NAPC 2001

June 26 - July 1 2001 Berkeley, California

Abstracts, Cl - De
(5/17/01)

EARLY OCCURRENCE OF C₄ GRASSES IN MIDDLE MIOCENE NORTH AMERICA BASED ON STABLE ISOTOPES IN TOOTH ENAMEL

CLEMENTZ, Mark T., and Paul L. Koch, Dept. of Earth Sciences, University of California, Santa Cruz, CA, USA

The timing of the appearance of C₄ grasses within terrestrial ecosystems has been reported to have occurred between 8 and 5 Ma in North America, Asia, Africa, and South America. This conclusion is based on isotope analysis of soil carbonates and tooth enamel from a few taxa within each study area. The enamel carbon isotope value reflects the diet of an organism, and can serve as a measure of consumption of C₄ plants, which have significantly higher carbon isotope values than C₃ plants. Because herbivores are selective foragers, analysis of only a few taxa, instead of whole faunas, may reduce the possibility of accurately gauging when C₄ plants became a significant component of terrestrial vegetation. Sampling of entire large-bodied terrestrial faunas, including both browsers and grazers, provides a more accurate estimation of C₄ presence in terrestrial ecosystems. We analyzed the carbon isotope composition of herbivore tooth enamel from proboscideans, equids, camelids, antilocaprids, and rhinoceratids from sites in Oregon, California, and Nebraska ranging in age from 12 to 10 Ma. Carbon isotope values for grazers and browsers in California and Oregon were within the range of expected values for consumers of C₃ vegetation. However, in Nebraska, carbon isotope values were well outside the range of values expected for C₃ consumers, with maximum values at -4 per mil. Also, we observed a distinct separation in carbon isotope values between grazing and browsing taxa, with grazing taxa yielding significantly higher carbon isotope values. Decoupling of browser and grazer carbon isotope values in Nebraska and low carbon isotope values for whole faunas in California and Oregon suggest that change in the carbon isotope composition of atmospheric CO₂ was not responsible for the isotope differences we have detected. Therefore, we conclude that by 12 Ma, C₄ plants were already a significant component of terrestrial vegetative biomass within the mid-continent of North America.

GRAPHIC CORRELATION OF THE UPPER DEVONIAN (FRASNIAN AND FAMENNIAN)

COATES, John, Wright State University, Fairborn, OH, USA

The upper Devonian (Frasnian and Famennian) has been extensively studied with respect to macrofossil data, but there is a lag in systematic high-resolution biostratigraphic stuides. A detailed biostratigraphic study of eight outcrops, in addition to the Standard Reference Section (SRS), was done in the central southern Appalachian basin in southwest Virginia. The stratigraphic units from the oldest to youngest are the Millsboro (Givetian), Brallier, Mallory, Briery Gap, Blizzard, Pound, and Red Lick. The Mallory, Briery Gap, and blizzard are Frasnian, while the Pound and Red Lick are Famennian. Data from Brame 2001 was used in this study. The SRS contains a wide range of comparable taxa that were compared to the seven other outcrops. A quantitative analysis was performed on these comparisons to determine the Line of Correlation (LOC). An accurate correlation was determined by extrapolating a section from the Composite Standard and then compared to the mature Composite Standard. Once the LOC is constrained, an accurate LOC is achieved. A mature Composite Standard is analyzed for sediment accumulation rates, Frasnian and Famennian extinction events and sequence stratigraphy of the Upper Devonian. After a mature Composite Standard is formed it will be tested against data from another section from the Appalachian Basin.

THE EVOLUTIONARY AFFINITIES OF CNIDARIAN-GRADE EDIACARAN FOSSILS: TESTS USING MOLECULAR DIVERGENCE DATES

COLLINS, A.G., Museum of Paleontology and Dept. of Integrative Biology, University of California, Berkeley, CA, USA; and B.M. Waggoner, Dept. of Biology, University of Central Arkansas, Conway, AR, USA

Most of the latest Neoproterozoic "Ediacaran fossils" have been referred to the phylum Cnidaria in the past. Justification for these assertions has been on morphological grounds that range from vaguely defined similarities to detailed comparisons. In particular, representatives of the living Chondrophorina (Hydrozoa), Pennatulacea (Anthozoa), and Scyphozoa have all been putatively identified in the Ediacaran biota. We test these hypotheses using analyses of divergence dates implied by an extensive phylogeny of extant cnidarians using 18S rRNA. Since 18S rRNA can easily be shown to not evolve in a clock-like manner, we infer molecular divergence dates by employing recently developed Bayesian methods that do not require clock-like evolution. We investigate the effect of using several calibrations of the molecular divergence dates, each depending on various assumptions about the taxonomic affinities of various Ediacaran fossils. If a calibration based on one interpretation of a controversial fossil yields a glaringly improbable age for a better-known clade, that interpretation is likely to be incorrect.

GLOBAL ORDOVICIAN FAUNAL TRANSITIONS IN THE MARINE BENTHOS: PROXIMATE CAUSES

CONNOLLY, Sean R., Dept. of Marine Biology, James Cook University, Townsville, QLD, Australia; and Arnold I. Miller, Dept. of Geology, University of Cincinnati, Cincinnati, OH, USA

During the Ordovician Radiation, domination of benthic marine communities shifted away from trilobites, towards articulate brachiopods, and, to a lesser degree, towards bivalves and gastropods. In this paper, we identify the patterns in origination and extinction probabilities that gave rise to these transitions. Using methods adapted from capture-mark-recapture (CMR) population studies, we estimate origination, extinction, and sampling probabilities jointly in order to avoid confounding patterns in turnover rates with temporal variation in the quality of the fossil record. Not surprisingly, higher extinction probabilities in trilobites relative to articulate brachiopods, bivalves, and gastropods were partly responsible for relative decreases in trilobite diversity. However, articulate brachiopods also had higher origination probabilities than trilobites, indicating that relative increases in articulate brachiopod diversity would have occurred even in the absence of between-class differences in extinction probabilities. This contrasts with inferences based on earlier Phanerozoic-scale, long-term averages of turnover probabilities, and it indicates that a major cause of this faunal transition has been overlooked. Temporal patterns in turnover rates suggest that the relative importance of origination differences and extinction differences as determinants of these faunal transitions shifted over the course of the Ordovician.

A NON-INVASIVE FLOATING GRID MAPPING SYSTEM

COOLEY, Joseph B., Christopher L. Organ, and Tobin L. Hieronymus, Museum of the Rockies, Bozeman, MT, USA

In quarries where the concentration of bone is very high or the fossil layer is very thick, mapping on a grid system can be quite difficult. The inability to place and maintain accurate grid corner markers throughout a quarry can cause inaccurate mapping of a quarry. During the summer of 1999 the Museum of the Rockies excavated a hadrosaur quarry that had very high concentrations of bone. To solve the problem of placing grid corner markers throughout the quarry we created a floating grid system. Along the back wall of the quarry wires were anchored and spaced at one meter. On each wire the corners of each grid was marked by tape. When a grid needed to be mapped the wires were extended to mobile posts where they were attached and leveled. A one meter by one meter into 10 centimeter by 10 centimeter squares was suspended from the grid wires by equal lengths of wire attached to each corner. Longer wires allowed for mapping of the specimens found lower in the quarry while shorter wires were used to map specimens higher in the quarry. After the grid was mapped the grid wires were rolled up and stored along the wall where they did not interfere with the excavation. Preservation of the fossils was maintained while the mapping was very accurate.

COLOR PATTERN STABILITY IN SEAGRASS NERITID GASTROPODS FROM THE NEOGENE OF THE DOMINICAN REPUBLIC

COSTA, Fábio A.H., Exelixis, San Francisco, CA; and Ross H. Nehm, Columbia University, Teachers College, New York, NY, USA

Morphological studies of species-level stasis and change have been conducted on a wide-variety of taxa throughout the geological timescale. These studies have focused almost exclusively on aspects of skeletal size and shape; no studies appear to have investigated the macroevolutionary dynamics of color pattern polymorphism. Here we report on our detailed analyses of intraspecific and interspecific patterns of color polymorphism in two neritid gastropods from the Neogene of the Dominican Republic. We demonstrate that color pattern polymorphism is more stable than shell morphology over macroevolutionary timescales. Neritina figulopicta preserves intricate color patterns classifiable into seven categories at the following frequencies: Interrupted 4%; Zigzag 20%; Textile 36%; Banded 9%; Diagonal 4%; Network 26%; and Spotted 1%; Neritina virginea of the Recent western Atlantic is hypothesized to be a close relative of N. figulopicta. Shell color patterns alone do not distinguish these two species, although slight differences in color pattern frequencies do occur. In contrast, these species differ in submicroscopic aspects of their teeth and plicae. The range and frequency of color pattern polymorphism has remained stable in this lineage for a minimum of 13 MY, whereas shell morphology has changed. Smaragida viridis preserves intricate color patterns classifiable into seven categories at the following frequencies: Absent 12%; Restricted 40%; Interrupted 25%; Straight 6%; Zigzag 12%;Textile 4%; and Banded 1%. An additional pattern, classified as D, has only been observed in a few populations of extant Mediterranean specimens. Patterns R, S, and Z are found in DR and Recent specimens of S. viridis but are absent from other living species of Smaragdia. The range and frequency of color pattern polymorphism in S. viridis has remained stable for a minimum of 13 MY, whereas slight geographic and temporal differences in shell morphology have occurred.

EVOLUTION OF HIGH-LATITUDE MARINE INVERTEBRATE FAUNAS: A REVIEW

CRAME, J. Alistair, British Antarctic Survey, High Cross, Cambridge, UK

Distinct high-latitude and polar marine invertebrate faunas can be traced back in time to at least the Late Paleozoic era. A number of them contain strong bipolar elements and it would seem likely that these were formed by some type of global climatic differentiation. Although comprehensive data sets are still at a premium, it is becoming apparent that these high-latitude and polar faunas are also of consistently lower taxonomic diversity than their lower-latitude counterparts. Latitudinal diversity gradients are a persistent feature of the fossil record, although on nothing like the scale of those seen at the present day. They may be taken as an indication that, when averaged over time, there is a significant difference in the rates of evolution between tropical and polar regions.

The dramatic steepening of gradients through the Cenozoic era may be attributable to a pulse of tropical speciation. This in turn could have been driven by purely intrinsic factors, such as evolutionary escalation and intense competition between certain shallow-water clades. However, there is also evidence to suggest that extrinsic factors, such as climate change, promoted Cenozoic diversification on a variety of temporal and spatial scales. In particular the Neogene radiation of many taxa has been linked to the onset of pronounced glacioeustatic climate cycles. These same cycles undoubtedly had a global effect but were more pronounced in the tropics due to the greater amount of available habitat space there.

We cannot yet say that rates of extinction were significantly higher for marine invertebrate taxa in the polar regions. Even the most dramatic Cenozoic temperature declines average out to no more than a fraction of a 1°C per thousand years. Levels of productivity may be more important than temperature per se in controlling the composition of polar faunas.

INTERTIDAL MOUNDS OF TROPICAL CALLIANASSIDS PROVIDE SUBSTRATES FOR COMPLEX UPOGEBIID SHRIMP BURROWS: MODERN AND PLEISTOCENE EXAMPLES FROM THE BAHAMAS

CURRAN, H. Allen, Dept. of Geology, Smith College, Northampton, MA, USA; and Anthony J. Martin, Dept. of Environmental Studies, Emory University, Atlanta, GA, USA

Burrowing by thalassinidean shrimp in modern tropical, shallow subtidal to intertidal carbonate environments is widespread and a powerful bioturbation agent of sandy substrates. Deep and intense burrowing by callianassid shrimp commonly occurs on the margins of hypersaline lagoons throughout the Bahamas, such as Pigeon Creek on San Salvador Island. Extensive sand flats along Pigeon Creek are deeply and thoroughly bioturbated by the callianassid Glypturus acanthochirus. In addition to dominating the deep tier, burrowing activity of the callianassids results in a highly mounded intertidal surface. Individual burrow cones commonly coalesce with time to form composite mound surfaces that become stabilized with development of microbial mats. These stabilized surfaces set the stage for colonization by shallow-tier burrowers, particularly the upogebiid shrimp, Upogebia vasquezi, and several species of fiddler crabs.

Burrow systems of Upogebia vasquezi are distinctive and complex. They typically consist of a pair of U-shaped burrows in close proximity or crisscrossing, with knobs or short tunnels at their bases. The entirety of the burrow pair is surrounded by a thick, externally pelleted wall. Inside burrow diameters range from 210 mm, and burrow depths are 1015 cm, in contrast to the much deeper callianassid burrows. These complex upogebiid burrows also occur as trace fossils in late Pleistocene lagoonal facies on San Salvador. Initially reported as fragmentary burrow fills, whole burrow systems virtually identical to the modern upogebiid burrows more recently have been found at several localities. The fossil burrows are most abundant immediately below a terra rossa paleosol marking late Pleistocene stillstand and regression of seas associated with onset of Wisconsinan glaciation. This stratigraphic occurrence makes these complex upogebiid trace fossils potentially useful as both paleoenvironmental and sea-level position indicators for Quaternary carbonate sequences throughout the Bahamas and other geologically similar regions.

DIGITAL BIOTA: OVERVIEW OF BIOLOGICALLY INSPIRED SOFTWARE SYSTEMS FOR MODELING BEHAVIOR AND EVOLUTION

DAMER, Bruce, Contact Consortium, Scotts Valley, CA, USA

In 1997, a special conference involving paleontologists, computer scientists and artists, was held in Banff, Canada and featured a trek to the Burgess Shale. The event was meant to create cross-disciplinary connections linking the study of evolution and biology with the developing practice of software systems exhibiting biological and evolutionary properties. Using computer-based demonstrations the speaker will review two classes of software systems presented at the Digital Burgess Conference and consider their relevance to the paleontological community.

One set of systems model aspects of the environment in which biological systems exist, simulating 3D space, gravity, terrains, safe and hazardous areas. Simplistic "digital biological entities" (biots) are placed in these virtual worlds and "learning" behaviors through adaptive forms of signaling produce behaviors akin to organisms in nature. Adapting such a system to paleontology might result in a system able to derive the construction of fauna responsible for fossil traces in some of the oldest Cambrian sediments.

A second class of software systems attempts to create the preconditions and carrying capacity to allow a large number of "digital biots" to evolve a simple "genome" data structure and express morphological changes through competition and reproduction. The dynamics of large, rapid population shifts and travel over networked computer systems creates an evolutionary environment not found in biology. Observing these systems causes one to speculate on the basic algorithmic nature of living systems divorced from physical representation (i.e., carbon-based biology). One might consider how life could be "elsewhere" (as in Astrobiology) or how novel forms of life might emerge in the future (say, from human technology). While not often engaged in by scientists, this kind of thought experiment is useful in that it can broaden both professional and personal intellectual horizons and cast new light on the nature of living systems.

A PHYLOGENETIC EXAMINATON OF THE NEAREST-LIVING-RELATIVE METHOD FOR RECONSTRUCTING PALEOCLIMATE AT MAMMALIAN FOSSIL LOCALITIES

DAVIS, Edward B., Dept. of Integrative Biology and Museum of Paleontology, University of California, Berkeley, CA, USA

Overlapping climatic tolerances of extant taxa are commonly used in paleoclimate reconstruction. This method is limited by the stratigraphic ranges of living taxa. Paleoclimate hypotheses have been extended deeper in time through assuming that the nearest living relatives of extinct taxa provide appropriate climatic analogs. These methodologies implicitly assume that the climatic tolerances of taxa do not change through time, and the nearest-living-relative method assumes that there is a phylogenetic control on the climatic tolerances of evolving lineages.

The assumptions of the nearest-living-relative methodology can be tested for mammal lineages through a phylogenetic analysis that examines the association of various important climatic parameters with various taxa. Accordingly, this study applied a phylogenetic approach to understand the relationship between climatic features (such as maximum and minimum January and July temperatures, annual precipitation, and seasonality) and evolution of extant species within Marmota and Microtus. Species within these genera have been considered important paleoclimate indicators due to their abundances, distinctive dental characters, and present restriction to certain microhabitats. The association between phylogenetic hypotheses based on molecular data and climatic parameters, both derived from published records, was tested using Felsenstein's independent contrast method. The technique involved mapping the climatic tolerances of various species onto the hypothesized phylogenetic relationships and thereby determining if groups of species were delineated by identifiable climatic boundaries.

Preliminary results indicate a correlation between phylogeny and climate tolerances for Microtus species endemic to North America. If additional analysis substantiates these results, the nearest-living-relative method could prove to be an important tool in reconstructing the paleoclimates of some fossil mammal localities.

AZOOXANTHELLATE CORAL IN SPACE AND TIME:
BIOGEOGRAPHY AND DIVERSITY PATTERNS FROM THE NEOGENE TO THE RECENT IN THE CARIBBEAN AND SURROUNDING AREAS

DAWSON, John P., Dept. of Geoscience, University of Iowa, Iowa City, IA, USA

In order to understand spatial and temporal patterns of azooxanthellate corals in the Caribbean, a database of Neogene to Recent azooxanthellate corals in the Caribbean and surrounding areas has been compiled. The Recent record consists of 129 species of azooxanthellate corals from the 19 geographical/political regions in the Caribbean and surrounding areas. The total species-by-region data matrix was divided into two sub-matrices representing the shallow water taxa (less than 200 meters) and the deep-water taxa (greater than 200 meters). These two sub-matrices were used to analyze how geographic distributions change with depth. The total matrix and the two sub-matrices were analyzed using r-mode and q-mode cluster analyses using Bray-Curtis' similarity coefficient and UPGMA clustering algorithm. In addition, detrended correspondence analysis of the regions was performed.

Results for the total data matrix revealed three major groups of regions and one ungrouped region. One of these groups has a primarily insular, tropical faunal component and includes the center of diversity for the Caribbean. A second grouping lacks the primarily insular, tropical faunal component but has a subtropical Carolinian faunal component. The shallow water sub-matrix displays the same groups as the total matrix. However, the deep-water sub-matrix has some changes in its groupings and indicates a more uniform, deep-water fauna throughout the Caribbean.

The Neogene record consists of 49 species of azooxanthellate corals from nine regions in the Caribbean. Initial cluster analysis results of the Neogene data indicate that the center of the Caribbean appears to have been the center of diversity for the azooxanthellate corals since the Neogene. However, there has been large turnover of the fauna at the Pliocene-Pleistocene boundary with only eight Neogene species present in the Recent.

THE ORIGIN, EVOLUTION, AND BIOGEOGRAPHY OF WALRUSES (CARNIVORA: ODOBENIDAE)

DEMÉRÉ, Thomas A., Dept. of Paleontology, San Diego Natural History Museum, San Diego, CA, USA

The monophyletic Odobenidae or walrus clade includes a single extant species, Odobenus rosmarus, as well as at least 20 fossil species arranged in 14 genera. Phylogenetic and stratigraphic data indicate that odobenids first evolved in the North Pacific region sometime before 18 Ma (late early Miocene) with basal taxa being confined to the eastern (Proneotherium) and western (Prototaria) parts of this region during the early middle Miocene. The later diverging odobenid Neotherium is found in the eastern North Pacific in the late middle Miocene. In the North Pacific during the early late Miocene species of the generalized odobenid Imagotaria are found in both the western and eastern North Pacific. A major radiation in the late Miocene produced two odobenid crown clades, the Dusignathinae (includes the extinct genera Dusignathus, Gomphotaria, and Pontolis) and the Odobeninae (includes, in addition to the modern walrus Odobenus, the extinct genera Aivikus, Protodobenus, Pliopedia, Alachtherium, Prorosmarus, and Valenictus). The fossil record indicates that dusignathine walruses remained endemic to the eastern North Pacific throughout their evolutionary history. In contrast, odobenine walruses, although evolving in the North Pacific during the late Miocene, dispersed into the eastern and western North Atlantic via the Arctic Ocean by early Pliocene time. The last of the dusignathine walruses is known from the late Pliocene of the eastern North Pacific. Odobenus evolved in the North Pacific and dispersed into the Arctic Ocean and eventually the North Atlantic probably during one of the early interglacial events of the latest Pliocene and Pleistocene. During the Pleistocene there was possibly a single circum-arctic species of Odobenus that extended its range into near temperate latitudes in both the Pacific and Atlantic during interglacial periods. The two extant subspecies of Odobenus rosmarus may represent the product of range fragmentation and allopatric speciation during a glacial period of maximum Arctic sea ice volume.