NAPC 2001

Abstracts, Ca - Ci
(5/17/01)

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FOSSIL LEGUME FRUITS FROM THE LOS AHUEHUETES LOCALITY, TEPEXI DE RODRÍGUEZ, PUEBLA

CALVILLO-CANAADELL, Laura, Posgrado en Ciencias Biológicas, Instituto de Geología, UNAM, México; and Sergio R.S. Cevallos-Ferriz, Depto. de Paleontología, Instituto de Geología, UNAM, México

Fossil legume fruits have been collected in the Oligocene Los Ahuehuetes locality near Tepexi de Rodríguez, Puebla. Their morphological comparison with fruits of extant plants underscores their attained diversity since the Paleogene in low latitude North America. Although diversity and variability in fruit morphpology within genera and species of Leguminosae constrains the identification of isolated fossil material, some morphological characters are useful to suggest their taxonomic afinity. Among them, fruit texture (e.g., woody, coraceous or chartaceous), suture prominenece (e.g., thick, thin, winged), presence of straight vs constricted margin, apex shape (e.g., long or short tapered, rounded), presence of externally well marked septa, as well as, the form, size, orientation and ornamentation of the seeds contained in the fruits, are important in supporting the presence of Alpuleia (Caesalpinoideae), Cladrastis (Papilionoideae), Inga, Calliandra and Mimosa (Mimosoideae). The presence of these plants further highlights the diversity and varied biogeographic relationships of the Tertiary low latitude flora of North America, and adds elements for future discussion of the hypothesis that suggests this geographic area was a secondary center of legume diversification.

TESTING THE MOLECULAR CLOCK WITH BIVALVES

CAMPBELL, David C., Dept. of Biology, St. Mary's College of Maryland, St. Mary's City, MD, USA

Molecular clock calculations often lack adequate chronological control, with many studies extrapolating from a single date, sometimes the product of previous extrapolation. A sample size of one provides no statistical validity. The good fossil record of the Bivalvia and relatively wide taxonomic sampling for molecular data give a unique opportunity to determine rates of molecular evolution using multiple calibration points. Recent morphological and molecular studies provide a phylogenetic framework for the analysis.

The 18S gene is the most extensively studied for the bivalves. In most cases, it is relatively conservative, about 1800 base pairs. Two clades show substantial variable insertions, up to a few hundred base pairs, and thus clearly deviate from clock-like behavior. Anomalodesmata diverged from other extant clades by the early Ordovician, but Cardioidea is Triassic in origin and most of its extant variation arose in the Tertiary. Eliminating the variable regions from the analysis somewhat improves the clock. COI, the most extensively sequenced protein-coding gene for bivalves, shows signs of mutational saturation in some Cenozoic divergences. Thus, it also requires either elimination of variable sites or use of a likelihood model to be of much use as a clock. The rates of molecular evolution in the Bivalvia appear too variable to support the use of a simple clock model. Detailed paleontological and phylogenetic analyses are necessary to determine multiple calibration points for testing the assumption of roughly constant rates.

PHYLOGENETIC AND EVOLUTIONARY IMPLICATIONS OF PENNSYLVANIAN SILICIFIED MARINE GASTROPODA FROM INDIANA

CAMPBELL, Matthew R., Dept. of Geological Sciences, Indiana University, Bloomington, IN, USA

A silicified marine invertebrate fauna from Weller Falls, Warren County, Indiana provides exceptional preservation of gastropods. Preliminary work has recovered 14 families and 24 genera, including taxa smaller than 5 mm. Few late Paleozoic aragonitic and calcitic mollusks have original shell material preserved to show critical protoconch and adult taxonomic characters (Nutzel, Erwin, and Mapes, 2000; Kues and Batten, 2001). The exceptional preservation of this fauna will enable more accurate assessment of the morphological and taxonomic diversity and patterns of faunal change. I will select the taxa with the best data for cladistic analyses, from the species to the subclass level. I will revise taxonomic assignments as warranted by better preservation of both individual specimens and the range of variability in populations in my material. Protoconch whorl characteristics are critical for assigning gastropods to higher taxonomic levels including order and subclass. Knowledge of higher-level affinities of the fossils is crucial for establishing phylogenetic connections with older and younger faunas.

The Weller Falls fauna is dominated by a diverse molluscan fauna, which is a pattern more characteristic of the Mesozoic. Faunas dominated by brachiopods, bryozoans, and echinoderms are more typical of the Paleozoic (Sepkoski, 1984). This similarity of a Pennsylvanian fauna with the Mesozoic pattern records the background patterns of gastropod evolution during the transformation to the Mesozoic shallow marine faunas.

IMPLICATIONS OF RAPID FORAMINIFERAL CHANGES DURING THE QUATERNARY

CANNARIATO, Kevin G., and James P. Kennett, Geological Sciences, University of California, Santa Barbara, CA, USA; and Ingrid L. Hendy, Earth and Ocean Sciences, University of British Columbia, Vancouver, BC, Canada

Microfossils can provide detailed histories of Earth's environmental systems because of their abundance, diversity, environmental sensitivity, geochemical packaging, and continuous accumulation. These aspects have been exploited to reconstruct rapid changes in Northeast Pacific margin coastal marine ecosystems and environments associated with late Quaternary millennial-scale global climate change.

Planktonic and benthic foraminiferal assemblages and isotopic values exhibit major oscillations synchronous with Dansgaard-Oeschger cycles. Planktonic foraminifera record rapid switches in sea-surface temperature and hydrography of the California Current. Interstadials exhibit rapid, major warmings (including brief overshoots) and a stratified water column while stadials exhibit coolings and a less stratified water column. Benthic assemblages record major oxygen-minimum, zone-strength fluctuations related to productivity and ocean ventilation oscillations. These fluctuations were widespread along the margin weakening, perhaps disappearing during stadials and strengthening during interstadials. Repeated turnovers of entire benthic faunas occurred rapidly without extinction or speciation. Interstadials exhibit consistent faunal successions. Benthic assemblage and carbon isotope oscillations suggest sedimentary methane flux variations while brief benthic and planktonic excursions reflect methane release throughout the water column and possibly into the atmosphere.

The rapid benthic and planktonic assemblage switches, highly tolerant, opportunistic planktonic assemblages, and consistent benthic faunal successions imply extreme sensitivity and adaptation of both ecosystems to the rapid environmental changes that marked the late Quaternary. This suggests that broad segments of the biosphere are well adapted to natural, rapid climate change. Late Quaternary millennial-scale-climate change may have affected the tempo and mode of speciation and extinction. Specific benthic assemblages and isotopic values may be indicative of high levels of methane in sedimentary microenvironments.

ORGANIC AND INORGANIC CARBON ISOTOPE PATTERNS ACROSS THE PERMIAN-TRIASSIC BOUNDARY IN THE MEISHAN SECTION, SOUTH CHINA

CAO, Changqun, and Wei Wang, Nanjing Institute of Palaeontology and Geology, Chinese Academy of Sciences, Nanjing, China

Data of carbon isotopic change across the P-T boundary have been repeated reported from the global boundary stratotype in Meishan. Nevertheless, previous studies are mostly limited to the inorganic matter from the beds near the boundary level. We investigated the carbon isotopic composition for both the organic and inorganic matter throughout the Changhsingian and Induan beds and found the following data interesting in understanding the End-Permian Mass Extinction. d¹³C values shift down from +2.9 per mil to -1.3 per mil at Bed 24 of the Clarkina yini Zone, forms the negative excursion in Bed 25­27 of the Clarkina meishanensis Zone with a drop of +1.3 per mil. After rising to 1.2 per mil at top of Bed 27 of the Hindeodu parvus Zone, d¹³C value turns into the second negative excursion form Bed 28 to Bed 36 of the Isarcicella isarcica Zone and the lower Clarkina carinata Zone with a drop of 2.5 per mil and then, comes back to +2.2 per mil throughout the lower C. carinata Zone. New detailed profile of d¹³C confirm a depletion of d¹³C in Bed 25 and 26 but the previously reported drop in d¹³C value from -2 to -6 per mil at the basal levels of Bed 27 might reflect strong weathering. d¹³C_org value drops down from -27.1 per mil at Bed 23 to -31.2 per mil at Bed 26, raises rapidly to -25.2 per mil at the top of Bed 27. It becomes very changeable from Bed 28 to 36, with a curve of low value between -29.4­-26.1 per mil, and a curve of high value from -25 per mil to -24 per mil, but then keeps a value of about -23.878 per mil in the higher level. An analysis on composition of kerogen shows that the d¹³C_org is intimately related to the source of organic matters. Kerogen from limestone of Bed 28-36 contains high fraction of woody fragments; d¹³C_org of these samples form a high value curve. Kerogen of the other samples is dominated by non-woody matter; profile of d¹³C_org value of these samples is well consistent to the d¹³C. The long term and double phases depletion of d¹³C may not reflect a single triggering event but a complex web of causality.

THE LIMBLESS ANIMAL BANFFIA CONSTRICTA FROM THE BURGESS SHALE (MIDDLE CAMBRIAN, CANADA): A STEM-GROUP ARTHROPOD?

CARON, Jean-Bernard, Dept. of Palaeobiology, Royal Ontario Museum, and Dept. of Zoology, Ramsay Wright Zoological Laboratories, University of Toronto, Toronto, ON, Canada

First described as an annelid by Walcott in 1911, the affinities of Banffia constricta have remained unclear so that it has been included most recently in the Problematica.

Banffia is here restudied on the basis of 383 new specimens coming from the youngest Burgess Shale fauna, 50 meters stratigraphically above the Walcott Phyllopod bed. Banffia has a bipartite body divided equally between an anterior bivalved fused carapace articulating with a posterior trunk composed of 40 to 50 segments. Animals range from 5.5 to 10 cm in length. The entire body is twisted spirally clockwise as seen from the front; this asymmetry is interpreted as a secondary modification of a bilateral condition. A prominent crown-like structure differentiated into three different circlets surrounds the antero-ventral mouth. A possible sensory cilium lies posteriorly to the mouth. An axial tube running towards the pointed rear end of the trunk is interpreted as a gut; it is sometimes filled with sediment. Parallel to the gut, a possible circulatory system encompasses dorsal vessel and metameric diverticula. The anus is terminal.

Banffia is considered to have been an epibenthic gregarious animal, probably a filter or deposit feeder. It may have crawled on the sea bottom and buried itself using its flexible twisted trunk, leaving its mouth at the interface water-sediment.

The presence of a bivalved carapace acting like as an exoskeleton, primitive cephalization, a segmented trunk, a dorsal vessel, a terminal anus and a ventrally rotated mouth all suggest affinity with the Arthropoda at the stem-group level, a scenario that implies secondary loss of limbs.

Affinities with Xidazoon, Vetulicola and Banffia confusa, limbless and problematic fossils from the Lower Cambrian Chengjiang fauna of China, are discussed.

TIME-AVERAGING IN ARTICULATE BRACHIOPOD ACCUMULATIONS: A QUANTITATIVE ESTIMATE OF TEMPORAL RESOLUTION FROM A HOLOCENE TROPICAL SHELF (SOUTHERN BRAZIL)

CARROLL, Monica, and Michal Kowalewski, Geological Sciences, Virginia Tech, Blacksburg, VA, USA; Marcello G. Simões, Inst. Biosciences, UNESP, Botucatu, Brazil; and Glenn A. Goodfriend, Earth Sciences, George Washington University, Washington, DC, USA

Surface accumulations of shells contain more than snap shots of the present moment in time. Absolute dating methods have been applied previously to mollusk shells to quantify how much time may be averaged in these accumulations and, by analogy, in fossil shell beds found in the geologic record. Brachiopods, predominant in Paleozoic shell beds, have not been previously studied. This study shows that by analyzing the racemization rate in Holocene shells of the brachiopod Bouchardia rosea, we reliably estimate the age of individual shells and provide quantitative estimates of time-averaging.

Brachiopod shells (n=80) from 4 subtidal sites (5.7 to 22 m depth), were selected for this study and 23 taphonomic criteria were evaluated for each. The specimens were then individually dated using amino-acid racemization (D-alloisoleucine/L-isoleucine of A/I. AMS radiocarbon ages of five specimens were used to determine the in situ rate of racemization. The results indicate that A/I ratio of brachiopod shells is an excellent predictor of their age (r²=0.91). Furthermore, the intercept of the A/I-¹⁴C relationship (predicted ¹⁴C for A/I=0) indicates a mean ¹⁴C reservoir age of 450 yr, which is consistent with other estimates for the region. The analysis indicates that time-averaging patterns observed in brachiopod shell accumulations are very similar to those derived previously for mollusks. These similarities include (1) temporal mixing on the scale of hundreds to thousands of years (std. deviation=520 years); (2) strongly right-skewed distributions; and (3) taphonomic condition is a poor predictor of age. Analysis of temporal resolution by locality indicates that time-averaging may vary notably at a local scale. Two of the localities did not display the characteristic right-skewness, and their time-averaging was much less extensive (std. deviation ~150 years vs. ~1100 years).

In summary, despite notable differences in biology, ecology and shell microstructure and mineralogy, brachiopods appear to be similar to mollusks in the scale and patterns of time-averaging.

LATEST CRETACEOUS RECORD OF MODERN BIRDS FROM ANTARCTICA: CENTER OF ORIGIN OR FORTUITOUS OCCURRENCE?

CASE, Judd A., Dept. of Biology, Saint Mary's College of California, Moraga, CA, USA

The record for Cretaceous birds in Gondwana is dominated by enantiornithine ("opposite") birds (Australia—Early Cretaceous; Argentina—latest Cretaceous) or other non-carinate birds (i.e., Rahonavis and Vorona, Madagascar, latest Cretaceous). However, the avian record from the latest Cretaceous of Antarctica is very different, to date, the Antarctic avian record is solely that of neognathous neornithine (=modern) bird lineages.

A burhinid charadriiiform (= a shorebird—e.g., a thick-knee or a stone curlew; early Maastrichtian Cape Lamb Mbr., plus other charadriiforms from the late Maastrichtian Sandwich Bluff Mbr., on Vega Island), presbyornithid anseriforms (= a duck-like wading bird; late Maastrichtian Sandwich Bluff Mbr. on Vega Island) and a gaviiform (= a loon; late Maastrichtian on Seymour Island) have been recovered from marine deposits of the James Ross Basin, Antarctic Peninsula. Presbyornithids represent an early or the earliest lineage of anseriforms, a basal neognathous clade. The presence of late Maastrichtian presbyornids on Vega Island is suggestive that Antarctica may have played a role in the origin of this clade. The burhinid charadriiiform from the earliest Maastrichtian makes the shorebird clade the oldest known avian lineage from Antarctica.

Antarctica has played a vital role in the dispersal, if not the evolution of the ratites (i.e., ostriches, rheas, emus etc.), which may be the first derived clade of neornithine birds. The dispersal of this clade throughout Antarctica to adjacent landmasses (Indo-Madagascar, Australia and New Zealand), possibly from southern South America, would have most likely occurred in the early Campanian through the Maastrichtian in Gondwana based on both tectonic and molecular data. A second endemic group to Gondwana and Antarctica are penguins, spheniscid spheniciforms, a group closely related to other seabirds, such as loons (gaviiforms), petrels (procellariiforms) and frigate birds (fregatids). The fact that loons and penguins have early records in "greater Antarctica" is suggestive that the entire seabird clade may have a Gondwanan origin.

The paleognathous ratites, and three of the seven major clades of neognathous birds all have a direct association with Antarctica in the latest Cretaceous. These facts lead to the speculation that the origin and early evolution of modern birds may have been in Antarctica representing another example of high latitude heterochroneity. On the other hand, it may be just a fortuitous occurrence that only modern birds have been recovered from Maastrichtian localities in the James Ross Basin and their presence be part of a larger world-wide, but yet unknown distribution of latest Cretaceous modern birds.

TERTIARY FLORAS FROM MEXICO AND THEIR SIGNIFICANCE IN UNDERSTANDING LOW-LATITUDE NORTH AMERICA VEGETATION

CEVALLOS-FERRIZ, Sergio R.S., Depto. de Paleontología, Inst. de Geología, UNAM, México

For decades, the origin of low-latitude North American vegetation has been explained as the result of the mixture, in this intermediate geographic area, of high-latitude North and South American elements. There are, however, two main ideas based on the timing of this integration. Perhaps the most popular idea suggests that the integration of low-latitude vegetation in North America took place in relative recent time, as the Panamanian land bridge was established. In contrast, the idea of a long and complicated biogeographical history for many lineages which today are common in the South American vegetation, but were diverse and important elements in the Tertiary vegetation of North America, is being proposed by other researchers. Sustaining either of these hypotheses is difficult due to the paucity of fossil information in low-latitude North America. Recent research in this area, however, supports the idea of a long history in which low-latitude vegetation during the Tertiary seems related to high-latitude vegetation, even if neotropical elements are introduced into the discussion. The great Panamanian exchange during the Plio-Pleistocene certainly influenced low-latitude North American vegetation, but the magnitude of this event also needs to be reevaluated. Selected examples based mainly on members of Anacardiaceae, Berberidaceae, Leguminosae, Moraceae, and Cornaceae highlight the need to continue understanding the fossil record of low-latitude North America to further support any idea on the origin of its extant vegetation.

EVOLUTIONARY STASIS AND TAXONOMIC STABILITY: THE BRYOZOAN METRARABDOTOS IN TROPICAL AMERICA

CHEETHAM, Alan H., Dept. of Paleobiology, Smithsonian Institution, Washington, DC, USA

The fine-scale pattern of morphological evolution in the bryozoan Metrarabdotos published in 1986 was based predominantly on extensive Neogene material collected by the Dominican Republic Project that yielded more than 100 species of cheilostome bryozoans. Subsequently, intensive collecting by the Panama Paleontology Project in Panama, Costa Rica, and other areas has doubled the number of bryozoan species from the Neogene of tropical America, contributing important new material to the record of Metrarabdotos.

A complete re-analysis of morphometric data from the original and new material combined produces relatively little alteration in the pattern of pronounced intraspecific stasis punctuated by sudden interspecific change. The new analysis does reveal five species not previously discriminated, but this addition is offset by merging of two previously distinct species, for a net gain of four to a total of 20 species of Metrarabdotos now known in the tropical American Neogene.

The robust character of the evolutionary pattern owes much to the centrality of the Dominican Republic material in the record of Metrarabdotos. More than half (12) of the 20 tropical American Neogene species occur in the Baitoa, Cercado, Gurabo, and Mao formations in the Cibao Basin, twice as many as known from any other region. Six species are known only from the Dominican Republic, half again as many as in any other region. Moreover, the mean continuity and density of sampling (2.9 My and 12.8 stratigraphic levels per species) are six and seven times as great, respectively, as the mean values for other regions. The mean resolution between sampling levels (0.2 My) across all species in the Dominican Republic is equaled by that of only one species elsewhere (Pacific Panama). However, this asymmetry in regional distribution is reversed for other bryozoan taxa; most notably, the cupuladriids occur in more diversity and greater stratigraphic continuity in Central America.

SEM OBSERVATION OF PRECAMBRIAN SPONGE EMBRYOS FROM SOUTHERN CHINA, REVEALING ULTRASTRUCTURES INCLUDING YOLK GRANULES, SECRETION GRANULES, CYTOSKELETON, AND NUCLEI

CHIEN, Paul, Biology, University of San Francisco, San Francisco, CA, USA; Jun-Yuan Chen, Chinese Academy of Sciences, Nanjing, China; Chia-Wei Li, National Tsing Hua University, Taiwan; and Fred Leung, Biology, University of Hong Kong, Hong Kong, China

Sponges are the most common organisms in the Precambrian Wengan fauna at Wengan, Guizhou (south China) that have produced numerous embryos, which have been phosphatized in early diagenesis in various stages of degradations. Under the present study are the embryos of a sponge (previous interpretation as a possible bilaterian by Xiao et al., 1998), that bore a size range of 0.5 mm to 0.8 mm, representing different developmental stages. X-ray energy spectra analyses show that the fossil embryos seem to be rich in the elements such as Ca, P, Mg, O, and B. The surrounding matrix is similar in composition except it is also rich in Mg. Inside these eggs and embryos, large numbers of granules were generally present. These granules show striations under a confocal microscope matching the periodicity of known invertebrate yolk granules and therefore they are interpreted as yolk material. As the number of cells in an embryo increase, the number and the size of yolk granules decrease. At more advanced stages of development, numerous mono-axial spicules begin to appear. Preparations of the isolated embryos, under scanning electron microscopes, show surface characteristics and cleavage patterns very clearly. Inside the fractured embryos we have identified a number of structures that are well preserved in three dimensions, and they are interpreted as secretion granules, mucus material, cytoskeleton, and the nucleus. Detailed ultrastructures of these organelles will be described.

LATE ORDOVICIAN INCREASE IN TRILOBITE SIZE AND ITS EVOLUTIONARY IMPLICATIONS

CHURCHILL-DICKSON, Lisa, Augusta, ME, USA

Cephalic size has been shown to be a good indicator of overall body length in trilobites. An analysis of 19 Ordovician trilobite genera from Laurentia shows a significant increase in cephalic size from the Mohawkian to the Cincinnatian. The average size of the 19 genera during the Mohawkian was 6.3 mm (number of individuals = 138), as compared to the genus average in the Cincinnatian of 7.9 mm (number of individuals = 72). This represents a 20% percent increase in size and is significant at alpha = 0.05, using a two-tailed, robust rank order test.

Twenty-three formations and 14 geographically distinct localities were sampled for the Mohawkian data. Eighteen formations and 11 localities were sampled for the Cincinnatian. Geographic coverage was similar for both. Preliminary analyses of lithologies and relative bathymetric ranges of each formation did not reveal any apparent sampling or preservation biases in the data. Silicified faunas are present in the Mohawkian data and while they do contribute slightly to an overall lowering of the average generic sizes, their influence is not statistically significant.

The increase in trilobite size during the Cincinnatian suggests a change in the trilobite's environment. The increase affected seven of the 10 families studied and two evolutionary faunas (13 Whiterockian genera and three Ibexian genera). Three of the families (two Whiterockian genera and one Ibexian genus) showed a decrease in size. Possible causal agents for the overall increase in size at the genus level may include a shift in resource allocation related to the lowering of sea level following the Mohawkian high stand. Additional research is needed to determine the extent of this size increase in the trilobite clade, if it is observed in other clades and if it played a role in determining survivorship in the end-Ordovician extinction.

STRATIGRAPHY AND DEPOSITIONAL ENVIRONMENTS OF PLEISTOCENE AGE IN CENTRAL PALM BEACH COUNTY, FLORIDA

CINELLI, Anthony C., Dept. of Geography and Geology, Florida Atlantic University, Boca Raton, FL, USA

A 20 m exposed section in a de-watered quarry in central Palm Beach County is lending new insight to the Pleistocene stratigraphy of southeastern Florida. Interpretation of the preliminary data implies two trangressional-regressional sequences separated by two unconformities within the condensed section. The Chione elevata-dominated molluscan assemblage suggests a tropical environment similar to the modern subtidal back reef community of Biscayne Bay. Few specimens occur in life position. A well-preserved majority of articulated and disarticulated individuals suggests that a postmortem accumulation of shells took place in a protected environment. De-watering allows data to be gathered over 15 m below the normal water table. Due to the region's low relief and high water table, paleontological collecting and stratigraphic work in southeastern Florida has generally been achieved by methods of indirect observation such as cores, well logs and dredged spoil piles.