NAPC 2001

Abstracts, We - Z
(5/22/01)

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PALEOECOLOGY OF EUTREPHOCERAS DEKAYI: EVIDENCE FROM LIGHT STABLE ISOTOPES

WEINREB, David, Peabody Museum of Natural History, Yale University, New Haven, CT, USA; and Neil H. Landman, Div. of Paleontology (Invertebrates), American Museum of Natural History, New York,NY, USA

The oxygen isotope composition of calcium carbonate shells of fossil cephalopods is principally a function of the water temperature at the time of deposition, although it may also reflect the salinity. The aim of the present study was to assess seasonal fluctuations in water temperature, marine chemistry, and habitat recorded in the isotopic composition of shells of the Cretaceous nautilid Eutrephoceras dekayi (Morton 1834). We sampled the nacreous shell material from 198 septa from eight specimens of E. dekayi from the Pierre Shale (Late Campanian) and Fox Hills Formation (Maastrichtian) of South Dakota. Samples were examined by scanning electron microscopy and X-ray diffraction to confirm that the original aragonite had not been diagenetically altered. Values of d¹⁸O and d¹³C vary throughout the ontogeny of each specimen by as much as 1.5 and 5.0 per mil respectively. If the variations in d¹⁸O are due to temperature, they would suggest fluctuations in water temperature of nearly 10 degrees Celsius. The observed trends may be attributed to one or more of the following events: seasonal variation in temperature and isotopic composition of sea water, vertical migration of E. dekayi in the water column, and, finally, geographic migration during ontogeny. Eutrephoceras dekayi may have migrated seasonally between on-shore and off-shore habitats. It would have experienced isotopically light water in on-shore habitats producing septa that are depleted in d¹⁸O relative to those deposited in offshore habitats. There is no difference in isotopic composition between embryonic and post-embryonic septa.

TERTIARY FOSSIL WOODS OF NORTH AMERICA

WHEELER, Elisabeth A., Dept. of Wood and Paper Science, North Carolina State University, Raleigh, NC, USA

Fossil wood assemblages can be the only source of information about ancient vegetation for some localities, or occur with pollen, leaves, fruits, and seeds. In both cases, woods contribute to our knowledge of past diversity. Much of the information on fossil and modern woods is computerized, which aids determining affinities and tracking wood structural changes through time. Correlations of extant woods' features with climate have potential for developing means of interpreting paleoclimate. Western North America has many localities with well-preserved woods, most have not been studied. The fossil wood record, especially for dicots, and its real and potential contributions are reviewed. Localities discussed in detail include the Paleocene of Big Bend National Park, Texas, and the middle Eocene Clarno Nut Beds.

PARTIAL HADROSAUR SKELETON WITH SKIN IMPRESSION, HELL CREEK FORMATION, MCCONE COUNTY, MONTANA

WIDEMAN, Natalia K., Raymond M. Alf Museum of Paleontology, Claremont, and California State University, San Bernardino, CA, USA; and Don L. Lofgren, Raymond M. Alf Museum of Paleontology, Claremont, CA, USA

Partially articulated skeletal material from the posterior region of a large hadrosaur referred to Anatosaurus sp. was collected in 1997­2000 by field crews from the Raymond Alf Museum of Paleontology. The partial skeleton was found at the base of a channel sandstone deposit very high in the Hell Creek Formation, about 8 m below the base of the overlying Tullock Formation. Material recovered included an articulated right leg with a dermal impression, an ischium, and a partially articulated tail with ossified tendons. The dermal impression was preserved lying juxtaposed to the astragalus and represents the integument of the hadrosaur's right heel. The impression is characterized by polygonal pavement tubercles ranging in diameter from 4.5 to 14 mm and having an average diameter of 7 mm. While preservation of integument is not uncommon in hadrosaurs, a dermal impression of the heel has never been reported. The partially articulated tail, when reconstructed, is 5 m long and contains over 77 caudal vertebrae, making it one of the longest tails known for Anatosaurus. The anterior 30 vertebrae are in articulation with the remainder distributed in close association. Ossified tendons were preserved in abundance only on the side of the articulated portion of the tail that was lying in contact with the substrate. Also, only vertebrae in articulation retain chevrons. The selective removal of chevrons and selective preservation of ossified tendons indicate that some of these elements were winnowed by fluvial processes while others remained articulated.

Students from The Webb Schools made a significant contribution to the discovery, collection, preparation, and study of this partial hadrosaur skeleton. This unique program of having high school students involved in all aspects of paleontological research was initiated by Raymond Alf in 1937 and continues to be a major educational component in the mission of the Alf Museum, the only paleontology museum located on a secondary school campus in North America.

THE BIOGEOGRAPHIC IMPACT OF AN EPEIRIC SEAWAY ON LATE CRETACEOUS AND PALEOCENE SOUTH AMERICAN PALYNOFLORAS

WILSON, Gregory P., and Nan Crystal Arens, Dept. of Integrative Biology and Museum of Paleontology, University of California, Berkeley, CA, USA

Paleogeographic reconstructions and some sedimentological data suggest that during the Cretaceous, South America was split into northern and southern portions by an epeiric seaway. Although the location, extent, and duration of this ancient seaway still remains unclear, some propose that the resulting separation produced a northern South American biota that more closely resembled other equatorial biotas, distinct from a southern South American biota that more closely resembled other austral biotas.

Previous biogeographic arguments qualitatively address this question using vertebrate data. We chose pollen and spore data to quantitatively evaluate this hypothesis because palynological data offers greater geographic coverage from a larger number of localities than macrofloral or faunal data. Palynoflora data from nine South American countries, ten equatorial representatives (southeastern North America and northwestern Africa), and five austral representatives (Antarctica, India, Madagascar, Australia, and New Zealand) were assembled into a database that includes more than 450 genera from more than 150 localities spanning the Cretaceous and Paleocene epochs. Principal components and cluster analyses on the palynological data separate northern South America from southern South America during the Maastrichtian and Paleocene ages. During these epochs, northern South America clusters with the equatorial representatives; whereas, southern South America clusters with austral representatives. However, we must also test the role of known latitudinal gradients in producing these patterns. These results suggest that biogeographic barriers, such as epeiric seaways, may have played a significant role in the evolution of distinct terrestrial biotas in South America during the Late Cretaceous and Paleocene and may have affected the dispersal of organisms throughout Gondwana.

"PSEUDOBRYOZOANS" AND THE PROBLEM OF ENCRUSTER DIVERSITY IN THE PALEOZOIC

WILSON, Mark A., Dept. of Geology, The College of Wooster, Wooster, OH, USA.; and Paul D. Taylor, Dept. of Palaeontology, The Natural History Museum, London, UK

Fossil marine communities that encrust hard substrates are important in our understanding of biodiversity through time. These organisms are often well preserved, have distinct adaptive histories, and inhabited relatively consistent environments through the Phanerozoic. A problem, however, has been the erroneous or questionable assignment of some common Paleozoic runner-type encrusters to the bryozoans, thereby introducing errors into diversity estimates and paleoecological reconstructions. In a review of the evolutionary paleoecology of hard substrate communities, we have identified two such groups of "pseudobryozoans."

The Suborder Hederelloidea comprise six genera of supposed cyclostome bryozoans ranging from the Silurian into the Permian. Hederelloids may not be bryozoans because: (1) their upper zooid size exceeds that known in bryozoans; (2) zooids are often budded from the sides of a broad stolonal tube; (3) the fibrous calcite wall structure is a fabric unknown in Paleozoic bryozoans; and (4) zooids can be long, sinuous, prostrate tubes atypical of bryozoans.

A second group of "pseudobryozoans" is represented by five encrusting genera (Allonema, Ascodictyon, Eliasopora, Vinella, Condranema) included in two families of ctenostome bryozoans in the Treatise (Bassler, 1953). However, these genera have calcified skeletons and thus are not ctenostomes. They consist of radiating clusters or ramifying chains of vesicles and/or narrow stolons. Some have a minutely porous skeleton, but none have apertures of sufficient size to permit the passage of a bryozoan lophophore.

Removal of these "pseudobryozoans" reduces the diversity of encrusting bryozoans in the fossil record, especially in the Devonian, and leaves several unanswered questions about the true affinities and biology of these important components of Paleozoic hard substrate communities.

PALEOGENE CLIMATIC AND FLORISTIC CHANGES AT MIDDLE TO HIGH LATITUDES IN NORTH AMERICA

WOLFE, Jack A., Dept. of Geosciences, University of Arizona, Tucson, AZ, USA; and Howard E. Schorn, Museum of Paleontology, University of California, Berkeley, CA, USA

The Arctic has been viewed as one of the prime areas for biogeographic modeling. During the 19th century, some Arctic Tertiary plants were identified as belonging to the same clades as plants now disjunct at middle latitudes of the Northern Hemisphere continents. These plants provided the basis for the Arcto-Tertiary concept: that there existed at high latitudes during the Paleocene and Eocene a wide-spread temperate forest of conifers and broad-leaved deciduous trees and shrubs, and, in response to gradually cooling climate, this forest gradually migrated equatorward, being found by the Miocene at middle latitudes and thence becoming ever more restricted by climatic changes resulting from late Cenozoic tectonism.

During the 1960s and 1970s, evidence accumulated that the Paleocene and most Eocene high-latitude floras were highly dissimilar to the later coniferous and deciduous vegetation. The high-latitude flora was dominated largely by deciduous conifers, trochodendroids, hamamelidids, and other archaic angiosperms. Not until the late Eocene were more advanced pinaceous conifers and amentiferous angiosperms diverse and abundant at high latitudes. At middle latitudes, however, the pinaceous conifers and amentiferous angiosperms were abundant and had diversified by the end of the early Eocene, especially in uplands in western North America.

The high latitude Eocene flora underwent a change during the Eocene that was parallel to the change that had already occurred at high altitudes at middle latitudes somewhat earlier in the Eocene. These changes were gradual in comparison to the marked floristic changes that resulted from climatic change during the very early Oligocene.

USING LEAVES FOR PALEOCLIMATIC ESTIMATES

WOLFE, Jack A., Dept. of Geosciences, University of Arizona, Tucson, AZ, USA

CLAMP (Climate-Leaf Analysis Multivariate Program) was proposed as a method applicable to fossil-leaf assemblages to estimate their environmental parameters. The leaves of each species of woody dicot are measured relative to 31 character states, which encompass margin (e.g., lobing, presence and distribution of teeth), sizes, shapes of apex and base, and overall shape, including length:width. At present, the database contains 173 modern samples, most of which were collected near or surrounding meteorological stations, and especially in a limited area that might simulate an area that supplied a fossil sample. A requirement for simulation is that each sample is obtained from an area at the same altitude as where the meteorological data were recorded.

Originally CLAMP used ordination by Correspondence Analysis, and thus a given fossil assemblage could only be indirectly analyzed. The development by ter Braak of Canonical Correspondence Analysis (CANOCO), however, now allows direct gradient analysis, and addition of a fossil sample does not influence the ordination. Further, where the original ordination and estimate was essentially two-dimensional, the estimates of environmental parameters developed by Herman and Spicer are now four-dimensional, i.e., the first four axes of the ordination are used to estimate values of each parameter. In two dimensions, the standard deviation of, for example, mean annual and warm-month mean temperatures are 1.8 and 2.2°C, but using four dimensions are 1.2 and 1.6°C. These estimates are based on 144 samples, a database that excludes subalpine samples that form a cluster by themselves in physiognomic space.

We (Spicer, Herman, and I) have recently constructed a website, which allows anyone to access the CLAMP databases. Also included are templates for sizes, definitions for all character states, a size template, and localty data, including relations of modern samples to meteorological
stations: http://tabitha.open.ac.uk/spicer/CLAMP/Clampset1.html. As samples are added, the site will be updated.

DATING DIVERGENCE TIMES OF THE METAZOAN RADIATION USING GENOMIC SEQUENCES: PROGRESS, PITFALLS, AND PROSPECTS

WRAY, Gregory A., and James P. Balhoff, Dept. of Biology, Duke University, Durham, NC, USA

The diversification of metazoans remains one of the most intriguing of all evolutionary radiations. During the past several years, calibrated rates of DNA sequence divergence have provided a new and controversial perspective into the metazoan radiation. Two salient conclusions can be drawn from the analyses that have been published to date: first, the balance of molecular evidence clearly indicates that the bilaterian phyla began to diverge hundreds of millions of years before the base of the Cambrian; and second, sequence data have not (at least so far) proven able to date divergences with either precision or accuracy. Understanding the sources of error, uncertainty, and bias involved in estimating divergence times from sequence data represents a challenge whose solution promises to enhance significantly our understanding of evolutionary history. The primary source of both error and uncertainty is commonly assumed to be variation in rates of substitution, but in reality a variety of factors make a significant contribution; sources of bias vary according to methods of analysis. Many, and perhaps most, of these factors can be reduced significantly. Methods for dating divergence times using sequence data are rapidly improving, and the amount of sequence data available for analysis is growing even faster. The prospects for increasingly accurate and precise dating of key divergence times in the history of life are excellent.

ARTICULATED SPONGES IN AN EARLY CAMBRIAN BIOTA AND EPIFAUNAL TIERING AT THE PRECAMBRIAN-CAMBRIAN TRANSITION

XIAO, Shuhai, Dept. of Geology, Tulane University, New Orleans, LA, USA; Xunlai Yuan, Nanjing Institute of Geology and Palaeontology, Academia Sinica, Nanjing, China; and Ronald L. Parsley, Dept. of Geology, Tulane University, New Orleans, LA, USA

The maximum height of ecological tiering in epifaunal, suspension-feeding communities was low (typically <+10 cm) in the Early Paleozoic and increased greatly during the middle Paleozoic diversification. However, maximum epifaunal tiering in the earliest Cambrian (particularly Nemakit-Daldynian and Tommotian) is poorly understood because fossils in these stages are predominately disarticulated small shelly fossils. Articulated sponges and orthothecid hyoliths occur in the basal Hetang Formation in Anhui Province, South China. These sponges and orthothecids are bracketed by small shelly fossils of the Meishucunian (broadly Tommotian) age: Anabarites-Protohertzina below and Jianshanodus-Hagionella above. The Hetang sponges are therefore probably Tommotian in age. Articulated sponges in the Hetang Formation are commonly decimeters in height, some as high as 50­100 cm. In conjunction with data from other exceptionally preserved Neoproterozoic to Cambrian Lagerstätten such as the Ediacaran, Chengjiang, and Burgess Shale biotas, the Hetang fossils indicate that non-bilaterian suspension feeders (sponges and possibly cnidarians) were the major above-sediment tierers during the Precambrian­Cambrian period. They reached tiering levels of at least a few decimeters at the beginning of the Cambrian Explosion of bilaterians. Only in the post-Cambrian Paleozoic Fauna did bilaterians attain comparable heights in epifaunal, suspension-feeding communities.

PHYLOGENETIC PATTERNS AND DEVELOPMENTAL TIMING IN THE CENOMANIAN ACANTHOCERATID AMMONITE METOICOCERAS

YACOBUCCI, Margaret M., Dept. of Geology, Bowling Green State University, Bowling Green, OH, USA

Members of the ammonite family Acanthoceratidae radiated within the newly formed Western Interior Seaway of North America during the Middle and Late Cenomanian. A genus-level study of this radiation has demonstrated the importance of developmental plasticity in fueling the explosive endemic evolution of the group. The acanthoceratid genera involved show a mosaic pattern of character evolution, indicating the independent derivation of multiple descendant lineages from one or a few ancestors. But does such an evolutionary pattern extend down to the species level, within a single radiating genus? Or is the diversification of a genus within the Western Interior more orderly, with branching events evenly spaced in time and among lineages?

Metoicoceras originated, radiated within the Western Interior, and became extinct within a 1.3 million-year interval in the Middle and Late Cenomanian. A new species-level cladistic analysis of Metoicoceras and its dwarf offshoots helps to clarify its evolution. Most Metoicoceras species display a mosaic suite of characters, resulting in poor cladistic resolution. The early radiation of the genus may have involved the independent derivation of species from a single ancestral plexus. However, the latest-appearing species show a more hierarchically-arranged character set, suggesting that the genus may have "settled down" evolutionarily had it survived.

Analysis of changes in developmental timing involving the appearance, disappearance, and relationships of ornamentation sheds light on the origin of Metoicoceras from a species of Plesiacanthoceras. These changes indicate that a fundamental and conserved shift in the ornament growth program accompanied the initial appearance of the new genus. Such a shift appears to involve only minor changes to the overall growth program, suggesting that the genus-level origination event was relatively easy to accomplish.

ENVIRONMENTAL MICROPLAEONTOLOGY: PAST, PRESENT, FUTURE (EXEMPLIFIED BY FORAMINIFERA

YANKO-HOMBACH, Valentina, Avalon Institute of Applied Science, Winnipeg, MB, Canada

Microplaeontology has a long honourable history which includes the five major periods: "Discovery" (5th century B.C.­beginning of XIX century), "Descriptive" (first half of XIX century), "Systematic" (second half of XIX century­beginning of XX century), "Industrial" (1920s­1950s) and "Fundamental" (1950s­1990s). At present we are facing the dawn of the sixth, "Environmental" period, which will develop in a burgeoning field of scientific endeavour by 2050 (Culver, 2000).

The rapid growth of the "Environmental" period can be traced by the number of foraminiferal publications during the last decade of the 20th century. Foraminiferal literature shows an exponential rise of papers on environmental issue. The number of publications on recent foraminifera was steady and moderate while the total number has decreased. Despite of increase of "pollution application" papers, their number is still small (Yanko et al., 1999). The paleoenvironmental approach still dominates over the cytological approach probably because most microplaeontologists are trained in geology rather than in biology. Quantitative parameters of total (live and dead) or dead assemblages are used as environmental indicators although their use should be abandoned as misleading and exchanged by utilization of live foraminiferl populations (Murray, 2000).

New cross-disciplinary approaches are needed to develop environmental micropaleontology. One of them, chemical-ecological approach, focuses on the interaction of organisms with xenobiotics and their ability to protect themselves against xenobiotics by using defence mechanisms. This approach creates a new way of early warning monitoring
and paleoenvironmental reconstructions of stressed environment (Bresler and Yanko, 2000). The advantages of this cross-disciplinary research promise great benefit to both humanity and to the furtherance of environmental micropaleontology.

A COMPLEX MEGAFOSSIL 1.5 BILLION YEARS OLD FROM MONTANA AND WESTERN AUSTRALIA

YOCHELSON, Ellis L., National Museum of Natural History, Washington, DC, USA; K. Grey, Geological Survey of Western Australia, Perth, Australia; and Mikhail A. Fedonkin, Paleontological Institute, Russian Academy of Sciences, Moscow, Russia

"Problematic bedding-plane markings" (Horodyski 1980) are authentic, abundant fossils (Horodyskia moniliformis Yochelson and Fedonkin 2000) from Glacier National Park in the lower part of the Appekuny Formation, dated at 1.5BY. Fossiliferous beds are of finely laminated clay-sized silica particles. Compressed specimens are on both upper and lower surfaces. Early growth consists of narrow horizontal tubes from which closely-spaced spheres develop; an informal name is string of beads. Beads are reconstructed as wide cones, growing upward a maximum of 0.5 cm. On any one string, all beads are the same diameter. The number of beads per string decreases with increasing bead diameter, but the ratio of diameter to spacing remains nearly constant. "Problematic bedding-plane markings" from western Australia (Grey and Williams 1984) are an abundant, unnamed species of Horodyskia, possibly about 300 MY younger. They are restricted to a narrow interval in the Stag Arrow Formation and equivalents and have been traced more than 400 kilometers. Strings grew on a mud substrate after deposition ceased; they are preserved as impressions on the base of the overlying sandstones. Beads grew cone-shaped, narrower than those from Montana. Beads are constant in number on a string so that larger individuals are more closely spaced. Because all beads are similar along a string Horodyskia is judged to be a colonial organism. It had a tough outer integument, which implies a softer interior, and therefore tissue differentiation. This fossil doubles the known range of megafossils in the geologic record.

Grey, K., and I. Williams.1990. Precambriam Research 46.

Horodyski, R.J. 1980. Journal of Paleontology 56.

Yochelson, E.L., and M.A. Fedonkin. 2000. Proc. Biological Soc. Washington 113.

INTERAGENCY COOPERATIVE MANAGEMENT OF FOSSIL RESOURCES IN THE JOHN DAY BASIN, OREGON

ZANCANELLA, John, Bureau of Land Management, Prineville, OR, USA; and Scott E. Foss and Theodore J. Fremd, John Day Fossil Beds National Monument, Kimberly, OR, USA

John Day Fossil Beds National Monument (NPS) and the Prineville District of the Bureau of Land Management (BLM) initiated a program of cooperative management of fossil resources in 1987. Scientific investigators representing museums, academic institutions, and federal agencies worked in collaboration to meet common resource management goals of research and educational outreach. In 1997 the program was expanded to include fossil management of all four BLM districts of eastern Oregon. The many research projects that cover this 10,000 square-mile area have resulted in the construction of a nearly complete composite stratigraphic section in eastern Oregon from 45 Ma to 5 Ma. A continued collaboration with outside investigators has allowed the compilation of detailed sections of lithostratigraphy, complete with biostratigraphic (floral and faunal), magnetostratigraphic, chronostratigraphic, paleosol, and paleoecological interpretations. This "blurring of the boundaries" of scientific disciplines has allowed workers to understand the lateral and temporal variability of paleontological deposits. The maintenance of such useful data results in an environment in which researchers prefer to work in collaboration with the agencies, rather than as freelance permitted investigators. The cooperation of federal agencies, museums, universities, and other educational and research institutions has facilitated the acquisition and management of useful temporal and geographic paleontological data more effectively than could have been accomplished by any single institution.

FIRST FOSSIL RECORD OF EPICAUTA? (COLEOPTERA) OF THE ATOTONILCO EL GRANDE FORMATION (BLANCANO), HIDALGO, MEXICO

ZARAGOZA-CABALLERO, S., Laboratorio de entomología, Instituto de Biología, UNAM, México; and Patricia Velasco-de León, Carrera de Biología Facultad de Estudios Superiores Zaragoza, UNAM, México

In the town of Sanctorum, in the municipality of Atotonilco el Grande, the basal part of the Atotonilco el Grande Formation is exposed with an approximate thickness of 350 m. This sequence, deposited under volcanic activity consists of alternating beds of fine-grained sandstones, limolitas, shales and some gypsum horizons that very in thickness from 5­7 cm. More than 80 specimens have been collected from this locality. These include two types of fishes, gastropods, ostracods of different families, an anuro, fragments of other vertebrates, as well as fragments of equisetales, girogonitos, abundant leaf impressions of Populus, Platanus and other angiosperms and some impressions of arthropods. One of the best preserved and complete impressions is of an insect belonging to the order Coleoptera, that by its characteristic morphology can be assigned to the family Meloidae, possibly belonging to the genus Epicauta Dejean. Species of this family have been cited from the Oligocene of Florissant, Colorado and apparently, this genus has not been cited previously for México (Fosiles Mexicanos Tipo, Perrilliat, 1989). However, this publication primarily discusses insects in amber. México is not known for its record of insect impressions for the Tertiary, and therefore the study of the impression Epicauta, representing the first record of Coleoptera, adds to our knowledge of fossil insects of Mexico.

EARLY CAMBRIAN REEFAL PALEOCOMMUNITIES: WITHOUT STASIS

ZHURAVLEV, Andrey Yu., and Elena B. Naimark, Paleontological Institute, Russian Academy of Sciences, Moscow, Russia; and Rachel A. Wood, Dept. of Earth Sciences, University of Cambridge, Cambridge, UK

The first metazoan reefal paleocommunities appeared and developed during the first half of the Early Cambrian on the Siberian Platform. The delayed (ca. 10 m.y.) appearance of archaeocyaths in other regions beyond the limits of the Siberian Platform decreases the possibility of an incorrect estimation of a species pool. The preservation of fossils is good for the determination of species in sampling units. Observed direct organism-organism interactions indicate that assemblages under consideration represent natural communities and exclude the problem of a contamination by allochthonous species. The available computations of 88 species from 53 sampling units (regression coefficient, evenness value, cluster analysis) as well as the indication of dominant species argue that earliest Cambrian reefal paleocommunities were very volatile entities even within persistent facies. Our data do not reveal community stasis in Early Cambrian reefs either. Only the guild structure kept pass through Early Cambrian reefal paleocommunities occupied similar habitats. This phenomenon was expressed in an obligate presence of certain guilds within the same facies and an interchange of close relatives within a guild. These intrinsic factors were responsible for a higher evenness expressed in Early Cambrian reefs and for a broad predictability of a taxonomic species set in the limits of a peculiar facies. Despite the absence of the most features of the coordinated stasis the Early Cambrian reefs were not entirely accidental aggregates of species. A limited set of guilds consisting of related species kept a community structure resistant under certain environmental conditions while hub species supported a community resilience. Among the features maintaining the coordinated stasis in the Silurian-Devonian paleocommunities, could be the overall increase of species longevity from the Cambrian forth.

EARLY CAMBRIAN SINSK DYSAEROBIC BIOTA (SIBERIAN PLATFORM

ZHURAVLEV, Andrey Yu., Andrei Yu. Ivantsov, Valentin A. Krassilov, Anton V. Leguta, and Galina T. Ushatinskaya, Paleontological Institute, Russian Academy of Sciences, Moscow, Russia

The Sinsk biota (Early Cambrian, Botoman Stage, Siberian Platform) inhabited an open-marine basin within the photic zone, but in conditions characterized by lowering oxygen tensions. All the organisms of the biota were quite adapted to a life in dysaerobic conditions. It is possible that the adaptation of many groups of Cambrian organisms, which composed the trophic nucleus of the Vodoroslevaya Linza paleocommunity from of the Sinsk Lagerstätten, to low oxygen tensions allowed them to diversify in the earliest Paleozoic, especially during the Cambrian. Nowadays these groups comprise only a negligible part of communities and commonly survive in settings with low levels of competition. For instance, cephalorhynchs are restricted to the meiobenthos, caves, and dysaerobic muds. Nonetheless, the organization of the Vodoroslevaya Linza paleocommunity was not simple: It comprised diverse trophic groups and the tiering among sessile suspension-feeders was well developed with the upper tier at the 50 cm level. In number of individuals, the community was dominated by sessile suspension/filter-feeders (53%, sponges, cnidarians, brachiopods, chancelloriids), vagile detritophags (19%, bradoriids), as well as nektobenthic (11%, Eldonia), vagile epibenthic (9.4%, some trilobites, other arthropods, tardipolypodians) and infaunal carnivores/scavengers (2.8%, cephalorhynchs), and vagile suspension-feeders (2.8%, some trilobites). The same groups, but in a different order, comprise the bulk of the biovolume: vagile epibenthic (68.2%) and nektobenthic carnivores/scavengers (21%), sessile suspension/filter-feeders (7.5%), and vagile detritophags (1.2%). The Vodoroslevaya Linza and Phyllopod Bed (Burgess Shale) fossil communities share a number of significant features. These include a high diversity of different groups of organisms, a relative percentage of fauna in terms of number of individuals, and biovolumes of major groups, feeding types, and life habits, which suggests a relative stability (during ca. 25 m.y.) of Cambrian communities occupying similar subtidal settings.

ROLE OF THE HIGH LATITUDES IN THE EMERGENCE OF CENOZOIC MOLLUSCAN FAUNAS OF THE SOUTHERN HEMISPHERE

ZINSMEISTER, William J., Dept. of Earth and Atmospheric Sciences, Purdue University, West Lafayette, IN, USA; and Jeffery D. Stilwell, School of Earth Sciences, James Cook University, Townsville, QLD, Australia

The high southern latitudes played a critical role in the development of the Cenozoic molluscan faunas following the Terminal Cretaceous Extinction Event. The sequence on Seymour Island located on the north tip of the Antarctic Peninsula some 7000 km from the Chicxulub impact site contains an exceptional fossil record and provides important new insight into the re-establishment of the shelf faunas during the earliest Paleocene. The presence of a two to three meter Fish Bone Bed immediately above the iridium anomaly is believed to represent multiple fish kill events associated with the unstable marine conditions immediately following the boundary event. The occurrence of floods of individuals of several opportunistic and disaster species above the bone bed is interpreted as the initial recovery and re-population of the shelf faunas. The decline of opportunistic species, appearance of cosmopolitan and refugia migrants, and the diversification of the molluscan faunas in the Danian part of the Lopez de Bertodano and Sobral formations mark the re-established and diversification the early Cenozoic shelf faunas.