PaleoBios 21(1) Supplement
© 2001 University of California Museum of Paleontology
1
2001 California Paleontology Conference
ABSTRACTS
HOX GENE CO-OPTION DURING SEA UR-
CHIN DEVELOPMENT: REGULATORY EVO-
LUTION OF BODY PLANS
ARENAS-MENA, CESAR, Div. of Biology 156-29, Cali-
fornia Institute of Technology, Pasadena, CA 91125 (e-
mail: arenas@cco.caltech.edu)
The cluster of Hox genes is utilized only during postembry-
onic development of the larval stage, where colinear domains
of expression are found bilaterally in the mesodermal
somatocoels. In addition, several expression domains of
individual Hox genes are found in echinoid specific struc-
tures. New gene expression patterns are obtained mainly by
means of new transcriptional regulatory inputs. Thus it will
be no surprise to find regulatory modules responsible for
these sea urchin specific patterns.
Evolutionary-developmental processes are obviously in-
tertwined, and so should be their study. Comparing the
accumulation of random mutations in nonfunctional nucle-
otides reveals the location of the regulatory regions con-
trolling gene expression. This approach is underway
between two sea urchins genetically isolated some 50 mil-
lion years ago. The main morphology of the species is
similar; therefore conservation of some regulatory domains
is expected. The combination of bioinformatic tools with
functional analysis will reveal the relationship of the tran-
scriptional regulatory apparatus structure with the morpho-
logical outcome. Most developmental change is being
associated with transcriptional modifications, but stasis may
not necessarily correspond with identical regulatory net-
works.
DESCRIPTION AND PHYLOGENETIC AS-
SESSMENT OF PYGMY POSSUMS AND
FEATHERTAIL POSSUMS OF THE EARLY
MIOCENE IN SOUTH AUSTRALIA
CASE, J.A., and L. CIMINELLO, Dept. of Biology, Saint
Mary's College of California, Moraga, CA 94575 (e-
mail: jcase@stmarys-ca.edu)
Fossil material collected from the Tirari Desert, South
Australia represents a new genus of pygmy possum, family
Burramyidae, and a new genus of feathertail possum, family
Acrobatidae. The collected material was recovered from the
Wipajiri Formation at Lake Ngapakaldi in the region east of
the Lake Eyre and can be assigned to the early Miocene
epoch, approximately 22 million years ago, as noted by
Woodburne et al. (1993). The new burramyid differs from
the previously described fossil species of burramyid possums
noted by Pledge (1987) and Turnbull et al. (1987) primarily
by a less bladed third premolar, as well as other characters.
In phylogenetic analysis, the new burramyid does not cluster
with the genus Cercartetus, but rather allies itself with the
species of Burramys, where it is the sister group to this clade.
The family Acrobatidae, previously had no fossil record, but
the new acrobatid genus is similar enough to modern
representatives to offer proof of its existence, especially a
lower molar cristid obliqua that cuts across the talonid basin
to the lingual side of the tooth. In phylogenetic analyses
comparing many characters, the new acrobatid is separated
from the modern genera Acrobates and Distochoerus.
Dental morphologies indicate the new burramyid, like
Burramys parvus, would have had a diet consisting of
insects, fruits, and seeds. The new acrobatid has a molar
morphology very similar to both Acrobates pyjmaeus and
Distochoerus pennatus and would also probably feed on
nectar pollen and exudates.
LARGE EARLY CAMBRIAN BURROWS
FROM THE WOOD CANYON FORMATION,
DEATH VALLEY AREA, CALIFORNIA
CORSETTI, CARA L., Dept. of Geology, Univ. of Cali-
fornia, Santa Barbara, CA 93106; FRANK A.
CORSETTI, Dept. of Earth Sciences, Univ. of South-
ern California, Los Angeles, CA 90089-0740; and
STANLEY M. AWRAMIK, Dept. of Geol., Univ. of
California, Santa Barbara, CA 93016 (e-mail:
cara@geology.ucsb.edu)
A community of previously undescribed vertical burrows is
found in the nearshore, shallow marine, tide-dominated
mixed siliciclastic-carbonate Upper Wood Canyon Forma-
tion (Lower Cambrian), Death Valley region, U.S.A. Pre-
liminary data indicate that burrow depth and diameter are
large in comparison to other described Cambrian ichnogenera;
some burrows attain a depth of 25 cm and diameter of 6.1
cm. Burrow diameter varies from 1 to 6.1 cm, and burrow
depth varies from 5 to 25 cm and most likely represents
several ichnogenera. Most appear to be vertical tubes, but
some are u- and j-shaped. An unusual spiraled trace (de-
scribed by others as related to the Harlaniella ichnogenus)
occurs in the same units in association with the vertical, u-
shaped, and j-shaped burrows.
The Skolithos ichnofacies, also known from the nearshore
environments in Cambrian time, has been shown to pen-
etrate deeply into the sediment, but it is commonly mono-
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PALEOBIOS, VOL. 21, SUPPLEMENT TO NUMBER 1, 2001
specific and therefore not complexly tiered. Alternatively,
the great range in size, depth, and form seen in the Wood
Canyon ichnofauna may indicate that a complex
paleocommunity was utilizing the same infaunal ecospace;
thus, the nearshore environment was complexly tiered by
Early Cambrian time. Offshore ichnocommunities (below
storm wave base) do not show similar tiering until much
later in the Phanerozoic. The ichnofauna from the Wood
Canyon Formation may demonstrate that infaunal commu-
nity structure follows other evolutionary trends seen in the
fossil record: complexity appears first in nearshore environ-
ments and later in offshore environments.
PALEOECOLOGY OF BENTHIC META-
ZOANS IN THE EARLY CAMBRIAN
CHENGJIANG FAUNA: EVIDENCE FOR
THE CAMBRIAN SUBSTRATE REVOLU-
TION
DORNBOS, STEPHEN Q., and DAVID J. BOTTJER,
Dept. of Earth Sciences, Univ. of Southern California,
Los Angeles, CA, 90089-0740 (e-mail:
sdornbos@usc.edu)
As the depth and intensity of bioturbation increased through
the Proterozoic-Phanerozoic transition, the substrates on
which marine benthos lived changed from being relatively
firm with a sharp sediment-water interface to having a high
water content and blurry sediment-water interface. Micro-
bial mats, once dominant on normal marine Proterozoic
seafloors, were relegated to stressed settings lacking intense
metazoan activity. This change in substrates has been termed
the agronomic revolution (Seilacher and Pfliiger, 1994), and
the impact of this substrate transition on benthic metazoans
has been termed the Cambrian substrate revolution (Bottjer
et al., 2000). Because the Early Cambrian was a transitional
time in this substrate revolution, benthic metazoans adapted
to typical Proterozoic-style soft substrates might have coex-
isted with benthic metazoans adapted to more typical Phan-
erozoic-style soft substrates. Paleoecological examination of
the Early Cambrian Chengjiang fauna is perhaps the ideal
way to begin testing for this coexistence. Suspension feeders
well-adapted for survival on typical Proterozoic-style soft
substrates are characterized by small size and a sediment-
resting or shallow sediment-sticking lifestyle and include, for
example, the enigmatic Chengjiang suspension feeder
Dinomiscbus, a shallow sediment sticker. Suspension feeders
well adapted to typical Phanerozoic-style soft substrates are
characterized by attachment abilities, rootlike holdfasts,
broad body mass distribution, or deep sediment-sticking.
Examples from the Chengjiang fauna include the suspension
feeding cnidarian Cambrorhytium, which lived attached to
available hard substrates. Mobile benthic metazoans of the
Chengjiang fauna also show adaptations to both substrate
styles. Thus, instead of being simply early evolutionary
experiments, some Cambrian benthic metazoans with seem-
ingly unusual morphologies were actually just well-adapted
for survival on non-actualistic microbial-mat-bound soft
substrates typical of the Proterozoic.
A COMPILATION OF CHITON FOSSIL SPE-
CIES
EERNISSE, DOUGLAS J., Dept. of Biological Science,
California State Univ., Fulleiton, CA 92834 (e-mail:
deernisse@fullerton.edu)
A preliminary compilation of nominal fossil chiton (Mol-
lusca: Polyplacophora) species was assembled in 1989, and
this database was simultaneously implemented in custom
HyperCard stacks for Macintosh computers as a part of a still
unreleased Chiton Stacks software package. Ongoing efforts
to bring this database up to date for publication have so far
emphasized a corresponding compilation for worldwide
Recent species. Still, the parallel fossil compilations have
revealed some interesting patterns that enhance understand-
ing the history and diversification patterns of this important
ancient molluscan lineage. The fossil parts of this software
feature the automated construction of maps depicting geo-
graphic and stratigraphic data for the 336 species recognized
as of 1989, along with the display of synonymy, type locality,
and various other data for these species. This presentation
amounts to a progress report for the status of ongoing
updates of these databases, as well as a review of plans for the
eventual WWW implementation of the living and fossil
chiton systematic and biogeographic presentations by spe-
cies.
WHAT IS THE RELATIONSHIP BETWEEN
DIVERSITY AND ABUNDANCE? EXAMPLES
FROM THE LOWER-MIDDLE ORDOVICIAN
BOUNDARY OF THE GREAT BASIN
FINNEGAN, SETH, and MARY L. DROSER, Dept. of
Earth Sciences, Univ. of California, Riverside, CA 92521
(e-mail: sfinn@citrus.ucr.edu)
The traditional focus of paleobiological and paleoecological
research has been on issues of diversity. The study of diversity
trends provides essential insights into patterns and processes
of ecological and evolutionary change. However, diversity is
only one aspect of ecological systems. An in-depth under-
standing of paleoecological change also requires data on
depositional environments, biogeography, and abundance.
Diversity and abundance may be decoupled at a variety of
temporal, taxonomic, and geographic scales. Low-diversity,
high abundance taxa are well-documented in both the
Modern and the fossil record as colonizers of disturbed
environments, and underline the importance of considering
abundance and diversity separately. Analyses of abundance
data may lead to recognition of patterns of ecosystem
transformation not apparent from taxonomic diversity data
2001 CALPALEO ABSTRACTS
3
alone. As the previous example illustrates, this may be
particularly true during so-called "critical intervals."
One such interval is the Lower-Middle Ordovician
boundary. A growing body of evidence suggests that the
sweeping evolutionary and ecological changes of the Or-
dovician radiations are disproportionately concentrated
around this interval. Preliminary data from the boundary
interval of the Great Basin indicate that there is a significant
disconnect between diversity and abundance of brachio-
pods at this time. A dramatic increase in the abundance of
brachiopods is seen at the Lower-Middle Ordovician
boundary in a variety of environments. This increase in
abundance significantly precedes the Middle Ordovician
diversification of brachiopods, and represents an important
step towards the establishment of the ecosystem types that
characterize much of the subsequent Paleozoic. There is
also evidence, though controversial, of a converse pattern
of decoupled diversity and abundance among trilobites.
While they undergo a major radiation at the base of the
Middle Ordovician, the abundance of trilobite material
declines significantly in studied sections. More study is
needed to confirm the geographic and temporal extent of
this trend.
EARLY TRIASSIC PROLIFERATION OF
MICROGASTROPODS: AN UNUSUAL GLO-
BAL PHENOMENON
FRAISER, MARGARET L., RICHARD J. TWITCHETT,
and DAVID J. BOTTJER, Dept. of Earth Sciences,
Univ. of Southern California, Los Angeles, CA 90089-
0740 (e-mail: fraiser@usc.edu)
Estimated at nearly 5-10 million years long, the Early
Triassic (Scythian) represents the biotic recovery interval
following the most devastating biotic crisis in the history of
life, the end-Permian mass extinction. This biotic recovery
interval is the longest following any mass extinction and was
a period of low-diversity, simply structured communities.
Early Triassic invertebrate marine faunas have been charac-
terized as morphologically simple, opportunistic,
unspecialized, and cosmopolitan. Previously, many primarily
qualitative studies have indicated that Lower Triassic strata
are typically dominated by only a few species of bivalves and
tiny snails. In particular, Lower Triassic shallow-water car-
bonates composed nearly entirely of microgastropods are a
prominent component of Tethyan strata. This research is the
first quantitative study to disclose how truly unique
microgastropod-bearing rocks are to the Early Triassic. Field
work in the western U.S.A., Japan and Europe has revealed
that microgastropods are commonly the primary rock-
forming allochems in tropical paleolatitude Lower Triassic
outcrops. Similarly, analysis of the literature reveals refer-
ences to Lower Triassic carbonates "rich in microgastropods"
or containing "abundant small snails" from every ocean and
for every stage  of the Early Triassic.  The rarity of
microgastropod-bearing limestones in pre-extinction Per-
mian strata and Middle Triassic strata demonstrates that the
global occurrence of microgastropod-dominated carbonates
in the Early Triassic is indeed an unusual phenomenon. One
possible explanation for this phenomenon is that
microgastropods behaved as "biotic recovery opportunists"
during the Early Triassic and thrived in high-stress, low
resource shallow-water carbonate environments during the
aftermath of the end-Permian mass extinction. The dwarfed
size of Early Triassic gastropods could largely be due to the
effects of environmental stress such as decreased primary
productivity during the Early Triassic.
THE BEGINNING OF MESOZOIC BIVALVE
REEFS: EARLY JURASSIC "ZITHIOITS" FA-
CIES BIOHERMS
ERASER, NICOLE M., and DAVID J. BOTTJER, Dept.
of Earth Sciences, Univ. of Southern California, Los
Angeles, CA 90089-0740 (e-mail: nmfraser@usc.edu)
Prior to the Cretaceous reef-building rudists, the Early
Jurassic is notable for bioherms constructed by a unique
group of large aberrant bivalves that collectively form the
"Lithiotis" facies: Lithiotis, GerveUeioperna-, Lithiopema,
Cochlearites and Mytilopema. These bivalves dominated
nearshore tropical ecosystems of the Early Jurassic
(Pliensbachian) and abruptly went extinct at the end of the
Early Jurassic (Toarcian). The dearth of reefs constructed by
colonial organisms and the preponderance of filter-feeding
bivalves in nearshore tropical environments is a common
feature of later Mesozoic environments, beginning in the
Early Jurassic and culminating in the large Late Cretaceous
rudist reefs.
"Lithiotis" facies bioherms in Oregon, California, Italy,
and Morocco have been used in this study. Line-intercept
transects, bulk sample collection and species identification
have been completed for each site. Original aragonite was
preserved in some Italian specimens; 5lsO, 813C and Mg/
Ca analyses are currently being performed on these speci-
mens to quantitatively assess paleoenvironments. While
most of the " Lithiotis" bioherms in Oregon and California
are relatively low-diversity with minor constituents of
nereinid gastropods and red algae, the Moroccan and some
Italian sites exhibit higher diversity with corals, sponges and
brachiopods.
The increased presence of bivalve-constructed reefs in
the Early Jurassic could have resulted from increased nutri-
ent delivery to the shelves. The consequent increased rates
of bioerosion and algal growth allowed filter-feeding
bivalves to outcompete stenohaline groups such as
sderactinians. An alternate hypothesis for the occurrence of
bivalve constructed bioherms is that these organisms are
adapted to euryhaline environments. While this explanation
may be appropriate for the Oregon and some of the Italian
sites, it is inadequate to explain the occurrence of "¦Lithiotis"
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PALEOBIOS, VOL. 21, SUPPLEMENT TO NUMBER 1, 2001
facies bivalves with stenohaline organisms such as corals
and sponges in Morocco and other Italian sites.
A DIAGENETIC TRIGGER OF EXCEP-
TIONAL PRESERVATION IN THE
WHEELER SHALE (MIDDLE CAMBRIAN,
UTAH)
GAINES, ROBERT R., MARY L. DROSER, and MAR-
TIN J. KENNEDY, Dept. of Earth Sciences, Univ. of
California, Riverside, CA 92521 (e-mail: rgaines
@citrus.ucr.edu)
Two types of exceptional preservation occur in the Wheeler
Shale: common soft-bodied preservation and an Elrathia
trilobite concentration-lagerstatte. Both types of preserva-
tion share a common early taphonomic pathway. 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-x\ch
beds are generally confined to mutually exclusive biofacies.
While both biofacies are characterized by medium to thickly
laminated (1-8 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 carbon-
ate-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, excep-
tional 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, form-
ing trilobite "nodules." Non-pyritic burrows are slightly
more common in this biofacies and penetrate to a maxi-
mum depth of 1.2 cm. We infer that the soft-bodied
biofacies accumulated under anoxic conditions in the ab-
sence 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 pro-
moted more rapid decomposition of labile tissues and
facilitated colonization by a benthic fauna.
A REEVALUATION OF THE SNAKE DAM
EGGSHELL: PHYLOGENETIC AND TEMPO-
RAL IMPLICATIONS
GRELLET-TINNER, GERALD, Dept. of Vertebrate Pa-
leontology, Natural History Museum of Los Angeles
County, Los Angeles CA 90007; Dept. of Earth Sci-
ences, Univ. of Southern California, Los Angeles CA
90089-0740 (e-mail: greUet@usc.edu)
In 1971, M. Woodburne discovered an avian eggshell
fragment at the Snake Dam locality, South Australia. The
specimen now catalogued as UCR 17877 (Univ. of Califor-
nia at Riverside), rested on claystones of the Miocene
Etadunna Formation. UCR 17877 exhibits a deeply sculpted
surficial ornamentation, and its thickness averages 4 mm.
Because of this unusual thickness and of the lack of associated
skeletal material the identity of UCR 17877 has remained
controversial. The remarkable thickness led previous paleon-
tologists to estimate the weight of the whole egg at 14 kg,
close to that of the extinct Malagasy Aepyornis maximus.
However A. maximus is not known in Australia. The rarity
of UCR 17877 morphological attributes and the lack of
associated embryonic material led Williams and Rich to
assign this specimen to Dromomis, a giant Australian extinct
flightless bird. If corroborated this discovery would predate
by 8 MY the first known occurrence of Dromomis in the
fossil record.
Previous studies have demonstrated the phylogenetic
potential of eggs and eggshell characters. In this research, I
reinvestigate the phylogenetic placement of UCR 17877 by
describing its morphology and performing a cladistic analy-
sis of several avian taxa including Genyornis (a Plio-Pleis-
tocene dromornithid), six paleognaths (extant and extinct),
and Anseri-Galliformes. Results show that Genyornis and
UCR 17877 are united by two synapomorphies, thus sup-
porting the inclusion of UCR 17877 within
Dromornithidae, a group closer in this analysis to
Anseriformes than to any other neognaths. Furthermore,
they confirm the recent phylogeny of Murray and Megirian
based on cranial morphology suggesting that
Dromornithidae are excluded from Paleognathae and be-
long to Anseriformes. Regression equations between egg-
shell thickness and body mass of female neognaths advocate
for Dromomis as parent of UCR 17877. The presence of
Dromomis in the Australian Lower Miocene is now there-
fore strongly supported.
MARINE PALEOECOLOGICAL CHANGES
ACROSS THE TRIASSIC-JURASSIC EXTINC-
TION BOUNDARY, NEW YORK CANYON,
WEST-CENTRAL NEVADA
HANK3NS, KARINA G., and DAVID J. BOTTJER, Dept.
of Earth Sciences, Univ. of Southern California, Los
Angeles CA 90089-0740 (e-mail: hankins@usc.edu)
The mass extinction in the marine realm at the end of the
Triassic is considered one of the five biggest extinction events
of the Phanerozoic, but it is not well studied due to a lack of
good sections spanning the boundary. Even less is known
about the dynamics of the recovery interval that followed.
2001CALPALEO ABSTRACTS
5
One of trie most complete and fossiliferous marine sequences
of Triassic-Jurassic strata is located at New York Canyon in
the Gabbs Valley Range of west-central Nevada, which
houses the proposed global stratotype section for this
boundary. This area has been the focus of extensive biostrati-
graphic studies and facies change analyses (Taylor et al.,
1983; Hallam and Wignall, 2000), and the paleoecology of
Upper Triassic strata has been assessed by Laws (1982).
However, the ecological changes that took place across the
boundary in this area have not received detailed analyses.
This study represents a first attempt at analyzing the
nature of paleoecological changes across the boundary and
into the recovery interval in the New York Canyon area,
with changes in paleocommunity composition and struc-
ture as the primary focus. Preliminary observations of the
Lower Jurassic Sunrise Formation reveal that a low-diver-
sity epifauna of relatively small bivalves and gastropods
exists in the shallower-water facies, while brachiopods and
ammonites dominate the more offshore facies. Intervals of
intense bioturbation occur within Lower Jurassic strata and
large, resistant, primarily horizontal burrows appear in the
Sinemurian New York Canyon Member. However, the
diversity of trace fossils throughout these beds remains low.
These observations indicate that facies changes play an
important role in the record of the recovery from the end-
Triassic extinction at New York Canyon, and are consistent
with a prolonged recovery from this crisis as described in
Hallam (1996). Further investigation may shed light on the
possible causes of the extinction itself, and the reasons for a
slow recovery.
SAUKTID-DIKELOCEPHALID TRILOBITES
AND THEIR IMPLICATIONS FOR LATE
CAMBRIAN PALEOGEOGRAPHIC AND
PALEOENVIRONMENTAL RECONSTRUC-
TIONS
HENDERSON, WAYNE G., and NIGEL C. HUGHES,
Dept. of Earth Sciences, Univ. of California, Riverside,
Riverside, CA 92521 (e-mail: waynehdn@citrus.ucr.edu)
Genera assigned to the Saukiidae and the Dikelocephalidae
have long been considered closely related. Among the
Dikelocephalidae, a markedly expanded cephalic doublure is
synapomorphic for dikelocephalids, and Saukiidae, as cur-
rently defined, is likely paraphyletic. Nevertheless, the saukiid
cranidium has a distinct morphology and, while the
Dikelocephalidae are exclusively Laurentian, txilobites with
the saukiid glabellar morphotype occur globally in equatorial
regions. This distribution is particularly surprising as Cam-
brian polymerid trilobites are generally considered to show
high degrees of continental endemism, and saukiids are
particularly known for their preference for near shore habi-
tats.
Ulrich and Resser (1933) first described the Saukiidae in
detail, erecting 104 species in five genera from the Upper
Mississippi Valley. An additional 25 genera and 200 species
of saukiids have since been described, occurring across
equatorial core and outboard Gondwana, Laurentia, Sibe-
ria, and Kazakhstan, and they have been extensively used
for biostratigraphic zonation. Saukiid species and genera
have frequently been described as endemic to these regions
even though there are few, if any, morphological features to
distinguish them from species found on other
paleocontinents.
Accordingly, there is critical need to refine species con-
cepts. We are (1) evaluating character variation within large
collections from single bedding planes to establish the
bounds of intrapopulation variation, and (2) constructing a
character matrix for phylogenetic analysis of all well-pre-
served saukiids based strictly on morphological criteria.
Such analysis will point to the resolution of taxonomic
relationships within these groups and provide the basis for
evaluating Late Cambrian endemism and biogeographic
links.
THE PROBLEMS AND PLEASURES OF
SCLERITOMES-THE ENIGMATIC
MACHAERIDIA
HOGSTROM, ANETTE E.S., Dept. of Earth Sciences,
Univ. of California, Riverside, CA 92521 (e-mail:
anette@ucracl .ucr.edu)
The scleritome-bearing metazoan Machaeridia has an exten-
sive stratigraphic record (Lower Ordovician-Middle Per-
mian) and occurs globally as part of many marine faunas.
Machaeridian scleritomes suffer from the same preservational
problems as most multi-element skeletons and very easily fall
apart when the animal dies making isolated sderites and
sclerite fragments the most common form of preservation.
Today machaeridian remains are being reported from several
parts of the world and may even constitute a dominant
element in some faunas.
There is an obvious limitation in reconstructions based
on isolated sclerites and rare articulated specimens have
played a crucial role in understanding the machaeridian
scleritome. All scleritomes have two to four longitudinal
series of calcific sclerites and range from quite straightfor-
ward types with the sclerites forming a dorsal cover to more
complex ones essentially enveloping the entire animal.
The complex scleritome of lepidocoleid machaeridians
has a high preservation potential and articulated specimens
are commonly lepidocoleids. The flexible scleritome of
lepidocoleid machaeridians opens and closes along the ven-
tral side, the animal is also able to enrol spirally in a manner
similar to a millipede, all suggesting a segmented bodyplan.
Epimorphic development of the scleritome, with all sclerite
segments present initially, is supported by the uniform
appearance of ornamentation and growth lines, and the
presence of occasional growth increments traceable be-
tween sclerites in articulated specimens.
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PALEOBIOS, VOL. 21, SUPPLEMENT TO NUMBER 1, 2001
The bodyplan of machaeridians indicates that the most
likely affinities of the group do not lie with the arthropods
and other moulting animals within the Ecdysozoa, but
rather as a stem group to molluscs or annelids within the
Lophotrochozoa clade.
EVENT BED DEPOSITION IN THE
CINCINNATIAN SERIES: IMPLICATIONS
FOR TAPHONOMIC PROCESSES AND AS-
SESSING MICROEVOLUTTONARY
CHANGES WITHIN FLEXICALYMENE
HUNDA, BRENDA R., and NIGEL C. HUGHES, Dept.
of Earth Sciences, Univ. of California, Riverside, CA
92521 (e-mail: brendahu@citrus.ucr.edu)
Despite intense scientific interest there is currendy little high
resolution data available to understand how organisms
respond to multiple episodes of environmental change at
time-scales ranging from 1,000 to 1,000,000 years. The
prerequisites for such a study include exceptional preserva-
tion of multiple fossiliferous horizons and a high-resolution
stratigraphic framework. Recent stratigraphic analyses of the
Cincinnatian Series now provide an exceptionally precise
spatial and temporal framework for assessing microevolu-
tionary changes within individual species and species lin-
eages.
Initial studies in the area have shown that storm-related
episodes of rapid mud deposition smothered populations of
live Flexicalymene, preserving unique and substantial samples
of contemporary individuals alive some 450 million years
ago. Thin section analysis has revealed a similar depositional
regime at Mt. Orab, within the Arnheim Formation, with
at least seven gradational beds within a 0.46m mudstone
unit. Differences in size distribution, density, and attitude
of the trilobites suggests that Mt. Orab beds differ from the
specific behavioral aggregations seen within the "granu-
losa" bed of the Kope Formation, although both are
thought to represent contemporaneous populations. Simi-
lar "event bed" preservation occurs throughout the
Cincinnatian Series, offering the possibility of repeated
sampling of contemporary populations sequentially
throughout the Series. Morphometric analysis of these
contemporary populations of Flexicalymene will constrain
patterns of morphological variability at the population level,
providing a firm basis for understanding the morphological
variation evident within Cincinnatian Flexicalymene, and its
relationship to multiple episodes of environmental change
within a sequence stratigraphic framework.
COMPARATIVE PALEOBIOLOGY OF TWO
DIFFERENT MIDDLE TRIASSIC MARINE
ENVIRONMENTS FROM WESTERN PANGEA
(U.S.A.)
HUYNH, TRAN T., and DAVID J. BOTTJER, Dept. of
Earth Sciences, Univ. of Southern California, Los Ange-
les CA 90089-0740 (e-mail: huynht@usc.edu)
Following the end-Permian mass extinction, it wasn't until
Middle Triassic times that normal benthic conditions re-
turned and various groups were reestablished worldwide.
This period marks the initiation of the Mesozoic marine
radiation, as measured by global diversity trends. Recent
work on the Early Triassic recovery interval has allowed for
better assessment of the paleobiologies changes that oc-
curred in the bentfiic realm at the transition from the Early
to Middle Triassic.
Preliminary examination of different paleoenvironments
represented by Middle Triassic Star Peak Group strata
(western U.S.A.) suggests that the ecological and evolu-
tionary character of the initial Mesozoic marine radiation
varied between depositional settings. Compared to Early
Triassic assemblages of nearshore environments, less cos-
mopolitan members and increased levels of tiering com-
plexity characterize the Middle Triassic fauna. Lazarus taxa
continued to return to level-bottom nearshore settings at
this time, filling in more Bambachian megaguilds. In con-
trast, deep water assemblages of the Middle Triassic are
significantly different from those found in the Early Triassic
from similar depositional settings. The fossil associations of
deeper-water environments are comprised of cephalopod
and bivalve taxa that are more typical of later Mesozoic
assemblages. Thus, while nearshore environments exhibited
community-level patterns of reassembly by Lazarus taxa,
evolutionarily distinct offshore assemblages emerged at the
initiation of the Mesozoic radiation in the western U.S.
LATE OLIGOCENE TO EARLY OR MIDDLE
MIOCENE CONTINENTAL VERTEBRATE,
MARINE INVERTEBRATE, AND LAND
PLANT BIOSTRATIGRAPHY OF THE SESPE,
VAQUEROS, AND TOPANGA CANYON FOR-
MATIONS, CENTRAL SANTA MONICA, LOS
ANGELES COUNTY, CALIFORNIA
LANDER, E. BRUCE, Paleo Environmental Associates,
Inc., 2248 Winrock Avenue, Altadena, CA 91001-3205;
DAVID P. WHISTLER, Vertebrate Paleontology Dept.,
Natural History Museum of Los Angeles County, 900
Exposition Boulevard, Los Angeles, CA 90007; JOHN
M. ALDERSON, 10628 Rountree Road, Los Angeles,
CA 90064; LANNY H. FISK, F & F GeoResource
Associates, Inc., 564 La Sierra Drive #203, Sacramento,
CA 95864; STANLEY I. WALKER, 29013 Lillyglen
Drive, Canyon Country, CA 91341; and ERIK S. and
CRYSTAL B. ANDERSON, 190 Sequoia Avenue,
Ventura, CA 93603
Extinct continental vertebrate, marine invertebrate, and land
plant taxa constitute a number of stratigraphically super-
posed fossil faunal and flora assemblages in the Piuma
2001 CALPALEO ABSTRACTS                                                                   7
(Upper) Member (PM) of the continental Sespe Formation
(SF), the marine Vaqueros Formation (VF), and the marine
Saddle Peak (lower) Member (SPM), continental Fernwood
(middle) Member (FM), and the marine Cold Creek (upper)
Member (CCM) of the Topanga Canyon Formation in the
central Santa Monica Mountains. The late Oligocene Lower
Piuma Road (PR) Local Fauna (LF), near the base of the
lower PM, includes the late early to latest Arikareean cricetid
Leidymys nematodon. The Carbon Canyon Tongue of the VF
separates the lower and upper PM and contains the lower
Vaquerosian gastropod Turritella inezana bicurina. The
Lower PRFlorule, near the base of the upper PM, contains
the sabal palm, Sabalites miocenica. The upper PRLF, near
the top of the upper PM, includes the early Hemingfordian
cricetid Tatkolamys. The SPM contains the upper Vaquerosian
bivalve Vertipecten bowersi. The Stunt Road LF, which
includes the late Hemingfordian equid Parapliohippus
carrizoensis, and the Calabasas Peak Motorway Florule,
which includes the sycamore-like form genus Platanoxylon,
occur in the FM. An unnamed marine tongue in the FM
contains the Temblorian gastropod Turritella tembbrensis.
The overlying Conejo Volcanics are as old as 16.0 ± 0.6 Ma
(late early [?] to early middle Miocene). The stratigraphic
alternation of these continental vertebrate/land plant and
marine invertebrate assemblages reflects three transgressive-
regressive cycles and a subsequent transgression that fol-
lowed the collision of the East Pacific Rise and the Pacific
margin of the North American Plate during or immediately
after the unnamed post-Refiigian, pre-Vaquerosian marine
molluscan stage and the regional biochron of the earliest
Arikareean oreodontid Sespia, but preceded clockwise rota-
tion of the Western Transverse Ranges province.
EARLY TRIASSIC GASTROPODS IN THEO-
RETICAL MORPHOSPACE
MARENCO, PEDRO J., and DAVID J. BOTTJER, Dept.
of Earth Sciences, Univ. of Southern California, Los
Angeles CA 90089-0740 (e-mail: marenco@usc.edu)
Theoretical morphology offers a unique approach to study-
ing the effects of mass extinction on morphological distribu-
tions. Changes in theoretical morphospace occupancy can
provide insights into broad scale evolutionary patterns.
Previous work on the effects of mass extinctions on the
theoretical morphospace distribution of the biconvex
Brachiopoda as well as ammonites and nautiloids have served
to further the understanding of the evolutionary effects of
mass extinction on those groups. A theoretical morphospace
analysis of gastropods through the survival and recovery
intervals of the Permian-Triassic mass extinction may eluci-
date morphological responses to environmental conditions
following the mass extinction event as well as provide
insights into the Lazarus phenomenon.
A PHYLOGENETIC STUDY OF
HADROSAURIAN DINOSAUR SKIN
NEGRO, GIULIANA, Dept. of Vertebrate Paleontology,
Natural History Museum of Los Angeles County, Los
Angeles, CA 90007; Facolta' di Scienze Matematiche,
Fisiche e Naturali, Universita' Degli Studi di Torino,
Italy
Our knowledge of the external appearance of dinosaurs is
exclusively based on the rare occurrence of fossilized skin,
which occurs both as impressions left on sediment and as
mineralization of three-dimensional integument. Several
examples of fossilized integument are known for sauropods
and theropods, as well as ceratopsian and hadrosaurian
ornithischians. Unlike the skin of most modern reptiles,
dinosaurian skin is not squamate or imbricated, but it
typically consists of non-overlapping tubercles that resemble
those of Helodermatidae, the Gila Monster and its relatives.
Most occurrences of dinosaur fossilized skin are associated
with hadrosaurian remains. The abundance of hadrosaurian
integument provides the basis for investigating the potential
of skin characters for phylogenetic inference. Hadrosaurian
skin is characterized by tubercles with a size and form that
although they can vary in different parts of the body, they do
form distinctive patterns. Comparisons between individuals
of the same species reveal that these distinctive skin patterns
constitute diagnostic characters. In addition, some charac-
ters can be found in the same body regions of different
species, thus documenting the hierarchical arrangement of
characters necessary for phylogenetic analysis. Undoubtedly,
the rare preservation of dinosaur integument constrains
possibilities for conducting wide-ranging phylogenetic analy-
ses using skin characters. Nonetheless, this study shows that
skin characters carry phylogenetic signal. Species and
supraspecific dinosaurian taxa (e.g., Hadrosauridae) can be
diagnosed on the basis of skin characters and therefore those
characters should be incorporated into cladistic analyses of
dinosaurian relationships.
DECOUPLING OF THE TAXONOMIC AND
ECOLOGICAL SIGNIFICANCE OF THE
LATE DEVONIAN MASS EXTINCTION: EVI-
DENCE FROM FOSSIL CONCENTRATIONS
PHELPS, WILLIAM T., and MARY L. DROSER, Dept.
of Earth Sciences, Univ. of California, Riverside, River-
side, CA 92B21 (e-mail: phelps@citrus.ucr.edu)
Fossil concentrations provide a proxy for faunal abundance
and community dominants when depositional and
taphonomic processes are accounted for. Examination of
large-scale shifts in faunal abundance and community domi-
nants is key to evaluating the extent of ecological change
within an ecosystem.
To assess the ecological changes associated with the Late
Devonian mass extinction, Late Devonian and Early Missis-
8
PALEOBIOS, VOL. 21, SUPPLEMENT TO NUMBER 1, 2001
sippian fossil concentrations from limestones of the western
U.S.A. were examined. These limestones formed in a shal-
low water, soft-substrate environment within a single depo-
sitional basin under broadly similar environmental
conditions.
Large-scale taxonomic changes in shallow marine fauna
across the extinction are well documented. However, no
Bambachian Megaguilds were vacated, and most groups
recover in the Mississippian to near pre-extinction diversity
levels. This suggests that pre- and post-extinction commu-
nities may have remained broadly similar. However, fossil
concentration analyses show a much different pattern. De-
vonian fossil concentrations are generally polytaxic but
dominated by brachiopods, while Mississippian fossil con-
centrations are typically monotaxic (i.e., separate crinoidal,
gastropod, and rugose coral dominated fossil concentra-
tions) and dominated by crinoidal fossil concentrations; the
number of brachiopod concentrations decreases consider-
ably. This shift from brachiopod dominated polytaxic com-
munities to crinoid dominated monotaxic communities
suggests there were large-scale shifts in ecological structure
within this shallow marine community, which are not pre-
dicted by the taxonomic data.
In contrast, the Late Ordovician extinction had a taxo-
nomic loss similar to the Late Devonian extinction but
Silurian communities retained the fundamental structure
seen in the Ordovician. These results, coupled with the loss
of large-scale reefs at the Devonian extinction, thought to
be largely a result of the loss of stromatoporoids (Scrutton,
1988), point to the importance of retaining keystone and
dominant taxa in maintaining ecosystem integrity.
DEVELOPMENT OF MICROBIAL FABRICS
IN EARLY TRIASSIC OCEANS
PRUSS, SARA B., and DAVID J. BOTTJER, Dept. of
Earth Sciences, Univ. of Southern California, Los Ange-
les, CA 90089-0740 (e-mail: spruss@usc.edu)
The Early Triassic represents a period of recovery from the
largest extinction in the history of life, the end-Permian mass
extinction. During this time, marine microbial fabric devel-
opment has been documented globally. Research by Kershaw
et al. (1999) shows the occurrence of what may be a
microbialite crust at the Permian-Triassic boundary in South
China. This crust is suggested to have been formed by a
disaster biota that thrived in the presence of unusual oceanic
conditions occurring at the P-T boundary. The absence of
grazers has also been cited as increasing the potential for such
microbial development. Recent work by Lehrmann (1999)
shows the presence of biostromes and microbial mounds
from the Lower Triassic Nanpanjiang Basin in South China.
These biostromes and mounds occur in two horizons: one in
Griesbachian strata and one in Smithian-Spathian strata. In
some places, these beds attain thicknesses of 15 meters
suggesting that these microbial features occurred as reefs.
Stromatolites and thrombolites have also been reported
as mass extinction disaster forms from late Early-Triassic-
age strata in the Western United States (Schubert and
Bottjer, 1992). These microbial structures from the Virgin
Limestone Member of the Moenkopi Formation have been
recently reinvestigated to determine if they represent true
reefs. In places microbial mounds occur as isolated patch
reefs, although elsewhere they coalesce to form tabular
biostromes. These mounds are an agglomeration of smaller
subunits that have wavy laminations and thrombolitic tex-
tures. Measurements on isolated mounds show that they
attained a relief of 1-2 meters above the seafloor. These
results, together with those from previous studies, demon-
strate that small reefs, although rare, can be found through-
out the early Triassic. These primarily microbial
constructions represent the earliest reef systems of the
Mesozoic.
PALEOECOLOGY OF MIDDLE ORDOVI-
CIAN SHELL CONCENTRATIONS OF THE
GREAT BASIN, WESTERN UNITED STATES
THIEL, DIANA L., and MARY L. DROSER, Dept. of
Earth Sciences, Univ. of California, Riverside, CA 92521
(e-mail: dianat@citrus.ucr.edu)
The Ordovician radiation was a time of dramatic taxonomic
and ecologic change for benthic marine faunas. Studies of
fossil concentrations through this interval reveal an increase
in physical dimensions and shifts in taxonomic composition.
However, the details of these changes have not been previ-
ously examined and potentially provide insight into commu-
nity dynamics. The Middle Ordovician Kanosh and Lehman
Formations (Ibex, Utah) are particularly rich in fossil con-
centrations. The Lehman Formation represents deposition
in a very shallow marine carbonate environment while the
Kanosh Formation represents deposition in a restricted basin
situated on a rimmed carbonate platform. Similar taxonomic
groups, namely orthid brachiopods, ostracods, echinoderms,
and uncommon molluscs and trilobites, are found through-
out both formations.
Although approximately 12% of the beds are truly
polytaxic, nearly 2/3 of the beds in both units are exclu-
sively brachiopod (>95% brachiopods) or brachiopod domi-
nated (>70% brachiopods). Those that are dominantly
brachiopod beds include only 2 or 3 faunal elements. Both
formations are characterized by brachiopod-ostracod shell
beds. While the species types vary between the units, fossil
concentrations have low brachiopod diversity within beds,
and typically contain only 1 species of brachiopod (others
may occur, but are rare) along with either palaeocopid or
leperditocopid ostracods. While gastropods occur rarely in
the brachiopod/ostracod beds, most commonly, gastro-
pods form their own monotaxic beds. Bivalves similarly
form monotaxic beds within the Lehman Formation. Com-
monly, within a shell bed, a single species exhibits a wide
2001CALPALEO ABSTRACTS
9
range of sizes. This along with the lack of abrasion and
other indicators of transport suggest that most of these
beds represent relatively little taphonomic modification of
original skeletonized assemblages. Thus, unlike Modern
and more recent counterparts, these shell beds are remark-
ably low in taxonomic diversity despite the dramatic in-
crease in overall marine diversity and the relatively high
formational diversity.
FLUCTUATIONS IN THE QUALITY OF THE
LATE PERMIAN TO EARLY JURASSIC FOS-
SIL RECORD: CAUSES AND CONSE-
QUENCES
TWITCHETT, RICHARD J., Department of Earth Sci-
ences, University of Southern California, Los Angeles,
CA 90089-0740 (e-mail: twitchet@usc.edu)
The diversity of fossil taxa fell sharply during the Permian-
Triassic and Triassic-Jurassic intervals, with a moderate
recovery in between. These periods of low diversity are
characterized by increasing numbers of Lazarus taxa, and
hence a decrease in the completeness of the fossil record. For
example, a mere 10% of sponge families known to have been
present in the Early Triassic are represented by actual fossils,
compared to 50-70% in the Late Permian. This pattern
applies to all benthic groups, and most pelagic groups, thus
far studied. These data suggest that our perception of the
magnitude of so-called extinction events may have been
clouded by the fluctuating quality of the fossil record.
There are several potential causes of the poor quality of
the P-Tr fossil record. Firstly, silicified assemblages, con-
taining a high diversity of taxa due to excellent preservation
and ease of recovery, have not been found in the Early
Triassic. In addition, those taxa that are actually recovered
are often poorly preserved. They are also much smaller than
their pre-crisis relatives (the Lilliput Effect), which is most
likely a response to primary productivity collapse. When
food supply is dramatically reduced, animal biomass must
also be reduced. This can be achieved by reducing popula-
tion size and/or reducing body size. Taxa that suffer a drop
in abundance become rarer, more prone to real extinction,
and will be less likely to enter the fossil record (apparent
extinction). Finally, sea level rise can also reduce apparent
diversity. During transgression, shallow marine strata, which
contain high benthic diversity, are deposited towards the
basin edge where they are more prone to erosion and loss
during subsequent sea level fall. All of these possibilities are
testable. The hypothesis that diversity decline has been
caused by apparent extinction, rather than real ("mass")
extinction, has yet to be rejected.