NAPC 2001

Abstracts, Me - Ny
(5/17/01)

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CONODONT RESPONSE TO THE PERMIAN-TRIASSIC EXTINCTION

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

Strong provincialism characteristic of the Late Permian results in very different patterns for the Permian-Triassic event around the globe; three conodont intervals are distinguished. The Changhsingian interval is dominated by neogondolellids including the changxingensis lineage in the Equatorial Warm Water Province (EWWP) and the sheni lineage in both the North Cool Water Province (NCWP) and peri-Gondwana Cool Water Province (GCWP). The latest Changhsingian and Early Griesbachian is marked by the dominance of the Hindeodus-Isarcicella lineage and rarity of the changxingensis lineage in EWWP, abundance of both an early carinata lineage and the Hindeodus-Isarcicella lineage in GCWP, and dominance of the sheni lineage and rarity of the Hindeodus-Isarcicella lineage in NCWP. Clarkina carinata marks the Late Griesbachian and is abundant in GCWP and NCWP and is rare in EWWP. The Permian-Triassic boundary is not represented by extinction of conodont lineages, but only by phyletic evolution and pseudoextinction of conodont taxa as determined by a population approach to taxonomy. The major extinction of conodont lineages both precedes and postdates the boundary. The Iranognathus lineage in EWWP and the Vjalovognathus lineage in GCWP became extinct in mid-Changhsingian and the Hindeodus-Isarcicella lineage in the Late Griesbachian. The C. carinata interval represents a survival interval, and the appearance of Neospathodus near the base of the Dienerian marks the beginning of a recovery phase. This pattern is comparable to conodont events during the Sakmarian and Artinskian, which is represented successively by the extinction of Carboniferous holdover taxa, a survival interval with Sweetognathus whitei and Mesogondolella bisselli, and a recovery phase in which Neostreptognathodus appears. This latter interval is usually interpreted as a response to gradual climate change and it appears that the Permian-Triassic extinction resulted from a similar gradual process, eventually leading to an abrupt ecologic collapse that is most evident in the EWWP, but not a sudden impact.

TRACE FOSSILS IN SILURIAN AND DEVONIAN STRATA FROM THE DELAWARE WATER GAP NATIONAL RECREATION AREA, NEW JERSEY

METZ, Robert, Dept. of Geology and Meteorology, Kean University, Union, NJ, USA

The type section of the Wallpack Center Member of the Decker Formation (Upper Silurian) includes 25 m largely of calcareous sandstones, with subordinate limestones and siltstones deposited under shallow subtidal conditions. The trace fossils Planolites, Palaeophycus, Cruziana, and Rusophycus, representing a Cruziana ichnocoenosis, are found in crinoid- and brachiopod-rich, parallel laminated limestones indicative of somewhat low energy conditions. In contrast, major portions of the section, though poorly fossiliferous, display abundant cross- and trough cross-stratified calcareous sandstones reflecting higher energy associated with a shallow subtidal environment.

The nonbiohermal facies of the Lower Devonian Shawnee Island Member of the Coeymans Formation is represented by silty and sandy limestones, interpreted to have been formed in a dynamic shallow neritic environment. Several units record a Cruziana ichnocoenosis consisting of abundant Planolites, Palaeophycus, and Chondrites, associated with horizontally-stratified and locally rippled deposits. This ichnocoenosis reflects an interbiohermal opportunistic resident fauna. Stratigraphically above these are thin layers and lenses of crinoid-rich limestones. A low density Skolithos ichnocoenosis is also present. It is monospecific, associated with scour-and-fill structures, and the enclosing sandy limestone commonly overlies crinoid-rich lenses and layers. This ichnocoenosis represents colonization by suspension feeders, likely following a previous influx of crinoidal debris that effectively ended occupation by the Cruziana ichnocoenosis.

THE OLIGOCENE BRIDGE CREEK FLORA, JOHN DAY FORMATION, OREGON

MEYER, Herbert W., National Park Service, Florissant, CO, USA; and Steven R. Manchester, Florida Museum of Natural History, University of Florida, Gainesville, FL, USA

The Oligocene Bridge Creek flora of the John Day Formation is one of the most extensive and widely known Oligocene megafloras from North America. The flora has been used extensively in reconstructing regional climate, phytogeography, and the evolution of plant communities. It represents one of the best examples of the broad-leaved deciduous vegetation that became widespread in the Northern Hemisphere following the Late Eocene/Early Oligocene climatic deterioration. Our taxonomic revision of the flora involved examination of large new collections of leaves, fruits, and seeds, in addition to the original type collections. This revision is based upon seven distinct assemblages within the Bridge Creek flora, each based upon one to several localities within close geographic and stratigraphic proximity. The flora is more diverse than previously recognized, with about 125 species known collectively from all assemblages including three ferns, nine conifers, and over 110 angiosperms. The dominant conifer is Metasequoia. Most of the angiosperms are deciduous and include the families Platanaceae, Ulmaceae, Fagaceae, Betulaceae, Juglandaceae, Tiliaceae, Rosaceae, and Sapindaceae (including Aceraceae). Broad-leaved evergreen taxa are rare in the flora. At least eleven of the genera are extinct, but the majority are extant with greatest representation in the deciduous forests of eastern North America and eastern Asia. Based upon the predominant taxa as well as physiognomic criteria, the Bridge Creek flora represents vegetation comparable to the extant Mixed Mesophytic forest of Asia, although the fossil flora was apparently less diverse. Three of the assemblages within the John Day Basin have been ⁴⁰Ar/³⁹Ar dated, with individual dates ranging from 32.24 to 33.62 Ma. Comparable assemblages from the Crooked River Basin have not been dated, although floristic similarities suggest that they are isochronous with the John Day Basin assemblages.

ENVIRONMENTAL BIASES OF SILURIAN FOSSIL KONSERVAT LAGERSTÄTTEN

MIKULIC, Donald G., Illinois State Geological Survey, Champaign, IL, USA; and Joanne Kluessendorf, Weis Earth Science Museum, University of Wisconsin-Fox Valley, Menasha, WI, USA

Discoveries of exceptionally preserved fossils provide important opportunities for paleontological and evolutionary studies. Many of these Fossil Konservat Lagerstätten (FKL) comprise unusually well preserved or articulated specimens of common taxa with hard parts; however, some represent the only evidence of otherwise unknown soft-bodied or lightly sclerotized organisms. These latter examples may be critical to determining the true diversity, evolution, and abundance of life through time.

A number of FKL containing soft-bodied or lightly sclerotized organisms have been found in Silurian rocks of the Great Lakes region of North America. These occurrences are not confined to a single time interval or geographic area, but they do represent a limited range of environments and depositional settings. For example, the Llandovery Waukesha biota (Wisconsin) preserves a variety of easily transported taxa concentrated in a sediment trap. Because of short-term anoxic conditions, the Wenlock Thornton and Ludlow Lecthaylus biotas (Illinois) are preserved in what otherwise appear to be sparsely fossiliferous interreef strata. The Kokomo Limestone (Indiana) and Waubakee Dolomite (Wisconsin) contain limited Wenlock-Ludlow biotas preserved in marginal marine, hypersaline environments that only rarely supported a very low diversity of organisms.

Clearly, most of the Silurian FKL are related to short-term events in atypical environments that usually contained few shelly taxa. These strata would otherwise appear nearly barren (except for bioturbation in some strata). FKL are absent from the classic Silurian reefs and other shallow-shelf environments in the area, which contain an abundance and high diversity of shelly taxa. This contrasts with the Cambrian Burgess Shale-type biotas, which represent more typical marine environments with common and diverse shelly taxa.

STYLES OF BEHAVIORAL COMPLEXITY RECORD BY PALEOZOIC TRACE FOSSILS

MILLER, Molly F., Dept. of Geology, Vanderbilt University, Nashville, TN, USA

Morphologically intricate trace fossils, used as proxies for complex behavior, are interpreted as the result of complicated behavior over an animal's entire lifetime—behavior finely tuned to glean maximum resources with minimum energy expenditure.

Evaluation of Paleozoic trace fossils allows recognition of four distinct styles of complex behavior and also raises questions about what constitutes complex behavior. Included are: (1) Intricate, invariant, programmed behavior recorded in well-known complex trace fossils such as Spirophyton, Zooophycos, and Diplocraterion. (2) Behavior that is complex in consisting of multiple simple behaviors performed by a single organism, as indicated by one trace fossil merging into another (e.g., four types of trace fossils [Skolithos, Palaeophycus, Cruziana, and chevron traces] made by a single producer are found in Permian braided river deposits, Antarctica). (3) Behavior in which an animal constructs complex and simple structures, as demonstrated by direct connection between the two types of structures (e.g., Zoophycos merging into Planolites, Devonian, New York). (4) Two scales of complex behavior reflected in multiple specimens of a distinctive, complicated trace fossil arranged in a pattern (e.g., specimens of Diplocraterion are organized into clear zig-zags in Ordovician limestone, Tennessee.) Implications: (i) Whereas complex behavior has been defined as behavior that is intricate and invariant, behavior involving (nonrandom) switching between several different behaviors, even if they are simple, implies even greater complexity because a decision-making process is required. (ii) Several complex behavioral styles involve compound trace fossils, suggesting that some complicated structures are not life-long abodes. (iii) Because recognition of compound trace fossils commonly requires extensive exposure, styles of behavioral complexity recorded in compound trace fossils too often remain undetected.

AN INTRODUCTION TO COMPLEX TRACE FOSSILS

MILLER, W., III, Dept. of Geology, Humboldt State University, Arcata, CA, USA

Rather than continuing to treat them as preservational rarities or taxonomic anomalies, complex trace fossils should be seen as a class of animal artifacts never adequately addressed in paleobiology. These intricate, often large biogenic structures are essentially unexploited sources of information on the ecology and evolution of animal behavior, and include burrow systems such as Zoophycos, compound structures, and the graphoglyptids, to name the most important marine examples (comparable terrestrial examples such as termite "nests" are more accessible and better understood.) These structures do not appear to reflect a single or dominant behavior or environmental interaction, but instead seem to record the re-engineering of proximal habitats, modulation of disturbances, and the control or manipulation of food supplies by trace producers. Most of them probably resulted from long intervals of occupation (relative to generation times of producers) and complex, variable behaviors/interactions. Continuing debates about dominant function, therefore, are unlikely to produce definitive ecologic and ethologic interpretations. How should we begin a more effective treatment of complex biogenic structures?

Thinking about complex trace fossils in a different way is the first step toward understanding their biologic significance. From a methodologic point of view, component behavioral tokens—individual signs of construction, operation and maintenance embedded within the overall structure—could be delineated, interpreted and used in systematic comparisons with other biogenic structures, including modern burrow systems. From a conceptual perspective, complex trace fossils could be viewed as devices of physiologic projection or as extended phenotypes (suggesting adaptive/exaptive heritable traits!) of trace producers. A renewed effort to discover the trace-makers that build structures like Zoophycos and the graphoglyptids, and more concerted investigation of animal burrowing behavior in general, also would advance the biologic interpretation of these remarkable structures.

METADATA: A NEW WORD FOR AN OLD PROBLEM

MOLINEUX, Ann, Non-vertebrate Paleontology Laboratory, Texas Memorial Museum of Science and History, The University of Texas at Austin, Austin, TX, USA

The prefix "meta" is used in the sense of beyond or transcending the "data," it is information that sheds more light on the raw data and is thus an integral part of any database. It is critical that such metadata be available for researchers, particularly those who are interested in communities or paleoecological structure. In the case of paleontology, knowledge of who collects the specimens, or when they collected them, may be as important as the specimens themselves.

An example is developed here to illustrate this point. During research in the Pennsylvanian section of north central Texas, it became evident to this author that there was not only bias in the fossil record, but also a clearly observable "bias" in what was collected by various researchers. This is not meant to imply that the collectors were intentionally biased, but rather that they were collecting for specific reasons often with narrowly defined objectives. Results from cluster analyses, notwithstanding the vagaries these techniques, strongly indicated that the groups created were based as much on the collector as they were on the facies collected. The observed bias would have been invisible had the specimen data only included locality information and not details about the original collector.

The original documentation of any specimen is imperative archival information, but so are the research papers or dissertations that incorporate valuable methodological insights into their collection scheme. Verbal histories, nowhere in print, are irreplaceable data that should also be considered and incorporated into the database. Even the manner of specimen preparation is significant. Such metadata is considered to be a critical part of the developing database at the Non-vertebrate Paleontology Lab of the TMMSH.

A NEW RANCHOLABREAN VERTEBRATE FAUNA FROM NORTHEASTERN MÉXICO

MONTELLANO-BALLESTEROS, Marisol, Depto. de Paleontología, Instituto de Geología, Universidad Nacional Autónoma de México, México

Few continental vertebrate faunas have been recorded from this part of the country. After a report from the local people of the Ejido de San Lázaro, in the western part of the State of Tamaulipas, fieldwork was carried out in the area. As a result several sites bearing fossil vertebrates were located and fossil remains were collected. The fossil material is derived from a light-yellow clay. The sediments are filling wide and shallow valleys that are cut by seasonal streams. Most of the fossils are moderately preserved, although there are few exceptional cases such as a complete turtle's carapace.

The fossil material includes an almost complete carapace of a glyptodont; it preserves the lateral, central, cephalic and posterior regions; and some postcranial elements such as both humeri, phalanxes, metacarpals, pelvis and vertebrae were also recovered. The material is referred to the genus Glyptotherium. Three species of this genus have been described for the Pleistocene of Mexico. Unfortunately, two of them lack geographic and stratigraphic information and are based on non-diagnostic characters. This is the northernmost record of glyptodonts in México.Equid remains were also recovered (a damaged skull, isolated teeth and postcranial elements); they are referred to the Pleistocene species Equus conversidens. Isolated molars of Mammuthus and Bison were found. Turtle remains are the most abundant material in the study area. These include complete and fragmentary carapaces, sometimes associated with postcranial elements. The material is referred to the genus Gopherus, which is now present in the area, but of a much smaller size. The presence of Bison indicates a Rancholabrean age; and the taxonomic composition suggests open areas with grasses supporting an abundant herbivorous megafauna.

TEMPORAL CHANGES IN CORAL COMPOSITION IN MOOREA DURING THE HOLOCENE

MUCHOW, Rhea S., Dept. of Geography, University of California, Berkeley, CA, USA

The study of coral reef ecosystems is valuable because their health serves as an indicator for both local and global environmental change. Amid recent coral disturbance events in Moorea, the current percent cover of Porites spp., a genus of coral more tolerant to disturbance events, is in question. To test the hypothesis that Porites spp. has the potential to dominate the reefs of Moorea and secondly to investigate the responses of Acropora spp. and Pocillopora spp. to environmental changes in the Holocene, the percent cover of live and fossil coral was collected at three sites on the island. The data from the live coral reefs was compared to fossil coral reefs dated 3,340 to 6,070 years B.P. in order to detect temporal changes in coral composition. Results show that there has been no significant change in the percent cover of Porites spp. or Acropora spp. However, the 1983 cyclone may have altered the percent cover of Pocillopora spp., favoring an increase in growth. This study suggests that over a long temporal scale, coral communities may be well equipped for disturbance events and climate changes, although short perturbations temporarily favor certain species.

FACIES BIASES AND LEAF PHYSIOGNOMIC CLIMATE ESTIMATES: NEW CONSTRAINTS ON THE MAGNITUDE OF EOCENE­OLIGOCENE CLIMATE CHANGE IN THE PACIFIC NORTHWEST

MYERS, Jeffrey A., Dept. of Earth and Physical Sciences, Western Oregon University, Monmouth, OR, USA

Leaf physiognomic analysis of middle Tertiary paleofloras of the Pacific Northwest, combined with increasingly precise geochronology for many flora-bearing sequences, yields a detailed record of climate and vegetational change spanning the Eocene­Oligocene transition. However, paleofloras from subduction margin basins have inherent biases and limitations that impact physiognomic climate estimates: (1) source vegetation is patchy and heterogeneous; (2) floras are of limited lateral distribution, preserved in a range of local depositional/preservational facies, and commonly cannot be "facies averaged"; (3) many floras are of low or moderate diversity. Comparison of age-equivalent assemblages from floodplain and lacustrine facies of the middle Eocene Clarno Flora, central Oregon, and late Eocene Cedarville Flora, NE California, suggest that: (i) autochthonous leaf litters from stable floodplain facies are biased by selective decay of thin-leaved species and yield maximum physiognomic estimates of temperature and precipitation; (ii) mid-lacustrine assemblages are dominantly comprised of wind-transported, small, thin, and broad leaves from disturbance-tolerant lake margin vegetation, and yield minimum estimates of temperature and precipitation; (iii) rapidly buried autochthonous and parautochthonous floodplain, paludal, and nearshore lacustrine assemblages typically possess high species diversity and are most likely to yield precise physiognomic climate estimates. Comparison of assemblages from different facies requires a 3°C to 5°C facies correction for estimates of mean annual temperature (MAT), while estimates of precipitation can vary by up to 100% between lacustrine and floodplain assemblages. Facies corrected estimates of Eocene-Oligocene transitional climate change in the interior Pacific Northwest indicate a ~4°C MAT cooling step at 38.5 Ma, a ~3°C increase in MAT near 37 Ma, followed by a second MAT decline of ~4°C between 35 and 33.7 Ma. Cooling steps were accompanied by a significant decline in precipitation, along with increased temperature and precipitation seasonality. The facies corrected record agrees closely with previous interpretations, although the magnitude of temperature and precipitation change is significantly reduced when facies differences are taken into account.

BIOSTRATIGRAPHY AND PALEOECOLOGY OF CENOZOIC FORAMINIFERA FROM THE TOFINO BASIN, OFFSHORE VANCOUVER ISLAND, BRITISH COLUMBIA

NARAYAN, Y.R., and C.R. Barnes, School of Earth and Ocean Sciences, University of Victoria, Victoria, BC, Canada; and M.J. Johns, Pacific PaleoQuest, Brentwood Bay, BC, Canada

The Tofino Basin, offshore Vancouver Island contains a thick sequence (~3700m) of Cenozoic marine clastic sediments. Previous micropaleontological studies of the Tofino Basin have been limited to a few preliminary reports. Foramininfers have been recovered from 1500 core samples from six offshore hydrocarbon exploration wells, drilled by Shell Canada Resources during the late 1960s. This study provides a biostratigraphic framework using benthic and planktic foraminifers. Subsurface data are compared with Tertiary foraminifers from the Carmanah Group outcrops, which expose ~1200m of middle Eocene to early Miocene sediments on southwestern Vancouver Island. The Tofino Basin stratigraphic sequence is also correlated to the Olympic Peninsula of northwestern Washington. Depositional environments are interpreted and ancient seawater composition is measured using 87Sr/86Sr signatures of foraminiferal tests. The unidirectional Tertiary strontium isotope curve complements the biostratigraphy in correlating the subsurface and coastal sequences. Tofino Basin foraminifers range in age from Eocene to Pliocene. Eocene foraminifers and microflora indicate a warmer climatic period, however preservation is poor and foraminifers are relatively scarce. Abundant, diverse, and well preserved faunas occur in Oligocene to Pliocene strata. Most faunas, with the exception of the Eocene, suggest relatively deep, bathyal depositional environments, with temperate to cold water temperatures. However, some faunal transitions from bathyal (Uvigerina, Cassidulina) to neritic (Oolina, Nonionella, Buccella), indicate fluctuating substrate conditions during the Oligocene-Miocene. Episodic uplift and sea-level fluctuations in this region have resulted in rapid facies changes, which are recorded by the lithology, foraminifer diversity and palynomorph distributions.

DRILLING PREDATION ON ECHINOID PREY: CHANGES IN INTENSITY AND SITE SELECTIVITY THROUGH TIME

NEBELSICK, James, H., Institute of Geology and Paleontology, University of Tübingen, Tübingen, Germany; and Michal Kowalewski, Dept. of Geological Sciences, Virginia Tech, Blacksburg, VA, USA

Drilling predation on echinoids is a common phenomenon in both Recent and fossil echinoids. Cassid gastropods have been identified as the prime drilling predators of both regular and irregular echinoids. These produce a distinct, cylindrical drill hole, the shape of which is heavily affected by the presence of pores and plate boundaries in the test of the echinoid prey. Very high drilling predation rates have been recorded from Recent echinoid faunas with high variations with respect to prey species and environments. Studies on drilling predation on Recent clypeasteroids have shown that drilling frequencies appear to be independent of the taphonomic state of the tests. This suggests that predation traces on fossil echinoid faunas can be used as a basis for comparison of predation intensities and site selectivity. In this study, data on drilling predation on echinoids from Recent as well as fossil populations is combined with data from the literature. There are distinct differences of site selectivity between echinoids showing different skeletal morphologies: clypeasteroids with internal support (Echinocyamus) show a tighter distribution of boreholes than those without (Fibularia). This was analyzed by recording predatory drillholes with respect to their general position (oral or aboral side) or to specific plate features of the echinoid test (e.g., within ambulacral or interambulacral fields, within or external to the petalodium, proximity to the peristome or periproct). There is a distinct rise in maximum vales and mean values of predation intensity on echinoids prey from the Early Cretaceous (values less than 10%) to the Recent (up to 80%). This mirrors the increase of predation intensity on mollusks. The concurrent rise in drilling on echinoids and mollusks may have been caused by (1) the simultaneous radiation of drilling predators; (2) incumbent replacement of predatory clades after the end-Cretaceous extinction; and (3) decrease in facultative drilling behavior through time.

HADROSAURIAN SKIN IMPRESSIONS FROM THE JUDITH RIVER FORMATION (LOWER CAMPANIAN) OF MONTANA

NEGRO, Giuliana, Dept. of Vertebrate Paleontology, Natural History Museum of Los Angeles County, Los Angeles, CA, USA; and Albert Prieto-Marquez, Museum of the Rockies, Bozeman, MT, USA

A few isolated patches of skin impressions were found in the Judith River Formation (lower Campanian) of northeastern Montana, within a paucispecific bone bed that has produced more than 1,300 skeletal elements of the hadrosaurian dinosaur Brachylophosaurus canadensis. Two different impression morphologies have been observed. A skin patch covering an area of approximately 160 cm² of a sandstone block is characterized by non-overlapping tubercles, flattened, polygonal in shape, and with smooth surfaces. These tubercles present relatively large dimensions, averaging 7.5 millimeters in diameter. A mosaic of smaller tubercles is preserved as five patches on sandstone and mudstone. This second kind of tubercles, non-overlapping and subhexagonal to oval in outline, range from 4 to 5 mm in diameter. The study of the integument is limited by the impossibility to correlate the skin impressions with diagnostic osseous remains. However, comparison of the specimens with dinosaur skin shows that a similar integumentary morphology has previously been documented in hadrosaurian dinosaurs. Hadrosaurid skin consists of tubercles varying in shape and size in different body regions and in different species. Polygonal tubercles similar to those characterizing the specimens from the Judith River Formation have been observed in Edmontosaurus and Corythosaurus. In these taxa the tubercles are flattened and present smooth surfaces. The tubercle dimensions are relatively large, varying from 5 to 10 mm in diameter. Although no data indicating the provenance of the skin impressions are available, the integumentary morphology suggests the placement of the specimens among Hadrosauridae.

SPECIES-LEVEL MORPHOLOGICAL STABILITY IN NEOGENE MARGINELLIDS FROM THE DOMINICAN REPUBLIC

NEHM, Ross H., Columbia University, Teachers College, New York, NY, USA

Despite recent interest in community stability and paleoecological controls on evolutionary processes, few rigorous species-level studies have been integrated with quantitative paleobiological investigations of community change. The richly fossiliferous Neogene stratigraphic sections of the Dominican Republic provide a unique system in which to investigate potential interactions between species-level and assemblage-level processes. Although many processes have been invoked to explain morphological stasis in Dominican species, no studies have investigated the possibility that community-level interactions play an important role in maintaining species-level stability. Seven species-lineages from the gastropod Family Marginellidae are prominent and well-preserved components of the fossil fauna of the Dominican Republic. Marginellid species occur abundantly from the middle Miocene to the early Pliocene of the DR in a variety of paleoenvironments and lithologies. Marginellid shells are taphonomically durable and well preserved in these deposits as a result of their thickness, extensive callusing, and reinforced aperture margin. Furthermore, very thin and fragile juvenile shells co-occur with robust adult shells in frequencies similar to those of living populations. Collectively, these factors make marginellids well suited for species-level studies.

Multivariate statistical comparisons of evolutionary patterns within and among adults of seven Prunum and Eratoidea species produced very few statistically significant morphological differences in relation to geography, paleoenvironment, lithology, or time. No net morphological change is realized in Prunum and Eratoidea species through a five-million-year sequence. Determining how biofacies stability correlates with marginellid species level patterns would greatly enhance our understanding of the processes that control the tempo and mode of speciation. Preliminary research suggests that major changes in faunal composition and paleoenvironment are not correlated with marginellid species-level change in this system.

A NEW SPECIES OF TRIRACHODON (CYNODONTIA): CONSEQUENCES FOR CYNODONT EVOLUTION

NEVELING, Johann, Council for Geoscience, Pretoria, South Africa; Johann Welman, National Museum, Bloemfontein, South Africa; and Bernard Battail, Musée National d'Histoire Naturelle, Paris, France

The Lystrosaurus and Cynognathus Assemblage Zones of the Karoo Supergroup in South Africa is considered to be the type sequence for terrestrial faunas of the Early to Mid Triassic. Recent work revealed a new, previously unknown, fossil fauna between these two, well defined, biozones. It shares almost no faunal elements with the Lystrosaurus Assemblage Zone, but consists of taxa closely related to, although slightly antedating, the fossil taxa of the Cynognathus Assemblage Zone.

Fossil material collected from the new fauna included small cynodonts assigned to the genus Trirachodon. Trirachodon is the most primitive of the gomphodont cynodonts and up to now it contained only one species, Trirachodon berryi, which is known to occur in the Cynognathus Assemblage Zone. The new Trirachodon material, however, extends the range of this genus down into the pre-Cynognathus Zone fauna mentioned above, where it is represented by a new species.

Subtle differences in skull geometry and bone morphology were documented between the two species of Trirachodon. By far the most striking example of variation within the genus is provided by the morphology of the postcanine teeth, with the new species representing a more primitive condition than Trirachodon berryi. Much of the variation between the two species is related to the feeding apparatus, indicating that diet played an important role in the evolution of this genus. It is envisaged that a changing palaeoclimate impacted directly on the diet, and ultimately the cranial anatomy, of Trirachodon. As many parallels can be drawn between the modifications documented within the genus Trirachodon and the evolution of cynodonts as a group, the new Trirachodon material provides a rare opportunity to better understand the environmental factors that influenced cynodont evolution.

A NEW LATE CRETACEOUS MARINE VERTEBRATE FAUNA FROM THE WEST COAST OF NORTH AMERICA

NICHOLLS, Elizabeth L., Royal Tyrrell Museum, Drumheller, AB, Canada; and Dirk Meckert, Courtenay, BC, Canada

The Late Cretaceous Nanaimo Group on Vancouver Island, British Columbia, is a sequence of sandstones, shales and conglomerates deposited in a forearc basin between the North American mainland and the accreting Wrangalia Terrane. Molluscs from the Nanaimo Group have been known for many years, but it is only recently that marine vertebrates have been recovered. We report a diverse fauna of fish, sharks, mosasaurs, plesiosaurs and turtles from the lower part of the Trent River Formation (Santonian­Campanian), near Courtenay, British Columbia. This is some 15 million years older than the marine reptile fauna from the Moreno Formation of California (Maastrichtian). However, like the California fauna, there are no polycotylid plesiosaurs, and the mosasaur is a new genus. This reinforces the provinciality of the Pacific faunas and their isolation from contemporaneous faunas in the Western Interior Seaway.

A RE-EVALUATION OF THE OCCURRENCES AND DISTRIBUTION OF CRETACEOUS DECAPOD CRUSTACEANS ALONG THE WEST COAST OF NORTH AMERICA

NYBORG, Brant O., Portland State University, Portland, OR, USA; Torrey G. Nyborg, Kent State University, Kent, OH, USA; Gregory Kovalchuk, The Dalles, Wasco Co., OR, USA; Francisco Palomino, INEGI, Aguascalientes, México; and Francisco J. Vega, Instituto de Geología, Ciudad Universitaria, Coyoacan, México

Recent discoveries of fossil decapod Crustacea in Oregon, USA and Baja California, Mexico as well as crab-bearing Cretaceous deposits in Alaska, Washington and California, USA, and British Columbia, Canada have initiated a re-evaluation of fossil decapod Crustacea phylogeny and modification of paleoceanographic distribution of Cretaceous decapod crustaceans. To date, no synthesis of the occurrences of decapod faunas from Cretaceous deposits along the west coast of North America have been made.

A previously undescribed fossil decapod crustacean fauna was collected from Albian age rocks within the Hornsbrook and Hudspeth formations of Oregon. This fauna includes undocumented species of Cretacoranina, Eodorippe, and an undescribed member of the family Raninidae. Material was also collected within newly discovered outcrops of the El Rosario Formation (Maastrichtian) in Baja California, Mexico, expanding the paleobiogeographic range of Icriocarcinus xestos. The aforementioned recent discoveries coupled with other crab-bearing Cretaceous deposits along the west coast of North America greatly expand the previously known abundance and diversity of Cretaceous decapod crustaceans, enhancing our understanding of the decapod fauna during this time interval.

This study results in new systematic, paleoecologic, evolutionary, and paleobiogeographic interpretations of the Cretaceous decapod crustaceans. This also results in major range extensions and reinterpretations of the Cretaceous families of fossil decapod crustaceans, allowing an extensive revision of the systematics of these organisms.

BIOSTRATIGRAPHY AND DECAPOD FAUNAS OF THE MIOCENE DEPOSITS OF THE PACIFIC NORTHWEST

NYBORG, Torrey G., Kent State University, Kent, OH, USA; Brant O. Nyborg, Portland State University, Portland, OR, USA; Ross E. Berglund, Field Associate, Burke Museum of Natural History and Culture, Seattle, WA, USA; and Elizabeth A. Nesbitt, Burke Museum of Natural History and Culture, Seattle, WA, USA

A high diverse fauna of undescribed fossil decapod crustaceans has been discovered within several Miocene localities in Oregon and Washington. Until now, the primary focus of research on Miocene marine faunas and stratigraphic correlations in this region has been on mollusks, foraminifera and marine vertebrates. Descriptions of these decapod faunas will enhance correlations and further the understanding of the biotic associations represented in Miocene deposits during the important transition from ancient to modern faunas.

Along with the detailed taxonomic study of the fossil crabs, the integration of biostratigraphic, magnetostratigraphic and isotopic stratigraphic studies will establish time constraints for these upper Miocene formations and enable reconstructions of both stratigraphic and paleogeographic ranges of the fossil decapod fauna of the Pacific Northwest of North America.

Paleobiogeographic reconstructions of the dispersal distributions of fossil decapod crustaceans based upon paleoceanographic modeling have shown a fairly low diversity of Miocene decapod faunas in the Pacific Northwest of North America, in contrast to Japan where the decapod faunal diversity was highest during the Miocene. Decapod crustaceans from Japan belong to 35 genera within 20 families in contrast to only 11 genera within nine families from the Pacific Northwest of North America. These differences are believed to be related to tropical influences between the Tethys and Indo-Pacific oceanic regions. However, there are marked generic-level similarities between Miocene age faunas of Japan and the Pacific Northwest of North America. The number of Pacific Northwest decapod crustaceans will be increased to at least 17 genera within 14 families, closing the gap between these two geographically distinct areas. This study demonstrates a strong North Pacific interchange between Japan and the Pacific Northwest of North America during the Miocene epoch.