NAPC 2001

Abstracts, Ph - Py
(5/22/01)

Jump to: Phelps | Pichardo | Pigg | Piller | Plotnick | Poetker | Porter | Powell | Price | Prothero | Pruss | Puckett | Pushkar

Return to Main Abstracts Page

EVEN DEEP TIME DEAD TELL TALES: DECOUPLING OF TAXONOMIC AND ECOLOGICAL SIGNIFICANCE OF MASS EXTINCTIONS AND THE IMPLICATIONS FOR MANAGEMENT OF MODERN DIVERSITY ISSUES

PHELPS, William T., and Mary L. Droser, Dept. of Earth Science, University of California, Riverside, CA, USA

Fossil concentrations provide a proxy for faunal abundance and community dominants, when depositional and taphonomic processes are accounted for. Examination of large-scale shifts in faunal abundance and community dominants is key to evaluating the extent of ecological change within an ecosystem.

To assess the ecological changes associated with the Late Devonian mass extinction, Late Devonian and Early Mississippian fossil concentrations from limestones of the western US were examined. These limestones formed in a shallow-water, soft-substrate environment within a single depositional basin under broadly similar environmental conditions.

Large-scale taxonomic changes in shallow marine fauna across the extinction are well documented. However, no Bambachian Megaguilds are vacated, and most groups recover in the Mississippian to near pre-extinction diversity levels. This suggests that pre- and post-extinction communities may have remained broadly similar. However, fossil concentration analyses show a much different pattern. Devonian fossil concentrations are generally polytaxic but dominated by brachiopods, while Mississippian fossil concentrations are typically monotaxic (i.e., separate crinoidal, gastropod, and rugose coral fossil concentrations) and dominated by crinoidal fossil concentrations; the number of brachiopod concentrations decreases considerably. This shift from brachiopod dominated polytaxic communities to crinoid dominated monotaxic communities suggests there were large-scale shifts in the ecological structure of this shallow marine community not predicted by the taxonomic data.

In contrast, the Late Ordovician extinction had a taxonomic loss similar to the Late Devonian extinction but Silurian communities retained the fundamental structure seen in the Ordovician. These results, coupled with the loss of large-scale reefs at the Devonian extinction, thought to be largely a result of the loss of stromatoporoids (Scrutton, 1988), point to the importance of retaining keystone and dominant taxa in maintaining ecosystem integrity.

NEW CAPRINID RUDISTS(BIVALVIA-HIPPURITACEA) FROMEL DOCTOR AREA, OF THE QUERETARO STATE, OF CENTRAL MÉXICO

PICHARDO, Yolanda B., and Javier P. Aguilar, Facultad de Ciencias de la Tierra, Universidad Autónoma de Nuevo León, México

El Abra Formation is exposed in large areas near the Municipality of San Joaquin, in the State of Querétaro, in Central México. This region is called Sierra Gorda because of its particular topography. It belongs to the southeastern part of the Sierra Madre Oriental. The reefal facies of this lithological formation is characterized by an abundant fauna of caprinid and radiolitid rudists as the dominant groups. They areassociated with gastropods, corals and other reefal organisms. Several workers havemade extensive studies of El Abra Formation from this area, principally the geology, tectonics, structural geology and mineral exploration (Bonet, 1956; Segestrom, 1961; Enos, 1985; Tolson, 1998). On the contrary, there are only afew articles with apaleontological approach.

The authors found in this location Caprinuloidea perfecta Palmer, Coalcomana ramosa Boehm and Pacificaprina pyriformis Chartrousse and Masse. This fauna is of Albian age, according to work by Alencáster (1987, 1991, 1998); Alencáster and Aguilar (1995) in El Madroño, the nearest area of El Abra Formation with the same reefal facies. The first two species are reported for the first time from this locality, while the last species isreported for the first timein Mexico and in America.

THE ROLE OF PERMINERALIZED PLANTS IN UNDERSTANDING PLANT DIVERSITY, PHYLOGENY, AND PALEOENVIRONMENT: THE MIOCENE YAKIMA CANYON CHERT

PIGG, Kathleen B., Dept. of Plant Biology, Arizona State University, Tempe, AZ, USA

Like the middle Eocene Princeton chert of southern British Columbia, the Yakima Canyon chert of central Washington State contains a diverse permineralized flora. This flora is of middle Miocene age (15.6 Ma) and in contrast to the Princeton chert, contains only temperate floral elements. Many of these are closely related to modern plants at several infrageneric levels, including section, subsection and even species. Included are the osmundaceous fern Osmunda wehrii (Osmunda subgenus Osmunda, Osmundaceae), Pinus foisyi, a pine of the California closed cone pine group (Pinus subgenus Pinus, section Pinus, subsection Oocarpae, Pinaceae), the white oak Quercus hiholensis (Quercus subgenus Quercus, section Quercus, Fagaceae), and the fern Woodwardia virginica (Blechnaceae), which is essentially identical to the modern Virginia chain fern of the Atlantic coastal plain. Unlike compression floras of the same age that are identified primarily on the basis of leaf morphology, the Yakima Canyon flora shows details of fruit and seed anatomy, and thus provides both an independent means for taxonomic assignment and a much greater degree of taxonomic resolution. Additional floral elements currently under study include both "typical" middle Miocene families (such as Taxodiaceae, Altingiaceae, Vitaceae, Cornaceae, and Rosaceae), as well as fruits and seeds that cannot be placed easily within modern genera and probably represent extinct taxa.

THE BIRTH OF THE MEDITERRANEAN SEA FROM A BIOGEOGRAPHIC PERSPECTIVE

PILLER, Werner E., Institute for Geology and Palaeontology, University of Graz, Austria; Mathias Harzhauser and Fred Roegl, Natural History Museum, Vienna, Austria; Oleg Mandic, Institute for Palaeontology, University of Vienna, Austria; James H. Nebelsick, Institute for Geology and Palaeontology, University of Tübingen, Germany; Fritjof Schuster, Fritz F. Steininger, and Ulrike Wielandt-Schuster, Senckenbergmuseum, Frankfurt/Main, Germany

The closure of the Tethyan Seaway is a major palaeogeographic and biogeographic incision and marks the origin of the Mediterranean as a biogeographic unit. It significantly changes global equatorial ocean water circulation by blocking the seaway between the Indo-Westpacific and the Mediterranean and makes exchange of marine biota between these bioprovinces impossible. However, it enables terrestrial organisms to move from Africa to Eurasia and vice versa. To trace the closure and related effects, in a multidisciplinary approach Oligocene and Early Miocene sections were studied in Central Iran (Esfahan-Sirjan Basin, Qom B.), the Zagros Mountains, Turkey (Mut B., Sivas B.), Greece (Mesohellenic Trough), and Egypt (Suez area). These well-dated sections clearly show that a continuous marine connection between the western Iranian area and the eastern Mediterranean existed up to the Late Burdigalian. Detailed analyses of various biota (corals, foraminifera, gastropods, bivalves, echinoderms) clearly furnish evidence that the Central Iranian basins, as key-area between the Western Indo-Pacific and the Eastern Mediterranean, display a Mediterranean character throughout the Oligocene and Early Miocene. Although a marine connection was present until the Late Burdigalian, exchange of biota became more and more limited during the Aquitanian and Early Burdigalian. Similarities, for example, to Pakistanian faunas are high during the Oligocene decreasing, however, distinctly during the Early Miocene. Only a few Pakistanian species reach west as far as the Qom Basin. However, some of the Burdigalian species reported from Iran are absent in Europe and may be a hint to an Indo-Pacific influx in an overall Mediterranean fauna. Indo-Pacific gastropod species, known from Burma or Java are well represented as far west as Pakistan, but did not extent to the Mediterranean. Thus the melting pot between Indic and Mediterranean gastropod faunas was located in the Pakistanian area during the Oligocene, while a takeover by Indo-Pacific gastropods occurred during the Early Miocene.

SIMULATIONS AND THEORETICAL MORPHOLOGY OF TRACE FOSSILS

PLOTNICK, Roy E., Dept. of Earth and Environmental Sciences, University of Illinois at Chicago, Chicago, IL, USA

Trace fossils represent the preserved interactions of trace making organisms with their environment. The form of traces should result from complex interactions among the organism's morphology, the behavior being carried out, the organism's perception of the environment, and the heterogeneity of the environment. Existing mathematical models for the biological formation of traces have tended to focus on a limited repertoire of behaviors, such as grazing. They do not include realistic patterns of environmental heterogeneity, differences in perception, or multiple behavioral responses. In addition, there have been virtually no attempts to model three-dimensional traces or traces that branch or anastomose. I will discuss two new approaches to modeling trace fossils.

New models for grazing and crawling traces are built on current research by ecologists into animal movement patterns and their interaction with environmental heterogeneity. These models explore the interactions of alternative spatial patterns of environmental heterogeneity with different perceptions and behavioral responses to it. They have the potential for suggesting how behavioral patterns for a given trace-making organism might change as a function of environmental differences, such as resource distribution. This could be a useful tool for determining such patterns of spatial heterogeneity in ancient environments.

Models for geometrically complex traces are based on recent developments in the computer-based study of morphogenesis. L-systems and related methods can be used for the generation of branching and three-dimensional theoretical morphologies. L-system descriptions can be quite complex and can incorporate realistic concepts of growth, including external environmental factors and signal transmission. They have been used previously for the production of simulated plants of startling realism. By altering the parameters used to generate the simulated fossils, a theoretical morphospace for trace morphology could be constructed.

MORPHOLOGY, STRUCTURE, AND COMPOSITION OF TROPICAL INTERTIDAL AND SUPRA-LITTORAL MICROBIAL MATS

POETKER, Shelene, Dept. of Integrative Biology, University of California, Berkeley, USA

Microbial mats covering a partially inundated mudflat on the island of Moorea, French Polynesia were studied during October and November 2000. Initial surveys indicated the presence of seven phenotypes. In order to test this classification and to characterize and describe the mats, 33 mats encompassing all seven types were examined using light microscopy. The mats were dominated by cyanobacteria belonging to the genera Lyngbya and Microcoleus. Other cyanobacteria genera including Oscillatoria, Phormidium, Xenococcus, and Chroococcus as well as unidentified cyanobacteria and diatoms were also present. Species dominance and frequencies differed between the pre-defined types. All mats were vertically stratified, although to different degrees, and thickness ranged from 1 mm to 30 mm. Although the number of laminations differed, most mats had an upper green gelatinous layer and a lower reddish layer. A PCA analysis comparing the environmental and compositional data for 27 mats challenged the pre-defined categories, suggesting that the mats are better grouped into four categories. These results along with a cluster analysis and findings in the literature indicate the presence of two primary types: a Smooth/Reticulate mat and a Blister mat, as well as two types along the periphery of these in various stages of lithification. Extensive extracellular polymer production was present in all mat types, and allowed the mats to bind sediment. Grazing and bioturbation were present in most mat types, and consisted primarily of nematodes and amphipods. Average salinity of the groundwater was 6.8% and temperatures ranged from 27.5­48°C, indicating an extreme hypersaline environment similar to those characterized for microbial mats in other tropical regions.

HIGH MORPHOLOGICAL DIVERSITY IN NEOPROTEROZOIC VASE-SHAPED MICROFOSSIL ASSEMBLAGES FROM THE CHUAR GROUP, GRAND CANYON; COMPARISONS WITH MODERN TESTATE AMOEBAE

PORTER, Susannah M., Dept. of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, USA; and Ralf Meisterfeld, Dept. of Biology II, Rheinisch-Westfälische Techn. Hochschule, Aachen, Germany

Recent studies of newly discovered vase-shaped microfossil (VSM) assemblages from the >742 ± 6 Ma Chuar Group, Grand Canyon, suggest affinities with testate amoebae. These fossils thus extend the stratigraphic range of testate amoebae by ~500 million years, and provide the earliest body fossil evidence for heterotrophic protists in marine ecosystems. Further investigation of these assemblages reveals that VSMs exhibited a much higher degree of morphological diversity than previously documented. Using the taxonomy of modern testate amoebae as a guide, we have provisionally identified nine new species of Chuar Group vase-shaped microfossils that augment the eight species already described globally. Comparisons with modern testate amoebae indicate that many of the test characters exhibited by this modern group were already present 742 Ma. Furthermore, character combinations in specific VSM taxa closely approximate those of particular modern testate amoeban taxa, including species in the families Euglyphidae, Trigonopyxidae, Centropyxidae, and Arcellidae. This provides further support for the view that many VSMs represent lobose and filose testate amoebae, and suggests that these groups not only originated but also had diversified during Neoproterozoic time.

INVERTEBRATE FOSSILS OF THE WILSON GROVE FORMATION (LATE MIOCENE­LATE PLIOCENE), SONOMA COUNTY, NORTHERN CALIFORNIA

POWELL, Charles L., II, U.S. Geological Survey, Menlo Park, CA, USA; and James R. Allen, Dept. of Geology, San Jose State University, San Jose, CA, USA

Fossil mollusks from the Wilson Grove Formation (WGF) represent shallow to deep marine environments and range in age from late Miocene to late Pliocene. The WGF outcrops from Petaluma north to northern Santa Rosa, and west of the Rogers Creek fault to the coast.

Wilson Grove Formation rocks representing shallow water environments occur along the eastern margin of the outcrop area at Meacham Hill and along the northern margin at River Road and the type locality at Wilson Grove. At Meacham Hill these shallow water deposits suggest a brackish bay environment, whereas at River Road and the type locality at Wilson Grove fossils suggest euhaline conditions. Mollusks from the River Road area also suggest water temperatures warmer than today along the adjacent coast. Deep water environments occur to the southwest along Estero San Antonio. Other outcrops of the WGF do not have enough taxa present for accurate biogeographic or environmental determination.

Outcrops of the WGF to the south suggest an earlier age than outcrops to the east and north. The late Miocene Roblar Tuff occurs at Steinbeck Ranch in the southern part of the outcrop area, whereas the occurrence of the bivalve mollusks Macoma addicotti (Nikas) and Nuttallia jamesii Roth and Naidu suggest a late Pliocene age for the northern outcrops at River Road. This age is suggested by the co-occurrence of these bivalve taxa at River Road and in the sea cliffs at Capitola, Santa Cruz County (Purisima Formation) where they have been dated using high resolution diatom biostratigraphy and magnetic polarity zonation.

These data suggest an overall pattern for the WGF of older and deeper to the south and younger and shallower to the north. Fossils in the eastern part of the outcrop area represent shallow water but are not age diagnostic.

USING CONSTRUCTIONAL DATA TO DETECT CONVERGENCE: AN UNDERUTILIZED APPROACH TO STUDYING ADAPTATION IN THE FOSSIL RECORD

PRICE, Rebecca M., Dept. of Geophysical Sciences, University of Chicago, Chicago, IL, USA

Although adaptation has always been a major focus of evolutionary biology, we have only recently begun to study it thoroughly with the advent of the comparative methods. Rigorous studies of the effects of adaptation through geologic time are still relatively rare, perhaps because comparative methods require robust phylogenetic hypotheses, which are not available for most taxa over long time intervals. The Fasciolariidae (Neogastropoda: Mollusca), for example, is an appropriate taxon for studying the dynamics of adaptation because it is long-lived (reputedly originating in the Valanginian and still extant), and because it exhibits variation in the shape of columellar folds, prominent ornamentation on the aperture of many neogastropods traditionally used in systematics and assumed to be adaptive. A thorough cladistic analysis of the family cannot be conducted without extensive taxonomic revision because the species and genera are poorly defined, and there are few reliable characters that may be synapomorphies. If columellar folds are adaptive, however, it is reasonable to predict that similar fold morphologies evolve repeatedly in different clades, assuming that columellar folds that are constructed differently represent independent derivations. Here, I test the hypothesis that an analysis of growth lines (observed through a combination of acetate peels and thin sections) will reveal multiple ways of constructing similar columellar fold morphologies in the Fasciolariidae and other high-spired gastropods. I use data describing the construction of the folds (sensu Miller, 1999) to detect convergence in five categories of columellar fold morphology. Tojo and Ohno (1999) showed that the folds in the potamidid Terebralia palustris are formed after the rest of the columella, but my preliminary analyses show that the folds of the fasciolariid Leucozonia nassa are constructed as the columella grows.

MAGNETIC STRATIGRAPHY OF THE EOCENE-OLIGOCENE EUGENE/FISHER FORMATIONS, WESTERN
OREGON: IMPLICATIONS FOR THE "TERMINAL EOCENE EVENT"

PROTHERO, Donald R., Dept. of Geology, Occidental College, Los Angeles, CA, USA; and Gregory J. Retallack, Dept. of Geology, University of Oregon, Eugene, OR, USA

The floras of the Eugene and Fisher Formations in the Eugene area of west-central Oregon were crucial to Wolfe's (1978) claim of a major cooling and drying episode that he labeled the "Terminal Eocene Event."

Recent magnetostratigraphic investigations, along with new radiometric dates, help to constrain the age of this floral event. Most of the available sections in the Eugene, Coburg, and Goshen area were sampled, and analyzed on a cryogenic magnetometer, using both thermal and alternating field demagnetization. The magnetization is largely held in magnetite and yields, single component primary magnetizations, which pass both a fold test and reversal test. There are three tuff horizons found throughout the area, which help correlate the sections, and calibrate them as well. The lowest (Bond Creek tuff) yields a date of 35.9 Ma, and the upper tuff yields a date of 31.8 Ma; the middle tuff is currently undated. Based on these dates, we correlate the type Eugene marine strata with Chron C13r (33.5­34.5 Ma, latest Eocene), the megathermal Goshen flora with late Chron C13r-early Chron C13n (33.0­34.0 Ma, earliest Oligocene), the cooler-adapted Coburg flora with Chron C13n (33.0­33.5 Ma, early Oligocene), and the Willamette flora with Chron C12r (31.0­33.0 Ma, or early and late Oligocene). These dates suggest that Wolfe's "Terminal Eocene Event" is actually earliest Oligocene (about 33.2 Ma), consistent with other global climatic indicators that show the major Antarctic cooling event occurred in the earliest Oligocene, not at the Eocene/ Oligocene boundary. In addition, recent reassessment of the paleobotanical evidence suggests that it was not as extreme a climatic event as Wolfe (1978) once suggested, although it was still very abrupt (less than half a million years).

DEVELOPMENT OF MICROBIAL FABRICS IN EARLY TRIASSIC OCEANS

PRUSS, Sara B., and David J. Bottjer, Dept. of Earth Sciences, University of Southern California, Los Angeles, CA, USA

The Early Triassic represents a period of recovery from the largest extinction in the history of life, the end-Permian mass extinction. During this time, marine microbial fabric development has been documented globally. Research by Kershaw et al. (1999) shows the occurrence of what may be a microbialite crust at the Permian-Triassic boundary in South China. This crust is suggested to have been formed by a disaster biota that thrived in the presence of unusual oceanic conditions occurring at the P-T boundary. The absence of grazers has also been cited as increasing the potential for such microbial development. Recent work by Lehrmann (1999) shows the presence of biostromes and microbial mounds from the Lower Triassic Nanpanjiang Basin in South China. These biostromes and mounds occur in two horizons: one in Griesbachian strata and one in Smithian-Spathian strata. In some places, these beds attain thicknesses of 15 meters suggesting that these microbial features occurred as reefs.

Stromatolites and thrombolites have also been reported as mass extinction disaster forms from late Early-Triassic-age strata in the Western United States (Schubert and Bottjer, 1992). These microbial structures from the Virgin Limestone Member of the Moenkopi Formation have been recently reinvestigated to determine if they represent true reefs. In places microbial mounds occur as isolated patch reefs, although elsewhere they coalesce to form tabular biostromes. These mounds are an agglomeration of smaller subunits that have wavy laminations and thrombolitic textures. Measurements on isolated mounds show that they attained a relief of 1­2 meters above the seafloor. These results, together with those from previous studies, demonstrate that small reefs, although rare, can be found throughout the early Triassic. These primarily microbial constructions represent the earliest reef systems of the Mesozoic.

EVOLUTIONARY FABRIC OF OSTRACODE FAUNAS FROM THE LATE CRETACEOUS (SANTONIAN-MAASTRICHTIAN) OF THE US GULF COASTAL PLAIN: RELATIONSHIP WITH SEA LEVEL DYNAMICS

PUCKETT, T. Markham, Dept. of Geological Sciences and Center for Sedimentary Basin Studies, University of Alabama, Tuscaloosa, AL, USA

Ostracodes and planktonic foraminifera were collected from two composite reference sections (CRS) in the marine Upper Cretaceous deposits of the US Gulf Coastal Plain, one in central Alabama and one in eastern Mississippi. One hundred eight ostracode taxa were recognized in the two CRSs, and their ranges were analyzed using graphic correlation. Planktonic foraminifera were used for chronostratigraphic control. These data are the record of evolution of these faunas for the interval between 86 and 69 Ma.

Three depositional sequences are recognized in these Upper Cretaceous deposits. The two older sequences (Santonian­early Campanian UZAGC-3.0 sequence, and the Campanian UZAGC-4.0 sequence) were deposited in a greenhouse climate, characterized by very slow rates of sea level change, whereas the younger sequence (Maastrichtian UZAGC-5.0 sequence) is of much shorter duration and was possibly controlled by glacial activity (icehouse).

The coastal onlap and offlap clearly affected the community structure and rate of evolution of the ostracode faunas. High rates of faunal turnover are observed around sequence boundaries, even though the boundary between the two older sequences (UZAGC-3.0 and UZAGC-4.0 sequences) is a Type II boundary and displays an insignificant hiatus. Although the high number of originations at the base of the section reflects initial quantification of incipient taxa, relatively high rates of origination occur in the lower part of the UZAGC-3.0 sequence. High rates of both originations and extinctions occur around the sequence boundary. Subsequent to this faunal turnover event, community stasis is observed by low rates of both origination and extinction. This community was stable for approximately three million years, is characterized by low diversity, and includes taxa adapted to living in an extremely fine-grained chalky substrate. Faunal turnover rates again increase near the boundary between the UZAGC-4.0 and UZAGC-5.0 depositional sequences.

PLIO-PLEISTOCENE DIATOMS OF ALASKA: APPLICATION TO HIGH-RESOLUTION PALEOENVIRONMENT RECONSTRUCTION

PUSHKAR, Vladimir S., Pacific Institute of Geography FEB RAS, Vladivostok, Russia; Marina V. Cherepanova, Institute of Biology and Soil Science FEB RAS, Vladivostok, Russia; and Julie K. Brigham-Grette, Dept. of Geoscience, University of Massachusetts, Amherst, MA, USA

The Gubik Formation of Arctic Alaska, Cape Blossom and Hotam Inlet Formations of western Alaska consist of at least six superposed marine, glaciomarine and terrestrial transgressive sequences. The diatom data recorded in these sequences, which include the Arctic Alaska Pliocene marine Nulavik, Killi Creek, Tuapaktushak beds, the Pleistocene Karmuk beds, and the Pleistocene marine Anvilian beds, the glaciomarine Baldwin Silt and periglacial Selawik beds (Baldwin Peninsula), allow us to demonstrate high-resolution paleoecological and paleogeographic reconstructions. Plio-Pleistocene extinct species, as well as other forms that make their first appearance near the Plio-Pleistocene boundary were used for age determinations. The studied deposits of the Nulavik, Killi Creek and Tuapaktushak beds correspond to the middle Neodenticula kamtschatica-Neodenticula koizumii Zone (3.4­3.1 Ma), the lower Thalassiosira convexa Zone (2.5­2.4 Ma), and the lower Pyxidicula zabelinae Zone (2.2­2.0 Ma), respectively. The Diatom sequences are clear evidence that the Late Pliocene was punctuated by at least three periods of high sea level, when conditions were dramatically warmer than now. These units are unconformably overlain by Karmuk deposits (analogy of Anvilian and Baldwin Silt beds), with index-species of the middle Proboscia barboi Zone (0.43­0.38 Ma) from a younger high sea level event containing diatoms consistent with dates to warm marine isotope stage 11. Glaciomarine and periglacial sedimentation (Baldwin Silt and Selawik beds) was initiated during the end of the stage 11 transgression and continued into cold stage 10. High-latitude glacier growth during a global interglacial period was facilitated by warm surface waters on flooded continental shelves and limited regional sea ice cover (Baldwin Silk time). These data are useful to clear understand the influence Arctic diatoms on the diatom assemblages of the western Pacific Arc-Island System. Russian Foundation for Basic Research (Grant 00-05-64837) supported this work.