extinctions or originations can be determined. This results in an increasing need to understand the state of the art of global plate reconstructions through the Mesozoic and Cenozoic, and global continental reconstructions through the Paleozoic, i.e. what we know and how well do we know it. The talk will summarize our present understanding of Mesozoic and Cenozoic plate motions using computer animations followed by a brief summary of the present understanding of individual continental apparent polar wander paths (APWP's) as well as motions in the global frame. Global and continental mean poles at approximately 20 Ma intervals have been computed for all of the major continents of the Phanerozoic using data from Van der Voo (1992) and plate motions derived from a detailed analysis of Mesozoic and Cenozoic seafloor spreading data. Comparison of mean continental poles reconstructed into the same reference frame shows that although there is general agreement, statistically different pole positions are quite commonly observed. This is particularly true for the Late Cretaceous and pre-Late Jurassic of the northern Hemisphere, and has resulted in some controversy concerning appropriate Atlantic fits. The differences in predicted (or reconstructed) paleo-latitudes are not trivial, particularly for areas of esatern Gondwanaland such as Australia and New Zealand, and are not easily visualized from a simple comparison of mean pole positions. A final focus will be with regards to reconstructions of Asia. Comparison of recently published Permian global reconstructions in the McKerrow and Scotese (1989) volume demonstrates that vast differences of interpretation persist and that paleontologists among others cannot accept exisiting reconstructions uncritically.

The Aporrhaidae is an important family of marine gastropods whose members are characterized by an expanded apertural lip. A phylogenetic analysis of this clade confirmed its monophyly although a few of the constituent genera, as presently defined, are polyphyletic. Stage-level diversity data for the Northern Hemisphere genera gathered through fieldwork, visits to museum collections and from the literature indicate an initial radiation of this clade during the middle Jurassic. This radiation produced 9 genera by the end of Callovian. Similar levels of generic diversity were maintained throughout latest Jurassic and the earliest Cretaceous. During the Jurassic the aporrhaids appear to have been geographically restricted to Europe and Africa. However, given the paucity of Jurassic marine sediments on most continents, this distribution is probably biased although absences in Japan and North America are probably genuine. The later part of the early Cretaceous history of this group is characterized by a major faunal turnover which resulted in the extinction of over 70% of the Jurassic genera and the evolution of at least 10 new Cretaceous genera. The group reached its highest diversity during the Albian, followed by a slight decline during the Cenomanian. This diversity peak is at least partially attributable to the exceptional quality of preservation during the Albian which is unsurpassed in any Jurassic or Cretaceous stages except the Maastrichtian. The average diversity for the rest of the Cretaceous stages remained around 12 genera and by late Cretaceous the group achieved a global geographic distribution. The aporrhaids suffered a severe setback during the Maastrichtian when at least 75% of the genera went extinct. The stratigraphic data presently available does not provide enough resolution to determine whether this extinction coincided precisely with the K-T event. At the generic level this extinction does not seem to exhibit any selectivity based on geographic range. Of the three end-Cretaceous survivors, Drepanocheilus and Arrhoges were widespread geographically while the third, Aporrhais had a restricted distribution. Similarly the taxa that perished included both endemic genera and widespread ones like Quadrinervus. The Cenozoic history of the clade is characterized by very low levels of generic diversity and restricted geographic distribution with only two extant genera.

From a macroevolutionary perspective, the late Neocomian turnover as well as the Maastrichtian extinction of aporrhaid genera are particularly interesting. The first event gave rise to a number of distinctive morphologies and coincided with the radiation of various groups of durophagous predators such as decapod crustaceans as well as with the rise of the carnivorous gastropods. The nature and timing of this change suggests that it could be a part of the broader Cretaceous faunal reorganization commonly known as the “Mesozoic marine revolution” (Vermeij, 1977). The end-Cretaceous event is interesting for its magnitude as well as its consequences. The aporrhaids maintained a remarkably stable generic diversity level from mid Jurassic to late Cretaceous, but never recovered from the Maastrichtian extinction. This pattern is in direct contrast to that exhibited by the sister group of Aporrhaidae, the Strombidae. The strombids exhibit extremely low generic diversity and restricted geographic distribution during the Cretaceous but radiated rapidly during the early Cenozoic. Such reciprocal diversity trends, combined with close phylogenetic relationship and functional similarity of the two groups as well as the presence of morphologic convergence, suggests extinction induced replacement and seems to be consistent with models proposed by, among others, Hallam (1987) and Rosenzweig & McCord (1991).

It is generally accepted that the extraordinary preservation of fossils in the Burgess Shale is at least partly due to the exclusion of large metazoan scavengers through rapid burial in an inimical environment. Disruption of individual organisms appears to have been largely the result of mechanical processes and/or microbial decay. The absence of bioturbation through much of the classic section, including Walcott's Phyllopod Bed, supports these arguments. However, macroscopic traces are known from other horizons within the Burgess Shale section and from lateral equivalents in the Stephen Formation a short distance south of the main locality.

The sparse ichnoassemblage includes bedding-plane exposures of portions of compacted, parallel-sided burrows containing skeletal debris comprising fragmented and disarticulated hyoliths, small trilobites, and bracniopods. Walcott originally figured one such trace as Planolites sp. ? and noted, but offered no evidence for, an association with the archaeopriapulid Ottoia prolifica. This notion was subsequently rejected by Conway Morris.

A recently collected specimen, from talus south of the main locality, contains a poorly preserved but recognizable body fossil of Ottoia within the outline of a “Planolites”. Although this juxtaposition may be accidental, a number of features of the association, and a consideration of the burrowing behaviour of modern priapulids, suggest that Ottoia could have been the generator of “Planolites”-like traces.

Long regarded as the earliest evidence for animal life, the fossils of the Ediacara fauna have come under increasingly close scrutiny as the result of a proposal made by A. Seilacher in 1983. At that time Seilacher suggested that the Ediacara fauna represents an extinct line of animal life (the Vendozoa) which pioneered a body form and modes of nutrition not seen in the Phanerozoic. More recently, Seilacher and others have suggested that most typical members of the Ediacara fauna were not even animals but were extinct foliate creatures analogous to algae or fungi which relied on endogenous photosymbionts or chemosymbionts for food and energy.

It would not be surprising if the Ediacaran organisms contained bacterial or eukaryotic endosymbionts as endosymbiosis at the organelle or unicell level is the norm rather than the exception for many protists and diploblastic metazoans. However, it is difficult to find the evidence to test this endosymbiont hypothesis because the Ediacaran fossils are merely impressions of soft bodies in sandstone or siltstone.

As there are no clear modern homologs of most of the Ediacaran organisms it is necessary to resort to logic and experiment to understand them. This has proved to be a formidable task but some progress is being made with complex forms such as Dickinsonia and Phyllozoon. Although no core member of the Ediacara fauna is unequivocally an early animal, there are more similarities to animals than to algae or fungi. There is no evidence at all that the vendozoans are fourth form of eukaryotic multicellular life.

What is known of dinosaurian biogeography suggests a centre of evolution first on a fragmenting Pangea-Gondwana and then on a consolidating Laurasia. By Cretaceous time members of Gondwanan low-latitude abelisaur-titanosaur assemblages often bore “back-fans,” while those in polar latitudes were relictual and/or highly derived. The time of last contact between South America and Africa is not well constrained, but links to Antarctica continued beyond the end of the Cretaceous. Many Gondwanan tetrapods appear to have waif-dispersed to Laurasia across southern Europe; few crossed in the opposite direction until the end of the period. Laurasian assemblages were then typically dominated by tyrannosaurids and hadrosaurids.

Land masses (“lost worlds”) periodically became isolated from Gondwana-Laurasia. (1) Eastern Asia was isolated between middle Jurassic through Neocomian time, although related temnospondyls and carnosaurs may have co-existed in Austral regions. Mamenchisaurs were the dominant giant terrestrial herbivores, while whip-tailed diplodocids filled the same role in Pangea. Groups of European-North American affinity then replaced many Asian endemics in a manner reminiscent of the Neogene mammalian turnover in South America. (2) In North America. Late Jurassic dinosaur assemblages exhibited Gondwana affinities, but by Late Cretaceous time they were dominated by forms of Asian ancestry. The apparent low diversity of Aptian-Albian dinosaur assemblages and absence of well-marked endemism may have been the result of a brief period of isolation. (3) European archipelagos were a filter bridge between northern lands and Gondwana analogous to the East Indies, which separate comparably different modern biotas in southeast Asia and Australia. (4) During Barremian time India probably hosted an polar dinosaurian assemblage, but low-latitude Gondwana forms (abelisaurids, titanosaurids) were present during at least part of this interval. Isolation ended with the immigration of northern taxa in Maestrichtian time.

Underexplored Mesozoic horizons of great biogeographic interest include (1) the Middle Jurassic-Neocomian of China for microvertebrate materials, (2) the pre-Maestrichtian Cretaceous of India, and (3) the post-Cenomanian of Africa, Australia and Antarctica. Paradoxically, the two recently discovered dinosaurian specimens of the latter age in Antarctica, which represent about as much biogeographic information as all described materials of similar age from Africa combined (none are known from Australia), are presently referred to families with Laurasian distributions.

The burial and preservation of significant quantities of marine organic matter in epicontinental basins results from low bottom water oxygen levels, and moderate to low sedimentation rates of fine-grained siliciclastic sediment under at least moderately productive waters. Because benthic biotas are extremely sensitive to such factors as bottom water oxygen, grain size, substrate consistency and sedimentation rate, there is a potentially predictive relationship between biofacies and Corg potential of marine strata. High-resolution biological, sedimentological and geochemical studies of Mesozoic organic-rich black shale facies, comprising major hydrocarbon source rocks, allow characterization of this relationship: a) A series of recurrent, bivalve-dominated benthic communities are defined based on trends in diversity, abundance, equitability and trophic specialization. They comprise biofacies which reflect oxygen and substrate gradients in time and space, and thus the Corg preservation potential of marine sediments/strata. The biotas are surprisingly robust in terms of population size and inferred biomass, and demonstrably colonized the benthic zone (as opposed to pseudoplanktic origins). They include both resident communities of taxa specifically adapted to low oxygen (dysoxic) conditions through physiological and anatomical means (e.g., expanded oxygen adsorptive surfaces), or possibly through bacterial chemosymbiosis, and event communities of less tolerant taxa reflecting short-term improvements in benthic conditions; b) many organic-rich sequences contain common event biofacies, indicating a dynamic benthic environment with frequent short-term fluctuations in oxygen and substrate. These are attributable to mixing during large storms, productivity blooms, rapid deposition from mass flows, or reduced sedimentation during condensation/bypass events. However, increasing frequency of events is not necessarily correlated with decrease in Corg levels; c) comparison of trends in the quantity and quality of Corg to biofacies patterns indicate that the most favorable Corg preservation is associated with “benthic boundary biofacies.” These biofacies represent a redox boundary at or near the sediment-water interface and a predominantly dysoxic to episodically oxic water column. The “benthic boundary” may have been associated with the presence of microbial (mainly sulphur bacterial) mats on the substrate surface, which could have regulated its position and contributed to the pool of sedimented Corg; d) mapping of benthic boundary biofacies in time and space within a basin makes possible correlation of Corg preservation potential to paleogeography and sea level history. Although the results of such analyses from the Greenhorn Formation, Western Interior basin, suggest highest Corg burial and preservation in fine-grained shale facies of distal offshore environments during sea level rise, high Corg is not necessarily associated with an anoxic water column. This suggests the need for reappraisal of stagnant basin scenarios for source rock formation. The most important factors in Corg accumulation and preservation may be the development of benthic boundaries and consequent maintenance of anoxia below the sediment-water interface in fine-grained, organic-rich substrates, and the contribution of bacteria to the flux of Corg into the sediment.

Mesozoic brachiopods were, at times, significant elements of marine invertebrate faunas. Current investigations suggest that Mesozoic brachiopods are more common in Mesozoic marine sequences from North America than has generally been assumed. Their neglect is no doubt in part due to the greater utility of other invertebrate and microfossil groups for biostratigraphy. Brachiopods may be preserved in original shell material or silicified. It is therefore necessary to consider which is the most appropriate method of extraction, depending on type of preservation.

Lacking planktotrophic larval stages, living articulate brachiopods are limited in their dispersal potential by virtue of their sessile, benthic mode of life. If, in addition, all post-Paleozoic articulate brachiopods possessed a non-planktotrophic larval stage endemism would be likely to develop if gene-flow became severed. This would mean that taxonomic investigation of articulate brachiopods has the potential to provide useful paleobiogeographic and paleogeographic information. Recent investigations have concentrated on making a preliminary survey of some brachiopod occurrences in the Western Cordillera of North America with these goals in mind.

The Upper Triassic brachiopod fauna from the Luning Formation of the Pilot and Shoshone Mountains, Nevada, is the most diverse known for the Mesozoic of North America in terms of number of brachiopod species (manuscript submitted with George D. Stanley). This is probably a reflection of how little detailed collecting and systematic study Mesozoic representatives of the phylum have received in North America. The fauna comprises both Tethyan and endemic species. The brachiopods are from the Paradise terrane, probably close to the North American craton in the Late Triassic. One Upper Triassic brachiopod fauna from the Antimonio Formation, Sonora, is by comparison with the Nevada faunas, depauperate, but they do share one common species. Additional time-equivalent brachiopod faunas from outboard terranes of North America and the “classic” European faunas monographed in the nineteenth and early twentieth centuries require investigation to determine their paleobiogeography and their contribution to paleogeography.

Jurassic brachiopods from North America have not been subjected to any major revision but they are present at certain horizons. Cretaceous faunas from the southern United States and Mexico contain genera known from Tethys in Europe. Mid-Cretaceous faunas from the Queen Charlotte Islands (Wrangellia terrane) and the Canadian Arctic Islands contain forms that are more typical of mid-latitude to Boreal regions, repectively, of Europe. This suggests a broad correspondence between brachiopod distributions and paleolatitude across considerable paleolongitudinal distances, an observation of relevance to interpreting Early Mesozoic paleobiogeographic distributions.

The current work is only scratching the surface of the Phylum's distribution in the Western Cordillera of North America. The aim is to provide a better understanding of brachiopod paleobiogeography, paleogeography, and the evolutionary history of the Brachiopoda during the post-Paleozoic, which does not appear to be their swansong.

To properly reconstruct the phylogeny of a taxon, it is necessary to determine homologies among taxa. The assumption that repeated structures are iterative homologues has resulted in phylogenetic confusion. Radial ribs have long been used as important taxonomic characters in bivalves, but a cladistic analysis of the Cardiidae has shown that radial ribs are not homologous across genera.

Pre-Aptian cardiids have either simple, unornamented ribs, or have lost the ribs entirely. The genus Granocardium originates in the Aptian and has large spines on every third or fourth rib interspace. This row of spines is connected by a raised striation. The interspace bearing these spines is raised relative to other interspaces. Criocardium, a subgenus of Granocardium, originates in the Upper Cretaceous and has rows of small spines, also connected by a raised striation, on the interspaces not occupied by large spines; these interspaces are not concomitantly raised.

When the character states of the large and small spines, their respective striations, ribs and interspaces are analyzed throughout the Cardiidae, it becomes apparent that adjacent pairs of ribs have fused independently on three occasions. In Cenozoic cardiids, the large spines and their striations are not between ribs but on top of them. On many taxa, the top of the rib is concave, reflecting the rib top's homology with the rib interspace of Granocardium. Furthermore, some taxa bear the remnants of Criocardium's row of small spines connected by a striation in the rib interspaces. The Maastrichtian Perucardia has an intermediate morphology, with the anterior and posterior slopes as in the Cretaceous Criocardium while the central slope has the ribbing pattern of Cenozoic cardiids.

Cladistic analysis demonstrates that Cretaceous cardiids once put into the Neogene genera Fragum and Bucardium are allied with Criocardium. Species placed in Fragum resemble that genus only in its trigonal shell shape; they share the interspace spines and several other characters witth Criocardium and belong in Profragum Badve 1977. Species placed in Bucardium on the basis of round shell shape and reduction in rib number are properly placed in Austrocardium Freneix and Grant-Mackie 1978, and share the interspace striation and other characters with Criocardium. Austrocardium is another example of rib fusion: a groove, homologous to a rib interspace, runs down the top of each rib; this accounts for the reduction in rib number.

A third example of rib fusion occurs in some species of the Cenozoic genus Hedecardium. Two ribs (each one homologous to a pair of ribs in Granocardium) undergo an additional episode of fusion, forming a single rib with two parallel rows of spines and striations on top of the rib; a single one of these ribs would therefore be homologous to four ribs on Granocardium.

Fusion of iterative homologues has been discerned in many arthropods. Pairs of metameric segments have fused, leaving individual segments with twice the number of anatomical structures usually associated with a single segment. Radial ribs are not metameric (but are iterative) since they radiate from a single point as opposed to being repeated in a linear sequence. Rib fusion operating alone would imply a fifty per cent reduction in rib number, and in Austrocardium the rib number is halved. Cenozoic cardiids have fewer ribs than their Cretaceous ancestors, but only by about twenty per cent. Fusion is only one of several processes that regulate rib number on cardiids.