Mass extinctions have played a significant role in the Phanerozoic evolutionary history. Not only have they resulted in the relatively rapid loss of numerous, ecologically and genetically diverse taxa, but, in most cases, they have culminated in the radiation of new lineages, communities and ecological structure based not only on the evolution of new taxa, but also on changes in dominance of surviving taxa. The hypothesis that these biotic crises may be periodic and caused by similar forcing mechanisms has generated the need to compare mass extinction survival and recovery intervals. The ultimate test of this hypothesis lies in the fossil record. For this study, the Cenomanian-Turonian (C-T) and Cretaceous-Tertiary (K-T) boundary intervals are analyzed. These boundaries are interesting for a number of reasons: 1) they both are well-studied at a high level of resolution at a number of localities; 2) the K-T event follows the C-T event by approximately 26 My reflecting the proposed extinction periodicity; 3) they represent two different levels of extinction intensity with the K-T affecting a far greater percentage of taxa; and 4) they occurred under very different environmental conditions. Initial analyses of generic and species range data for epifaunal and infaunal bivalves, ammonites, brachiopods, benthic and planktic foraminifers, ostracodes, and nannoplankton suggest that the basic patterns of survival and recovery are similar for C-T and K-T extinctions. Both extinction events show an initial survival interval in most groups, during which most of the species present represent survivors (including “Lazarus taxa”) or new species within surviving lineages. This gives way to a recovery interval characterized by an increasing number of new species within new lineages. Based on the rapidity with which new species evolve, these repopulation intervals suggest that the degree of survivorship among diverse groups must be far greater than generally believed, because the evolutionary rates appear to be too rapid to be accounted for by rapid radiation solely from generalist stocks. Although the general patterns appear to be quite similar between these two extinction-repopulation intervals, there are significant differences. The C-T mass extinction affected primarily epifaunal bivalves, benthic foraminifers, and ammonite taxa severely, while the K-T event resulted in a pronounced extinction among planktic foraminifers and infaunal bivalves. This suggests that at least the proximate causes of extinction for the two intervals were substantially different. Despite the greater overall magnitude of the K-T extinctions, the repopulation occurred more rapidly following this event. This suggests that the degree of vacated niches was greater and/or the environmental conditions returned to more favorable levels more rapidly. The C-T repopulation may have been delayed due to the deleterious background conditions which existed throughout much of the mid-Cretaceous. Finally, the K-T extinctions resulted in the disappearance of significant elements of the pre-extinction faunas and communities, such as the ammonites, inoceramids, and rudists, whereas the C-T event resulted in the temporary reduction in abundance and diversity in these groups, but they rapidly reobtained their dominance.

A well preserved archaeocyath fauna occurs in the Forteau Formation in Southern Labrador, Canada. Following on from the confirmation that archaeocyatha are aspiculate calcified sponges, detailed ecological work is now being undertaken on this fauna, a representative of the first reefal ecosystem in the fossil record.

One species, Metaldetes profundus, shows considerable variability in growth form, from open bowl-shaped forms in lagoonal settings, to a branching morphology in biohermal habitats. This species also appears to colonise a variety of substrate types and for this purpose often uses exothecal structures and holdfasts. M. profundus is also the dominant species numerically, comprising 80% of the fauna, except at the top of the bioherm horizon, where Archaeocyathus atlanticus becomes dominant. In contrast to previous studies' findings, bowl-shaped Metaldetes at the top of the bioherm horizon occupy the basal region of the bioherms, not the upper areas and provide a surface on which the bioherms can develop.

The unique form of Retilamina amourensis endows it with the ability to stabilise substrates so facilitating the colonization of a substrate. It is more common at the base of bioherms, providing a surface on which other archaeocyaths can settle. The calcimicrobes Renalcis and Epiphyton also appear to have played a major role in the initiation of the bioherms, occurring as 3–5cm thick layers on erosion surfaces, within which small, juvenile, upright M. profundus sticks, <1cm in diameter, are found, surrounded and supported by the dense calcimicrobe aggregate.

Digital 3-D analysis is being used to document the behaviour of the archaeocyaths, together with vertical and lateral zonation within the bioherms, especially with regard to the timing of calcimicrobe encrustation. Volumetric abundances of the archaeocyaths are also being calculated.

There are small faunal composition changes over the area: Archaeosycon billingsi, a solitary stick-like form is more abundant in the west than in the east and Archaeocyathus atlanticus, another stick-like form occurs in dense clusters in lagoonal environments, elsewhere being solitary.

The biochronologic use of nonmarine mollusks commenced in the northern Great Plains with the pioneering studies of F.B. Meek and F.V. Hayden in the 1850s and ‘60s. Their research focused on the chronostratigraphic organization of nonmarine and marine strata and included the naming of the Fort Union Group, which represents the Paleocene throughout the northern plains. Current research has focused on ascertaining the biostratigraphic distribution of nonmarine taxa throughout the post-Fox Hills Formation sections in the northern Great Plains, specifically in the Williston (WB: North Dakota, Montana, Saskatchewan), Powder River (PRB: Montana, Wyoming), and Crazy Mountains (CMB: Montana) Basins. The strata represented include the uppermost Cretaceous Lance (PRB) and Hell Creek (WB, PRB, CMB) Formations; Paleocene Fort Union Group, including (in ascending order) the Ludlow (WB)—Tullock (WB, PRB)—Bear (CMB), Slope (WB)—Lebo (PRB, CMB), Bullion Creek (WB)-Tongue River (WB, PRB)-Melville (CMB), and Sentinel Butte (WB)—lower “Wasatch” (PRB) Formations, and the Bear Den Member of the Golden Valley (WB) Formation; and the Lower Eocene Camels Butte Member of the Golden Valley Formation (WB) and main body of the “Wasatch” (PRB) Formation. About 2000 nonmarine molluscan localities have been collected from these strata and correlated with all of the approximately 200 relevant mammalian local faunas. The geologic section represented by each study area has a segment of the section that is biostratigraphically and biochronologically relatively well controlled by either molluscan or mammalian occurrences or both. These segments overlap sufficiently well to provide a nearly continuous composite section for the uppermost Cretaceous, Paleocene, and Lower Eocene. In the Montana portion of the Williston Basin, the uppermost Cretaceous (Lancian) taxon ranges of nonmarine mollusks and mammals are stratigraphically well controlled. Less abundant or less well-controlled occurrences elsewhere support the view that a diverse, molluscan assemblage, largely composed of highly sculptured unionid bivalves, is extinguished, relatively suddenly, near but before the end of the Cretaceous. The lower and lower middle Paleocene (Puercan and Torrejonian) section, as evidenced in isolated fossil occurrences, is a time of a substantially reduced number of low-diversity molluscan faunules consisting of a small mesogastropod-dominated snail fauna, a few taxa of which cross the Cretaceous-Tertiary boundary, and a small, unornamented (except for the umbonal region) fauna of unionids. The upper middle Paleocene (Torrejonian) and lower upper Paleocene (Tiffanian) contain a record indicating a resurgence in the molluscan fauna, particularly in the upland Paleocene terrains preserved in the upper Lebo and lower Melville Formations of the Crazy Mountains Basin. A relatively large number of localities contain a diversifying mesogastropod-dominated snail fauna, an increasing number of terrestrial taxa, and an increasingly diversified, but unsculptured, unionid fauna. The middle upper Paleocene (Tiffanian 3–4) faunal record, representing the “classic” Fort Union molluscan fauna of Meek and Hayden, was comparatively diverse, abundant, and dominated by freshwater snail taxa. Although known from substantially fewer localities, this interval also contains an increase in diversity and novelty of aquatic and terrestrial pulmonates. Unionids are locally abundant, but remain relatively undiverse. The uppermost Paleocene (presumed Clarkforkian) record in the Powder River Basin documents a continued increase in pulmonate taxa and a sustained, but compositionally different, diversity of mesogastropods. The unionid fauna is relatively unchanged. The Paleocene-Eocene (Wasatchian) boundary, based on mammalian, palynomorph, and plant criteria, is clearly shown by a widespread change in the composition of the molluscan assemblage. The overall faunal diversity is somewhat reduced, with a noted reduction in the diversity of certain freshwater mesogastropods, a few unionid taxa, and a continued increase in the representation of pulmonate taxa. In summary, uppermost Cretaceous and lower Tertiary strata in the northern Great Plains contain a sequence of nonmarine molluscan faunas that are sufficiently diverse and changing so as to permit the construction of a substantially more resolved biochronology than previously considered possible.

Homoplasy is present in virtually every known systematic analysis and exists at all levels of the Linnaean hierarchy. Despite the nearly universal presence of homoplasy, the patterns and causal mechanisms of it have only recently been addressed.

Sanderson and Donoghue (1989) examined the relationships between homoplasy (as measured by the consistency index) and taxonomic rank, the number of characters, and the number of taxa. Their analysis, which involved 60 data sets from the literature, showed a statistically significant and inverse correlation between the number of taxa and the amount of homoplasy exhibited.

In order to expand on Sanderson and Donoghue's important contribution, we attempt to dissect the causal mechanisms of homoplasy. As a working hypothesis, we assume that if the number of character states is limited, homoplasy should be a function of at least three factors: 1) the number of cladogenetic events (which is directly related to the number of taxa), 2) the percentage of characters that undergo change at each node, and 3) the probability of any one character changing at any one node. Because the absolute, or even relative, values of the last two factors are rarely known for a given taxonomic group, we used computer generated data sets in order to quantitatively determine the relative importance of these three factors to patterns of homoplasy. Characters were allowed to “evolve” on a preset tree topology; this process was repeated for a wide variety of values for each of the above factors. The correlation of each factor with the consistency index was then examined. In order to control for results that were unique to a given tree topology, the same data sets were generated onto two very different tree topologies (a extensively bifurcated tree and a Hennigian comb).

Our preliminary results indicate that homoplasy is much more sensitive to the percentage of characters that change at a given node then to the number of taxa involved (as determined by the amount of variance explained by a regression line). In addition, the nature of the above procedure allows for the analysis of the dynamic relationship between evolutionary rate and constraint (defined as a limitation in the number of character states possible). These two factors conspire to produce homoplasy. The effect of high rates of evolution on homoplasy is magnified by successively greater constraints on character states; conversely, high rates of evolution in conjunction with low degrees of constraint lead to lesser levels of homoplasy.

The Buckhorn Asphalt (Desmoinsean, Pennsylvanian) of south-central Oklahoma has yielded a diverse and exquisitely preserved, shallow marine Molluscan fauna, including many minute taxa. This window into the shallow marine biota of the late Carboniferous, provides insight regarding evolutionary relationships of several molluscan clades and the Mesozoic Bivalve radiation. It confirms a Pterineidae ancestry for the Bakevelliidae, and allows documentation of crucial character states such as: shell microstructure, ligament ultrastructure, geochemical composition, prodissoconch 1 and 2 stages, as well as hinge dentition and ligament details for members of both families. Three previously undescribed species of pterioid bivalve, provide new data on this clade. These forms include: 1) a pterineid closely related to Leptodesma, with an alivincular ligament type, 2) the earliest known bakevelliid, possessing a rudimentary multivincular ligament, and 3) a transitional form which has but one shallow ligamental pit located beneath the beaks. These ancestral forms consist of minute species that develop character states used as family defining features in the Mesozoic. This study extends the range of the predominantly Mesozoic bakevelliids, and documents the early evolutionary development of the ligament type which characterizes the group.

Additionally, these taxa demonstrate the Carboniferous origin of the Mesozoic bivalve radiation, and provide invaluble data concerning the roots of the radiation prior to the firm establishment of Mesozoic clades. The key family defining character was established in the Carboniferous yet did not come to fruition until the Mesozoic. These taxa also enable one to establish multiple working hypotheses regarding the functional and adaptive significance of this ligament type. The multivincular ligament may: 1) conserve constructional material, 2) facilitate a more endobyssate life position, or 3) simply be a neutral character of little or no adaptive value. The exceptional preservation of the Buckhorn Asphalt biota provides a unique opportunity to evaluate such evolutionary and paleoecological relationships.

Recent 13C solid state nuclear magnetic resonance studies have demonstrated differences in the composition of sporopollenins (the inert biomolecule forming spore and pollen walls) from the major groups of extant plants. This substance is also the main constituent of fossil spore walls.

We have obtained 13C NMR spectra from three species of Carboniferous lycopod megaspores, and in one case, the associated microspores. Additionally, spores from the Devonian plant Parka decipiens Fleming have been analyzed. The spectra obtained are relatively similar although at present it is unclear how much of this similarity results from diagenesis.

The spectra of the fossil spores have been compared to those obtained from extant lycopods and from other plant groups. The fossil lycopod spores share some of the distinctive features of modern lycopod sporopollenin but are, none the less, very different. The spectra of the fossil species also demonstrate the loss of constituents known to form a significant part of the sporopollenin in extant species. Our studies show that some of the chemical characteristics of sporopollenins are retained in fossil spores, allowing the investigation of evolutionary changes of sporopollenin within a group and facilitating the assignment of taxonomically enigmatic fossil species. Further investigation of a range of fossil material, combined with data obtained from pyrolysis, should provide further information on the composition of sporopollenin from different plant groups and on its diagenesis.

The Leguminosae are consistently one of the two or three most important angiosperm families in diversity and abundance in modern African and American tropical and subtropical lowland ecosystems. Many legumes are colonizers of disturbed sites while others are components of more mature communities. The great diversity and abundance of legumes reflects characteristics that have made them important components of tropical ecosystems. One of the most significant of these is the ability of most legume species to enrich the soil through the activities of bacteria in their root nodules. Legumes are also important as sources of food to vertebrate and invertebrate pollinators alike. Legumes have well known plant-pollinator relationships with bats, birds, hymenoptera, and lepidoptera and their diversity is sometimes linked with their strong association with specialized animal pollinators. Legumes also enjoy a variety of unusual defense strategies based on various interrelationships with ants. Thus, the evolution of specialized interrelationships with a diversity of organisms has helped the legumes become a family of considerable importance in American and African tropical ecosystems.

Legumes are well represented in the fossil record and the paleobotanical data now available demonstrate that the family was an important component in tropical ecosystems by the Paleocene/Eocene. Sediments of the Mississippi Embayment in southeastern North America are yielding the most abundant and diverse assemblage of fossil legumes. The individual legume taxa in this specific subtropical to tropical flora represent a wide variety of different biogeographic distribution patterns. Legume fossils that are most closely related to extant taxa that occur only in tropical South America today are the most common components of this assemblage. Other biogeographic distribution patterns include American-Asian disjuncts, Asian, African, and Pantropical taxa. Although several of the fossil taxa are widespread in the North American Tertiary, these cases are restricted to taxa that have an Old World Tropics or American-Asian disjunct distribution today. The South American taxa seem to have been largely restricted to the Mississippi Embayment system.

The Paleocene/Eocene legume fossil flora suggests that nitrogen fixation and highly specific insect pollination mechanisms were well established by that time. In addition, bat pollination in legumes may have been established by the upper Eocene. Specialized foliar glands, which are indicative of defense strategies involving ants, are present by at least the Oligocene. Although fruit and seed dispersal in legumes is largely abiotic, a wide variety of fruiting structures and abiotic dispersal mechanisms occur in the family and many of these were present by the Eocene.

This study of the fossil record of the Leguminosae is demonstrating that the legumes were well established and diverse by the Paleocene/Eocene and that many of the functions and relationships that make them important in modern tropical ecosystems were established by that time.

Lately, we proposed a hypothesis that the ancestral angiosperm was a diminutive, rhizomatous to scrambling perennial herb with small simple flowers. Our phylogenetic studies suggest that arborescent to shrubby magnolialians with large, multiparted, complex flowers are derived, rather ancestral as commonly thought. We suggest that the early angiosperm, due to its rhizomatous habit, would have been able to survive in more ephemeral habitats. A test of this idea would be to examine the sedimentological context of early angiosperms.

Despite a number of reports of early angiosperm megafossils from Barremian to middle Albian (mid- to late Early Cretaceous) age sediments, only the Potomac Group of the eastern U.S.A. has provided a stratigraphic sequence of early angiosperm diversification. Furthermore, study of this sequence has also linked observations on floristic assemblages to the lithofacies in which they occur, leading Doyle and Hickey to report an ecological expansion of early angiosperms from relatively near-channel environments to a much broader range of flood plain sites during the Barremian/Aptin to latest Albian/early Cenomanian interval represented by Potomac Group deposition. From this those authors inferred that the early angiosperms were “riparian weeds” that grew on moderately unstable, near-channel sites subject to periodic flooding and episodes of alluviation.

We recently expanded on these inferences by examining the sedimentology of Dutch Gap, an early angiosperm site at the earliest level of the Potomac Group (Barremain/Aptian-Pollen Zone I) near Richmond, VA. Sediments here appear to represent the meander belt of a fluvial setting. A series of multi-storied channel units at the site are filled with arkosic, medium to coarse, sub-angular sand with pebble- to boulder-size clasts of gneiss, claystone and mudstone concentrated at channel bases, reactivation surfaces, and on lateral accretion surfaces. These channels are cut into inferred levee and splay deposits that consist of thin interbeds of sand and silt alternating with dark grey, micaceous mudstone to claystone. This sequence fines in an inferred distal direction from the channels and the mudstone/claystone interbeds thicken at the expense of the coarser units until they coalesce into relatively thick, dark grey clay beds with only thin silty laminae. These beds are thought to represent floodbasin deposits.

The megafossil plants recovered from our studies at Dutch Gap exhibit a clear pattern of association with each other and with these lithofacies. Angiosperms (Celastrophyllum, Rogersia, and an unnamed new form) together with ferns are found in relatively silty interbeds that lie in what appear to be distal levee settings, while the backswamp was dominated by the bennittitalean Dioonites buchianus. Conifers of diverse kinds are dominant only in pinkish, silty clay clasts that are inferred to have been transported from drier flood-plain environments.

This study provides added evidence of an association between early angiosperms and moderately unstable, channel-margin sites and, in addition, calls attention to the potential that detailed sedimentological investigations have of providing important evidence on early angiosperm paleoecology.

After surviving the notorious Permian-Triassic boundary-events, the conodont-bearing animals underwent a number of crisis at the end of Induan, Olenekian, Ladinian, Early Carnian and during Middle Norian to Rhaetian times, before their final extinction at the end of the Triassic. The causes responsible for speciation, radiation and extinction seem possibly related to global sea-level changes, although the Norian-Rhaetian speciations and final extinction of conodonts may have been controlled by competitional pressure at the trophic and reproductive level, possibly by newly appeared taxa, e.g. bonefishes.

Families, defined herein by their multielement-apparatus, are three in number (4 genera, 1 being new) in Induan, two (8 genera, 6 new) in Olenekian, one (2 subfamilies, 5 genera, 3 new) in Anisian, Ladinian and Early Carnian before the Carnian crisis, and one (1 subfamily, 2 genera, 1 new genus) in Late Carnian, Norian and Early Rhaetian, until extinction of the last conodont taxon at the end of the Rhaetian.

Palaeogeographic distribution of Induan Anchignathodus, Induan - Olenekian Ellisonia and Neospathodus, Induan - Early Rhaetian Neogondolella and Olenekian Plativillosus are boreal to equatorial. Olenekian Furnishius, Parachirognathus, Hadrodontina and Pachycladina are found in cratonic cordilleran and Werfen facies. Latest Olenekian, respectively Anisian to Early Carnian Gladi- and Paragondolella define low-latitude mesopelagic Tethys. Ladinian Sephardiella extends from shallow Tethys to Boreal realms, whereas Neogondolella and Pseudofurnishius dwelled respectively in restricted Anisian to Early Ladinian Germanic and semi-open Ladinian Sephardic provinces. The specialization of post-Induan taxa into environmental niches became first reduced from the generic to specific level and disappeared entirely in Late Norian and Rhaetian. Latest Carnian - Latest Rhaetian Epigondolella species extended from low (Tethyan) to high (Boreal) latitudes, in pelagic and cratonic facies. Norian species of Paragondolella had a pan-thallassic, including Notal, distribution.

Triassic P-elements always show similar patterns of evolution of the platform and basal cavity as appearance of denticles on platform -edges, development of a free blade and splitting of basal cavity, causing broadening of platform. These characters are lost or abandoned in highly critical periods. Instead, ancestral morphs with reduced platforms, often without apparatus, or early ontogenetic stages, re-appear, from which evolution restarts. Norian-Rhaetian taxa, however, seem to play that scenario backwards, a process reminding of neoteny or paedomorphism. This process is accompanied by the irreversible reduction in the number of species of Late Rhaetian conodonts.

The widespread occurrence of stratigraphic sequences suggests that a large fraction of the stratigraphic record is systematically biased. For example, sequences in landward areas tend to have more symmetrical transgressive-regressive records as well as hiatuses of long duration. Sequences in shelf settings have highly asymmetrical regressive-dominated records, with relatively minor hiatuses and condensed sections. Deeper settings tend to have more symmetrical transgressive-regressive records, with significant condensed sections. This stratigraphic bias can both mask true paleontological patterns and create apparent patterns.

Sequence architecture implies that environments are continually changing, whether this change is obvious in lithofacies or not. Given that facies control has been documented in many benthic taxa as well as in planktic/nektic/nektobenthic groups that are biostratigraphically important (e.g., conodonts, ammonoids, and graptolites) continuous change in lithofacies suggests that faunas should continually change upsection–and that this change should reflect changing environments, not in situ evolution. Vertical changes in taxonomic composition and morphology are more easily explained as clines or ecophenotypic gradients, rather than as evolutionary sequences. Because stratigraphic sequences cause vertical facies successions to be repeated, fossil morphologies should repeatedly appear within a section, with their occurrences separated by a hierarchy of gaps, varying in scale from short-term taphonomic-bias gaps through parasequence-scale gaps to sequence-scale gaps. Morphotypes with stratigraphically discontinuous ranges commonly have been named separately despite the morphological similarity at different horizons, and in some cases, this pattern has been interpreted as iterative evolution. However, sequence architecture and facies control could easily produce this pattern. It is argued here that the Lazarus Effect of Jablonski is far more pervasive than previously acknowledged and can occur at a range of scales from a variety of processes.

The juxtaposition of dissimilar facies at sequence boundaries can produce apparent paleontological events, while facies control will mask true paleontological events. Apparent first occurrences will be concentrated immediately above sharp facies contacts at sequence boundaries, whereas apparent last occurrences will be concentrated immediately below sequence boundaries. However, a true first occurrence within a section will inevitably be delayed from the true first occurrence within the basin because of facies control; likewise, true last occurrences within a section will precede the true last occurrence within a basin. The magnitude of this delay/precedence will vary with the position of the section within the basin. The asymmetric sequences of midshelf settings can cause a delay of up to one full sequence; more symmetrical sequences of landward and basinward settings can create a of up to approximately one-half of a sequence.

What can be done about this source of bias? One solution is to create a tight eventstratigraphic correlation network in conjunction with a basin-wide array of sections to be able to track any given facies through time and space. A second solution, useful where such correlations are not possible or such an array of sections is not available, would be to compare within-habitat faunal and morphologic change between sequences.

Possibly the most intriguing possibility is that the same processes that create stratigraphic sequences also drive macroevolutionary change through geologically rapid reassortment of sedimentary environments and the redistribution of barriers to isolation.

Cyclothems (fifth - order depositional sequences) are the fundamental stratigraphic motif of the Upper Pennsylvanian and Lower Permian of the North American mid - continent. Through this interval, sequences display an overall second order regression modulated by intermediate frequency sea-level fluctuations. Thus, shelfward incursions of offshore (basinal) facies are more extensive in the lower Upper Pennsylvanian, while merely shoaling facies characterize marine units of many higher sequences.

Within basal Upper Pennsylvanian (Missourian) sequences, species of the Erisocrinacea are ubiquitous members of nearshore and offshore crinoid assemblages. However, the species Erisocrinus typus and Delocrinus subhemisphericus display significant ecophenotypic variation between facies: smaller mean and maximum size characterizes offshore/transgressive populations while larger size characterizes nearshore/regressive populations. It is proposed that these are hydrographically - controlled phenotypes: offshore, quiet bottom waters inhibit effective filtration, imposing a metabolic energy threshold beyond which larger morphologies are not viable while nearshore populations are able to assume larger body sizes.

Shifting now to the Catacrinidae within the Erisocrinacea, as the frequency of interbasinal drowned shelf conditions waned through the Late Pennsylvanian, new species, inhabiting regressive facies, increased maximum body size and diversity for the family. Thus, lower Virgilian assemblages are highly variable in characteristic size, with smaller, ancestral D. subhemisphericus dominant in offshore facies while robust D. vulgatus, Pyndaxocrinus sp., and Arrectocrinus sp. dominate nearshore facies. Speciation may have involved the stabilization and subsequent diversification of the earlier nearshore phenotype.

Through the remainder of the Virgilian and into the Early Permian, near the terminal late Early Permian regression, larger morphologies, represented by D. brownsvillensis, D. vastus, and A. abruptus, dominate midcontinent crinoid assemblages; smaller offshore species had been lost, thus increasing body size for the clade as a whole.

Thus, it appears that the same parameters which controlled morphological expression at the fifth - order level (ecophenotypic variation) may also have acted at the second - order level (phylogenetic trend). The interrelationship between sub-cycle and super-cycle sea - level and metabolic viability is paramount to understanding potential morphologies for this clade. However, these factors may not have ultimately influenced clade diversity.

It has often been assumed that the intensively studied dinosaur faunal assemblages of western North America and the Gobi Desert of Mongolia and China represent “typical” Late Cretaceous terrestrial vertebrate communities. This assumption has led to a paleoecological scenario in which a global ecological shift occurs from the dominance of high-browsing saurischian (i.e., sauropod) to low-browsing ornithischian (i.e., iguanodontian, marginocephalian, ankylosaurian) herbivore communities. Furthermore, the assumption that the Asiamerican dinosaur faunas are communities “typical” of the Late Cretaceous has forced the conclusion that the sauropod-dominated Argentine population must have been an isolated relict ecosystem of primitive taxa (i.e., titanosaurid sauropods, abelisaurid ceratosaurs). Recent discoveries and reinterpretations of other Late Cretaceous assemblages, however, seriously challenge these assumptions.

Paleogeography and paleobiogeography have demonstrated that terrestrial landmasses became progressively fractionated from the Late Jurassic (Kimmeridgian-Tithonian) to the Late Cretaceous (Campanian), owing to continental drift and the development of large epicontinental seas (the Western Interior Seaway, the Turgai Sea, etc.). The Maastrichtian regressions resulted in the reestablishment of land connection between long isolated regions (for example, western and eastern North America). These geographic changes are reflected in changes in the dinosaurian faunas. These assemblages were rather cosmopolitan in the Late Jurassic (Morrison, Tendaguru, and Upper Shaximiao Formations) but became more provincialized throughout the Cretaceous.

Cluster analysis of presence/absence data for the theropod, sauropod, and ornithischian clades indicates that previous assumptions for Late Cretaceous dinosaurian paleoecology are largely in error. These analyses instead suggest that sauropod lineages remained a major faunal component in both Laurasia (Europe, Asia) and Gondwana (South America, Africa, India, and Australia). Only the pre-Maastrichtian Senonian deposits of North America were lacking sauropodomorphs. Furthermore, the abelisaurid/titanosaurid fauna of Argentina is, in fact, probably more typical of Late Cretaceous dinosaurian communities. Rather, it is the coelurosaurian/ornithischian communities of Asiamerica (and particularly North America) that are composed primarily of dinosaurs of small geographic distribution. Thus, the Judithian, Edmontonian, and Lancian faunas, rather than being typical of the Late Cretaceous, most likely represent an isolated island-continent terrestrial vertebrate population, perhaps analogous to the extremely isolated vertebrate communities of Tertiary South America. Furthermore, the shift from high-browsing to low-browsing herbivore “dynasties” more likely represents a local event in Senonian North America and does not represent a global paleoecological transformation of Late Cretaceous dinosaur community structure.

Planktic foraminiferal species are generally assigned to higher taxa on the basis of shared morphologic characters and stratigraphic age. These assignments are usually justified on the basis of apparent phyletic relationships. Extant species assigned to the same genera usually exhibit similar trophic and reproductive behavior and are associated with similar watermasses. Paleogeographic and stable isotopic data suggest that coeval fossil species also generally exhibit similar paleoecologic and paleoceanographic associations within well-constrained genera.

Despite shared morphologic characters and stratigraphic and paleoenvironmental associations, many higher taxa of planktic foraminifera are not believed to be monophyletic. Many superspecific taxa are widely accepted as paraphyletic (i.e. Guembelitria, Heterohelix). Such paraphyly has commonly resulted from maintaining a different generic or familial name for descendant species that diverge strongly from their ancestral bauplan. Additionally, some higher taxa appear to be polyphyletic (i.e. Eoglobigerinidae, Globorotalia).

As presently defined, superspecific taxa–commonly paraphyletic–can generally be used to examine relative radiation and extinction rates within and between different planktic foraminiferal adaptive zones. For example, analysis of Paleocene genera demonstrates rapid earliest Paleocene origination and radiation of sea-surface-dwelling and deeper-dwelling biserial and trochospiral genera. This earliest Paleocene radiation is quickly followed by disappearance of these surface-dwelling genera and some deeper-dwelling genera, in turn followed by major radiation within new surface-dwelling trochospiral genera in the mid and Late Paleocene. Such analysis documents the relative diversity and succession of major adaptive groups, regardless of their phylogenetic relationships.

The phyletic status of existing superspecific taxa does not preclude macroevolutionary study of monophyletic groups—or require that presently paraphyletic taxa be subsumed into larger monophyletic taxa. It simply requires that study of monophyletic groups be explicitly based on cladograms or phylogenetic trees. Such studies can address topics of clear macroevolutionary interest, including (i) the relative diversity and longevity of different monophyletic groups and (ii) general patterns of origination and extinction within clades. Additionally, while phylogenetic analysis is not necessary to determine patterns of succession and diversity of within and between adaptive groups, it can amplify our understanding of such patterns. For example, the earliest Paleocene appears to be marked by extremely rapid radiation within two monophyletic groups. The first reaches peak diversity within the earliest Paleocene and dominates earliest Paleocene planktic foraminiferal assemblages, but decreases radically in diversity and abundance within the Early Paleocene. The second continues to diversify throughout the Paleocene and dominates mid and Late Paleocene faunas. Consideration of phylogenetic and paleoecologic relationships within and between both monophyletic groups clearly reveals convergent evolution of deep and surface-dwelling morphotypes, and of biserial and trochospiral forms.

The Bembridge Limestone Formation (BLF), Late Eocene of Headon Hill, Isle of Wight, England, contains a diverse array of mammals (around 50 spp.) distributed through 10 levels. Its lower part (“lower fauna”) marks the appearance of a significant number of species, genera and one family unknown from earlier English Late Eocene strata. Towards the top of the BLF there is a reversion to faunas (“upper fauna”) more typical of the underlying Headon Hill Formation. This represents their last appearance in England. The succeeding Bembridge Marls Member fauna is similar to that in the lower part of the BLF. These changes are provincial in scale and may be climate induced (reflecting a slight warming followed by terminal Eocene cooling). Superimposed on these changes are smaller-scale more frequent fluctuations linked to alternating marl and black mud lithologies which may represent local habitat changes. In order to obtain overall understanding of the environment of deposition and taphonomic bias influencing these mammalian assemblages an integrated multidisciplinary study is being undertaken.

Plant macrofossils are unfortunately extremely rare in this sequence. Those few which are present typify the fresh-water marsh vegetation widespread in the Late Eocene/Early Oligocene of England. In contrast mammalian faunas indicate more wooded conditions. Seeds like those of the modern free-floating fresh-water plant Stratiotes occur in three levels. However, they are poorly-preserved. The chemical composition of the seed coat as revealed by flash pyrolysis gas chromatography indicates a very simple polyphenol macromolecule probably resulting from transformations of more complex polyphenols in well-preserved Stratiotes seeds.

Determinable palynomorphs are very rare and largely restricted to the part of the sequence which contains the “upper fauna”. They suggest a tranquil fresh-water depositional setting as do several molluscs and charophytes. Palynomorphs also include fungal remains, fern spores and a few tree pollen, the latter possibly from regional vegetation. However, the bulk of the palynological organic matter consists of brown structureless organic matter (SOM), resin-like particles and “platy kerogen”. In the lower beds, pale shelly muds with potamidids and corbiculids lack mammals and contain palynological organic matter dominated by resin-like particles and with abundant pyrite. These beds probably reflect brackish influence, the loss of which largely coincides with the reappearance of abundant mammals (“lower fauna”), occurrence of Stratiotes and of charophytes. Resin-like particles remain dominant in the palynological organic matter. “Platy kerogen” dominates three units including that containing the first occurrence of the “upper fauna”. Subsequently resin-like particles again dominate. Brown SOM is scattered throughout but is well represented in two units one of which contains “lower fauna” the other “upper fauna”.

Variations in palynological organic matter are reflected in the chemical composition of residues studied. Results from five black muds show that samples which mainly contain resin-like particles are dominated by n-alkanes and n-alk-1-enes in their pyrolysates. However, there is no indication of known resin chemical signatures. This indicates that the organic matter in these residues is mainly derived from cuticles (cutan) and/or cell wall remains (algaenan) of fresh-water algae. Samples containing “platy kerogen” and brown SOM are dominated by aromatics and phenols in their pyrolysates indicating an origin from woody materials. Work in progress on stable isotope analyses of the residues may further clarify the nature of the organic input.

Geological and paleontological data derived from the Upper Cretaceous Two Medicine Formation of Montana indicates that at least some dinosaur species exhibited complex social behaviors comparable to many living birds. Two species of duck-billed dinosaurs, a hypsilophodontid and a troodontid, nested in colonies and attended their respective young. Duckbilled dinosaurs had altricial young, whereas the hypsilophodontid and troodontid had precocial young. Morphological evidence indicates that several of the cranial elements of the nestling duckbills experienced retarded development, and a retention of juvenile features. Following their respective nesting periods duck-billed and horned dinosaurs aggregated into large herds, and apparently migrated seasonally. Cranial ornamentations possessed by duck-billed and horned dinosaurs were most likely used for sexual display and mate recognition.

Osteohistological data indicates that the duck-billed dinosaurs hatched from their eggs at .50 to .75 meters in length, and exited their nests at 1.5 to 2 meters in length, at an age of about one month. These dinosaurs reached 3 to 4 meters in length their first year, and 7 to 8 meters in length after about 5 years. Growth and metabolic rates decreased substantially upon reaching adult size.

The names proposed world-wide for Devonian bryozoans have been evaluated with respect to replaced names, synonyms, and nomina dubia [Horowitz and Pachut (1993), Journal of Paleontology, in press]. The resulting list contains 1738 specific names assigned to 199 genera in 45 families. Approximately 75% of Devonian bryozoan species are reported from a single stage. Not more than 10%, and usually 4–6%, of the species reported in any Devonian stage are also reported in the succeeding stage.

The largest decrease in observed bryozoan diversity occurs between the Givetian and Frasnian stages, reducing the number of species by 77%, genera by 64%, and families by 42%. These values are less than those reported for the range-through method for the entire fauna of the Permian mass extinction (Raup, 1979) but larger than percentage extinctions (presumably based on range-though data) for four other Phanerozoic mass extinctions tabulated by Valentine and Walker (1987).

The range-through method dampens the observed differences in taxonomic diversity among Devonian stages at all taxonomic levels. The range-through number of species/stage is based upon both direct applications of the range-through method and on the assignment of ranges known only to early, middle and late Devonian to include appropriate Devonian stages. Generic and familial diversity increases monotonically from Lochkovian through Givetian stages. Thereafter (Givetian to Frasnian), range-through values for specific (69%), generic (31%), and familial diversity (10%) decrease. Specific and familial decreases across the Givetian-Frasnian boundary are comparable to those reported for non-Permian mass extinctions by Valentine and Walker, but the generic decrease is not as great. These results are consistent with Valentine and Walker's random mass extinction model.

Observed bryozoan diversity across the Frasnian-Famennian boundary increases while values calculated using the range-through method decrease by approximately 5–15%. This does not suggest a major bryozoan extinction event. Conversely, the decrease in bryozoan diversity across the Givetian-Frasnian interval is similar to an important Devonian extinction among rugose corals. The reason(s) for these extinctions is not yet clear. With respect to Devonian bryozoans, our inadequate understanding of the cause(s) of mass extinctions and the relatively coarse resolution of the stadial timescale does not permit differentiating between gradual or catastrophic scenarios.

In recent years it has been recognised as a result of careful field work that there are a series of extinction events affecting goniatites and clymenids during the Devonian and early Carboniferous which can be confirmed in many parts of the world. Many have been given names, such as the Daleje, Chotec, Kacák, Pumilio, Taghanic, Kellwasser, Nehden, Condroz, Annulata, Hangenberg and Alum Shale Events. The Taghanic Event, which falls within the Givetian stage, is a major extinction event, as is the Upper Kellwasser Event at the end of the Frasnian and the Hangenberg Event near the end of the Devonian. At major events many familial and generic taxa are lost and few stocks, often of a particular type, survive; at smaller events, lower taxon levels are affected. The events are usually associated with sedimentary perturbations of some sort. These are usually linked with transgression, or regressive/transgressive couplets, and frequently with anoxia or hypoxic conditions; it has given emphasis to the concept of the ammonoid record as a hioseismograph of environmental events. Where documented in detail a gradual decline before the event is noticeable, and although this may appear stepped on diagrams, this results from the time-blocks used in analysis. Probably gradual extinction events occurred at Milankovitch band interval culminations. There is usually a trauma period of very low diversity, but not necessarily of abundance. Subsequent innovation and diversity is gradual. There is no evidence for sudden events such as might be caused by bolides or large meteorites, however much they might be expected.

A programme of research has studied these events in Europe, North America, North Africa and Western Australia, that is, on separate continents where sealevel changes can be documented by movements over stable shelf or cratonic areas. This has suggested that many are linked with eustatic events. The association with hypoxia is not universal although that is common in the eastern North America-Europe-North Africa area, then closely juxtaposed after the initiation of the docking of Gondwanaland against Laurussia. Comparisons of the Australian sealevel curves with those of North America and other areas suggest a correlation of pulses, especially for the Frasnian. But anoxic events have not been located at the Kellwasser and Hangenberg events in Western Australia, for example, to match those of other areas.

Since there are at least ten of these events, not all of the same power, in the interval from the late Lower Devonian to the basal Carboniferous, and since only two of them closely conform to stage boundaries (end Frasnian and end Famennian) it is misleading to plot these as stage or series blocks and to suggest there are extinctions at stage boundaries. Only in two cases (Upper Kellwasser and Hangenberg) would this be approximately true, but the staged decline at both would make even those misleading.

It is too early to speculate whether the events are periodic, or result from episodic culminations of different orbitally forced periodicities. However, many successions show small-scale rhythmic repetitions of facies which, when well developed, are the hallmark of some events. This might suggest a climatic control. The Taghanic Event, however, seems well correlated with the Taghanic Onlap (formerly known as the basal Upper Devonian transgression) suggesting a (plate) tectonic cause. It is important as a next stage to document the paleoecological changes of other groups over these events; already it is clear that other invertebrate groups are significantly affected by some. Precise documentation of tectonic events is also needed in the search for a cause.

Despite suggestions to the contrary by Norman Newell, in 1971, the presence of in-place, interlocking framework remains primary among the list of criteria used to recognize “true reefs” in the rock record. This is a logical outgrowth of observations made in modern systems, emphasizing 1) high carbonate-production rates of modern corals, 2) their commonly upright and interlocking architecture, and 3) the abundance and diversity of closely packed organisms on the surface of many modern reefs.

Applying a framework-dominated model to ancient reefs, however, has led to repeated frustration and the assumption that the problem is by and large related to the changing nature of reefs through time. Our present attempt to apply uniformitarianism to modern reefs and their ancient counterparts was perhaps best summarized by H. A. Lowenstam, “The present is the key to the Pleistocene… perhaps”.

A growing data base from cores through modern reefs implies that much of the problem is related to real differences between what we think constitutes the interior of modern reefs and what is really there. Recognizable coral generally constitutes less than 30% of the reef fabric, based on examination of over 50 cores from a variety of reef types throughout the eastern Caribbean region. Volumetrically, loose sediment and void space comprise a significantly higher portion of the reef interior. Furthermore, obviously in-place and interlocking “framework” is conspicuously absent. Branching Acropora palmata is invariably found in a variety of orientations, implying largely detrital emplacement rather than the preservation of intact and undisturbed colonies. Head corals are generally separated by intervals of detritus or open cavities, rather than sitting atop older colonies. Where rigidity of the reef fabric can be observed, it is almost always a function of secondary encrustation by coralline algae and/or post-depositional marine cementation.

The patterns seen in cores are supported by previous budget calculations of carbonate cycling in modern reefs around St. Croix. Bioerosion reduces original carbonate material to sediment, leaving recognizable coral to represent only a small part of the total reef volume. While still a significant component of the total reef fabric, few of the recognizable corals are bound together, and it is difficult to clearly demonstrate that the samples were recovered from life position (although some probably were). At Salt River, recovery was very low, and corals have been demonstrably moved from their original sites of growth.

Effective modeling of ancient reefs must take into account the importance of secondary processes that reduce and redistribute the original carbonate material produced by corals. Combined with physical reworking, cementation and encrustation, these destructive processes result in a deposit that resembles more a pile of reef debris than the coherent assemblage of in-place, interlocking framework usually conjured up to represent the modern-reef interior. While still of great importance, constructional processes that are so evident on the reef surface must be viewed within the context of other physical, chemical and biological processes that are reflected in the growing body of core data from modern reefs in the western Atlantic and throughout the world.

The Lower Oxford Clay, a marine formation of Middle Jurassic (Callovian) age exposed in central and southern England, merits the attention of paleontologists and geochemists for several reasons. It was the subject of a classic of biostratigraphic and evolutionary paleontology by Brinkmann on the ammonites; sexual dimorphism and bioprovinciality in the same group has since been intensively studied by Callomon and others. Its exploitation by the brick industry has enabled the assembly of one of the most extensive collections of marine vertebrates by the Leeds brothers and later workers; these include the world's largest ever fish, and superbly preserved ichthyosaurs, plesiosaurs and crocodiles now dispersed to museums throughout Europe and beyond. Dinosaurs, while rare, are also diverse. The benthic fauna is dominated by abundant but not diverse molluscs, believed tolerant of soupy bottom conditions and periodic dysoxia. Coccoliths and dinoflagellates represent the phytoplankton. Aragonite, calcite and phosphate biominerals are excellently preserved. In our main study area burial did not exceed 500m.; organic matter is immature. Early diagenesis resulted in the formation of carbonate concretions that preserve original sediment fabrics elsewhere destroyed by compaction; later diagenesis brought about further mineralogical changes.

Work since the 1970's has resulted in much improved understanding of the Lower Oxford Clay biota and its trophic relationships. It is useful to compare it to the more calcareous Middle and Upper Oxford Clay. The biostratigraphy is extremely well-known. The well-preserved fossils invite microstructural and geochemical studies. Economic concerns add impetus to the study of actual or potential hydrocarbon source rocks. Yet the Lower Oxford Clay is full of enigmas and questions still. It looks quiet-water but has many diastems, not all recognizable by classic criteria like shell beds. The fossil preservation might imply a high sediment delivery rate, but the sediment accumulation rate is low. It is organic-rich, but not anoxic. Where did the enigmatic ‘pendent’ bivalves live? Whence the nutrients to support the rich biota? To what extent do organic compounds survive from the primary producers, or does heterotrophic reworking dominate? Can we refine or quantify trophic relationships? We should also be able to use our ‘laboratory’ for experiments of wider significance for paleotemperatures or paleo-CO2 levels.

In the Oxford Clay group of papers we attempt to summarize where traditional paleoecological analysis has led us to so far, and to show how the new approaches made possible by advances in isotopic and biomolecular paleontology can revise and refine our ideas, solve old problems and, no doubt, raise new ones. We believe our collaborative approach has much to offer for paleontologists and geochemists, as also exemplified by the other contributions to the symposium.

Whereas many studies have examined the performance of various character-data sets in phylogenetic analysis, little work has been done on the effect that various classes of taxa have on phylogenetic reconstruction. In particular, the “fossil versus living taxa” debate has concentrated mainly on the effects of fossils in reconstructing vertebrate and plant relationships. While this work has contributed to the understanding of the role that fossils play in systematics, a computer model clarifies the relationship among the main determinants of the fossil-taxa problem. In addition, simulations of phylogenies over a wide spectrum of evolutionary rates clarify the relative efficiencies of various tree-estimation procedures.

In this study, computer generated phylogenies were used to examine the relationship between the temporal position and completeness of additional taxa in a phylogenetic analysis and the rate of evolution or, equivalently, the temporal scope of the phylogenetic problem. In the simulations, four fossil taxa of varying temporal position and completeness were added to an analysis that included four living taxa. Additional taxa varied in completeness (25%, 50%, 75%, and 100% completeness) and in temporal position (0%, 33%, 66%, and 100% of the distance from the ancestor to the living time plane). Fifty trees were generated each for low, low intermediate, high intermediate, and high rates of evolution or temporal scope. Because additional taxa that are 100% complete and 100% of the distance to the living time plane are equivalent to the addition of living taxa, this study directly compares the effects of addition of living versus fossil taxa in phylogenetic analysis.

The importance of fossil taxa varied depending on their completeness and temporal position and on the rate of evolution under which the phylogeny was generated. In general, high completeness and temporal position near the ancestor of a clade improved phylogenetic resolution as measured by the percentage of the tree-length distribution that contains the real tree. Furthermore, the conditions of completeness and temporal position under which fossil taxa improved phylogenetic resolution over living taxa became less restrictive as the rate of evolution or the temporal scope of the tree increased.