NAPC 2001

Abstracts, He - Ho
(5/17/01)

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TAPHOFACIES ANALYSIS OF UPPER CARBONIFEROUS MICROFOSSILS (HUGHES CREEK SHALE, EAST-CENTRAL KANSAS)

HEATH, Winfield S., and Roger L. Kaesler, Dept. of Geology, University of Kansas, Lawrence, KS, USA

Taphofacies analysis has become a crucial tool in paleoenvironmental analysis, but microfossils have largely been overlooked in this field. To remedy this, we examined the Hughes Creek Shale Member of the Foraker Limestone (Upper Carboniferous) of the Midcontinent. We applied Brett and Baird's (1986) methods of taphofacies analysis to the study of both macro- and microfossils. Comparing the taphonomy of the ostracodes, fusulinids, and smaller foraminifera with that of the macroinvertebrates allowed us to define microtaphofacies that are correlative with those of the macrofossils.

We show that, with some limitations, microfossils lend themselves readily to taphofacies analysis. For example, reorientation cannot be considered because of the disruptive methods necessary to disaggregate shale samples. Interpretation of the biostratinomy of microfossils is further complicated by such diagenetic effects as chemical alteration and compaction. However, where macrofossils are absent or destroyed, as in cuttings from boreholes, microfossils may provide the only means of analyzing taphofacies.

We assessed fragmentation and disarticulation, both of which may have been partially introduced during disaggregation of the shales, as well as corrosion, epibiont activity, and pyritization. All types of damage except pyritization in the foraminifera were present in the samples studied. A system of ranks allowed us to compute factors indicating the extent of taphonomic alteration of the microfossils and to distinguish between relative amounts of biostratinomy and diagenesis. Results indicate similarity in taphonomy of foraminifera, ostracodes, and all organic shells combined; but significant differences occur between the relative amounts of biostratinomy and diagenesis in each of these groups.

CONODONT CLINES AND PUNCTUATED EVOLUTION AT PERMIAN SERIES BOUNDARIES

HENDERSON, Charles M., Dept. of Geology and Geophysics, University of Calgary, Calgary, AB, Canada; and Shilong Mei, Dept. of Geology and Geophysics, University of Calgary, Calgary, AB, Canada, and China University of Geosciences, Beijing, China

Recognition of geographic clines in Permian neogondolellids provides a new context in which to characterize the evolution of Permian conodonts. During the Kungurian and Guadalupian, a large cusp, low, narrow and frequently discrete posterior carinal denticles, low and discrete anterior blade denticles, and usually an elongate platform represent neogondolellids from higher latitudes such as the Sverdrup Basin. In contrast, a relatively small cusp, tightly spaced and relatively large posterior denticles, high and strongly fused anterior blade denticles, and a relatively short platform characterize neogondolellids from equatorial areas such as South China and West Texas. Neogondolellids from mid-latitudes such as the Phosphoria Basin are intermediate in morphology. Late Kungurian populations are represented by Mesogondolella idahoensis in cool-water faunas and M. siciliensis in warm-water faunas. Differences in the cusp, carina, and blade should be recognized at the subspecies level since gradational morphotypes suggest gene flow across the entire region. A punctuated evolutionary event occurs at the Kungurian-Roadian boundary with the introduction of the serrated Jinogondolella nankingensis. A cline develops in the Early Roadian from Jinogondolella nankingensis nankingensis (Ching) in equatorial areas to Jinogondolella nankingensis gracilis (Clark and Ethington) in mid to high latitudes. However, with continued climatic change and corresponding development of conodont provincialism this gene flow was cut off and evolution of these subpopulations proceeded along different paths. A series of Guadalupian Jinogondolella species developed in equatorial regions by phyletic gradualism. Another punctuated evolutionary event characterizes the Guadalupian-Lopingian boundary with the evolution of Clarkina. In the Sverdrup Basin the Jinogondolella lineage ends quickly because of cooling in northwest Pangea and the evolution of Mesogondolella proceeds along a very gradualistic path until the Permian-Triassic boundary when global warming allows an influx of new neogondolellids.

SAUKIID-DIKELOCEPHALID TRILOBITES AND THEIR IMPLICATIONS FOR LATE CAMBRIAN PALEOGEOGRAPHIC AND PALEOENVIRONMENTAL RECONSTRUCTIONS

HENDERSON, Wayne G., and Nigel C. Hughes, Dept. of Earth Sciences, University of California, Riverside, CA, USA

Genera assigned to the Saukiidae and the Dikelocephalidae have long been considered closely related. Among the Dikelocephalidae, a markedly expanded cephalic doublure is synapomorphic for dikelocephalids, and Saukiidae, as currently defined, is likely paraphyletic. Nevertheless, the saukiid cranidium has a distinct morphology and, while the Dikelocephalidae are exclusively Laurentian, trilobites with the saukiid glabellar morphotype occur globally in equatorial regions. This distribution is particularly surprising as Cambrian polymerid trilobites are generally considered to show high degrees of continental endemism, and saukiids are known for their preference for near shore habitats. Ulrich and Resser (1933) first described the Saukiidae in detail, erecting 104 species in five genera from the Upper Mississippi Valley. An additional 25 genera and 200 species of saukiids have since been described, occurring across equatorial core and outboard Gondwana, Laurentia, Siberia, and Kazakhstan, and they have been extensively used for biostratigraphic zonation. Saukiid species and genera have frequently been described as endemic to these regions even though there are few, if any, morphological features to distinguish them from species found on other paleocontinents. Accordingly, there is critical need to refine species concepts. We are: (1) evaluating character variation within large collections from single bedding planes to establish the bounds of intrapopulational variation, and (2) constructing a character matrix for phylogenetic analysis of all well-preserved saukiids based strictly on morphological criteria. Such analysis will point to the resolution of taxonomic relationships within these groups and provide the basis for evaluating Late Cambrian endemism and biogeographic links.

WITHIN-SPECIES ADAPTIVE RESPONSES TO MID-PLEISTOCENE CLIMATE CHANGE: ISOTOPE SCLEROCHRONOLOGICAL ANALYSES OF SUBTROPICAL NEOGASTROPODS OF FLORIDA

HERBERT, Gregory S., Dept. of Geology, University of California, Davis, CA, USA

A stable isotope sclerochronological analysis was carried out on Pleistocene fossil and Recent Urosalpinx perrugatus (Conrad), a predatory gastropod from the west coast of Florida, in order to understand the underlying developmental basis of evolutionary size decrease in this species in the context of Pleistocene climate change. Early Pleistocene shells attain 40 mm in shell length, whereas middle Pleistocene and Recent shells attain only 25 mm. Isotope profiles were generated for early Pleistocene (Bermont Fm., 1.6­1.1 Ma), middle Pleistocene (Fort Thompson Fm., 0.9­0.2 Ma), and modern shells. Living populations were also observed throughout the year to aid in the interpretation of periodicities in isotope profiles.

The results show that while there is no change in hatching season, annual growth rates, or season of growth cessation, total duration of shell growth shifted from two years in Bermont shells to one year in Fort Thompson and modern shells. The presence of a single size class in modern populations suggests a one-year life span in post-Bermont fossil and modern populations. Similar size decreases were found to occur within other neogastropod species with the same timing suggesting the possibility of direct adaptation to a common forcing mechanism operating across lineages.

The Bermont/Ft. Thompson boundary coincides with the mid-Pleistocene climate transition (~0.9 Ma), a period when glacial-interglacial cycles shifted from 41-kyr to 100-kyr cycles. The much larger ice sheets formed during the 100-kyr cycles would have resulted in dramatic increases in the frequency and severity of winter storms reaching the northern Gulf of Mexico and accompanying increases in juvenile mortality in nearshore marine organisms. Early maturation as an adaptive response would have allowed rapid population replacement under these conditions. This study illustrates the value of targeted sclerochronological analyses of life history evolution for understanding the biological effects of Pleistocene climate change.

CONIFER POLLEN CONES FROM THE EARLY TERTIARY OF BRITISH COLUMBIA, CANADA

HERNÁNDEZ-CASTILLO, Genaro R., and Ruth A. Stockey, Dept. of Biological Sciences, University of Alberta, Edmonton, AB, Canada

Large number of fossil conifers have been described from the Upper Cretaceous and Early Tertiary of North America. Most of these conifer species correspond to taxa within the Cupressaceae/Taxodiaceae. However, the internal anatomy of cones is only known for a few of these taxa. Two fossil pollen cones have been collected at the Late Eocene Appian Way Locality, just south of Shelter Point on the coast of Vancouver Island, British Columbia. The fossils are permineralized, and were studied using the cellulose acetate peel technique and Scanning Electron Microscopy. Cones are attached to stems that bear oppositely arranged leaves with a single vascular bundle and an adaxial resin canal. The cone axis bears decussately scale- like leaves that subtend and enclose the microsporophylls. Microsporophylls are peltate with upturned distal tips and a central resin canal. Three abaxial pollen sacs are born on each sporophyll. The walls of pollen sacs are composed of thick rectangular elongated cells, and contain abundant non-saccate, papillate pollen grains. These cones show closest similarities to those in the Cupressaceae/Taxodiaceae. Curved papillae on pollen grains, the opposite arrangement of scale leaves, and the number of pollen sacs per microsporophyll suggest affinities with the genus Metasequoia. These cones are associated with numerous taxodiaceous leaf and twig remains at the locality that show similar anatomical characters to those of pollen cones, and will be the subject of further study in the attempt to reconstruct this conifer as a whole plant.

THE FINAL EPISODE OF EARLY CAMBRIAN METAZOAN REEF-BUILDING IN WESTERN LAURENTIA: HIGH-DIVERSITY ARCHAEOCYATHAN-CALCIMICROBE REEFS IN THE UPPER HARKLESS FORMATION OF ESMERALDA COUNTY, NEVADA

HICKS, Melissa, and Stephen M. Rowland, University of Nevada, Las Vegas, NV, USA

Archaeocyathan-calcimicrobe reefs occurred globally in low-latitude settings in the Early Cambrian. In western Great Basin, Nevadella Zone (late Atdabanian to early Botomian) reefs are well known in the Campito and Poleta Formations. Previously unstudied reefs also occur in the overlying Bonnia-Olenellus Zone in the Harkless Formation. Here, we describe patch reefs in the upper Harkless Formation that are late Botomian or early Toyonian in age, approximately coeval with the well-studied reefs of the Forteau Formation of eastern Canada.

The patch reefs range in size from 1 m long and 0.5 m high to 15 m long and 1 m high. They were constructed in shallow water by a consortium of archaeocyaths and calcimicrobes (Renalcis), and they contain the remains of a diverse assemblage of organisms. Archaeocyaths comprise an estimated 50% or greater of the reefs by volume, apparently creating a rigid framework conducive for extensive lateral and vertical growth. Renalcis is found pervasively within the reefs, acting as a binding entity that added strength and stability to the archaeocyathan framework.

A surprising diversity of benthic and nektonic organisms occur within the framestones and surrounding packstones. Trilobites, which are the most abundant benthic organisms found, are commonly fragmented and have micritic envelopes. Echinoderm plates, ostracods, brachiopods, Salterella, Chancelloria, and (in one locality) corallomorphs are all found in varying quantities within and surrounding the reefs. Synsedimentary cementation and early lithification occurred in all reefs. This early lithification facilitated the formation of cryptic niches, thereby enhancing the diversity of reef dwellers.

These late Early Cambrian reefs represent the final stage of metazoan reef-building prior to the resurgence of microbialite reefs in the Middle and Late Cambrian. Our data suggest that the diversity of the reef ecosystems was at its Lower Cambrian peak just before metazoan reefs disappeared for approximately forty million years.

LATE CRETACEOUS LEAF COMPRESSIONS FROM SOUTHEAST MISSOURI

HILDERBRAND, John, and Bruce L. Stinchcomb, Dept. of Geology, St. Louis Community College at Florissant Valley, St. Louis, MO

Leaf-bearing Cretaceous clays are exposed in the northern part of the Gulf Embayment on Crowley's Ridge as well as in a structurally complex area to the north at Marble Hill, Bollinger County, Missouri. Angiosperm leaf compressions in brown clay are found near Ardeola Missouri on Crowley's Ridge which include the puzzling genus Banksia sp., as well as other genera which have related species in the overlying Eocene Wilcox Group. These plants are in the McNairy Formation of Maestrichtian age and represent some of the youngest angiosperm compressions found in the Gulf Series. A different flora is found in clays associated with a graben at Marble Hill, Mo., where representatives of the genus Ficus sp. and Magnolia sp. are suggestive of the earlier Tuscaloosa flora of E.W. Berry. Geologists in the 1940s, who discovered Cretaceous clays in the southeastern Ozarks suggested that some or all of them might be Lower Cretaceous in age. The angiosperm flora present in the Marble Hill area would negate against this, as angiosperms are rare in the Lower Cretaceous. These leaf-bearing clays may correlate with vertebrate bearing clays of the Chronister Site, seven kilometers to the Northwest. The exact age of the Chronister Site is unknown, however based upon recently found hadrosaur material is thought to be Campanian.

EVIDENCE FOR PREDATORY DRILLING IN LATE PALEOZOIC BRACHIOPODS AND BIVALVE MOLLUSKS FROM WEST TEXAS

HOFFMEISTER, Alan P., Michal Kowalewski, and Richard K. Bambach, Geological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA; and Tomasz K. Baumiller, Museum of Paleontology, University of Michigan, Ann Arbor, Michigan, USA

Bored invertebrates have been described from every period of the Paleozoic. Although many of these borings are non-predatory in nature, good evidence exists for the parasitic and/or predatory origin of mid-Paleozoic (especially Devonian) borings in pelmatozoans and brachiopods. There is, however, little information on the frequency and nature of Late Paleozoic drill holes. Silicified fossils bulk collected by G.A. Cooper from Permian strata in the Glass Mountains of West Texas provide an ideal opportunity to look for evidence of predatory drilling during this interval.

The collections contain numerous drilled brachiopods and bivalve mollusks. The drill holes are perpendicular to the shell, smooth sided, often beveled in a manner similar to drill holes produced by naticid gastropods today, and have other characteristics consistent with a predatory/parasitic origin. Among 3140 brachiopods examined, 58 specimens contain unquestionable drill holes (frequency of 1.8%) and 15 specimens questionable drill holes (frequency of 2.3%). The 654 bivalve mollusks examined included 23 specimens with unquestionable drill holes (frequency of 3.5%) and 5 specimens with questionable drill holes (frequency of 4.3%). Drilling intensity is significantly higher in bivalves than in brachiopods (Fisher's exact test, p=0.02). Drilled brachiopods occur throughout the section (Upper Pennsylvanian-Upper Permian), but drilling frequencies vary notably through time and among sampled facies.

This study confirms that drilling predators and/or parasites were present in the Late Paleozoic. However, drilling intensity at that time rarely exceeded 5%, and thus was much lower than the Late Mesozoic and Cenozoic intensities that typically exceeded 20%. The Late Paleozoic intensities are consistent with those for the rest of the Paleozoic and suggest that the intensity of drilling predation/parasitism in marine benthic ecosystems remained low throughout the Paleozoic and did not increase until some time in the Mesozoic.

BODYPLAN OF THE PROBLEMATIC METAZOAN MACHAERIDIA

HÖGSTRÖM, Anette, Dept. of Earth Sciences, University of California, Riverside, CA, USA

Enigmatic scleritome-bearing metazoans such as the Machaeridia constitute formidable challenges from several perspectives. All scleritomes suffer the same preservational problems in that they very easily disarticulate after the organism dies making isolated sclerites and sclerite fragments the most common form of preservation and a limiting factor when reconstructing morphology and anatomy of the organism.

Machaeridian scleritomes range from relatively straightforward types forming a dorsal cover to complex ones, more or less enveloping the entire animal. However, all scleritomes are composed of 2­4 longitudinal series of calcitic sclerites. The complex scleritome of lepidocoleid machaeridians closes and opens along the ventral side and also allows the animal to enroll spirally for protection, suggesting a segmented bodyplan, although not strictly metameric.

Epimorphic development of the machaeridian scleritome, with all sclerite segments present initially, is supported by the uniform appearance of ornamentation and growth lines, and the presence of occasional growth increments traceable between sclerites in articulated specimens. This is in contrast to the adding of sclerites through development in other scleritome-bearing taxa, as seems to be the case in coeloscleritophorans, but Halkieria does also exhibit shells growing by accretion.

The bodyplan of machaeridians does not agree with the concept of Ecdysozoa as a clade of moulting animals and thus rules out possible affinities with the arthropods. However, an inclusion within the Lophotrochozoa clade does not resolve the problem of machaeridian affinities to a higher degree, but tentatively places machaeridians as a stem group to the molluscs or the annelids.

PHYLOGENY OF THE APLODONTIDAE (MAMMALIA:RODENTIA) AND SOME IMPLICATIONS FOR OLIGO-MIOCENE BIOGEOGRAPHY

HOPKINS, Samantha S.B., Museum of Paleontology and Dept. of Integrative Biology, University of California, Berkeley, CA, USA

Aplodontid rodents today are represented by only a single extant species, Aplodontia rufa, but they have a particularly extensive and diverse fossil record in the late Oligocene and Miocene of northwestern North America. Extensive studies of North American aplodontids, particularly those from the John Day basin of Oregon, have indicated relatively rapid in situ evolution of molar morphology within genera. Less forthcoming have been intrafamilial relationships between genera, in part because cladistic methods have not previously been applied to interpreting the systematics of the group. Here a first attempt at phylogenetic interpretation is presented, focused around understanding the evolutionary and biogeographic relationships of a new mid-Miocene aplodontid from Hepburn's Mesa, MT. The new species differs greatly in both size and cusp morphology from other material known from the Miocene of North America, which is limited to derived, hypsodont forms, such as Allomys and Liodontia. A phylogenetic reconstruction of aplodontid relationships shows that the Hepburn's Mesa material falls within the Ansomyinae, a group previously known only from Eurasia. This group is sister to the taxon that includes the Allomyinae, Meniscomyinae, Aplodontinae, and Mylagaulidae, which are the groups that took part in the radiation of hypsodont aplodontids in the late Oligocene and were the most abundant aplodontid clades in the mid-Miocene. The relationships among aplodontid groups suggest that several higher taxa, including the Prosciurinae and the Meniscomyinae, may be paraphyletic. The phylogeny also has implications for the biogeographic history of aplodontids, as they appear to have immigrated multiple times between Europe, Asia, and North America in the Oligocene and Miocene. With the cessation of this immigration in the mid- to late Miocene and the extirpation of aplodontids from Asia and Europe, aplodontids and mylagaulids began to decline in diversity, and were reduced to the single extant species by the late Pleistocene.

CAN ANALYSES OF THE CARBON ISOTOPE RATIOS
OF HORSE TEETH AND BONES BE USED TO PRECISELY RECONSTRUCT THE C₃/C₄ RATIO OF LOCAL GRASSLANDS?

HOPPE, Kathryn A., and Ronald Amundson, Div. of Ecosystem Sciences, University of California, Berkeley, CA, USA

Researchers are increasingly using analysis of the carbon isotope ratios of herbivore teeth and bone collagen to reconstruct paleoecological conditions. The carbon isotope ratio of grazing herbivores directly reflects the abundance of C₃ vs. C₄ grasses in their diet, and has been used to reconstruct the abundance of C₄ grasses in ancient grasslands. Additionally, since the C₃/C₄ ratio of local grasses correlates with changes in growing season temperature, analysis of the carbon isotope values of herbivore teeth and/or bones may also serve as a proxy for paleoclimatic conditions. However, the precision of such reconstructions is currently limited because the correlation between the isotope ratios of modern equids and the C₃/C₄ ratio of local grasslands has not been quantified. Of particular concern is the contribution of other C₃ plants (e.g., trees, shrubs and herbs) to the diet, and thus the carbon isotope ratio, of equids. We quantify this relationship through analyses of the isotope values and average diets of modern feral horses from grasslands in Oregon (100% C₃) and New Mexico (>95% C₄). The carbon isotopes of tooth enamel and bone collagen are compared with the isotope values of local plants and microhistological analyses of fecal samples. Analysis of fecal samples demonstrates that horses from both locations consumed significant amounts (5% to 25%) of shrubs and/or herbs. The carbon isotope values of Oregon horses are consistent with a diet of 100% C₃ plants. Values for New Mexico horses suggest that the diets of these horses consisted of 80% to 100% C₄ grasses, with an average of 93%. It therefore appears that while analyses of the carbon isotope of horse teeth can be used to identify regions where C₄ grasses are present, this proxy is likely to underestimate the percentage of C₄ grasses in an ecosystem.

THE SPECIES OF AMPHISTEGINA (FORAMINIFERIDA) IN THE LATE NEOGENE OF THE DOMINICAN REPUBLIC

HOTTINGER, Lukas, Naturhistorisches Museum Basel, Basel, Switzerland

Seven species of the foraminiferal genus Amphistegina were described from the Late Miocene Cercado and Gurabo for mations of the Dominican Republic by Bermudez in 1949. They are defined by exterior characters. Their morphology ranges from very thick, tuberculate shells with an almost rectangular outline in axial section (A. tuberculata) to much flattened-lenticular shells (A. guraboensis). A revision of the taxa must take into account internal characters in order to reveal the strong dimorphism of generations in this group. The particular preservation of the material from the Dominican Republic admits splitting techniques, as used in nummulites, to open the shells in appropriate quantities. The revised taxa are distributed in the sedimentary sequence with overlapping-echeloned ranges from thick shells at the bottom to thin shells at the top until their disappearance from the foraminiferal assemblages. The relay of ranges in the sedimentary succession is interpreted as reflecting deepening-upward environmental change during deposition rather than an evolutionary process. This is supported by the occurrence of the porcelaneous archaiasinids and soritids at the shallow end of the gradient and by the dominance of the larger agglutinated forms (Textulariella and consorts) at the deep end. Similar relations between depth of deposition and shell morphology are known from similarly diverse Amphistegina communities in the extant environmental gradient of the Indopacific Ocean.