NAPC 2001

HAGADORN, James W., and Kenneth H. Nealson, Div. of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA

X-radiographic computed tomography (CT) is a nondestructive technique for examining the 3-D distribution of x-ray attenuation within objects. CT data consists of a series of cross-sectional attenuation plots, or slices, through a sample. By isolating areas of uniform attenuation within each slice and stacking slices together, an isopycnal volume is created. Where attenuation corresponds to paleobiologically-related heterogeneities, isopycnal volumes of matrix-encased fossils can be created without physically removing fossils from samples.

  Although widely used in vertebrate paleontology, CT has not been used to study invertebrate fossils which are soft-bodied, encased in matrix, or preserved as 3-D casts/molds—like many Precambrian fossils. Our work suggests that CT can yield reasonable 3-D models of such fossils. For example, analyses of the Neoproterozoic disc-shaped fossil Aspidella reveals stalk-like structures buried within the rock, immediately overlying bed sole impressions of putative discoidal holdfasts. In larger samples (>10 cm³) analyzed at 250 mm slice thicknesses, sufficient attenuation contrast exists between the fossil molds and surrounding matrix to allow construction of isopycnal volumes of these stalk-like structures. Similarly, isopycnal volumes of silicified cloudiniids from Mexico and Nevada (analyzed at 8 mm slice thicknesses) are comparable to morphologic features identified in previous studies. Although volume-based morphology can be discerned in a variety of other phosphatized, pyritized, clay-replaced, calcified, agglutinated, and silicified Phanerozoic microfossils, we have not yet resolved attenuation differences sufficient for visualizing clay-replaced fossils within shales or aragonitic/calcitic/dolomitic fossils within carbonates. As a first step toward imaging Proterozoic acritarchs and filaments, analyses of silicified Phanerozoic microbiotas >25 mm in diameter have yielded isopycnal volumes comparable to morphologic features identified through conventional petrographic techniques.

HALLOCK, Pamela, Dana E. Williams, and Heidi Crevison, College of Marine Science, University of South Florida, St. Petersburg, FL, USA

Coral-reef communities are threatened worldwide by stresses ranging from localized impacts to global change. Resource managers urgently need indicators of the biological condition of reef environments that can relate data acquired through remote-sensing, water quality and benthic-community monitoring to stress responses in reef organisms? Reef-dwelling foraminifera, especially taxa that host algal symbionts, show great potential for use as indicators of reef vitality: (a) Foraminifera are widely used as environmental and paleoenvironmental indicators. (b) Zooxanthellate corals and foraminifera with algal symbionts have similar environmental requirements. (c) A readily identifiable and abundant genus, Amphistegina, exhibits similar stress responses to those found in corals. (d) The relatively short life spans of foraminifera as compared with colonial corals facilitates differentiation between long-term decline and episodic stress events. (e) Foraminifers are relatively small and abundant, permitting statistically-significant sample sizes to be collected quickly and relatively inexpensively. (f) Collection of foraminifera has minimal impact on reef resources.

The "FoRAM" (Foraminifers in Reef Assessment Monitoring) protocol is the synthesis of 30 years of research on reef sediments and reef-dwelling larger foraminifera. The three-tiered procedure includes sediment-constituent analysis, which can address questions of historical change and reference-site suitability; analysis of live foraminiferal assemblages to indicate the suitability of sites of concern for organisms with algal symbionts; and analysis of Amphistegina populations for evidence of specific stressors to which these foraminifera respond similarly to corals. Future research to identify and quantify physiological and molecular responses to specific stressors will further facilitate use of larger foraminifers as bioassay organisms in reef research.

HANCOX, P. John, Dept. of Geology, University of the Witwatersrand, Johannesburg, South Africa; and Bruce S. Rubidge, Sean P. Modesto, and Alain J. Renaut, Bernard Price Institute for Palaeontological Research, University of the Witwatersrand, Johannesburg, South Africa

Dicynodonts are a clade of herbivorous non-mammalian synapsids that are important components of Late Paleozoic and Early Mesozoic terrestrial faunas. The systematics and phylogenetics of the Permian forms is now well established, however that of their Triassic counterparts is still poorly understood, with cladograms to date being only of the hand crafted type. Here we present the first computer generated (PAUP) phylogenetic study of the Triassic dicynodonts, based mainly on first hand observation of the type material from several countries. The scope for long distance correlation of nonmarine, dicynodont bearing strata, has long been recognized, and dicynodonts have previously been used to define various land vertebrate ages (LVAs), chronofaunas, land-vertebrate faunas, empires, intervals, biochrons, faunal epochs and land-vertebrate faunachrons (LVFs). This study is therefore vital, not only to our understanding of the systematics of the Triassic dicynodonts, but also for studies on the biogeography and biochronology of these forms.

HANGER, Rex A., Dept. of Geography and Geology, University of Wisconsin-Whitewater, Whitewater, WI, USA

During the Late Paleozoic, faunas of the west coast of Pangea plus the offshore island arc terranes, were dominated by brachiopods, corals, fusulinids, bryozoans and mollusks. Outcropping today in western North America, the presence of both Asiatic and endemic taxa among the terrane faunas led to far-travelled, "exotic" interpretations for the arcs themselves, in accord with tectonic models incorporating west-directed subduction throughout the Late Paleozoic. Such models allowed arc terranes to exist at extreme (1000s of km) distances outboard within Panthalassa. Recent dating and provenance analysis of detrital zircons (Soreghan and Gehrels, 2000) reveal many patterns, most of which link western North American arc terranes to sources on the Pangean continental margin. These data constrain original arc paleogeographic positions as proximal to the margin, favoring tectonic models that incorporate east-directed subduction, irreconcilable to the original interpretations of paleobiogeographic data.

Previous "exotic" interpretations were based largely on the presence of a single, or very few, "key" taxa. Using databases of whole faunas of brachiopods and bryozoans, plus supplemental data from corals and fusulinids, probabilistic similarity analyses, testing against a null model of random distribution in space, reveal new paleobiogeographic patterns. Although some significant relationships exist with Asiatic faunas, the preponderance of statistically significant arc terrane affinities lie with the western Pangean continental margin. Rather than being antagonists, paleobiogeography and detrital zircon provenance are reciprocal illuminators, both indicating a proximal location for most western North American island arc terranes during the Late Paleozoic.

HANKINS, Karina G., and David J. Bottjer, Dept. of Earth Sciences, University of Southern California, Los Angeles, CA, USA

The mass extinction in the marine realm at the end of the Triassic is considered one of the five biggest extinction events of the Phanerozoic, but is not well studied due to a lack of good sections spanning the boundary. Even less is known about the dynamics of the recovery interval that followed. One of the most complete and fossiliferous marine sequences of Triassic-Jurassic strata is located at New York Canyon in the Gabbs Valley Range of west-central Nevada, which houses the proposed global stratotype section for this boundary. This area has been the focus of extensive biostratigraphic studies and facies change analyses (Taylor et al., 1983; Hallam and Wignall 2000), and the paleoecology of Upper Triassic strata has been assessed by Laws (1982). However, the ecological changes that took place across the boundary have not received detailed analyses.

This study represents a first attempt at analyzing the nature of paleoecological changes across the boundary and into the recovery interval in the New York Canyon area, with changes in paleocommunity composition and structure as the primary focus. Preliminary observations of the Lower Jurassic Sunrise Formation reveal that a low-diversity epifauna of relatively small bivalves and gastropods exists in the shallower-water facies, while brachiopods and ammonites become increasingly abundant in the offshore facies. Intervals of intense bioturbation occur within Lower Jurassic strata and large, resistant, primarily horizontal burrows appear in the Sinemurian New York Canyon Member. However, the diversity of trace fossils throughout these beds remains low. These observations indicate that facies changes play an important role in the record of the recovery from the end-Triassic extinction at New York Canyon, and are consistent with a prolonged recovery from this crisis as described in Hallam (1996). Further investigation may shed light on the possible causes of the extinction itself, and the reasons for a slow recovery.

HANNIBAL, Joseph T., The Cleveland Museum of Natural History, Cleveland, OH, USA; and H. Gregory McDonald, Geologic Resources Division, National Park Service, Denver, CO, USA

Crayfish from the Pliocene of the Idaho/Oregon region were first described by Cope and later reevaluated by carcinologist Mary Rathbun. Examination and preparation of new three-dimensionally preserved material and museum specimens of Pacifastacus chenoderma (Cope) reveal a number of undescribed characters confirming Hobb's placement of the species in the genus Pacifastacus as well as Rathbun's observation that the species is morphologically similar to extant crayfish of the region, including P. connectens.

Preservation of material, with the exception of the carapace posterior, can be very good, although there is no single complete specimen. The epistome, mandible, renal aperture, and other parts seldom if ever seen in fossil crayfish are preserved. Well-preserved cuticle exhibits layering. Some cuticle is crazed, some is broken into bits, and some is crushed to various degrees.

The species is robust, and has a spiny, acute rostrum and pointed pleurites. This armament may be a protective adaptation to Pliocene predators such as the large extinct species of pike-minnow Ptychocheilus found in Lake Idaho sediments. An extant species of Ptychocheilus present in the Snake River feeds on crayfish. At least one fossil crayfish has a mark that may be attributable to a vertebrate bite.

Large crayfish gastroliths (up to 13 mm in diameter) have been collected from the Pliocene of this region since the time of Cope and Marsh. The size of the gastroliths is what would be expected for the size of the body fossils. Thin sections show that these gastroliths are layered much like those of modern crayfish, confirming their identification. Thus, these gastroliths do document the existence of crayfish at localities where body fossils are lacking. Gastroliths are occasionally found in pairs, which may indicate that they came from a single crayfish.

HANSON, Dale A., Dept. of Geological Sciences, University of Oregon, Eugene, OR, USA; and Theodore J. Fremd, John Day Fossil Beds National Monument, Kimberly, OR, USA

Two major vertebrate fossil assemblages occur in the Camp Creek area (near Logan Butte, Oregon), separated by the "Picture Gorge Ignimbrite" of the John Day Formation. Long characterized as faunally identical to the well-known eastern basin assemblages, recent stratigraphically analyzed collections have revealed a similar, but significantly different fauna. The lower assemblage is characterized by agriochoerids (32% of identified specimens), tragulids (24%), oreodonts (8%), equids (6%), and numerous species of canids (4%) and nimravids (2%). It also produced the only known examples of the marsupial Herpetotherium merriami, the ursoid Parictis primaevus, the enigmatic Allocyon loganensis, and small nimravids. The Turtle Cove fauna, in contrast, consists of 35% tragulids, 25% oreodonts, and 6% rhinocerotids, with agriochoeres representing less than 2% of the faunas. Notable by their absence are the diminutive nimravids and Allocyon. The upper assemblage at Camp Creek is characterized by several families of rodents, making up 59% of identified specimens, the exclusive occurrence of the large oreodont Merycochoerus, and a near absence of other artiodactyls. The observed disparities between the lower assemblage and the Turtle Cove fauna, previously thought to be temporal, are probably due to local paleoenvironmental factors including proximity to flowing water and elevational effects. Sedimentological evidence supports this conjecture. The southern basin is characterized by numerous channel deposits, almost absent from the eastern basin. These channel deposits range from clayey to sandy lithologies, and are typically incised one to three meters into the underlying sediments. Newly sampled tuffs from the southern basin, correlated with those from Turtle Cove, allow us to confirm that these are, in fact, isochronous assemblages, providing an unusual opportunity to compare temporally equivalent but ecologically different associations.

HARRIES, Peter J., Dept. of Geology, University of South Florida, Tampa, FL, USA

During the past two centuries, mass extinction events have played an important role in the development of paleontologic thought and theory surrounding a spectrum of issues. Although these earlier studies identified numerous extinction horizons in the geologic record, most of the data collected were not highly resolved from a stratigraphic standpoint and, therefore, many of these data sets were of insufficient resolution to answer important questions related to mass extinction dynamics. However, primarily during the past two decades, there has been a large effort devoted to discerning the details of mass extinction events#&151;both in terms of extinction and repopulation—with the ultimate goal of better understanding causation as well as ecologic and evolutionary changes associated with these events. This research, which has spanned numerous biotic crises of wide ranging magnitudes and geography, has created a record of faunal ranges that is considerably more resolved than those that previously were available. In virtually all cases, these better-resolved data have revealed that mass extinction events are far more complex than previously thought. Most mass extinction events appear to be have occurred in a step-wise fashion, and the presence of this pattern suggests that these events represent complex biotic responses to environmental and ecologic perturbations. Although some of these patterns may reflect sampling and preservational biases, in the cases where statistical tests have been applied to test the robustness of the range data, they have shown that the patterns are not artifacts. Despite the increased resolution and insight that has been gained, there are, however, limits to the resolution that can be obtained and hence the questions that can be answered. These limits ultimately reflect the depositional, stratigraphic, and preservational fidelity of the record and act as the final control on whether data of sufficient detail can ever be collected to answer certain questions.

HARWOOD, David M., Dept. of Geosciences, University of Nebraska-Lincoln, Lincoln, NE, USA; and Vladimir A. Nikolaev, Komarov Botanical Institute, St. Petersburg, Russia

Silicified scales tentatively attributed to the Chrysophyceae occur in Upper Proterozoic chert from Alaska. The oldest Xanthophyceae are Carboniferous in age. Diatom assemblages appeared by the Late-Early Cretaceous and began radiating toward diverse Late Cretaceous floras, although a significant turnover occurred in the mid-Cretaceous. Early diatoms had a long history of silicified resting stages and non-silicified to weakly-silicified vegetative cells, parallel to some modern Chrysophyceae and Xanthophyceae. One theory of diatom origin suggested a link between the diatom valves and siliceous scales of chrysophytes, yet these do not have a resting stage with paired valves, and they are haploid, not diploid as in the diatoms. The problem of ploidy was addressed by the suggestion that a diploid silicified cyst stage, like that of Parmales became the dominant phase in the diatom life cycle. We suggest a similar life-cycle shift, but features shared by Lower Cretaceous diatoms and some Xanthophyte orders focus our attention here. Features in common including diploidy, oil production, silica impregnation of the cell wall, silicified resting stages with paired valves, similar pigments, benthic habitat, cylindrical colonies, long pervalvar axes, overlapping valves and similar size. Lower Cretaceous diatoms from Antarctica and Australia offer a new framework to compare the morphology, ecology and life history of the Chromophyte algae. These oldest records of diatoms involved benthic filamentous colonies of long, cylindrical cells and heavily silicified resting spores, which radiated during the mid-Cretaceous into the planktic realm and a diversity of benthic substrates. This may have been stimulated by mid-Cretaceous transgression/regression cycles, which opened new niches and introduced taxa to changing environmental gradients of salinity, nutrients, etc. New diatom genera appear during the Late Cretaceous and Paleogene at a rate of ~1.6 genera/m.y. and disappear at a rate of ~1.3 genera/m.y.

HASIOTIS, Stephen T., Dept. of Earth Sciences, Indiana State University, Terre Haute, IN, USA

Alluvial, lacustrine, aeolian, and transitional-marine deposits of the Upper Jurassic Morrison Formation in the Rocky Mountain region contain varying degrees of hidden biodiversity representing terrestrial and freshwater ecosystems. The morphology, distribution, and lateral and vertical tiering of ichnofossils provide information on trophic interactions preserved by organism behavior, and ecological and climatic changes experienced during the deposition of the Morrison. The trace fossils in soil ecosystems represent ecological innovations in (1) food hoarding, (2) adaptations to disturbance from flooding and precipitation, (3) unpredictable hypercarbic and hypoxic conditions, and (4) subterranean reproductive strategies employing a holometabolous life cycle. The traces representing these ecological behaviors vary in abundance in paleosols, from isolated occurrences associated with pedogenic features to thousands of crosscutting traces that obliterate all bedding and pedogenic structures.

The Morrison ichnofossil record in immature to mature paleosols reveals that the major components of detritivore-based food webs and essential innovations for fossorial life in soil ecosystems were present. Ichnofossils represent community members of energy pathways and niches for detritivores (saprophagous, coprophagous, and necrophagous roles), herbivores, omnivores, and carnivores in the terrestrial ecosystems. Traces of permanent to transient soil-dwelling life styles illustrate adaptations to varying degrees of environmental disturbance, osmoregulation crises, and hypercarbic and hypoxic conditions. Food hoarding was incorporated into the subterranean reproductive strategies of several different groups of temporary and periodic soil-dwelling invertebrates. Co-evolved morphological, physiological, and behavioral adaptations to hypoxia and hypercarbia resulted from food stored with larvae and adults in belowground settings. Social behavior in insects and mammals was a solution to competition for resources and space in the soil ecosystem.

HASIOTIS, Stephen T., Dept. of Earth Sciences, Indiana State University, Terre Haute, IN, USA

The recognition and interpretation of complex ichnofossils, particularly in the Mesozoic, is a relatively recent phenomenon. Complex ichnofossils represent unique solutions through degrees of social cooperation to the perils of terrestrialism and fossorial life. The evolution of social cooperation and eusocial behavior (only in insects) is an innovation that has been evolved multiple times by different insects and mammals for performing chores and dealing with hazards associated with foraging for food, rearing the young, nest defense, burrow maintenance, and more, in terrestrial environments. These ichnofossils also preserve major innovations in soil ecosystems that include (1) food hoarding, (2) adaptations to disturbance from flooding and precipitation, (3) enduring unpredictable hypercarbic and hypoxic conditions, and (4) reproductive strategies by employing a subterranean life cycle.

Complex ichnofossils are highly variable in architecture and reflect the type of organism, the number of individuals per nest, the length of time the structure is used, and the degree of sociality. A pattern of interconnected galleries and chambers of varying length, width, height, and number usually distinguish complex traces. Insect societies, such as termites (Isoptera), ants (Hymenoptera), and the higher bees and wasps (Hymenoptera: Aculeata), show the greatest variability in trace fossil complexity-simple to extremely elaborate structures. Individuals cooperate to construct and maintain the nest, collect and grow food supplies, feed nest members, protect the nest from invaders, and care for the young. To a lesser extent, reptiles, therapsids, and mammals also exhibit these behaviors, which is also reflected in the complexity of the trace fossil. These organisms also maintain the nest temperature and humidity, as well as to avoid hypercarbic and hypoxic gas levels. Situations are resolved by individuals working together to maintain and alter the nest architecture to bring appropriate atmospheric and climatic conditions to the subterranean community.