NAPC 2001
June 26 - July 1 2001 Berkeley, California
Abstracts, Sm - Sti
(5/22/01)
Jump to: Smith, D. | Smith, F.
| Smith, M. | Smith, S. |
Smith, U. | Sommerer |
Sour-Tovar | Souto | Spencer
| Stanley, G. | Stanley, S.
| Starratt | Stephen
| Stidham | Stinchcomb
Return to Main Abstracts Page
TAPHONOMIC BIAS AND INSECT DIVERSITY: A LESSON
FROM THE BEETLES AND FLIES
SMITH, Dena M., CU Museum of Natural History, University of Colorado,
Boulder, CO, USA
Labandeira and Sepkoski's 1993 work on the fossil record of insects was
very important because it showed that insects have an extensive fossil
record and that this record could be used to examine both paleontolgical
and neontological hypotheses. However, exceptionally preserved, insect-rich
assemblages may have had a great influence on this diversity curve. For
example, large peaks in diversity in the Late Jurassic and in the Early
Cenozoic may be attributable to the fossil rich Karatau assemblage and
the Baltic Amber. How important is insect taphonomy in determining patterns
of insect diversity over time? To answer this question, I reanalyzed the
coleoptera (beetles) and the diptera (flies). Both of these insect orders
are diverse and abundant today, they have a long fossil record (dating
to the Permian), and they are also ecologically diverse. However, their
distinct morphological features make them susceptible to different taphonomic
biases, providing an opportunity to look at how differing preservational
bias can affect within and among group diversity patterns.
Here, I present updated diversity data for the diptera and coleoptera
and examine the type and number of depositional environments represented
in each time interval, the condition of described taxa, and the change
in species richness within deposits over time. Large increases in insect
diversity during the early Cenozoic do appear to be artifactual as Labandeira
and Sepkoski suggested. Not only are there more types of depositional
environments during this time interval, but the quality of these deposits
in terms of insect preservation are also exceptional. Differing preservational
bias between the diptera and coleoptera seems to most strongly affect
the condition of specimens and not long-term diversity patterns. Conducting
future analyses that only examine equivalent depositional environments
through time may help to give a less taphonomically biased picture of
insect diversity trends over time.
FOSSIL PHYTOLITH CARBON ISOTOPE RECORDS OF GRASS
PHOTOSYNTHETIC PATHWAYS
SMITH, Francesca A., Dept. of Geophysical Sciences, University of Chicago,
Chicago, IL, USA
The development of grasslands ecosystems in the Tertiary provides a context
for current and future responses of grasses and crops to anthropogenic
climate and atmospheric changes. Although a variety of methods have been
used to characterize past grasslands (i.e., paleobotanical records, vertebrate
functional morphology, paleosol characteristics, herbivore tooth enamel
d13C, and soil carbonate d13C), none of these proxies
capture a record of the photosynthetic pathway (C3 or C4
of grasses specifically), as distinct from overall vegetation. Carbon
isotope ratios of fossil grass phytoliths (silica bodies produced primarily
by grasses), on the other hand, provide a direct record of grass photosynthetic
pathway and therefore can detect proportions of C3 and C4
grasses. In order to examine changes in C3/C4 of
grasses in the Great Plains during the Tertiary, phytoliths were extracted
from paleosols from Kansas and Nebraska and the occluded carbon was combusted
and analyzed isotopically. In contrast to the tooth enamel d13C
record that shows no significant C4 component prior to 7 Ma
(Wang et al., 1994; Latorre et al., 1997), the d13C of phytoliths
suggest a significant contribution from C4 grasses prior to
7 Ma, potentially as far back as the Early Oligocene. The phytolith d13C
reflects an expansion of C4 grasses at about 7 Ma, similar
to the shift observed in the tooth enamel d13C record. Therefore,
the change from a C3 to a C4 diet observed in the
tooth enamel could have been caused entirely by a shift in the photosynthetic
pathway of the grasses, rather than the previously proposed shift from
a C3 woodland to a C4 grassland (Wang et al., 1994).
After the expansion of C4 grasses seen at about 7 Ma, phytolith
d13C shifts back toward C3 values in the Early Pliocene.
Potential drivers for these shifts are temperature, seasonality of precipitation
and atmospheric CO2/O2 ratios. Given paleo-pCO2
reconstructions indicating little change throughout the Neogene, the favored
drivers are primarily climatic.
DISCOVERY OF A CRANIUM OF STYLEMYS (REPTILIA:
CHELONIA) FROM THE TURTLE COVE MEMBER OF THE JOHN DAY FORMATION, CENTRAL
OREGON
SMITH, Matthew E., and Theodore J. Fremd, John Day Fossil Beds National
Monument, Kimberly, OR, USA; and Roger C. Wood, Stockton State College,
Pomona, NJ, USA
Although turtle remains are distributed throughout much of the 45 million
year sequence represented by the deposits within the John Day Basin, almost
all specimens in existing collections are represented only by shell material
or limb elements. Particularly vexing is the lack of association of any
diagnostic skull material with these typically low-arched carapaces. Previously,
Stylemys from the John Day Formation has been described based solely
on shell morphology due to a lack of cranial elements.
Here, we report the discovery of a nearly complete cranium of a tortoise
referable to Stylemys (Leidy, 1851) in situ with several
carapace fragments. This is the first reported occurrence of any chelonian
skull material associated with postcranial elements from the John Day
Formation. The stratigraphic position can be pinpointed with precision
within the K1 unit of the Turtle Cove Member, approximately 8m above the
Deep Creek Tuff recently dated to 27.5 ma. Little has been published on
fossil turtles from the Northwest since the work of Hay and Gilmore's
work in the early 1900s. The presence of additional material within a
definable pedofacies suggests a unique opportunity to provide additional
paleoecologic information, as well as population and taphonomic data,
about the occurrences of these relatively abundant but rather poorly understood
tortoises.
FURTHER INVESTIGATIONS OF AROID SEEDS FROM THE
PRINCETON CHERT
SMITH, Selena Y., and Ruth A. Stockey, Dept. of Biological Sciences,
University of Alberta, Edmonton, AB, Canada
Large numbers of fossil seeds of Keratosperma allenbyensis Cevallos-Ferriz
& Stockey have been identified in the Middle Eocene (Allenby Formation)
Princeton chert of British Columbia. These seeds have been previously
assigned to the Araceae, Subfamily Lasioideae based on anatomical characters.
Over 200 new specimens have been examined using the cellulose acetate
peel technique modified for hydrofluoric acid. Seeds are campylotropous
and have three rows of spiny ridges on the seed coat. Idioblasts that
probably contained raphides are found scattered in the outer integument.
The micropylar end of the seed has a thin-walled micropylar cover that
was easily displaced at the time of germination. A prominent hypostase
and podium are present at the chalazal end of the seed and an epistase
has been observed at the micropylar end. Endosperm is present in these
seeds and contains dark contents. Monocotyledonary embryos have been reported
but most seed cavities show tissues that contain large numbers of fungal
hyphae that replace embryo tissues. Anatomical comparisons with the extant
lasioids Cyrtosperma ferox Linden et N. E. Br. and Urospatha
sagittifolia (Rodsch.) Schott were made using paraffin and cryo embedding
and sectioning techniques. A reconstruction of the fossil seeds was made
from serial sections allowing the fossils to be compared to extant taxa
based on external morphology. Keratosperma allenbyensis are the
oldest known lasioid seeds in the fossil record and show closest similarities
to Urospatha from Central and South America.
INTEGRATED RESEARCH ON FOSSIL AND EXTANT FLOWERING
PLANTS VIA A DESCRIPTIVE DATABASE
SMITH, Una R., Los Alamos National Laboratory, Los Alamos, NM, USA
Although fossils are notoriously incomplete, what matters is not the
completeness of fossils per se, but rather the completeness of their descriptions.
Research on both fossil and extant taxa requires useful descriptions and,
in most cases, more complete descriptions are more useful. Paleobotanists
routinely describe fossil plants that are incomplete (e.g., dispersed
pollen, leaves, fruits, seeds, and pieces of wood), but often the most
difficult challenge is to obtain comparable descriptions of extant
plants. To address this challenge, I will demonstrate effective ways to
use a descriptive database of all extant flowering plants (Watson, L.,
and M.J. Dallwitz. 1992 onwards. The Families of Flowering Plants:
Descriptions, Illustrations, Identification, and Information Retrieval.
Version: 14th December 2000. http://biodiversity.uno.edu/delta/angio/).
This enormous database of extant plant descriptions can be used to: (1)
guide the painstaking work of identification and description; (2) evaluate
the validity and completeness of published descriptions; and (3) test
hypotheses of systematic affinity.
ARTIFICIAL EVOLUTION FOR INTERACTIVE ART AND
ENTERTAINMENT
SOMMERER, Christa, and Laurent Mignonneau, ATR Media Integration and
Communications Research Lab, Kyoto, Japan
The true power of evolution lies in its ability to exploit emergent collective
phenomena (Langton, 1996). One of the central concepts in Artificial Life
research is to create artificial evolution via artificial selection and
to test the possibilities of creating a self-sustaining system with open-ended
evolution.
Much inspiration for creating digital life forms on a computer screen
has been provided by Dawkin's "The Blind Watchmaker" Evolution
Simulation Software published in 1986. Reynold's work in 1987 simulating
the flocking behaviour of artificial birds was another milestone in establishing
the idea of applying artificial life principles to computer graphics software.
Ray's "Tierra" evolution simulator, created in 1991, finally
brought the possibilities of software evolution to larger attention. But
it was the emergence of advanced computer graphics technologies in the
early 1990s that helped artists, like Sims (1991) to study the visual
creation process itself.
Since 1994, we've applied artificial life principles such as artificial
genetics, mutation, and evolution to interactive art works. Our systems
include "A-Volve" (Sommerer et al., 1994), an interactive installation
where users can create and interact with artificial life creatures, that
live and evolve in a water-filled glass pool. Our "Life Spacies"
system (Sommerer et al., 1997) consists of a web page where users type
text messages to create Alife creatures. Here, written text is used as
the genetic code to shape the creatures' design and determine their behaviours
and interactions. Our latest system is called "IKI-IKI Phone"
(Sommerer, 2001), a large-scale multi-user Alife art game for mobile phones.
In this system networked users can create, evolve and exchange Alife creatures
using their i-mode-enabled mobile phones.
More information is available at www.mic.atr.co.jp/~christa/.
LOWER CARBONIFEROUS (OSAGEAN) INVERTEBRATES FROM
MEXICO: PALEOGEOGRAPHIC IMPLICATIONS
SOUR-TOVAR, Francisco, Sara A. Quiroz-Barroso, and Daniel Navarro-Santillán,
Facultad de Ciencias, UNAM, Ciudad Universitaria, Coyoacan, México
Invertebrate fossil assemblages from the Lower Carboniferous of Tamaulipas
and Oaxaca, states of East and Southeast Mexico, are typical of marine
environments associated with continental margins. Among the diverse invertebrates
found, it is noteworthy that a very high percentage of the species described
have also been reported as typical of several localities of the Mid-Continent
Paleoprovince. This similarity extends to previously described Pennsylvanian
faunas from Oaxaca, indicating that during most of the Carboniferous this
Paleoprovince extended from the central-east region of the United States
to at least the region now occupied by Oaxaca State, Southeast Mexico.
Among the Osagean species that allowed the establishment of the former
relationship, and which have been described for Oaxaca, we find the rostroconch
Pseudomulceodens cancellatus associated to the binomial of brachiopods
Actinoconchus lamellosus-Torynifer pseudolineatus and several species
of genus Syringothiris. This association is also found in Tamaulipas,
where brachiopod diversity is greater, and includes the presence of Barroisella
sp. Orbiculoidea sp., Rugosochonetes multicostatus, Rotaia
subtrigona, Camarophorella sp., Cleiothyridina tenuilineata
and Beecheria chouteauensis. Several ideas recently proposed
relate to the origin of tectonic terranes that formed east and southeast
Mexico, and it is believed that there are exotic terranes, possibly derived
from Gondwana and of Proterozoic or Early Paleozoic age. Although the
timing of this North American accretionary event is still under discussion,
faunal similarities suggest that the coupling of North America and these
terranes in the area studied, was a pre-Mississippian or Early Mississippian
event.
NEW OCCURRENCES OF COPROLITES FROM THE ARIRIPE
BASIN (UPPER JURASSIC AND LOWER CRETACEOUS, BRAZIL)
SOUTO, Paulo R.F., Departo. de Geologia, Inst. de Geologia, Universidade
Federal do Rio de Janeiro, Rio de Janeiro, Brazil
The aim of this study is to provide new paloentological information on
coprolites collected from different areas of the Araripe Plateau region,
northeastern Brazil. The material consists of samples collected from three
units: the Brejo Santo Formation (Upper Jurassic) and the Rio da Batateira
and Santana Formations (Lower Cretaceous). The Araripe Basin sediments
were deposited in shallow water of an epicontinental sea preserving a
series of richly fossiliferous strata with abundant fishes, some quelonians,
crocodiles and pterosaurs. The recent discovery of coprolites in these
sediments reveals new morphotypes. Comparative treatment and analysis
of the chemical components provides new information regarding the level
of spatial distribution and density for these paleocommunities. The coprolites
from the Brejo Santo Formation are large, cylindrical forms and smaller
ovoid forms with anisopolar and polar ends. Those from the Rio da Batateira
Formation are spherical to ovoid in shape and some are over two centimeters
in diameter. The two coprolite assemblages from the Santana Formation
include calcareous concretions (ichthioliths) collected from the Romualdo
Member. These oval and cylindrical forms have isopolar and anisopolar
ends. Internally, they show enterospires marks and the remains of shells
and bones. Coprolites from the Ipubi Member are covered by thin layers
of mudstone, are oval and cylindrical shaped and of different sizes.
POTENTIALLY FALSE INTERPRETATIONS OF DINOSAUR
NESTS AND NESTING, WITH AN EXAMPLE FROM THE ALLEN FORMATION, PATAGONIA,
ARGENTINA
SPENCER, Lee A., Earth History Research Center, Southwestern Adventist
University, Keene, TX, USA; and Elaine G. Kennedy, Geoscience Research
Institute, Loma Linda University, Loma Linda, CA, USA
The primary difficulty in accurately identifying dinosaur nest sites
and behaviors has been the lack of defining criteria, both paleontological
and sedimentological. If eggs are found, especially associated eggs or
abundant eggshell fragments, they are almost always assumed to be nests.
Sedimentological data has been minimized or ignored.
The Allen Formation in the Rio Negro Province, Argentina, preserves numerous
localities with either whole eggs or abundant eggshell fragments, which
have been interpreted as representing nesting areas. A 4 m2
quarry was excavated through part of a layer containing abundant eggshell
fragments utilizing both paleontological and sedimentological techniques.
The eggshell fragments were randomly oriented throughout a 1.5 m thick
mudstone; the mudstone lacked depositional structures;and the layer was
exposed over 1.5 km. The fragments were taxonomically diverse and were
mixed with other biota, including fish and turtle fragments as well as
plant debris. We interpreted the depositional environment as a storm surge
deposit.
Sedimentological structures were also noted at the site of whole eggs.
The eggs were found at the toe of a cross-bedded sandstone. The cross-beds
draped across the eggs and were not cut by any parental digging activity.
Rip-ups, mud lenses and mud stringers were noted in the basal portion
of the sandstone.
The sedimentological context of all sites examined involved transport.
No nest structures were seen. Preliminary studies in North America and
Europe have yielded data suggesting that nesting behavioral interpretations
there could also benefit from additional sedimentological research.
CHANGES AMONG REEF ECOSYSTEMS DURING THE EARLY
MESOZOIC
STANLEY, George D., Jr., Dept. of Geology, The University of Montana,
Missoula, MT, USA
Tropical reef ecosystems, devastated after the end-Permian event, did
not recover until 1214 million years laterwell into the Middle Triassic.
There are unanswered questions about the lengthy lag time and the Triassic
recovery did not follow a gradual logistical curve. The lag time and subsequent
rapid return of reef ecosystems and carbonate sedimentation in the Middle
Triassic, suggests that protracted marine environmental perturbations
arrested recovery.
Scleractinian corals appeared suddenly in the mid-Triassic without ancestors.
They likely evolved from soft-bodied, anemone-like animals that survived
the perturbations and later acquired calcification. After their debut,
these corals waited over 20 million years before assuming major constructional
roles on reefs. The first Mesozoic reefs in the Middle Triassic were dominated
by microbes, calcareous sponges, bryozoans, calcareous algae and microproblematica
which, at higher taxonomic levels, were similar to Permian reefs. Changes
took place during the Late Ladinian-Early Carnian interval, with increases
among sphinctozoid sponges, "Tubiphytes," and other microproblematica.
Late Carnian-early Norian reefs diversified with corals and sponges, and
a smaller mass extinction separates this interval from the maximum reef
development during the latest Triassic (mid-Norian to Rhaetian), when
new higher taxa appeared, sphinctozoid sponges expanded and corals came
to dominate. The appearance of more Permian Lazarus taxa during this interval,
than in the Middle Triassic is perplexing.
The end-Triassic mass extinction triggered a "sudden" reef
collapse like the Permo-Triassic pattern, but the Early Jurassic lag was
shorter, lasting 68 ma. Panthalassan refuges are evoked to explain
the survival of some taxa. It was not until the mid-Jurassic that a new
stable ecosystem re-emerged, which included corals, stromatoporoids and
algae. Jurassic reef changes relate to survival of key taxa, climatic
amelioration, and the opening of the proto-Atlantic.
WEAK COMPETITION THROUGHOUT THE MARINE REALM:
CONSEQUENCES FOR POPULATION GROWTH, RATE OF SPECIATION, AND GLOBAL DIVERSIFICATION
STANLEY, Steven M., and Morton K. Blaustein, Dept. of Earth and Planetary
Sciences, Johns Hopkins University, Baltimore, MD, USA
Paleontologists have too often invoked competitive interactions to explain
patterns of evolution and extinction for marine taxa. Bob Paine's caging
experiments on rocky shores in the 1960s showed that, by preventing potentially
dominant species from excluding others, predation and physical disturbance
can allow numerous species to coexist. Similar caging experiments have
shown that intense predation prevents food or space from limiting population
sizes of most soft-bottom species. Even on organic reefs, where space
is at a premium, the presence of competitive networks suppresses competitive
exclusion. Ironically, weak competition in the marine realm should reduce
rates of speciation. Incipent species must arise frequently as small,
reproductively isolated populations, but in order to succeed they must
expand numerically. For terrestrial taxa in which niche partitioning occurs,
an incipient species can expand immediately by exploiting a previously
unutilized resource. In the marine realm, however, where thousands of
species utilize the same kinds of food and space, a typical incipient
species joins what might be termed a meganichea communal niche shared
by numerous species separated by trivial differences in resource requirements.
Lacking unique access to a limiting resource, the population of the incipient
species will not easily expand beyond its small initial percentage of
the total population occupying its meganiche; extinction is therefore
likely. This condition has probably contributed to low overall rates of
speciation in the marine realm and to accelerated speciation following
mass extinctions, when populations of incipient species have exploded
because predation has weakened. Weak competition in the marine realm is
also incompatible with the idea of logistic increase and saturation at
a diversity plateau for Paleozoic taxa. In fact, weak competition accounts
for the unbridled diversification of marine life since the Permian mass
extinctions, which decimated taxa normally characterized by high rates
of extinction (the Paleozoic Fauna).
DIATOM EVIDENCE FOR FLUCTUATIONS IN THE FRESHWATER
BUDGET AT RUSH RANCH, NORTHERN SAN FRANCISCO BAY, CALIFORNIA: A 3,000
YEAR RECORD
STARRATT, Scott W., U.S. Geological Survey, Menlo Park, CA, USA
Diatoms from tidal marsh sediment cores collected at Rush Ranch, north
of Suisun Bay were used to reconstruct the history of salinity variability
in the northern part of San Francisco Bay over the past 3000 years. This
site was chosen because it is located midway between the normal marine
environment of San Francisco Bay and the freshwater environment of the
Sacramento and San Joaquin Rivers. The composition of modern diatom assemblages
in fresh-water, brackish water, and saltwater marshes are utilized to
calibrate the late Holocene assemblages. Variations in both individual
taxa and a simple ratio (which summarizes the relationship between salinity
and individual taxa) serve as proxies for salinity. The ratio summarizes
proportions of taxa commonly found in freshwater, brackish water, and
intertidal environments. While this ratio is useful in determining large-scale
salinity variations, it does not account for changes in the abundance
of individual taxa. Dominant taxa in each assemblage vary downcore, indicating
that variation in salinity is only one parameter in a complex set of factors
that control the temporal and spatial distribution of diatoms in San Francisco
Bay marshes. At the Rush Ranch site there appears to be evidence of broad-scale
salinity cycles. Prior to European contact about 150 years ago, there
are two intervals dominated by freshwater taxa and two intervals dominated
by intertidal taxa. Although these cycles do not appear to be directly
related to well-established global climate patterns, minor fluctuations
during the last 1800 years resemble the lake level record for Mono Lake,
California, implying contemporaneous increases in precipitation on both
sides of the Sierra Nevada. Other proxies (13C and pollen)
at Rush Ranch show similar broad-scale cycles in salinity.
DIATOM STUDIES IN THE WESTERN UNITED STATES:
FROM ECONOMIC DEPOSITS TO INDICATORS OF PAST CLIMATE CHANGE
STARRATT, Scott W., U.S. Geological Survey, Menlo Park, CA, USA
Diatoms were first reported from rocks of the western United States more
than one hundred years ago. While the economic importance of those deposits
was recognized, it was almost seventy years before their potential use
in biochronological and paleolimnological studies was recognized. The
oldest known freshwater diatom flora is at least middle Eocene in age.
While there is limited evidence of Paleogene diatomaceous deposits, there
is a marked increase in both the number of deposits and the diversity
of the floras beginning in the early Miocene. The association of these
deposits with numerous layers of volcanic ash, as well as diverse mammalian
faunas, has led to a well-constrained chronology for the evolution of
freshwater diatoms in the western US. It is possible to broadly divide
the floras into four evolutionary assemblages, based primarily on centric
planktonic genera. The earliest assemblage (middle Eocene through early
Miocene) includes members of the Aulacoseiraceae and various families
of pennate diatoms. The Neogene and Quaternary assemblages include members
of the Hemidiscaceae and Thalassiosiraceae. The evolution of early Miocene
assemblages coincides with major radiations of marine taxa, high stands
of sea level and the creation of tectonic basins throughout the Great
Basin. Floral evolution in the middle and late Miocene may have been related
to major oceanographic and climatic changes which resulted in increased
rates of diatom evolution. While the morphological similarity of many
of the late Neogene and Quaternary taxa to modern forms simplifies paleoenvironmental
interpretation, this taxonomic longevity makes them difficult to use in
high-resolution stratigraphic studies. Taxonomic and stratigraphic resolution
will likely be improved through increased use of the scanning electron
microscope and comparison with well-dated floras from other regions of
the world.
THE IMPACT OF REPRODUCTIVE STRATEGY ON CEPHALOPOD
EVOLUTION
STEPHEN, Daniel A., Dept. of Geology & Geophysics, Texas A&M
University, College Station, TX, USA
It is well known that species richness is far greater for ammonoids than
for nautiloids, and that in general ammonoid taxa have much shorter durations
than nautiloid taxa, but the cause of this disparity has puzzled paleontologists
for years. Why did the Ammonoidea become so taxonomically diverse and
rapidly evolving, while the Nautiloidea did not? One possible solution
to the mystery of cephalopod phylogenetic patterns is that taxa in clades
characterized by short stratigraphic ranges and high total diversity had
a semelparous reproductive strategy (parental mortality follows mass spawning
event), whereas taxa in clades with long stratigraphic ranges and low
total diversity had an iteroparous reproductive strategy (repeated, isolated
breeding events). Previous workers have noted that "r-selected"
species tend to be semelparous with many, relatively small offspring,
and that "K-selected" species tend to be iteroparous with few,
relatively large offspring. Although the correlation between reproductive
strategy and r-versus-K population dynamics is not without exception,
it has been suggested that cephalopod embryonic size correlates with reproductive
strategy, small embryos indicating semelparity and large embryos indicating
iteroparity. To examine these questions, I analyzed original data from
the Carboniferous of the southern mid-continent as well as data from the
literature. For ammonoid genera in the data set, mean embryonic shell
size is 0.91 mm, and mean taxonomic longevity is 13.5 m.y. For nautiloid
genera in the data set, mean embryonic shell size is 8.46 mm, and mean
taxonomic longevity is 47.7 m.y. Differences between ammonoids and nautiloids
are statistically significant, and these preliminary results support the
hypothesis that reproductive strategy has played a major role in shaping
the evolutionary history of the Cephalopoda.
GRASSHOPPER EVOLUTION AND THE SPREAD OF GRASSES
STIDHAM, Thomas A., and Caroline A.E. Strömberg, Dept. of Integrative
Biology and Museum of Paleontology, University of California, Berkeley,
CA, USA
Grasshoppers (Orthoptera: Caelifera) are a diverse clade of herbivores
especially common in grassland and savanna habitats, where they can consume
more grass than sympatric mammalian ungulates. Analysis of grasshopper
feces demonstrates that they do ingest phytoliths, and therefore phytoliths
likely cause observed mandibular wear. Despite their great diversity,
grass consumption appears to be restricted to the derived acridoid grasshoppers.
At present, the oldest acridoids are Eocene, contemporaneous with early
fossil grasses. Several subfamily-level clades in the crown-group of the
grass-eating Acrididae first appear in Miocene prior to the proposed spread
of grasslands in the middle Miocene. In addition, many of the fossil members
of these grass-eating clades have been collected in deposits that contain
grass pollen and grass macrofossils. Given the apparent origin of derived
acridoids in the Eocene and their Miocene radiation, these grasshoppers
appear to have tracked the evolution of grasses and expansion of grasslands
over geologic time. Additionally, grass consumption may have been a key
innovation in grasshopper evolution that allowed them to take advantage
of a new food resource and allow them to diversify.
UPPER CAMBRIAN/LOWER ORDOVICIAN PLATED MOLLUSKS
OF THE OZARK UPLIFT
STINCHCOMB, Bruce L., Dept. of Geology, Florissant Valley Community College,
St. Louis, MO, USA
A variety of problematic fossils of undoubted molluscan affinity occurs
near the Cambrian-Ordovician boundary in the Ozark Uplift of Missouri
and Arkansas. Controversy exists as to whether these fossils represent
early and primitive amphinurans or whether they are representatives of
an extinct molluscan class or classes. Support of the latter position
is suggested by the following: (1) Some plated mollusks exhibit horseshoe
shaped pattern of muscle scars identical to those of undoubted monoplacphorans.
Such musculature is totally unlike that of the amphinurans. (2) Valves
of many plated mollusks, such as Matthevia, are morphologically
quite different from the valves or plates of amphinurans. (3) With extensive
collecting, a seven or eight valved specimen should have been found, as
other multiplated organisms such as trilobites, have been found in an
articulated condition in the same horizons associated with plated mollusks.
Rare, articulated, plated mollusks have been found, but only with two
to four valves. Support for plated mollusks being amphinurans include
the presence of ornamentation in the form of small shell perforations,
which are similar to the perforations occupied by aesthetes of modern
amphinurans, and the similarity in morphology of some plated mollusk valves
to those of undoubted amphinurans.
Various models have been suggested for these plated mollusks. These include
a sixteen-valved "monster" based upon large numbers of valve
assemblages, the "stegosaur" model of Yochelson for Matthevia
and a single valve (tapeworm) model in which each valve covered only a
single animal which broke away from a "string" of such animals
which could reproduce by asexually "budding." This model explains
the occasional two- to four-valved specimens, which are sometimes found.
|