NAPC 2001

Abstracts, Sa - Sk
(5/22/01)

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BEST-FIT INTERVALS: MEASURES OF THE RESOLVING POWER OF PALEONTOLOGICAL FIRST- AND LAST-APPEARANCE EVENTS

SADLER, Peter M., Dept. of Earth Sciences, University of California, Riverside, CA, USA

The locally preserved range of a fossil taxon includes gaps that result from the patchy distribution of organisms and the incomplete preservation or recovery of fossils. The same factors cause stratigraphic sections to underestimate the length of taxon ranges. Because the effects vary with taxon and location, stratigraphic sections contradict one another concerning the sequence of first- and last-appearance events. Like the gaps within a range, the contradictions between sections may be used to gauge the reliability of range ends and test the significance of preserved patterns of extinction and origination. Probabilistic confidence intervals built from gap sizes tend to treat short-lived taxa like long-lived taxa with poorly preserved ranges. Short ranges provide too few gaps for useful analysis, but their position in sequence is not compromised.

Computer algorithms resolve the contradictions between sections by finding a sequence of range-end events that minimizes the net misfit with all the local range charts. Operationally, the task is analogous to finding the most parsimonious cladogram. Usually the solution is not unique; more than one sequence of events may share the best fit. For each event, resolving power can be quantified as a "best-fit interval"—the range of positions in sequence that the event occupies in the full set of equally best-fit sequences. Overlapping best-fit intervals indicate events whose timing cannot be separated by the fossil record. Culling the available events down to those whose best-fit intervals do not overlap produces a maximum consensus sequence that typically exceeds the temporal resolution of traditional biostratigraphic zonation by a factor of five to ten. Considering all the best fit intervals leads to standing diversity curves that are free of the artifacts of zonal subdivisions.

TRACING THE FATE OF AVALONIA: MICROPALEONTOLOGICAL ANSWERS TO A GEOLOGICAL CONUNDRUM

SAMUELSSON, Joakim, Sédimentologie et Paléontologie, UPR du CNRS Géosciences, Université de Rennes 1, Rennes Cedex, France; and Marco Vecoli, Institut für Geologische Wissenschaften, MLU Halle/Wittenberg, Halle (Saale), Germany

Most early Paleozoic palynomorphs, especially the acritarchs and the chitinozoans, were probably planktonic. Consequently, the spatial distribution of those palynomorphs was essentially controlled by climatic factors, i.e., indirectly by paleolatitude and paleocurrents. Thus, at least during late Arenig and Llanvirn times (late Ibexian and middle Whiterockian in North American terms), acritarchs and chitinozoans can be effectively used as paleogeographic indicators. Although of enigmatic biological affinities, the distribution patterns of chitinozoans are relatively well understood, and consequently, they are especially useful in a paleogeographic context. The microcontinent Avalonia was part of the high-latitude Gondwana paleocontinent until it drifted off in Middle Ordovician times. Subsequently, Avalonia started to collide with Baltica probably in the Ashgill (late Cincinnatian), and with Laurentia in the Early Silurian. Thus, as an a priori hypothesis, chitinozoan faunas preserved in the oldest rocks of Avalonia ought to be similar to the contemporary cold-water Gondwana faunas. In younger rocks a successive incorporation of chitinozoans typical of middle latitudes as on Baltica and of the low latitudes as on Laurentia ought to take place. This pattern is already established for the benthic macrofauna, where in Caradoc (late Whiterockian to early Cincinnatian) times the Avalonian faunas started to mix with those of Baltica. A number of Avalonian successions analyzed for their chitinozoan faunas clearly reflect the a priori suggestion above: the oldest strata yielded a typical north Gondwana chitinozoan fauna. In the early Late Ordovican, an influx of chitinozoans also common in Baltoscandia is evident. Chitinozoans recovered from the inferred northern end of Avalonia support the idea of a narrowing Iapetus Ocean in latest Ordovician times. Furthermore, besides mirroring the drift history of Avalonia, the chitinozoan faunas can also be used together with coeval acritarchs to chronostratigraphically constrain the Avalonia-Baltica collision.

MORPHOLOGIC EVOLUTION OF CONGERINE BIVALVES IN THE LATE MIOCENE LAKE PANNON OF CENTRAL EUROPE

SANDERS, Hilary, and Dana H. Geary, Dept. of Geology and Geophysics, University of Wisconsin, Madison, WI, USA; and Imre Magyar, MOL Hungarian Oil and Gas Company, Budapest, Hungary

Covering parts of Central and Eastern Europe from approximately 12.5 to 4.0 million years ago, Lake Pannon serves as an exemplary "evolutionary laboratory." The stratigraphy, paleogeography, and paleoenvironments of Lake Pannon are well documented, and its deposits contain a diverse fauna recording an unparalleled endemic radiation of brackish and freshwater molluscs. The unique dreissenid bivalve, Congeria, is abundant in Pannonian deposits. This study examines patterns of Congeria's morphologic change through time and space. Museum specimens were supplemented with new field collections and investigated via outline analysis (eigenshape method), traditional morphometric techniques, and multivariate statistical analysis.

The morphologic evolution of the C. rhomboidea lineage is characterized by a shift from thin-shelled, ovoid forms, through intermediate morphologies, to robust, angular forms. Two species-level transformations occur in this lineage: C. praerhomboidea -> C. rhomboidea -> C. alata. Early representatives of the C. balatonica lineage are limited to thin-shelled, triangular forms with diminutive byssal openings. Over time, morphospace occupation by C. balatonica expanded to include more irregular, thickened forms displaying prominent byssal openings, with intermediate morphologies present. Both the morphologic diversification of C. balatonica and the turnover from C. praerhomboidea to C. rhomboidea are constrained stratigraphically within the Limnocardium decorum biozone (ca. 8.5­9.0 Ma), an interval of continued northwest-to-southeast deltaic progradation during which the lake shrank to half its former size. Coincidence of these events suggests that environmental changes influenced evolutionary change within Congeria.

HOLOCENE PALEOPRODUCTIVITY IN THE NORTHWESTERN PACIFIC DETERMINED BY FORAMINIFERAL ASSEMBLAGES IN A FJORD OF WESTERN VANCOUVER ISLAND, BRITISH COLUMBIA

SCHELL, Trecia M., Centre for Marine Geology, Dept. of Earth Sciences, Dalhousie University, Halifax, NS, Canada; and Audrey Dallimore, Dept. of Earth Sciences, Carleton University, Ottawa, ON, Canada

Scientific interest in the evidence linking oceanographic processes and fish population dynamics has increased since the highly publicized Pacific salmon collapse off the west coast of British Columbia and the collapse of the Atlantic cod fishery. To study this problem in a prehistorical context, Effingham Inlet was used as a study site; it is a 17-km long by 1-km wide fjord located at the apparent northern extreme of the California Current with a connection with the open ocean. Historical fish catch data suggest a large-scale expansion and contraction of this favorable habitat due to the large-scale changes in oceanic climate, i.e., upwelling and ENSO (El Niño Southern Oscillation).

Foraminiferal assemblages may be used as proxies for paleoclimatic and paleoceanographic conditions such as temperature, oxygen, salinity, and organic material production. Various combinations of those factors may indicate periods of enhanced and suppressed upwelling events, and the associated productivity. Once the paleoceanography of a region is understood, it may serve as a proxy for the suitability of a paleohabitat for a particular pelagic fish species. The restricted nature of Effingham Inlet, a fjord on western Vancouver Island, British Columbia is an ideal primary study site with its deep basins, shallow sills, laminated sediments and low sediment oxygen content, to provide an excellent sedimentological and paleobiological preservation record of these upwelling and other ocean-climate events.

The presence low oxygen tolerant foraminiferal faunas in the inner basin indicate that anoxic conditions predominate, but are not permanent. In addition, there are several discrete pulses of Buccella frigida followed by an increase in Fursenkoinia fusiformis abundance, indicating that there have been several incidents of inputs of freshly marine waters into the inlet (possibly upwelling events) followed by decreases in oxygen levels, presumably caused by high productivity events triggered by upwellings.

HEAPS OF ECHINOIDS IN A PENNSYLVANIAN ECHINODERM LAGERSTÄTTEN: IMPLICATIONS FOR FOSSILIZED BEHAVIOR

SCHNEIDER, Chris L., Dept. of Geological Sciences, University of Texas at Austin, Austin, TX, USA

An exceptionally preserved echinoderm community from the Winchell Formation at Brownwood, north-central Texas contains several thousand individuals of a large species of Archaeocidaris. Other fossils are less abundant and include crinoids, other echinoids, brachiopods, encrusting bryozoans, fenestellid bryozoans, edrioasteroids, and asterozoans. Pteridosperm and lycopsid leaf debris is abundant.

This recurring community is preserved along several horizons in a, sulfur-rich, channel-shaped, near-shore black shale. Fossils are complete and only slightly disarticulated with elements remaining in close association, indicating that decay occurred before final burial. Though some echinoids are overturned, there is little evidence of disturbance by scavengers or transport mechanisms.

Hundreds to thousands of Archaeocidaris echinoids occur within lagerstätten horizons. Within these aggregations, archaeocidarids cluster into smaller, dense groups, sometimes with overlapping spines. Extant echinoids have also been observed aggregating, often clustering similarly to these Pennsylvanian archaeocidarids. These modern echinoid aggregations have been interpreted as feeding, defensive, or spawning behavior. Because the echinoids and other fossils seem undamaged by predation, it is unlikely that the archaeocidarids represent a defensive aggregation. The Archaeocidaris echinoids at this locality were probably aggregating to spawn or to feast on the abundant plant debris. The rarer echinoid species were most likely present to scavenge leaf matter, as their distribution is much more scattered.

Unusual black material full of crinoid fragments is found within the tests of some archaeocidarids or oozed out between their interambulacral plates. This is interpreted as evidence of final meals. Crinoids are rare at this locality, so these remains may represent crinoids that were consumed elsewhere by the echinoids. Because of the abundance of plant debris, leaf matter may have also been a significant part of echinoid diet before death.

PHYLOGENETIC REVISION OF THE CARDIINAE (BIVALVIA, CARDIIDAE): INDIAN OCEANTROPICAL AMERICAN DISJUNCT DISTRIBUTIONS AND NEW ZEALANDSOUTH AMERICAN BIOGEOGRAPHIC
CONNECTIONS

SCHNEIDER, Jay A., Dept. of Geology & Geophysics, University of Wisconsin, Madison, WI, USA

A phylogenetic analysis of Cardiinae finds it to be paraphyletic. Cardiinae is therefore restricted to Cardium, Bucardium, Vepricardium, Dinocardium, Planicardium, Chesacardium, Acanthocardia s.s., A. (Rudicardium) and Schedocardia. The closest relatives of Cardiinae are the Eocene Sawkinsia and the "CFTL" clade containing Plagiocardium, Maoricardium, Clinocardiinae, Fraginae, Lymnocardiinae and Tridacninae (giant clams). The remaining taxa that had been placed in Cardiinae form a monophyletic group, sister taxon to Sawkinsia + Cardiinae + CFTL; a new subfamily is erected for this group. This new taxon contains Orthocardium, Loxocardium, Europicardium, Hedecardium s.s., H. (Titanocardium) and H. subgen. n., Agnocardia and Afrocardium. Many species in this new taxon had simply been (and continue to be) placed in Trachycardium (subfamily Trachycardiinae) based on superficial examination of shells. The only extant subtaxa in the new subfamily are Afrocardium and Europicardium. Hedecardium s.l. was not restricted to New Zealand as usually argued but was present in Myanmar and Australia, as well as being represented in South America by H. subgen. n. Renewed studies of the long-ignored marine invertebrate Cenozoic faunas of South America will yield additional examples of taxa long thought to be New Zealand endemics. The only other member of the new taxon with representatives in the western hemisphere is the extinct Agnocardia. Agnocardia's closest relative, Afrocardium, long misconstrued as a fragine, has been recorded only in Recent faunas, usually from the Indian Ocean. This disjunct biogeographic distribution is found to be a function of a century of misidentification of fossil and Recent species, for species attributable to Agnocardia occur in the Paleogene of Europe and Africa; likewise, species attributable to Afrocardium occur from the Eocene to Pliocene of Europe and Africa. A greater awareness of modern taxonomy of both fossil and Recent forms is necessary to avoid constructing erroneous biogeographic distributions and phylogenetic hypotheses.

CLAM-RING TIME-SERIES: A NEW METHOD FOR HIGH-RESOLUTION ENVIRONMENTAL RECONSTRUCTION

SCHÖNE, Bernd R., Dept. of Geosciences, University of Arizona, Tucson, AZ, USA

Modified dendrochronological methods can improve the temporal resolution of environmental reconstruction from bivalve mollusk shells. Mollusks grow by periodic accretion of skeletal material leaving daily, fortnightly and annual growth increments bordered by distinctive growth lines in their shells. Cross-dating individual growth increment time-series can help to find and verify overlapping life spans among different specimens from a given region. "Clam-ring" chronologies from individuals with overlapping life spans can be strung together to form master chronologies, which comprise much longer time periods than individual life spans. Master chronologies provide a source for the analysis of longer-term environmental periodicities and fluctuations. We measured annual growth increment widths in 67 Chione cortezi, C. fluctifraga and C. californiensis specimens collected alive at different times in the 1990s in the intertidal zone of the northern Gulf of California, Mexico. The specimens average seven to eight years in ontogenetic age. Standardized growth index time-series calculated from each specimen were cross-dated and strung together. Inter-annual growth patterns in specimens with overlapping life spans are strikingly similar. The Chione master chronology covers the period from 1982 to 1999. 75% of the variability in growth rates during the past ten years can be explained by water temperature and salinity. This study demonstrates that even relatively short-lived bivalve mollusks can be used to establish master chronologies, which reveal high-resolution environmental information over periods that are longer than the individual mollusk's life span.

THE TERTIARY HISTORY OF NORTH AMERICAN MEGAFOSSIL CONIFERS: THE FEW, THE PROUD, AND OFT TIMES NEGLECTED

SCHORN, Howard E., and Diane M. Erwin, Museum of Palentology, University of California, Berkeley, CA, USA

The modern coniferous (s.l.) flora of the Northern Hemisphere consists of 38 genera (~350­425 species), 36 exclusively Northern Hemisphere, and two podocarp genera more typical of the Southern Hemisphere. The greatest concentration of extant genera in the Northern Hemisphere is in Asia, s.l. (34 genera, 89%), North America (NA) has three (8%) restricted genera, and Europe-North Africa has one (3%). Some 30 (79%) of the extant genera were present in NA during some part of the Tertiary. Two extinct entities, not including form genera, are also recognized.

As in all walks of paleobotanical life, difficulties in identification of similar sterile and/or poorly preserved material, plus unwarranted misidentifications, plague our historical analyses.

Major events in the Tertiary history of North American conifers closely track the changing physiographic/climatic histories of the area. At a first level approximation we recognize four intervals of development, viz., the first three that document increasing diversity by "step-wise" addition of genera, and the fourth, leading to our modern forests, is one of loss of generic diversity by extirpation. Period I, ~65­50 Ma, low generic diversity of "archaic" conifers presently mono- or oligotypic, largely deciduous, individual taxa widespread, inhabited low elevation sites. Period II, ~50­32 Ma, with the exception of the loss of the deciduous Mesocyparis, the archaic genera continue. More elevated sites of deposition became available and document the spread and diversification of additional pinaceous and cupressaceous genera into North American forests. Period III, ~32­12 Ma, all previous genera continue and additional extant, and one extinct, genera are added. This interval, with its great physiographic diversity, and diverse yet equable moist climate, saw the largest number of extant conifer genera in North America, rivaling that of present Asia. Period IV, <12 Ma. Following the previous "additive" periods, the later Tertiary in North America is a time of loss of generic diversity, decreasing from the previous high, to the present 16 genera, in a period of ~2­3 Ma.

PRECURSOR EVENTS OF MEGATHRUST EARTHQUAKES AS DETERMINED FROM COASTAL MARSH DEPOSITS ON THE WEST COAST OF THE UNITED STATES USING FORAMINIFERA AS INDICATORS

SCOTT, David B., and Andrea Hawkes, Centre for Marine Geology, Dalhousie University, Halifax, NS, Canada; and Jere Lipps, Museum of Paleontology, University of California, Berkeley, CA, USA

We present results from two areas on the West Coast of the United States where large megathrust earthquakes are known to occur. They have been shown to occur in several places with frequencies of 200- to 500-year repeat times. However, we have determined, using a combination of benthic foraminifera and thecamoebians, that there are detectable precursor events that appear to happen 2­5 years before a major fault break. This is indicated by assemblages of both thecamoebians and foraminifera that suggest small (30 cm or less) subsidence events just prior to a major earthquake. The first indication was from an historical event, the great 1964 Alaska earthquake, where the exact sequence of events was known and there were coastal deposits with the subsidence event preserved. Secondly, we examined sequences from Netarts Bay, Oregon where previous workers had suspected that they had seen precursors using diatoms as indicators. In Netarts Bay the event occurred in a salt marsh deposit and showed a definite 30 cm subsidence just prior to major quakes and tsunamis. In Alaska, a forest fauna of thecamoebians changed to a slightly brackish fauna; this sequence was Pb210 dated by British colleagues to show that the 1 cm interval before the quake was not more than 5 years. If this phenomenon can be proven in other areas, it will give planners and managers a new tool for dealing with catastrophic earthquakes by providing a long lead-time to react before the event occurs.

A NEW FOSSIL MAMMAL ASSEMBLAGE FROM THE SOUTHERN CHILEAN ANDES: IMPLICATIONS FOR GEOLOGY, GEOCHRONOLOGY AND TECTONICS

SEARS, Karen E., Committee on Evolutionary Biology, University of Chicago, and Dept. of Geology, Field Museum of Natural History, Chicago, IL, USA; John J. Flynn, Dept. of Geology, Field Museum of Natural History, Chicago, IL, USA; Michael J. Novacek, Div. of Vertebrate Paleontology, American Museum of Natural History, New York, NY, USA; and Daniel Frassinetti, Depto. de Geología, Museo Nacional de Historia Natural, Santiago, Chile

Paleontological reconnaissance beginning in 1986 led to the discovery of a new and diverse fossil terrestrial mammal assemblage of Santacrucian SALMA (latest early Miocene) age in the southern Andes of Chile. This is the westernmost high latitude mammal fauna in South America and was the first discovery of a diverse (36 taxa) fossil mammal assemblage from Chile in nearly a century. The mammal fauna includes several marsupial species, most notably a very diverse assemblage of Paleothentes that includes a new species. The appearance of Paleothentes in the southern Chilean Andes extends their geographic range. In addition, the rich Paleothentes fauna shows some interesting morphological patterns that bear on species recognition. The discovery of a new Santacrucian fauna also allows refinement of the early to middle Miocene SALMAs, bearing on the controversial Friasian as typified within Chile.

The fossil mammals occur in a terrestrial sequence that conformably overlies a marine section of late Oligocene to early Miocene age. The marine-terrestrial sequence, and the fossils therein, bear significantly on theories concerning the extent of the late Tertiary Patagonian epicontinental seaway, and the onset of later Cenozoic phases of uplift in the southern Andes. Uplift in this region likely was initiated by the Santacrucian SALMA (16­17.5 Ma), although it remains uncertain whether the major uplift occurred in two phases or one. These discoveries support and expand upon previous suggestions that there are sharp paleogeographic, geologic and tectonic contrasts north and south of the Lago General Carrera/Lago Buenos Aires Area. Minimum estimates of uplift rate are 0.05­0.07 mm/yr (to as high as 0.22 mm/yr). These rates are comparable to those from other parts of the Andes. The timing and location of uplift may be correlated with major plate tectonic events nearby (impingement of the CMTJ and subduction of the East Pacific Rise).

INTERPRETING THE RECORD OF DINOSAUR EXTINCTION IN THE HELL CREEK FORMATION: AVOIDING SIGNOR-LIPPS AND OTHER BIOSTRATIGRAPHICAL PROBLEMS

SHEEHAN, Peter M., Milwaukee Public Museum, Milwaukee, WI, USA; and David E. Fastovsky, University of Rhode Island, Kingston, RI, USA; and Claudia Barreto, University of Wisconsin-Milwaukee, Milwaukee, WI, USA

The Hell Creek Formation is renowned for abundant dinosaur fossils, but only a few thousand individuals have detailed stratigraphic documentation. Analysis of this record is problematic because the Signor-Lipps Effect (SLE) increases with decreasing sample size. The SLE can be addressed statistically, but other approaches avoid the SLE effect entirely.

The extinction debate centers on two hypotheses: (1) Dinosaurs became extinct gradually, over either ~10 MY, ~2 MY or many thousands of years. Dinosaurs may have been extinct before the Chicxulub impact, suffered a final blow at the impact, or survived the impact. (2) Dinosaurs became extinct over a brief interval after the impact event.

One way to avoid SLE is to determine if communities were changing through the Hell Creek Formation. If dinosaurs were becoming extinct over 2 to 10 MY, communities should show evidence of changes analogous to changes in modern communities when they are disrupted. Two surveys of Hell Creek Formation dinosaur fossils indicate that the dinosaurian components of communities were stable through the ~ 2 MY of HCF time. Another way to avoid SLE is to compare dinosaur abundance at various intervals through the Hell Creek Formation. No trend of decreasing abundance has been found, although the record is highly variable from level to level. Additionally, although a precise record of the position of fossils in the Hell Creek Formation has been made, range charts constructed as though they present standard biostratigraphic data do not maintain superpositional relationships. Dinosaurs are so rare that individual fossils at a given level may be a kilometer or more apart. Deposition was sporadic with occasional floods, long intervals of soil formation, and occasional steams meandering over the landscape eroding older beds. As a result, over these distances, individual beds precisely the same distance below a marker level (such as the palynological K/T boundary) may be of very different ages, thus removing superpositional control.

FAUNAL SHIFT ACROSS THE PERMIAN-TRIASSIC BOUNDARY IN SOUTHERN TIBET

SHEN, Shuzhong, and Changqun Cao, Nanjing Institute of Palaeontology and Geology, Chinese Academy of Sciences, Nanjing, China

Little knowledge is available on whether the end-Permian mass extinction is paleogeographically varied or not in terms of timing and magnitude. An investigation into two Permian-Triassic boundary sections suggests a closely comparable pattern between Southern Tibet, South China and other areas. The base of the Triassic in both sections is indicated by the first appearance of Otoceras and Hindeodus parvus. At the Selong Xishan section, the Permian-Triassic transitional sequence consists of the Coral Bed, the Caliche Bed, the Waagenites Bed and the Otoceras Bed. The Coral and Waagenites Beds are characterized by containing abundant brachiopods, corals and bryozoans. These Permian-type benthic faunas were replaced by numerous ammonoids in the overlying Otoceras Bed. This biotic shift at the Selong Xishan section appears to have been accompanied by a major and rapid transgression event within a decimeter interval beneath the Permian-Triassic boundary, as evidenced by the occurrence of framboidal pyrites, a lithologic shift from grainstone to packstone and a shift from brachiopod-dominated to ammonoid/bivalve-dominated community. Associated with this transgression event and biotic changeover, a dramatic drop in d¹³C value from +3.2 in the Caliche Bed to -2.89 per mil in the Waagenites Bed is detected. In the Qubu section near Mt. Everest, there is about 50-meter shale and siltstone between the Otoceras Bed and the Qubuerga Formation with numerous Permian brachiopods. No fossils were found from the lower pale gray siltstone but some plant fragments; and ammonoids appear in the upper dark or varicolored shale. This part represents a rapid regression-transgression event of the latest-Changhsingian and is comparable to the Caliche Bed and the Waagenites Bed at the Selong Xishan section. This event and the carbon isotopic drop are widely known in carbonate Permian-Triassic sections in South China and other areas.

ANALYZING EVOLUTIONARY TRENDS IN NON-MAMMALIAN SYNAPSIDS: SCALE DEPENDENCE AND STRATIGRAPHIC VS. PHYLOGENETIC PERSPECTIVES

SIDOR, C.A., Dept. of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA

Evolutionary trends are commonly discussed with regard to the fossil record of non-mammalian synapsids (e.g., reduction of the post-dentary bones), but despite its widespread use, the term is used in different and sometimes conflicting ways. Stratigraphic and phylogenetic trends should be kept distinct conceptually, although congruent patterns can increase our confidence that they reflect a real underlying phenomenon. Simulation studies have demonstrated that unbiased, lineage-level evolution can produce clade-level trends under certain boundary conditions. Distinguishing among different types of trends, and postulating different mechanisms, is therefore critically tied to the hierarchical scale at which persistent directionality can be resolved.

Here, I quantify some of the morphological changes that occurred in the evolution of the synapsid lower jaw during the late Paleozoic and early Mesozoic, and address several previously proposed hypotheses concerning the nature and magnitude of morphological trends. I gathered measurements and discrete character data from the mandibles of 108 fossil synapsid taxa, including four linear measurements, two areas, and 82 qualitative characters. The stratigraphic range of each taxon was binned into one or more of 18 age ranks spanning Pennsylvanian though Jurassic time. Phylogenetic data included each taxon's clade rank and the number of branch points passed from the root of the synapsid cladogram used. Analyses were performed at multiple scales (e.g., Synapsida, its subclades that include mammals, and its subclade side-branches that do not include mammals). The results of these analyses show a complex pattern of both passive and active trends. For example, theriodonts as a whole show a persistent trend for increasing the size of the dentary, but analyses focusing on its subgroups (gorgonopsians, therocephalians, or different cynodont families) fail to show a corresponding pattern. Assessing the prevalence of trends in the synapsid fossil record will require reinvestigating long-held views with new techniques.

A NEW PALEOBOTANICAL DATABASE INITIATIVE

SIMS, Hallie J., and Scott L. Wing, Dept. of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA

Beginning in 1979, Niklas, Tiffney, and Knoll published a series of key papers documenting Phanerozoic land plant diversity based on a compilation of stratigraphic ranges from the paleobotanical literature. Although these authors identified omissions and sampling biases underlying their results, the work provided a first assessment of temporal patterns in diversity. Several subsequent studies have focused on narrower temporal intervals and produced significantly different patterns. More recent work has highlighted the value of locality-based occurrence data in identifying geographic and environmental gradients in macroevolutionary patterns. In addition, such occurrence data make it possible to identify and minimize effects of a range of sampling biases, including variation in sampling effort, preservation rate, and amount of available rock record. The Paleobotany Working Group (part of the Paleobiology Database; see http://flatpebble.nceas.ucsb.edu/public/) has begun a project to enter lists of taxonomic occurrences (and abundances where available) for Phanerozoic land plant localities. Data are drawn from the primary literature, museum collections, and unpublished fieldwork. As a group of specialists (currently fifteen members), we hope to update stratigraphic information and build a table of valid species, genera, and their synonyms. By making the data publicly available as a web-searchable database, the paleobotanical community will be invited (and perhaps incited?) to identify omissions and errors. The group is exploring several scientific goals, including producing a sampling standardized plant diversity curve, assessing changes in within-community diversity over time, and exploring trends in morphological evolution. However, the lists of valid taxa and occurrence lists from well-defined localities, vetted by specialists, can form building blocks for a wide range of research projects. We hope that this initiative will gain momentum within the community to maintain and contribute to a public repository of high-quality paleobotanical data.

ISOTOPIC ANALYSIS OF THE CHANDLER AND SAFFORD (CENTRAL ARIZONA) PROBOSCIDEAN FOSSILS

SKAFF, Andria L., and Carol M. Tang, Dept. of Geological Sciences, Arizona State University, Tempe, AZ, USA

Recently, two proboscidean fossils have been found in central Arizona and will be analyzed for carbon and oxygen isotopes. Many proboscidean fossils have been discovered in southern and northern Arizona, but few have come from the central part of the state, making these finds significant.

The remains of a Pleistocene Mammuthus columbi fossil were discovered in Chandler, Arizona in the Queen Creek floodplain deposits during the construction of a housing development. Various postcranial elements, both tusks and several molar fragments were recovered. The molars are so fragmented that it is impossible to determine the age of the individual, but the long bone epiphyses are fused implying that it was an adult at the time of death.

The remains of a Pliocene Rhycothere (Proboscidea: Gomphotheridae) were discovered in the badlands of the 111 Ranch locality near Safford, Arizona. The fossils consisted of several postcranial fragments and most of the right mandible containing two well preserved molars. The anterior molar was completely worn and parts had probably already fallen out at the time of death, and the posterior was partially worn with several unworn lophs. Trefoil patterns in the posterior molar and the high angle of the jaw symphysis allowed for identification. Molar fragments from another individual were also found at the locality and will be analyzed as well.

Using standard sampling techniques employed in previous isotopic studies of fossil proboscideans, samples of dentine and enamel were taken from the molars and tusk using dental drill bits in a flexible shaft drill. Five samples were taken from each molar or tusk in the least fragmented areas. Since proboscideans employ accretionary growth on their teeth, this should provide us with high-resolution information regarding the paleoenvironmental conditions present in the areas they inhabited and the life history of the individuals.