NAPC 2001

June 26 - July 1 2001 Berkeley, California

Abstracts, Ma - Mc

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MAGALLÓN, Susana, Michael J. Sanderson, and James A. Doyle, Section of Evolution and Ecology, University of California, Davis, CA, USA

Angiosperms, the taxonomically richest and ecologically predominant group of living plants, first appeared in the fossil record in Valanginian-Hauterivian strata (135 MA). Angiosperm remains occur abundantly and uninterruptedly following their first appearance in the record, and the stratigraphic sequence of appearance of taxonomic types does not contradict current hypotheses of angiosperm evolutionary diversification. Previous estimates of angiosperm age based on divergence of molecular sequences, although in conflict with one another, imply that angiosperms predate considerably their oldest fossil record. We address the question by integrating new data and new methods of analysis. Sequences of two highly conserved chloroplast genes psaA and psbB, for a sample of 63 land plants, are used as primary data. Because a strong conflict between phylogenetic signals of 1st and 2nd vs. 3rd codon positions was detected, we performed independent maximum likelihood analyses for the two data partitions. The resulting phylogenetic hypotheses coincide in placing Gnetales as sister taxon to Pinaceae, but identify different taxa as sister to angiosperms. Estimates of angiosperm age were obtained by enforcing a molecular clock, and by relaxing rate homogeneity by using Non Parametric Rate Smoothing (NPRS). Additional estimates were obtained by constraining the age of two nodes in the topology: seed plants (330 MA) and eudicots (125 MA). Angiosperm age estimates vary from 79 to 160 MA when molecular clock is enforced and from 173 to 220 MA when NPRS is implemented. Some of these estimates are close to the age derived from the fossil record, but confidence intervals are broad enough to include some of the previous dates. Subsequent age estimates will be based on an expanded data set that includes two additional chloroplast genes (atpB and rbcL), a new method for relaxing rate homogeneity based on a penalized likelihood approach, and a larger set of chronologically-calibrated nodes, based on reliably identified fossil taxa.


MALONE, Catherine, Dept. of Forestry and Natural Resources, Purdue University, West Lafayette, IN, USA

In the past, when morphological analyses of extant and extinct taxa did not yield a clear understanding of evolutionary relationships, it was nearly impossible to study the biogeographic history of a group because it was without a phylogenetic framework. However, molecular data have proven to be useful in this arena. Strongly supported molecular phylogenies can be combined with other types of data to investigate the evolution and radiation of a group. Such is the case with the large-bodied, primarily herbivorous lizards in the subfamily Iguaninae. The eight genera are distributed today throughout much of the western hemisphere and, in one instance, on Fiji and Tonga. The affinity of many iguanine genera for the neotropics has resulted in a poor fossil record due to low preservation potential in their favored habitats, and this has hindered paleontological research. Morphological analyses of extinct and extant taxa have failed to generate a robust phylogeny. Recently, several studies have used mitochondrial sequence data to generate a well-supported phylogeny of the iguanines. This study combines phylogenetic, bioegeographic, fossil, and paleocological information to examine the history of two iguanine taxa: West Indian rock iguanas (Cyclura) and green iguanas (Iguana). A rough molecular clock indicates that the Cyclura lineage originated between 15 and 35 million years ago. The phylogenetic pattern generated using mtDNA sequence data is consistent with the geologic history of the Greater Antilles. Phylogenetic analyses of the green iguana indicate a South American origin of the genus and a relatively recent radiation throughout Central America, possibly concurrent with the closing of the Panamanian Isthmus. The pattern of evolutionary relationships among green iguana lineages indicates several independent radiations into the Lesser Antilles.


MARINCOVICH, Louie, Dept. of Invertebrate Zoology & Geology, California Academy of Sciences, San Francisco, CA, USA

For most of the Cenozoic, the Arctic Ocean has been an extension of the North Atlantic faunal region, characterized by a few endemic northern species. However, at the beginning of the Cenozoic, the Arctic Ocean was populated by a largely endemic molluscan fauna whose species were, with few exceptions, absent from adjacent ocean basins. Another distinction of the Paleocene Arctic Ocean molluscan fauna was the presence of several relict genera previously known only in Mesozoic faunas. The delayed extinction of these once exclusively Mesozoic genera implies that end-Cretaceous extinction processes were not as effective in high northern latitudes compared to middle and low latitudes. Eocene Arctic Ocean marine mollusks are present in northern Canada but have yet to be extensively collected or studied.

There is a gap in known Arctic Ocean molluscan faunas from the Eocene to the late Miocene. The record resumes with latest Miocene or Pliocene faunas in northern Alaska. The dominance of North Atlantic taxa in the Arctic Ocean that had persisted since the Paleocene continued even after the opening of Bering Strait at 5.4­5.5 Ma. The southward flow of water through Bering Strait introduced distinctive Arctic-Atlantic mollusks into the North Pacific. This biogeographic scenario lasted some 2 m.y., until 3.6 Ma, when the rise of the Isthmus of Panama reorganized Northern Hemisphere marine circulation, and caused the flow through Bering Strait to reverse to the present northward direction. The ensuing invasion of North Pacific taxa into the Arctic Ocean and high-latitude North Atlantic is well documented and is the prevailing modern situation. Pleistocene glacial and interglacial episodes resulted in significant faunal turn overs in the Arctic Ocean, but the molluscan faunas continued to be derived from the North Pacific.


MARSHALL, Charles R., Dept. of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA; Simon Tavare and Oliver Will, Dept. of Mathematics, University of Southern California, Los Angeles, CA, USA; and Robert D. Martin and Christophe Soligo, Anthropologisches Institut and Museum, Universitat Zurich-Irchel, Zurich, Switzerland

Molecular-based divergence times often considerably pre-date the earliest known fossil representatives of the groups studied. For the order Primates, molecular data uniformly suggest a mid-Cretaceous origin, some 90 million years ago, whereas the oldest fossils are known from basal Eocene rocks only 54­55 million years old. The incompleteness of the fossil record suggests that divergence times estimated from molecular data should be older than the oldest known fossils, but an adequate quantification of that incompleteness is needed to evaluate the significance of discrepancies between molecular and fossil-based estimates. Here a new statistical method, based on an estimate of species preservation derived from a model of the pattern of diversification of the group, suggests a Cretaceous origin of Primates. This provides paleontological corroboration for the time of origin of primates predicted by molecular data. The method also suggests that no more than 7% of all primate species that have ever existed are known from the fossil record. Our estimated divergence time for primates is older than paleontological estimates based on other approaches. The underlying reason for the differences is primarily due to our use of data from the Recent (number of species), but also stem from the structure of the model.


MARSHALL, Cynthia L., Museum of the Rockies, Montana State University, Bozeman, MT, USA

One basal flight loss event is the most parsimonious explanation for flightlessness in the ratite clade. Therefore, if flight were lost only once in this group, a similar pattern of wing reduction would be predicted for ostriches and emus.

A series of ostrich, emu, tinamou, and chicken embryos were obtained and the growth patterns of the wings compared. The chickens and tinamous served as outgroups for phylogenetic pattern analysis. Wings of the ostrich, chicken, and tinamou embryos grew at similar rates. The wings of the ostrich embryos grew for a greater length of time, resulting in a longer wing. The emu embryo wings grew at a slower rate, resulting in a vestigial wing. The emu wing growth is slowed in comparison to the ancestral condition, demonstrating a pattern of paedomorphosis. In contrast, the ostrich embryo extends growth at the ancestral growth rate, demonstrating a pattern of peramorphosis. I propose that the emu/cassowary clade shares a small, non-flying ancestor that subsequently grew large, whereas the proto-ostrich was a flying bird until becoming too large to sustain flight capacity. Fundamentally different wing growth patterns in ostriches and emus supports both multiple flight loss events and separate mechanisms leading to flight loss within this clade.


MARTIN, Anthony J., Dept. of Environmental Studies, Emory University, Atlanta, GA, USA; and David J. Varricchio, Museum of the Rockies, Montana State University, Bozeman, MT, USA

The Late Cretaceous (Campanian) Two Medicine Formation exposed in the area of Choteau, Montana is well known for fossil evidence related to nesting behavior in dinosaurs such as Maiasaura and Troödon. Less noticed in this same area and in some of the same horizons as dinosaurian material is abundant evidence for insect nesting. This evidence consists of dense concentrations of fossil cocoons, some within or otherwise closely associated with numerous vertical burrows.

The sheer abundance of the cocoons, as many as 400 per square meter on some vertical sections, lent well to statistical analyses. One 2 m thick zone (nicknamed "Pete's Pupae Peninsula") provided 336 specimens for measurement, which yielded a mean length of 20.7 ± 5.8 mm and mutually perpendicular widths of 10.0 ± 2.7 and 10.8 ± 2.8 mm. Size data were normalized through calculations of volume, which resulted in a mean of 1.4 ± 0.9 cc. Notably different size ranges within this sample may represent different species of insects and thus may reflect insect diversity. The cocoons are interpreted as hymenopteran on the basis of their prolate ellipsoid shape, impressions of a tight silk weave on some specimens, and their common occurrence within vertically to obliquely oriented burrows.

The cocoon-bearing deposits from the Two Medicine best fit the recently defined Coprinisphaera ichnofacies of Genise et al. (2000), a terrestrial ichnofacies characteristic of paleosols dominated by insect nesting traces and cocoons. Furthermore, the predominance of nesting burrows (such as Palmiraichnus) with their body fossil components (cocoons) in ripple-bedded sandy and muddy deposits argue for an abandoned levee that was exposed subaerially and had well-drained soils. Within the Two Medicine, most horizons that represent Troödon nesting locales consistently yield these same insect cocoons and burrows. Thus, the insect fossils may provide clues to the types of soils these dinosaurs preferred for nesting.


MARTIN, James E., Museum of Geology, South Dakota School of Mines and Technology, Rapid City, SD, USA; and Theodore J. Fremd, John Day Fossil Beds National Monument, Kimberly, OR, USA

The Hemphillian North American Land Mammal Age (NALMA) was based upon assemblages including that of the Rattlesnake Formation of central Oregon as a principal correlative. Therefore, the faunal content of the Rattlesnake deposits is crucial to the definition of the Hemphillian NALMA. However, recent definitions of the igneous versus sedimentary units of the Rattlesnake succession have brought the lithostratigraphic framework for the faunal constituents into question. The Rattlesnake was described as a formation-rank unit during the first part of the last century. This formation included a basal detrital unit dominated by floodplain sediments, an interbedded ash-flow tuff (RAFT), and an upper detrital unit dominated by basalt conglomerates. More recent workers have elevated the RAFT to formation-rank status with no regard to the sedimentary units above and below. Therefore, we propose that the Rattlesnake Formation be elevated to group status, with all three intervals regarded as formation-rank units. As the group is extended beyond the John Day Basin, additional formations may be added to the group. In the type area of the Rattlesnake Group in the Picture Gorge area of central Oregon, the RAFT has been dated at 7.2 Ma, and the lower formation contains a tourmaline-bearing tuff, bracketing the fossil assemblages. Faunal constituents of the lower formation indicate an early Hemphillian interval; therefore, the radiometric dates aid in determination of absolute ages of the early Hemphillian.


MARTIN, Ronald E., Scott P. Hippensteel, Daria Nikitina, and James E. Pizzuto, Dept. of Geology, University of Delaware, Newark, DE, USA

Seasonal reproduction and preservation of foraminifera was monitored for three years at Bombay Hook National Wildlife Refuge (BHNWR, Smyrna, DE). Signal-to-noise ratios of marsh foraminiferal assemblages were increased by using "artificially time-averaged" assemblages to mimick the natural process of time-averaging. Cluster analysis of "seasonally artificially time-averaged" (SATA) assemblages, in which separate live and dead counts were added season-by-season, indicated that assemblages reflect the most recent test inputs from epi- and infaunal populations, and that these inputs record subtle variations in porewater chemistry caused by interannual variation of rainfall. Geochemical imprinting of assemblages tended to occur during the summer and fall. Depending on taphonomic setting, the contributions of recently-living populations to death assemblages may therefore be far more important than previously thought. As assemblages pass into the historical layer, they may have a "memory" of the most recent test inputs and environmental conditions, and downcore assemblages may be used to reconstruct earlier environmental conditions with much, much greater temporal resolution than previously thought.

The importance of living populations and recent test inputs to subfossil assemblages was further demonstrated in sea-level reconstructions for BHNWR for the past few hundred years. The latest Holocene foraminiferal records of marshes of BHNWR and Clinton, CT, were compared using a number of methods, but by far and away the best results were obtained using BHNWR ATA total (dead and live) assemblages. Use of ATA assemblages resolved 3 transgressions occurring over decadal-to-centennial scales that occurred within 5 cm of those reported for Clinton after correction for sedimentation rates and compaction.

Supported by NSF Grant No. EAR-9714155 to REM and JEP; a contribution of the University of Delaware Geology Department's Program in Near-Surface Geologic Processes.


MARTIN, Ronald E., Scott P. Hippensteel, Daria Nikitina, and James E. Pizzuto, Dept. of Geology, University of Delaware, Newark, DE, USA

Marshes exhibit inherently high temporal resolution because dense plant root systems inhibit bioturbation. Marshes therefore provide ideal opportunities for developing numerical models of fossil assemblage formation that can then be extended, with suitable modification, to offshore settings where most of the fossil record has formed. Numerical models are also heuristically useful, and unlike analytical models, are less likely to amplify noise in data.

Seasonal reproduction and preservation of foraminifera was monitored for three years at Bombay Hook National Wildlife Refuge (BHNWR, Smyrna, DE). Signal-to-noise ratios of marsh foraminiferal assemblages were increased by using "artificially time-averaged" assemblages to mimic the natural process of time-averaging.

We then simulated the formation of ATA assemblages using a diffusion-based model. Test inputs and the probability of preservation were based on ATA assemblages. Sedimentation rate (based on radiotracer profiles) was incorporated by periodically raising the domain to simulate inputs of new material with specific test content. Seasonal cores (0­60 cm) did not need to be corrected for autocompaction. Curves were fitted for each of the dominant species for 200 yrs, after which simulations stabilized; this duration agreed with sedimentation rates and residence times at 60 cm depth. Bioturbation rates were based on curves fitted to an exponential equation describing downcore abundances of colored glass beads in field experiments that mimicked the input of an impulse tracer. Based on field experiments, bead profiles yielded bioturbation rates of ~108 cm2 sec-2 (high marsh) to 10-6 cm2 sec-1 (low marsh). These rates fall at the low end of the range for shallow subtidal settings (~10-6­10-8 cm2 sec-1) and are comparable to deep-sea rates.

Supported by NSF Grant No. EAR-9714155 to REM and JEP; a contribution of the University of Delaware Geology Department's Program in Near-Surface Geologic Processes.


MARTÍNEZ-CABRERA, Israel, Depto. de Biología, Facultad de Ciencias, UNAM, México; and Sergio R.S. Cevallos-Ferriz, Depto. de Paleontología, Instituto de Geología, UNAM, México

Two anacardiaceous woods from the Tertiary of North America are described. The Fossil wood of Baja California Sur has xylem anatomical features that agree with the living genus Tapirira. Some of the shared diagnostic characters are vessel dimensions, vasicentric axial parenchyma, septate fibers, vessel-ray vessel-parenchyma pits with reduced borders and horizontally elongated (some angular), redial canals in the large multiseriate rays, number of epithelial and sheath canal cells, and ray type. The anacardiaceous wood from Wyoming shares features with the two modern genera Rhus and Schinus. In this case, the resemblance includes size and frequency of vessel, radial canals, septate and nonseptate fibers, scanty paratacheal parenchyma and vascular traqueids. Nevertheless, the presence in both living genera of tangential vessel arrangement, high relative proportion of square cells in the uniseriate rays, as well as other features, distinguish Rhus and Schinus from the fossil, which could thus be considered a new genus. The tropical genus Tapirira is found in the Neotropical region and Schinus in tropical South America. Meanwhile, Rhus grows in tropical and subtropical regions of the world and in temperate North America and Asia. These new records add to the robustness of the fossil record of the family in North America, which along with its high degree of generic endemism in the Mexican flora (Actinocheita, Bonetiella, Malosoma, Pachycormus and Pseudosmodingium), highlight the significance of the region in the evolution and diversification of the Anacardiaceae.


MARTÍNEZ-MILLÁN, Marcela, Instituto de Geología, Universidad Nacional Autónoma de México, México; and Sergio R.S. Cevallos-Ferriz, Depto. de Paleontología, Instituto de Geología, Universidad Nacional Autónoma de México, México

The Cornaceae, as considered in this study and following Noshiro and Baas, is composed of Cornus, Alangium, Curtisia, Mastixia, Diplopanax, Nyssa, Camptotheca and Davidia, has basically a temperate distribution. Other former cornaceous genera, such as Aralidium, Melanophylla, Toricellia, Helwingia, Aucuba, Corokia, Griselinia and Garrya are part of a different clade and have a similar distribution. A biogeographic analysis using BPA (Brooks parsimony analy sis) shows that North America has a close relationship with Asian areas indicating a Laurasian history for this family. Today, Cornus has a wide distribution reaching tropical zones but those tropical areas (Southeast Asia, Malaysia and Indonesia) are related to temperate Asia and North America, therefore suggesting a northern history. In the cladogram, The Mediterranean region is located outside the clade of the other temperate zones suggesting that this area is not related to the other north temperate regions whose connections must have been via Beringia and not via the North Atlantic. This contrasts with similar analyses with families Anacardiaceae and Moraceae in which a North Atlantic history must have taken place. Currently, four routes can be recognized to understand how low latitude North American vegetation was assembled, a North Atlantic connection of Laurasian elements (Anacardiaceae), a Beringia connection (Cornaceae), a South American connection (Moraceae) and a North Atlantic connection of South American elements (Moraceae).


MAYER, Paul S., Geology Section, Milwaukee Public Museum, Milwaukee, WI, USA

Until recently, samples of Antrim Shale and the upper part of the Milwaukee Formation were collected only as float from tunnel excavations and glacial till in Milwaukee County, Wisconsin. Core samples from Milwaukee Metropolitan Sewerage District's borehole I30-8-NS have yielded conodont faunas that provide biostratigraphic control for the lowest part of the Antrim Shale and the upper part of the Milwaukee Formation. A conodont fauna including Ancyrodella africana, A. alata s.s., A. rugosa, Palmatolepis transitans, Mesotaxis asymmetrica, and Polygnathus dubius was recovered from the lower one meter of the Antrim Shale. This fauna correlates with the Frasnian Zone 4, uppermost part of the Lithograph City Formation in Iowa. Associated with this fauna are lingulid brachiopods, scolecodonts, small pyritized gastropods, and ptyctodontid teeth. The contact between the Antrim Shale and the Milwaukee Formation is unconformable with clasts of the underlying Milwaukee Formation suspended within the Antrim Shale. The upper one-meter of the Milwaukee Formation yields a conodont fauna that includes Icriodus subterminus, Polygnathus dengleri, P. dubius, and Mehlina gradata. This fauna correlates with the upper part of the subterminus Fauna in the Coralville Formation of Iowa and probably with the upper part of the disparilis Zone. Associated with this conodont fauna is a silicified fauna dominated by brachiopods, bryozoans, crinoids, agglutinated foraminifers, and tentaculites. Below this one-meter section, presumably in Raasch's North Point Member, a conodont fauna including Icriodus subterminus and Polygnathus ovatinodosus was collected and appears to correlate with the subterminus Fauna of the Little Cedar Formation in Iowa. The fauna in this section is dominated by chonetid brachiopods, but also includes crinoids, tentaculites, and Zoophycos trace fossils.


McELWAIN, Jennifer C., Dept. of Geology, The Field Museum of Natural History, Chicago, IL, USA

The Triassic-Jurassic boundary marks the third greatest biodiversity crash in Earth history, an event, which together with the Permian-Triassic mass extinction, characterize the beginning of the Mesozoic. Although significant extinction occurred at higher taxonomic levels (i.e., family and order) among Permian plant groups at the Permian-Triassic boundary, marked order- and family-level floral extinctions are not evident at the Triassic-Jurassic boundary, suggesting that plant primary producers did not experience "mass" extinction at this time. Significant turn-over of both micro- and macro-floras have however been demonstrated at the species level, yet to date the pattern of these species level changes remains unknown. Furthermore, to what extent floral dynamics spanning the Permian-Triassic and Triassic-Jurassic boundaries may reflect relative differences in the magnitude and nature of environmental changes associated with both mass extinction events is difficult to establish. This is again due mainly to a comparative paucity of information on the nature of vegetation change spanning the Triassic-Jurassic boundary but also in part due to a lack of empirical atmospheric or climatic data spanning the Permian-Triassic and Triassic-Jurassic extinctions respectively. This paper therefore aims to investigate the dynamics and character (i.e., stepwise, gradual or sudden) of vegetation changes associated with the Triassic­Jurassic extinction event. Results from these analyses will be presented and integrated with existing paleo-atmospheric-CO2 and global temperature reconstructions based on fossil floras which demonstrate that the Triassic-Jurassic boundary was associated with a four-fold increase in atmospheric CO2 levels and 3 to 4°C increase in global temperature. Further tests of the "thermal damage hypothesis" (which suggests that super-greenhouse conditions contributed to high species-level turnover of Triassic­Jurassic boundary macrofloras, by raising leaf-temperatures above a highly conserved lethal threshold) will also be presented.


McFADDEN, Tim, Indra's Net Farm, Redwood City, CA, USA

We are in a big blossom—the development of the universe from the extremely low entropy level of the Big Bang. Using this model, the development of life on earth over the last few billion years is not a violation of the second law of thermodynamics (a local decrease of entropy), but just the laws of physics and chemistry churning along, as entropy increases. These laws were finely tuned, at the Big Bang, for biological life, as we know it.

The alternative is to view our planet as the most unlikely place in the whole universe. Where does the information to produce a punctuated jump in evolution come from, if not from the Big Bang? From spores from outer space?

ALife models of ecosystems and evolution may be very useful, but the ALife effort itself may not be very productive, if it does not also copy biological life from the big blossom. Today's computers do not benefit from the universe's fine-tuning for biological life, they're logical and dead—it's one wrong bit and you're toast. ALife lives in cyberspace, but cyberspace is dead. A biological system may have on the order of Avagadro's number parts and we don't understand how biological systems work yet, so we can't abstract away the complexity yet. Some amazingly complex patterns have been produced by ALife, but we do not have complexity for-free yet.

Is life a machine? This will become a practical question as we begin to understand the genome and to develop nanotech and designer viruses. If life is a machine, we can manipulate it and control it. DNA helped archaic life to remember proteins and became the first cyberspace. If life is a machine, then it can have a new cyberspace to use.


McGANN, Mary, U.S. Geological Survey, Menlo Park, CA, USA; and Gregory B. Deets, City of Los Angeles, Bureau of Sanitation, Environmental Monitoring Div., Playa Del Rey, CA, USA

The relationship between foraminifers and ocean pollution was initially studied forty years ago off southern California at four sewage outfalls. One of these, the Hyperion outfall in Santa Monica Bay, has recently been re-examined by local and federal agencies. Seven sediment cores and 33 surface samples obtained in 1997­1998 were analyzed to determine the foraminiferal response to historic pollution levels and subsequent abatement efforts.

Two of the cores were obtained near the 7-mile discharge point. Although faunal diversity doesn't vary much in the closest core, abundances of Bulimina denudata, Trochammina pacifica, and Eggerella advena increased significantly after remediation efforts were initiated in the 1980s. In contrast, both faunal diversity and abundance of B. denudata peaked in the second core in 1970 when polluted discharge was at an extreme. Five other cores recovered about 5­16 km from the 5- and 7-mile discharge points are generally similar to one another, showing a pattern of improved environmental conditions after remediation.

Parameters determined for the modern surface samples, such as faunal diversity, foraminiferal number, and live specimens/gram of sediment, have returned to near baseline values, with sites near the sewage outfalls similar to those at adjacent, unaffected areas. Despite these improved conditions, faunal patterns have not returned to pre-outfall levels. Continued dominance by species favoring organic waste (E. advena, B. denudata, and T. pacifica), and the inability of Nonionella basispinata and N. stella to re-colonize the impacted areas, suggests that these species remain affected by the quality of sewage effluent still being released, despite the new treatment methods now employed.

Although both macroinvertebrates and microorganisms can be used to gauge the effect of sewage discharge on living organisms, microfossils are a more powerful tool in that they can provide a historical record of this response with minimum effort and better sample integrity.


McGWIRE, Kenneth C., Desert Research Institute, Reno, NV, USA; and Stephanie D. Livingston, University of Nevada, Reno, NV, USA

Specimens representing prehistoric animals are rare, and expensive to recover, stabilize, conserve, and curate. Consequently, obtaining statistically representative populations of data for any taxonomic group has traditionally entailed extensive travel to widely dispersed curatorial facilities. This paper describes efforts to develop methods for: creating digital models of paleontological specimens; managing archives of these virtual specimens; serving these data over the internet; and efficiently searching, accessing, and analyzing data from such archives through a standard internet browser. The goal of this project is to develop a prototype system that could help stimulate new research directions in the field of paleontology and evolutionary biology by improving the ability to find, access, and analyze samples curated in different collections. The development effort focuses on increasing the ability to access and analyze biological data from a number of geographically dispersed collections by using modern digital imaging and data management techniques. A web site is being developed as a central access point to enable "one stop shopping" for digital paleontological archives on the internet. The system allows users to search the contents of multiple virtual collections. This interface also will allow visualization and measurement for performing analyses on virtual specimens from selected collections. Online measurements will be complemented by estimates of geometric uncertainty for the virtual specimens, based on models of distortions arising from data capture, the type of digital representation, and viewing conditions. Initial data collection will focus on an extensive characterization of dental specimens from North American mammoths, with physical specimens from Anza Borrego, Burke Museum, and Nevada State Museum collections making up the initial demonstration database. This sample database will serve as a focus point for interaction between paleontologists and database developers to ensure that the system meets well-defined scientific objectives.


McROBERTS, Christopher A., Dept. of Geology, State University of New York, Cortland, NY, USA

Following the end-Permian crisis, marine bivalves document the long-term increase in generic richness through the early Mesozoic. The Early and Middle Triassic was marked by a gradual recovery in generic richness and peaked in the early Late Triassic. As in other clades, recovery of bivalves following the end-Permian extinction was very gradual and was not completed (in terms of both richness and ecologic complexity) until the Ladinian. Although a Carnian-Norian extinction is not evident in the data and may be a regional event limited to the Tethyan Realm, the end-Triassic extinction is profound and apparently abrupt. Diversity metrics are not equally distributed among bivalve living habits. The generally epifaunal Pteriomorphia and Isofilibranchia exhibit higher extinction rates compared to the ordinarily infaunal Heteroconchia (especially the Veneroida and Trigonoida). This pattern of selective extinction led to a gradual increase in generic richness of infaunal suspension feeders through most of the Triassic. Contrary to previous hypotheses, this increase in infaunalization may not have been related to the evolutionary expansion of major predatory groups (e.g., shell-crushing cephalopods, crustaceans, sharks, fish, and reptiles) which had typically low abundances and limited distribution during the Triassic. Drilling predators, although present during the Triassic, are not considered prominent causes of mortality among Triassic bivalves. Instead, the infaunalization of bivalves during the Triassic may have been due to several interconnected abiotic and biotic causes associated with the recovery after the end-Permian mass extinction.