NAPC 2001

June 26 - July 1 2001 Berkeley, California

Abstracts, Fri - Gu
(5/17/01)

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A NEW UPPER CRETACEOUS (CENOMANIAN) FOSSILIFEROUS LOCALITY IN NORTH CENTRAL TEXAS

FRIEDMAN, Virginia, Dept. of Geosciences, University of Texas at Dallas, Richardson, TX, USA

A new, highly fossiliferous upper Cenomanian locality is described in the Eagle Ford Group of North Central Texas. The vertebrate marine assemblage includes a great abundance of fish remains including shark as well as plesiosaur and turtle specimens. Paleontologically, one of the remarkable features of this new locality is the abundance of bone-bearing coprolites. Beds rich in coprolites have potential use in biostratigraphic correlation. A large, nearly complete fish skeleton has also been recovered and may belong to a new species. This locality is an important section that further defines the stratigraphy and paleontology of the basal Eagle Ford Group of North Central Texas.

AN ENVIRONMENTAL GRADIENT DETERMINED BY CELTIS (ULMACEAE) FOSSILS FROM THE MIOCENE OF THE GREAT PLAINS OF NORTH AMERICA

GABEL, Mark, and Kristie Martin, Dept. of Biology, Black Hills State University, Spearfish, SD, USA

Celtis fossils were collected from 61 sites in mid- to late Miocene sediments of the Ogallala Group from South Dakota to Texas. Stable carbon isotope ratios were determined from endocarps. d¹³C values ranged from -28 parts per mil (ppmil) to -22 ppmil. d¹³C values by land mammal age were: Barstovian = -27.6 ppmil, Clarendonian = -26.8 ppmil, and Hemphillian = -25.7 ppmil. We found significant differences between Barstovian and Hemphillian values and between Clarendonian and Hemphillian values, but not between Barstovian and Clarendonian values. Linear regression of isotope values of samples from 49 sites for which approximate dates have been determined showed a correlation coefficient of 0.56.

TAPHONOMY OF SOFT-BODIED PRESERVATION AND PTYCHOPARIID LAGERSTÄTTE IN THE WHEELER SHALE (MIDDLE CAMBRIAN), HOUSE RANGE, USA; CONTROLS AND IMPLICATIONS

GAINES, Robert R., Mary L. Droser, and Martin J. Kennedy, Dept. of Earth Sciences, University of California, Riverside, CA, USA

Common soft-bodied preservation occurs in the Wheeler Shale, a unit famous for its Elrathia trilobite concentration-lagerstätte. The Wheeler Shale was deposited in a paleotopographic low which has been interpreted previously as a fault-bounded trough within a carbonate platform. Soft-bodied fauna and Elrathia-rich beds are generally confined to mutually exclusive biofacies. While both biofacies are characterized by medium to thickly laminated (18 mm beds) shale beds that grade in color from gray to black, with sharp basal contacts, they differ in faunal composition and degree of bioturbation. In both facies, carbonate mud was derived from the adjacent platform and terrigenous mud was delivered episodically during periods of enhanced continental runoff, or by along shelf currents.

Low levels of bioturbation in the well laminated carbonate-clay mud couplets reduced irrigation of seawater into the already impermeable clay-rich sediment. The onset of organic decay by means of sulfate reduction in anoxic sediments increased alkalinity and precipitated carbonate within pore spaces. Within the soft-bodied biofacies, exceptional preservation was facilitated by occluded porosity, which restricted bacterial activity. Rare horizontal pyritized burrows occur, typical of sediments formed under oxygen-depleted bottom waters. In contrast, within the Elrathia biofacies, dolomite precipitated in trilobite carapaces, forming trilobite "nodules." Non-pyritic burrows are slightly more common in this biofacies and penetrate to a maximum depth of 1.2 cm. We infer that the soft-bodied biofacies accumulated under anoxic conditions in the absence of a benthic fauna (fossils are allochthonous). The Elrathia biofacies likely represents deposition under dysaerobic conditions and contains a dominantly in situ benthos. Increased bottom water oxygen content promoted more rapid decomposition of labile tissues and facilitated colonization by a benthic fauna.

AN UNUSUAL ADAPTATION IN THE CAUDAL VERTEBRAE OF COELOPHYSIS BAURI (DINOSAURIA: THEROPODA)

GAY, Robert, Northern Arizona University, Flagstaff, AZ, USA

A new look at the caudal vertebrae in the Triassic theropod Coelophysis bauri reveals an unusual adaptation of the prezygapophyses. The prezygapophyses overlap the centrum of the previous vertebra between one quarter the length of the preceding centrum and the entire length of the preceding centrum. While other workers have noted this feature, the implications for the movement and function of the tail have not been discussed in detail. Herein is a discussion of this feature, and its biomechanical implications.

THE FREQUENCY OF GRADUALLY CHANGING LINEAGES IN ANCIENT LAKE PANNON: IMPLICATIONS FOR MODELS OF SPECIATION

GEARY, Dana H., Dept. of Geology and Geophysics, University of Wisconsin, Madison, WI, USA; Imre Magyar, MOL Hungarian Oil and Gas Company, Budapest, Hungary; Hilary Sanders, Dept. of Geology and Geophysics, University of Wisconsin, Madison, WI, USA; Sándor Gulyás, Dept. of Geology and Paleontology, University of Szeged, Hungary; and Pál Müller, MAFI, Geological Institute of Hungary, Budapest, Hungary

Ancient Lake Pannon existed in central Europe from approximately 124 Ma. During its history, the lake changed in water chemistry from brackish to fresh, and in areal extent, with a maximum at approximately 9.5 Ma. If Lake Pannon existed at its maximum size today, it would be the second largest and third deepest lake in the world. Lake Pannon harbored a spectacular endemic molluscan fauna; more than 900 species have been described.

Detailed morphometric studies have revealed a striking number of cases of sustained gradual change. Gradual changes have been described in lineages from several families, including cardiid and dreissenid bivalves, and planorbid and melanopsid gastropods. Changes involve a wide range of shell characters, including size, shape, and ornament. Intervals of change may be prolonged, lasting 12 million years or even longer.

In the cases of gradual change that we have studied, specimens or samples of intermediate morphology come from multiple locations widely scattered across the basin. Thus, gradually evolved new species were probably not arising through classic allopatry, with changes occurring in a restricted isolate. Instead, some other mechanism(s), operating basin wide on at least an intermittent basis, must have been common.

LATE CAMBRIAN JELLYFISH BEHAVIORAL TAPHONOMY IN CENTRAL WISCONSIN

GERSHWIN, Lisa-ann Gershwin, and Jere H. Lipps, Museum of Paleontology, University of California, Berkeley, CA, USA; R.H. Dott, Jr., Dept. of Geology & Geophysics, University of Wisconsin, Madison, WI, USA; and Dan Damrow, Mosinee, WI, USA

Fossilization of soft-bodied fauna has long held the intrigue of paleontologists. The soft-bodied Ediacaran fauna of the Late Precambrian, are well known and relatively abundant; however, except for the extraordinary fossils from the Solnhofen, Mazon Creek, and Burgess Shale formations, Phanerozoic medusae are rare. In Late Cambrian rocks (Mt. Simon or Wonewoc formation) of Central Wisconsin, well over 200 undescribed medusa-like impressions occur together, giving the unique opportunity to study a large number of specimens. However, unlike other fossil medusae, which are known from body impressions, this form is known mainly from behavioral impressions. We sought to test whether these impressions (A) are most likely to be jellyfish, (B) are very unlikely to be jellyfish, or (C) lack information for determination whether or not they could be jellyfish. Based on observations of live, stranded medusae, combined with taphonomic experiments on a variety of soft-bodied taxa, we concluded that they are jellyfish behavioral impressions. Based on this interpretation, we were able to deduce that the medusae, after stranding live, excavated the sand in characteristic patterns. Superimposed on some of the excavations are impressions of the oral morphology, allowing for comparison of this taxon to the Recent hydrozoan medusa Staurophora mertensii Brandt, 1835.

A LATE CRETACEOUS (EARLY TURONIAN) THERIZINOSAURID DINOSAUR (THERIZINOSAURIDAE, THEROPODA) FROM THE TROPIC SHALE OF SOUTHERN UTAH, USA

GILLETTE, David D., and L. Barry Albright, Museum of Northern Arizona, Flagstaff, AZ, USA; Alan L. Titus, Grand Staircase-Escalante National Monument, Kanab, UT, USA; and Merle Graffam, Museum of Northern Arizona, Flagstaff, AZ, USA

Therizinosauroidea (Therizinosaurus + Segnosauria) are rare and enigmatic dinosaurs known only from incomplete specimens from the Cretaceous of Asia. Species assigned to this clade include Alxasaurus elesitaiensis (Albian), Enigmosaurus mongoliensis, Erlikosaurus andrewsi and Segnosaurus galbinensis (Cenomanian-Turonian), and Therizinosaurus cheloniformis (Campanian-Maastrichtian) of the People's Republic of Mongolia, as well as Beipiaosaurus inexpectus (Early Cretaceous), Nanshiungosaurus brevispinus (late Campanian) and other unnamed specimens from People's Republic of China. Overall, osteology of therizinosaurs indicates bizarre adaptations, leading to suggestions that they were herbivorous theropods, highly aberrant sauropods, or relict prosauropods, and may have been partially aquatic. A nearly articulated therizinosaurid skeleton discovered in the Upper Cretaceous Tropic Shale of southern Utah, USA, was heavily encrusted by the Cretaceous bivalve mollusk, Mytiloides sp., cf. M. columbianus. That taxon, along with occurrences of the ammonoid Mammites nodosoides, precisely dates the stratigraphic position as late-early Turonian. The skeleton to date includes ribs, sacrum, paired right and left hindlimb elements (ilia, pubes, ischia, femora, tibiae, fibulae, astragali), seven metatarsals, ten pedal phalanges and fragments of others, caudal vertebrae, and chevrons. The highly unusual opisthopubic pelvis, tetradactyl pes, and other synapomorphies indicate assignment to this family, but generic determination must await completion of the excavation. The tibia length (approximately 63 cm) is approximately 90% the femur length (approximately 70 cm), and metatarsal IV length (23 cm) is approximately 33% the femur length, proportions similar to those described for other therizinosaurs. This discovery has important biogeographic implications regarding dispersal of terrestrial faunas between western North America and Asia during the early Late Cretaceous.

HOLOCENE CERION LAND SNAILS ON LONG ISLAND, BAHAMAS: A FOSSIL RECORD OF EXCEPTIONALLY HIGH SPATIAL AND TEMPORAL RESOLUTION

GOODFRIEND, Glenn A., Dept. of Earth and Environmental Sciences, George Washington University, Washington, DC, USA; and Stephen J. Gould, Museum of Comparative Zoology, Harvard University, Cambridge, MA, USA

The land snail Cerion is famous for its extreme geographic variation in shell morphology. In order to better understand the origin of the present patterns of geographic variation, we carried out a survey of the fossil record of Cerion on the east coast of Long Island in the Bahamas, an area with especially high morphological diversity. Holocene fossils of Cerion were found to be abundant and widespread in coastal eolian sand deposits. In areas where the sands form linear dunes (inactivated by vegetation), the fossil deposits are geographically continuous. Even on rocky coastal cliffs, pockets of eolian sands containing fossil Cerion were usually found at intervals of tens of meters. Thus the fossil record may provide resolution of geographic patterns on the order of tens of meters. A representative series of shells was dated by amino acid racemization (D-alloisoleucine/L-isoleucine, or A/I), calibrated against radiocarbon. These analyses show that the fossil record extends back to ca. 7000 yr BP. Deposits containing such older, middle Holocene samples were sporadic, whereas the last 30004000 yr was represented in most of the sites analyzed. The fossil record of the last ca. 1000 is particularly well represented. Dating results indicate considerable reworking of the deposits, so that shells must be dated individually rather than by stratigraphic considerations. At sites for which numerous individuals were analyzed, the record appears to be temporally continuous. Given the large sample sizes available for most locations (average of tens of shells per 25 cm interval of a 1 m² excavation), the temporal resolution of the fossil record is probably limited mainly by the resolution of the dating methods rather than by the continuity of the record itself. The age resolution of the amino acid racemization dating in this context remains to be tested quantitatively but is probably in the range of ca. 510% of the age.

SCLEROCHRONOLOGICALLY-CALIBRATED OXYGEN ISOTOPE PROFILES DETECT TIME-AVERAGING IN BIVALVE MOLLUSK ASSEMBLAGES

GOODWIN, David H., Karl W. Flessa, Bernd R. Schöne, and David L. Dettman, Dept. of Geosciences, University of Arizona, Tucson, AZ, USA

Although schemes exist for detecting time-averaging many are limited to Quaternary fossils or depend on an unreliable taphonomic clock. Here we present a detection method free from these limitations that utilizes oxygen isotope d¹⁸O) variation within sclerochronologically-determined years in bivalve mollusk shells.

In principle, clams that grew in the same place at the same time will have identical annual d¹⁸O profiles. To evaluate this assumption we collected four sets of bivalve mollusks (Chione cortezi) from the northern Gulf of California: (1) two clams living in the same place at the same time; (2) two living in different places at the same time; (3) two from the same place that lived at different times; and (4) two that lived in different places at different times. For each specimen we analyzed d¹⁸O values in the second or third year of growth. Using daily growth increments we assigned d¹⁸O samples to specific fortnights (+/- one fortnight). We devised three metrics to compare annual d¹⁸O profiles: annual isotopic amplitude (AIA), absolute isotopic values (AIV; max and min d¹⁸O values), and number of "non-synchronous enrichment events" (NEE). Enrichment events are defined as a set of three d¹⁸O samples where the first is followed by a second with a more positive value and is in turn followed by a third with a more negative value. Enrichment events result from either protracted cold periods and/or evaporative isotopic enrichment of the ambient water. Clams that grew in the same place at the same time have identical annual isotopic profiles. Clams living in different places at the same time have similar AIA and AIV but one or more NEEs. Clams that grew in the same place at different times or in different places at different times can have different AIA, AIV, and one or more NEEs.

While this method cannot detect the absence of time-averaging (clams living in different places or at different times could have identical annual isotopic profiles), it may be useful for detecting time-averaging in obrution deposits containing suspected census assemblages.

EVIDENCE FOR POSTMORTEM ENRICHMENT IN LATE CRETACEOUS DINOSAUR BONE USING MICROBEAM PIXE

GOODWIN, Mark B., Museum of Paleontology, University of California, Berkeley, CA, USA; and Graham Bench and Patrick Grant, Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, CA, USA

The effects of diagenesis on the geochemistry of fossils are poorly understood. The alteration of stable isotopes by fossilization creates uncertainty about the preservation of original biogenic isotope values. The use of stable oxygen isotopes from dinosaur bones and teeth to reconstruct dinosaur thermophysiology remains controversial due to potential overprinting by diagenesis. Studies using stable isotopes for dietary or physiological reconstructions are commonly based on the assumption that postmortem alteration of the fossil did not occur or that its effects are negligible. Successful isotope analysis of fossil bone for the purposes of determining paleophysiology depends upon the retention of original isotope atoms in the bone phosphate. If the chemical composition of dinosaur bone is affected by dissolution, recrystallization, or mineral substitution from the burial environment, the measured oxygen isotope ratio may reflect groundwater temperature, not dinosaur body temperature. PIXE, coupled with microsampling and mass spectrometry, is a potent analytical tool to assess diagenesis in fossils.

Nuclear microscopy using Proton Induced X-ray Emission (or microbeam PIXE) provides accurate quantitative values, multi-element detection, sub-micron spatial resolution to ppm or mg/g sensitivity, and elemental maps of micron regions of bone. A thin section from an exceptionally well preserved Late Cretaceous hadrosaur femur (UCMP 179501) from Alaska's North Slope was subject to PIXE analysis. This fossil does not show typical signs of alteration at a macro and micron scale, but is highly altered nonetheless. PIXE analysis reveals enrichment of Fe (180,000 ppm) and Mn (13,000 ppm) in the lamellae surrounding Haversian canals and neighboring tissue of several magnitudes higher than levels known in modern bone. A corresponding depletion of Ca and P also occurs. This enrichment is most likely due to diagenesis from the burial environment since Fe and Mn are present in modern bone in only minute amounts. PIXE analysis of a modern Caiman and Rhea confirm this.

FAUNMAP—THE SECOND GENERATION AND BEYOND

GRAHAM, Russell W., Dept. of Earth and Space Sciences, Denver Museum of Nature and Science, Denver, CO, USA; and Ernest L. Lundelius, Jr., Vertebrate Paleontology Laboratory, J.J. Pickle Research Center, University of Texas, Austin, TX, USA

FAUNMAP I is a relational database documenting fossil mammal localities in the contiguous forty-eight states of the US for the last 40 ka. The primary purpose of FAUNMAP I was to study changes in community composition, provinciality, and environmental heterogeneity in response to late Quaternary climate change. To this end, a literature search was conducted and the following types of data were recorded for individual sites: geographic location, site type, depositional environments, geologic age, numeric age, faunal composition, cultural affiliation, taphonomic pathways, and relevant literature. To facilitate fine scale temporal analyses, sites were subdivided into Analysis Units that could include geologic units, excavation units, cultural divisions, etc. as assigned by the original investigator. Sites had to have: (1) collections in a public repository, (2) geographic location, and (3) fine-scale chronological framework to be recorded. FAUNMAP I was linked to a Geographic Information System that allowed mapping changes in geographic distributions for more than 200 individual species for seven distinct time periods. Statistical parameters derived from manipulation of the database and other "treatments" could also be mapped. FAUNMAP I was made available through hard copy publications, database diskettes, and online menu guided queries for constructing maps. It has been used by other scientists in their research and publications, by graduate students for theses and dissertations, by land use planners and managers, and by pre-college and university educators, to mention a few. FAUNMAP II is being constructed in the same way but it has been expanded to include Plio-Pleistocene and Holocene faunas from the contiguous forty-eight states, Canada, and Alaska. FAUNMAP I and II will be available online through the Denver Museum of Nature and Science. Future endeavors include adding non-mammalian taxa to make FAUNMAP an ecosystem database and developing interactive programs to make data and interpretations more readily available to the general public.

THE “PHOEBICHNUS LOOK-ALIKE” - A FOSSILIZED ROOT SYSTEM? (AND A LARGE COMPOSITE ICHNOFOSSIL)

GREGORY, Murray R. and Kathleen A. Campbell Dept. of Geology, The University of Auckland, Auckland, New Zealand

Phoebichnus trochoides Bromley and Asgaard, is a large and unusual compound, deep-tier trace fossil described from the Jurassic of Jameson Land, Greenland and is of restricted occurrence in a few other Mesozoic sequences. The trace maker is an unknown marine organism. A remarkably similar structure, herein called a “Phoebichnus look-alike” is preserved in a Quaternary coastal dune setting from northern New Zealand. It has been identified as a rooting system. After excluding the local mangrove and tree ferns as possible progenitors, attention was placed on two large monocotyledons—the cabbage tree (Cordyline australis), a large tree-like member of the lily family, and the endemic Nikau palm (Rhopalostylis sapida). It is considered that this large, composite trace fossil reflects the rooting architecture of the latter. Apart from its age, the only discernable significant difference between P. trochoides and the “P. look-alike” is the absence of bi-directional, back-fill menisci in radiating rays of the look-alike. It is suggested that care should be taken when identifying the ichnogenus Phoebichnus trochoides (s.s.) in the absence of these menisci. Structures of a “P. look-alike” kind may be of local paleoenvironmental significance and help in the identification of damp, coastal dune settings.

AN ASSOCIATION BETWEEN A SPECIMEN OF DEINONYCHUS ANTIRRHOPUS AND THEROPOD EGGSHELLS: PHYLOGENETIC AND BEHAVIORAL IMPLICATIONS

GRELLET-TINNER, Gerald, Dept. of Vertebrate Paleontology, Los Angeles County Museum, and Dept. of Earth Sciences, University of Southern California, Los Angeles, CA, USA; and Peter J. Makovicky, Div. of Paleontology, American Museum of Natural History, New York, NY, USA

In 1931 Barnum Brown recovered from the Cloverly Formation a partial skeleton of the theropod Deinonychus antirrhopus (AMNH 3015) while excavating a specimen of the ornithopod Tenontosaurus tilletti. Unknown until recently, a few small blocks of matrix from this quarry contain abundant quantities of eggshell as well as rod-like bone fragments.

Examination of skeletal remains in these claystone blocks reveals that these bones are theropod gastralia, and not ossified caudal tendons diagnostic of ornithischians. Individual medial gastral elements are identical to isolated gastralia of D. antirrhopus.

Oological examination reveals that one accumulation of shells in the largest block of matrix may represent a crushed cross-section of an egg squeezed between the articulated gastral segments and a larger piece of cortical bone. The total eggshell thickness varies from 0.60 to 0.44 mm. Its surficial ornamentation appears linearituberculate. SEM radial sections display two structural layers with an aprismatic condition. The mammillae of layer 1 consist of acicular rhombohedral calcite crystals, similar to those in oviraptorids. Layer 2 crystallographic orientation obliterates the shell units originating from the base of layer 1.

In contrast to ornithischian eggshells structurally composed of one single transversal layer, theropod eggshells are known to display two structural layers. AMNH 3015 eggshells therefore cannot be attributed to T. tilletti. A random occurrence between an articulated specimen of D. antirrhopus and large quantities of closely apposed theropod eggshell seems unlikely. Thus in view of recent discoveries and what information is available from AMNH 3015, we suggest that we have the first known D. antirrhopus eggshells, although referring eggshells to specific taxa is speculative in the absence of identifiable embryo included in eggs. In addition, the position of the whole egg at less than 5mm from the gastralia might indicate a brooding behavior. Recent discoveries of nesting behaviors in Oviraptor and possibly in a specimen of Troödon indicate that brooding is primitive for Maniraptora, and would parsimoniously be expected to be present in Dromaeosauridae.

PREDATOR-PREY INTERACTIONS OF MOON SNAILS AND THEIR BIVALVE PREY

GREY, Melissa, Elizabeth Boulding, and Michael Brookfield, University of Guelph, ON, Canada

The naticid predator-bivalve-prey system is an excellent tool for the study of predator-prey relationships and is useful for both neontological and paleontological research. This is one of the few systems in which it is possible to measure theintensity of selection placed upon prey by their predators because drilling by naticid gastropods leave a unique borehole, representing unambiguous evidence of predation. Previous studies have attempted to use this system as models for coevolution and escalation however; none have estimated selection differentials. This is important because the strength and form of selection can be used to help predict evolutionary changes in response to changing patterns of predation.

The purpose of my study is to determine whether selective predation by naticid gastropods is correlated with adaptive evolutionary responses among their preferred prey. If naticids place high selection intensities on their prey, then prey may morphologically adapt. This is testable by estimating selection differentials from Recent and fossil assemblages. The two morphological characters I have measured are prey shell thickness and shell length. Previous studies indicate that these characters are important in naticid prey selection, as they may be refugia from naticid predation.

Selection intensities for Recent beach assemblages have been calculated for shell length and thickness for each of three prey families (Veneridae, Mactridae and Tellinidae). Logistic regressions show that, within each of these prey families, shell length and thickness do not significantly affect the probability of being drilled (p >0.05), indicating that naticids are not placing significant selection intensities on their prey. Selection differentials and logistic regressions will be calculated for assemblages from the Miocene and Pleistocene and within family comparisons will be made in order to determine whether there are trends in selection from the Miocene to the Recent.

THE GLOBAL POLLEN DATABASE

GRIMM, Eric C., Illinois State Museum, Springfield, IL, USA

The Global Pollen Database (GPD) contains Quaternary pollen data from the Americas, Europe, Africa, Asia, and the Indo-Pacific region. New data are organized and made available by various regional data cooperatives. The GPD began with the development in 1990 of the independent but compatible North American and European Pollen Databases (NAPD and EPD). The GPD was conceived in 1994 with the development of the Latin American Pollen Database, which was integrated with NAPD from the outset. Beginning in 1997, the GPD has incorporated data from the Indo-Pacific Pollen Database and non-restricted data from the EPD. The objective of the GPD is to assemble pollen data from Quaternary deposits and modern surface samples into a relational database and to make these data readily available to the scientific community. The database contains original pollen counts, radiocarbon dates, site data, bibliographic data, worker information, and other relevant data. The database makes an important distinction between archival data and research data. Archival tables store the count data, radiocarbon dates as reported by the radiocarbon laboratories, and other basic data not expected to change, except to add missing information or correct errors. Research tables store data that are derived by manipulation of the archival tables and are of an interpretive or subjective nature. Probably the most important of the research tables are those containing age models and chronologies, including the assignment of an age to each pollen sample. The GPD is available from the World Data Center-A for Paleoclimatology, which is housed at the National Geophysical Data Center in Boulder, Colorado. In addition to the database tables themselves, the data are available in several file formats via the World Wide Web (www.ngdc.noaa.gov/paleo/pollen.html).

ORIGIN OF STANDARDIZED CRINOID CUP PLATING

GUENSBURG, Thomas E., Div. of Math and Physical Sciences, Rock Valley College, Rockford, IL, USA; and James Sprinkle, Dept. of Geological Sciences, University of Texas, Austin, TX, USA

Newly discovered stem-group crinoids from the earliest Ordovician together with basal crown-group taxa provide evidence for the origin of standardized cup plating and a basis for designating new class-wide plate homologies. Stem-group cup plating consists of unorganized primaries and secondaries except for a poorly organized cup-base primary circlet (CBPC) and fixed ray plates high in the cup. The lower-middle cup of stem-group crinoids is proportionately larger with many more plates than crown groups and lacks differentiated radials, basals, and ?infrabasals. Consistent alternation of the CBPC with stem pentameres below and interruption by 12 posterior gap plates is evidence of homology to both infrabasals of dicyclic and basals of monocyclic crown groups. The lowest fixed ray plates of one early taxon are large with diverging ray ridges and are homologous to radials of crown groups. Higher fixed ray plates of stem-group taxa are homologous to fixed brachials among derived crinoids. Radials bearing specialized facets are found among derived clades lacking interray plates and having a sharp junction of cup and free arms. No evidence supports usage of biradial terminology. Wide posterior (CD) plating of stem-group crinoids is entirely interradial, originating centrally at the level of the lowest fixed ray plates. It is similarly positioned at or above the radials in camerates, but branches from the lower C-ray in disparids or from beneath the small raised C-radial in cladids. These deeply rooted posterior plating patterns contradict a few assignments based on monocyclic or dicyclic cup designs, and suggest the CBPC has been lost or another cup plate circlet has been added. Hybocrinids and perittocrinids, although monocyclic, have typical cladid posterior morphology, and merocrinids, although dicyclic, have disparid posterior morphology. This new cup plate homology system permits reassessment of early crinoid phylogeny based on more complete data than has previously been available.