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Dinosaur stuff from Rocky Mountain and Cordilleran Joint Meeting

From: Ben Creisler

Here are the abstracts for the other dinosaur-related talks and
posters at the Rocky Mountain (66th Annual) and Cordilleran (110th
Annual) Joint Meeting (19–21 May 2014)




ANDUZA, Danny and FOWLER, Denver W., Department of Earth Sciences,
Montana State University, P.O. Box 173480, Bozeman, MT 59717-3480,
Since the 1983 discovery of the unusual dinosaur Baryonyx walkeri
(Theropoda: Spinosauridae) there has been great interest in the
feeding behavior of spinosaurids as the group exhibits various
physical traits suggestive of piscivory, such as elongate
crocodile-like jaws; retracted nares; weakly-serrated conical teeth;
large digit I manual unguals; and large, robust forelimbs. However,
despite a general consensus over spinosaurid piscivory, there have
been few detailed behavioral comparisons with similarly adapted extant
piscivorous tetrapods. An exception is the eponymous “heavy claw” of
Baryonyx, suggested to have been used in gaffing (hooking) fish out of
the water in behavior akin to that of grizzly bears. However, this
hypothesis is problematic as grizzlies do not gaff fish in this
manner. To better characterize spinosaurid piscivory, we reviewed
piscivorous adaptations and related behaviors in extant fish-eating
tetrapods. We then assessed which of these behaviors were possible in
spinosaurids based on their morphology. The antero-posterior head
darting strategy employed by herons (genus Ardea) was found to be
unlikely as spinosaurs lack a strong sigmoid neck curve and their
orbits are poorly positioned for binocular vision. Rather, as in the
Indian gharial (Gavialis gangeticus), the jaws may have instead been
used in swift lateral sweeps to seize fish. Like grizzly bears (Ursus
arctos) and fishing cats (Prionailurus viverrinus), spinosaurids may
have employed their powerful forelimbs to stamp down on large fish,
impaling them on the manual claws against the river or lake bottom,
from which the prey could be manipulated with the jaws. As spinosaur
teeth lack prominent serrations, they do not appear to be well-suited
for prey dismemberment; it is likely that most fish would have been
swallowed whole, as in the majority of longirostrine piscivores.
However, the use of the forelimbs in breaking up prey items cannot yet
be ruled out. These findings not only furnish insight into feeding
behavior in spinosaurs, contributing to our understanding of these
bizarre and highly specialized dinosaurs, but also provide a window
into the evolution of piscivory in tetrapods.




SCHIMELFENING, Adam G., Department of Earth Sciences, University of
South Dakota, Vermillion, SD 57069,
adam.schimelfening@coyotes.usd.edu, WOODRUFF, D. Cary, Museum of the
Rockies, Montana State University, Bozeman, MT 59717, and NORDEN,
Klara K., School of Earth Sciences, University of Bristol, Bristol,
BS8 1RJ, United Kingdom
While receiving less scientific attention than the more popularized
formations within the state, the Morrison Formation (latest Oxfordian
- early Tithonian) of Montana represents an overlooked Mesozoic
ecosystem. These Montanan localities largely appear to be equivalent
to the upper portion of the Salt Wash Member (Kimmerdgian), and the
vertebrate fauna resemble typical Morrison assemblages - at least
three sauropod species, one Stegosauria, and one allosauroid theropod.
However one unusual feature in marked contrast to typical Morrison
localities is the sheer abundance of immature sauropod material. One
site from south central Montana represents a bone bed of over fifteen
individual diplodocids (maximum femur length 120 cm). Another site,
designated the O’Haire quarries, represents five immature sauropods
belonging to the genera Diplodocus and Apatosaurus (the majority under
two-thirds adult body length), and one individual of the theropod
Allosaurus. The O’Haire locality exhibits a normal graded sequence
containing alternating well cemented mudstone and fine grained, well
cemented sandstone facies approximately 1-2 meters in thickness. The
presence of mud rip-up clasts, cross-bedding, and other sedimentary
structures within these facies are interpreted as representing a
migrating point bar within a north flowing meandering fluvial system.
Skeletal remains near the sediment interfaces exhibit abrasion and
rounded edges (consistent with Fiorillo’s abrasion Stage 1), along
with sub-horizontal orientation which are all taphonomically
consistent with channel-lag deposits. This interpreted depositional
history indicates that unlike more typical or famed Morrison
localities, such as Dinosaur National Monument or Cleveland-Lloyd
Dinosaur Quarry, the O’Haire quarries do not appear to represent mass
catastrophic death assemblages; and are therefore representative of a
more natural environmental depiction.



SCOTT, Evan E., Department of Earth, Environmental, and Planetary
Sciences, Case Western Reserve University, 10900 Euclid Avenue,
Cleveland, OH 44106, ees20@case.edu, RYAN, Michael J., Dept. of
Vertebrate Paleontology, Cleveland Museum of Natural History, 1 Wade
Oval Dr, University Circle, Cleveland, OH 44106, and EVANS, David C.,
Dept. of Natural History, Royal Ontario Museum, 100 Queen's Park,
Toronto, ON M5S 2C6, Canada
The Late Cretaceous Belly River Group of southern Alberta consists of
three formations; in ascending order, these are the Foremost, Oldman,
and Dinosaur Park formations. The lower Belly River Group (Foremost
and Oldman formations) is recognized in Montana as the Judith River
Formation. Historically, the lower Belly River Group has not enjoyed
the rich collecting history of the overlying Dinosaur Park Formation
due, in part, to the lack of broad regions of dissected badlands.
Since 2005, the Southern Alberta Dinosaur Project has worked to
describe the fauna of the lower Belly River Group in order to better
understand regional patterns of dinosaur diversity and evolution in
the Late Cretaceous.
We report here a preliminary description of the first Gryposaurus bone
bed ("Wendy's" Bone Bed; WBB) from the Oldman Formation, located on
the southern Pinhorn grazing reserve of south-eastern Alberta in the
Milk River valley. The monodominant bone bed is in a mudstone
lithosome which probably represents an overbank deposit. It preserves
disarticulated, and sometimes associated, elements from all parts of
the body, but includes a significant proportion of limb and pelvic
bones. A small amount of non-hadrosaurid material (<1%) is present.
Based on cranial material, the hadrosaur present is referable to
either Gryposaurus or a closely related Gryposaurus-like saurolophine.
Taphonomic indicators suggest a short pre-burial interval. The
preserved material is dominated by juvenile and subadult-sized
elements that range from less than one-third to approximately
two-thirds of published adult-sizes for gryposaurs.

Juvenile sociality has previously been suggested for a variety of
different dinosaurs, including ornithopod taxa. It has been proposed
that the combination of oviparity and small hatchling-size in some
dinosaur taxa would have required a significant time and energy
commitment on the part of adults for the rearing of hatchlings,
leaving juveniles to congregate together away from the nesting site.
Preliminary examination of the WBB material supports the suggestion of
juvenile sociality in Campanian hadrosaurs.



PEREZ, Magaly and ROGERS, Raymond R., Geology Department, Macalester
College, 1600 Grand Avenue, Saint Paul, MN 55105,
The Judith River Formation preserves numerous vertebrate microfossil
bonebeds that represent skeletal accumulation in both lacustrine and
fluvial depositional settings. Previous studies have suggested that
microvertebrate fossils preserved in fluvial facies were reworked from
preexisting concentrations in lacustrine facies. Testing this
hypothesis requires careful comparison of collections from both
channel-hosted and lake-hosted sites. Here we describe the taphonomic
characteristics of a large sample of vertebrate bioclasts (n=7655)
derived from two richly fossiliferous lacustrine bonebeds, focusing on
the comparison of surface-collected material and bulk-sampled material
sieved and picked down to 500 microns. Surface collections, which
represent over a decade of recovery effort by field crews, were
characterized with regard to taxonomy, size, shape, breakage, and
weathering. Fossil shape was classified as compact, platy, elongate,
and conical. Weathering and breakage patterns were scored using
existing schemes specifically designed for fossil assemblages. Maximum
dimensions of surface collected fossils were measured with digital
calipers. The taphonomy of sieved samples was characterized in similar
fashion, although the size of bioclasts in this extremely fine-grained
fraction was documented using an image analysis system coupled with a
stereomicroscope. With regard to taxonomic representation, the surface
and sieve assemblages are quite distinct, with surface assemblages
dominated by dinosaur, fish (mostly ganoid scales and skull
fragments), and turtle and sieved samples dominated by fish (mostly
teleost vertebrae and scales). Shape characteristics are somewhat more
comparable between site types, but still distinct, with surface
assemblages dominated by platy elements and sieved samples dominated
by compact elements. Elongate and conical elements are relatively rare
in both collection types. Surface collected samples range in size from
2.1 – 82.9 mm, averaging 12.3 mm long axis. In contrast, sieved
samples range in size from 0.4 – 15.7 mm, averaging 1.7 mm long axis.
Distinctions between collections highlight the potential biases in
microvertebrate collections, and provide a means of assessing the
quality of faunal reconstructions derived from similar localities.




TEMPLEMAN, Tara, Honors College, University of New Mexico, MSC 06
3890, Student Health Building, 1 University of New Mexico,
Albuquerque, NM 87131, ttemp@unm.edu, VARRICCHIO, David J., Department
of Earth Sciences, Montana State University, Bozeman, MT 59717, and
MOORE, Jason R., Honors College, University of New Mexico,
Albuquerque, NM 87131
Egg Mountain is a late Campanian (~75 Ma) fossil-bearing locality from
the Two Medicine Formation of Montana. It is known for its abundant,
and in some cases exceptionally well preserved dinosaur nests and
mammal remains. These vertebrate remains are preserved in a sequence
of blue-grey, strongly carbonate cemented mudstones. The origin of
these mudstones has been debated: original interpretations suggested
they were lacustrine in nature, but more recent data support a
sub-aerial origin, with potential diagenetic overprinting
Using a combination of sedimentological, petrographic and isotopic
analyses we have better constrained the nature of a 2m stratigraphic
section of the upper Egg Mountain carbonates. The section shows a
sequence of alternating mudstone horizons differentiated primarily by
their degree of carbonate cementation. The stable isotope geochemistry
of carbonates from terrestrial settings is controlled by a number of
factors, including climate, biotic effects, and source water
chemistry, that interact in complex manners. These primary geochemical
signals can also be diagenetically modified post-burial. Carbon and
oxygen isotope ratios were measured from samples from each horizon
using a carbonate mass spectrometer. The average δ18O for the Egg
Mountain carbonates is -14.85, with a range from -14.26 to -16.17,
with the observed uniform, negative values suggesting likely
diagenesis from meteoric water. Carbon isotopic ratios are, however,
less susceptible to alteration through such diagenesis, so may
preserve a primary environmental signal. Average δ13C for the samples
is -7.91, with a range from -6.34 to -8.61. These values are markedly
more negative than those usually associated with lacustrine systems
from environments similar to the Two Medicine, but similar to those
found in soil carbonates deposited in arid environments. In
combination with the lack of sedimentological and petrographic
indicators of lacustrine deposition, we interpret the Egg Mountain
carbonates as primary pedogenic, but overprinted by diagenesis after
burial. This interpretation of the depositional environment of Egg
Mountain necessitates the reinterpretation of the palaeoecological
information preserved in its diverse fossil assemblage to reflect a
subaerial genesis.




FAULKNER, Benjamin, Geology Department, Macalester College, 1600 Grand
Avenue, Saint Paul, MN 55105, bfaulkne@macalester.edu, BRINKMAN, D.B.,
Royal Tyrrell Museum of Paleontology, Drumheller, AB T0J0Y0, and
ROGERS, Raymond R., Geology Department, Macalester College, 1600 Grand
Avenue, Saint Paul, MN 55105
The Campanian Judith River Formation of north-central Montana
preserves a multitude of vertebrate microfossil bonebeds that yield
abundant turtle fossils, but to date relatively little has been
published in relation to the formation’s turtle assemblage. Here we
report new data from the type area that reveal key aspects of the
Judith River turtle record. Turtle carapace fragments represent a
sizeable and highly recognizable fraction of the bioclasts recovered
from vertebrate microfossil bonebeds in the formation. To date we have
documented 1576 carapace fragments from surface collected samples of
21 microfossil bonebed sites (each site preserves at least 10
specimens), 1346 of which are identifiable based on diagnostic shell
morphology. With regard to representation in the identifiable sample,
trionychids are most common (n=923, 68.57%), followed by baenids
(n=258, 19.17%), Basilemys (n=122, 9.06%), and chelydrids (n=43,
3.19%). Though multiple genera of trionychids and baends are likely
represented, further classification was inhibited due to the
fragmentary nature of the sample and the paucity of associated
diagnostic skeletal material (e.g., skulls, vertebrae, claws) for
Focusing on the four largest collections (n>100 identifiable
specimens), the relative abundance pattern documented for the unit as
a whole holds, with trionychids comprising 52%-82% of site-specific
collections. This turtle sample is comparable in the abundance of
trionychids and baenids and the rarity of Adocus to a similarly sized
collection (1804 fragments) from the Dinosaur Park Formation in
Dinosaur Provincial Park. In assemblages from geographically closer
regions, the Manyberries/Onefour area in Alberta and the Kennedy
Coulee area in Montana, Adocus is more abundant. The rarity of Adocus
in the Judith River Formation type area is unexpected because this
taxon is fairly abundant in other localities to the south of Dinosaur
Provincical Park.




STROSNIDER, Darrin R.1, SCANNELLA, John B.2, HORNER, John R.2, and
VARRICCHIO, David J.1, (1) Department of Earth Sciences, Montana State
University, Bozeman, MT 59717, darrin.strosnider@msu.montana.edu, (2)
Museum of the Rockies and Department of Earth Sciences, Montana State
University, Bozeman, MT 59717
The Two Medicine Formation of northwestern Montana represents an
extensive record of the evolution of terrestrial ecosystems in the
Late Cretaceous of Laramidia. Whereas numerous non-avian dinosaur taxa
have been reported in the upper half of the formation, the faunal
composition of the lower half of the Two Medicine is more enigmatic.
Radiometric studies suggest that the lower portion of the Two Medicine
precedes the fossiliferous Dinosaur Park and Kaiparowits Formations
and is coeval with the Foremost Formation of Alberta as well as the
Wahweap Formation of southern Laramidia. The Wahweap has recently
produced the basal tyrannosaurid Lythronax and the basal ceratopsid
Diabloceratops. The brachylophosaurine Acristavus is present in both
the Wahweap and the lower half of the Two Medicine, suggesting that
there may be further overlap in the faunal composition of these units.
As such, the lower Two Medicine represents a critical window into the
evolution and biogeography of Cretaceous dinosaurs. Here we present a
survey of the fauna of the lower half of the Two Medicine Formation as
represented by material curated at the Museum of the Rockies. Dinosaur
taxa present include the hadrosaurids Acristavus and Gryposaurus as
well as the leptoceratopsid Cerasinops. Fragmentary material
indicating the presence of tyrannosauridae, hadrosauridae, and
ceratopsidae is also present. At least two morphotypes of small
theropod teeth referable to Paronychodon and Saurornitholestes are
recorded in this survey. Teeth referable to Saurornitholestes suggest
an extensive stratigraphic range for this taxon and highlight
potential systematic complications due to ontogenetic change.
Non-dinosaurian material includes the turtles Aspidertoides and
Naomichelys, crocodylians, gar, batoid fishes, and freshwater
gastropods. Localities surveyed have produced juvenile dinosaur
material and are rich in fossil eggshell, with at least three
morphotypes being represented including previously unrecognized
morphologies. Further study of the fauna of the lower Two Medicine
Formation will provide tests of hypotheses regarding dinosaur
biogeography and the development of Cretaceous ecosystems.



EVANS, David C., Dept. of Natural History, Royal Ontario Museum, 100
Queen's Park, Toronto, ON M5S 2C6, Canada, davide@rom.on.ca and RYAN,
Michael J., Dept. of Vertebrate Paleontology, Cleveland Museum of
Natural History, 1 Wade Oval Dr, University Circle, Cleveland, OH
The Judith River Formation (JRF) of Montana extends north into Canada
where it is recognized as the Foremost and Oldman formations (the
lower Belly River Group; BRG). The best exposures of these units are
adjacent to the Milk River, in SE Alberta. Although known to produce
dinosaur fossils for over a century, these units have been
comparatively poorly documented relative to the upper BRG (Dinosaur
Park Formation; DPF). For the last decade, the Southern Alberta
Dinosaur Project of the Royal Ontario Museum and the Cleveland Museum
of Natural History has documented the fauna and biostratigraphy of the
lower BRG in the Milk River region. The project has resulted in the
collection of over 5000 new dinosaur specimens; new data on dinosaur
biostratigraphy is summarized here for the first time.
The Foremost Formation has produced limited material, with only two
dinosaur taxa known from diagnostic cranial material: the basal
centrosaurine Xenoceratops foremostensis and the pachycephalosaurid
Colepiocephale lambei. The latter taxon also occurs in the
time-equivalent section of the JRF in Kennedy Coulee, MT.

The Oldman Formation consists of three successive units, 1) a lower
mudstone-dominated unit, 2) a middle sand-dominated unit, and 3) an
upper muddy unit. Our work has revealed that each of the three units
hosts a distinct ornithischian fauna. The lower unit has yeilded a
bonebed of the hadrosaurid Gryposaurus, and specimens of the basal
centrosaurines Albertacertatops nesmoi and an unnamed new taxon. The
middle unit correlates to the JRF in the region of Malta, MT; both
regions have produced multiple skeletons Brachylophosaurus canadensis.
The upper unit has produced the most diagnostic specimens, including
Euoplocephalus, Daspletosaurus nov. sp., and Saurornitholestes.
Ceratopsid fossils are particularly abundant, and include several
monodominant Centrosaurus apertus bonebeds, along with chasmosaurine
material assignable to Chasmosaurus and Anchiceratops. The fauna of
the upper unit is similar to that of the lower DPF at Dinosaur
Provincial Park, and supports the regional distribution of dinosaur
faunal zones proposed previously.

The next phase of the project is to assemble data from Montana into
this framework, in order to evaluate dinosaur faunal turnover
mechanisms on a high-resolution regional scale.




FREEDMAN, Elizabeth A., Department of Earth Sciences and Museum of the
Rockies, Montana State University, 600 W Kagy Blvd, Bozeman, MT 59717,
Hadrosaurine dinosaurs are well known from Campanian terrestrial
deposits in Montana and Alberta. However, much of their diversity
derives from the Two Medicine Formation of western Montana and Belly
River Group of Alberta, whereas exposures of the Judith River
Formation in central and eastern Montana have generally yielded less
diagnostic material. Recent fieldwork has focused on Kennedy Coulee in
northcentral Montana, which exposes part of the Judith River Formation
corresponding to the upper Foremost Formation and lower Oldman
Formation of the Belly River Group of Alberta. The terms for the
Albertan members are used here, as members of the Judith River
Formation have not been formally defined. The lower exposures of
Kennedy Coulee consist of the Taber Coal Zone and Herronton Sandstone
Zone of the Foremost Formation, and the upper exposures consist of the
lower pale beds of the Oldman Formation. The top of the uppermost
major coal of the Taber Coal Zone, the Marker A Coal, is used as a
regional correlation surface. All outcrop in Kennedy Coulee is
stratigraphically higher than the lowermost Two Medicine Formation,
which yields both Gryposaurus and Acristavus, and lower than the
Comrey Sandstone Zone of the Oldman Formation, which yields
Brachylophosaurini (clade including Acristavus, Brachylophosaurus +
Maiasaura) material has been recovered throughout Kennedy Coulee, with
a dentary in the Herronton Sandstone Zone, and all other material in
the lower Oldman Formation. Heights above the Marker A Coal are:
isolated dentary 0.4 m; partial skull and skeleton not diagnostic to
species level 15 m; fairly complete skull and skeleton of a new
species of brachylophosaurin 17.5 m, and an isolated nasal 28 m. The
isolated nasal bears similarities to the new Kennedy Coulee species as
well as Brachylophosaurus canadensis. Gryposaurus material is found in
the lower Oldman Formation of Kennedy Coulee, and includes a
monodominant bonebed of at least 8 individuals 26.6 m above the Marker
A Coal. Brachylophosaurini material stratigraphically brackets the
Gryposaurus material, indicating that these two clades coexisted in
the Kennedy Coulee area. There is no evidence for these clades
coexisting in any other part of the Judith River Formation or Belly
River Group, although they do coexist in the Two Medicine Formation.




LAWRENCE, Alexandra1, JACKSON, Frankie D.2, and ROGERS, Raymond R.1,
(1) Geology Department, Macalester College, 1600 Grand Avenue, Saint
Paul, MN 55105, alawrenc@macalester.edu, (2) Department of Earth
Sciences, Montana State University Bozeman, PO Box 173480, Bozeman, MT
We describe a unique collection of fragmentary fossil eggshell from
the type area of the Upper Cretaceous Judith River Formation in
north-central Montana. The sample under investigation was recovered
from four vertebrate microfossil bonebeds, which are localized
concentrations of fossils characterized by predominantly small,
disarticulated and dissociated vertebrate hard parts. Sites that
yielded eggshell specimens represent both lacustrine and fluvial
paleoenvironments. Sediment recovered from the four bonebeds was
processed in an automated sieve system that sorted fossils down to 500
microns. A total of 855 eggshell fragments were recovered from the
processed matrix, and 13 distinct morphologies identified. Eggshell
morphologies were identified at higher taxonomic levels when possible
through assessment of surface features and microstructure in radial
thin section. Diagnostic criteria included total thickness, the ratio
between the mammillary layer and the continuous layer, and the
structure of the mammillae as revealed by polarized light microscopy.
The most abundant morphology in our sample (n=464) exhibits horizontal
laminations and irregular wedges that radiate from the former basal
plate group, a morphology indicative of the fossil and modern
crocodilian eggshell. Another morphology (n=165) reveals distinct pore
canals and straight, narrow shell units whose height to width ratio
exceeds 5:1, and correlates well with previously described fossil
turtle eggshell. Two theropod ootaxa identified in the sample include
18 specimens of Porituberoolithus and 7 of Elongatoolithus; these were
identified, respectively, by their distinct teardrop shaped nodes on
the outer surface and the abrupt boundary between the continuous
mammillary layer boundary, along with other features. Continuing work
focuses on identification of the remaining eggshell morphtypes. These
preliminary results document the presence of multiple nesting species
in the coastal wetlands of the Upper Cretaceous Judith River
Formation. The abundance of crocodilian and turtle eggshell correlates
well with the known paleoecology of these sites based on the recovered
fossil bone sample.



HORNER, John R., Museum of the Rockies and Montana State University,
Bozeman, MT 59717, jhorner@montana.edu and FREEDMAN, Elizabeth A.,
Department of Earth Sciences and Museum of the Rockies, Montana State
University, 600 W Kagy Blvd, Bozeman, MT 59717
Over the past 30 years the Upper Cretaceous (Campanian) Two
Medicine/Judith River clastic wedge complex has yielded an impressive
inventory of hadrosaurid (Ornithopoda) dinosaur specimens, each
recorded with chronostratigraphic and sedimentological data. Specific
taxa have been found confined to particular stratigraphic horizons and
facies related to the regressive-transgressive cycle of the
Claggett-Bearpaw Sea. Hadrosaurids from the basal, initial regressive
sediments include the two primitive taxa Acristavus and Gryposaurus
latidens. Acristavus is hypothesized to be the cladogenic sister taxon
of the derived, contemporary genera Maiasaura and Brachlophosaurus.
Maiasaura is found in red, calichified mudstone sediments representing
the proximal (“upland”) wedge facies of the regressive maximum,
whereas Brachylophosaurus canadensis is found in the distal, near
marine sediments of the regressive maximum. A second species of
Brachylophosaurus (B. sp.) is also found in regressive sediments
located more proximal within the “lowland” portion of the wedge. B. sp
is hypothesized to be an anagenic precursor of B. canadensis. The
genus Gryposaurus presents a more cosmopolitan pattern where G.
latidens persists in upland sediments from the stratigraphically
lower, initial regressive sediments, up into the stratigraphic middle
red-bed sediments of the regressive maximum. An undescribed, derived
Gryposaurus (G. sp. A) co-existed in the regressive sequence alongside
B. sp., whereas a second undescribed taxon (Gryposaurus. sp. B) is
found in the upper transgressive sequence alongside the hadrosaurid
meta taxa, Prosaurolophus “blackfeetensis” and Hypacrosaurus
stebingeri. Apparent time-overlapping of some sister taxa suggest
cladogenic evolutionary events whereas the closely related,
stratigraphically separated taxa suggest that they were derived from
potential anagenic evolutionary events.




CHIN, Karen, Geological Sciences and Museum of Natural History, Univ
of Colorado at Boulder, UCB 265, Boulder, CO 80309,
Ecosystem engineers are organisms that physically modify the
environments they inhabit; this activity often has positive or
negative consequences for other members of the ecosystem. The Two
Medicine Formation provides fossil evidence of ecosystem engineering
in the Late Cretaceous, through preservation of suites of herbivorous
dinosaur coprolites. These specimens demonstrate that habitat
modification occurred on at least two spatial scales. Herbivorous
dinosaurs harvested, comminuted, microbially enriched, and relocated
vast stores of carbon resources, and the woody contents in the Two
Medicine coprolites point to extensive disturbance of rotting logs and
their detritivore communities. The 6-7 liter volumes of individual
specimens represent single defecation events, indicating that the
dinosaurs generated considerable dung each day. Net fecal
accumulations in a given area would have been augmented by extended
periods of occupation and by deposits from multiple dinosaurs. This
suggests that the suite of Two Medicine coprolites represents a small
subset of the dung originally deposited in the area. Ecosystem
engineering on a smaller scale is demonstrated by evidence for
coprophagy. Numerous back-filled burrows show considerable
translocation of dung into the sediment. Coprophagy and burial of
organic matter both facilitate biogeochemical transformations that
enhance nutrient cycling and plant growth.
The Two Medicine coprolites also reveal other ecosystem functions that
arose from large infusions of feces into the paleoenvironment. The
presence of ~60 largely entire gastropods in some of the coprolites
indicates post-depositional exploitation of dung by facultative
coprophages. At the same time, characteristic back-filled burrows
provide evidence for paracoprid dung beetle activity; this suggests
that dependable supplies of dinosaur dung helped maintain a diversity
of obligate coprophages. Although there is no evidence for it,
dinosaurs likely benefited from their coprophagous symbionts through
reductions in parasite populations. The inferred impacts of dinosaur
feeding activities can be compared to those of extant megaherbivores
that disrupt habitats while browsing and deposit copious quantities of
dung. Such fecal windfalls initiate substantial bottom-up effects on
food webs.



WILSON, Gregory P., Department of Biology, University of Washington,
24 Kincaid Hall, Box 351800, Seattle, WA 98195-1800,
gpwilson@u.washington.edu and VARRICCHIO, David J., Department of
Earth Sciences, Montana State University, Bozeman, MT 59717
The Late Cretaceous represents a critical but poorly understood period
in the evolution of mammals. Spectacular but rare specimens and dental
analyses suggest ecological diversification among non-therian mammals,
and molecular clock studies assert that many modern lineages
originated during this time. However, analyses of fossil data do not
support this claim for crown therians, and stem therians, although
taxonomically diverse, appear to remain morphologically and
ecologically uniform. A largely untested assumption is that these
Mesozoic mammals were constrained to be generalized, small-bodied,
nocturnal insectivores because of selective pressures (predation,
competition) imposed by dinosaurs at this time. The Cretaceous record
of mammals consists predominantly of isolated elements (e.g., jaws and
teeth), occurring within allochthonous and time-averaged microsite
assemblages. These records permit gross analysis of diversity and
disparity through time, but they are inadequate to fully address the
ecological factors potentially underlying these large-scale patterns.
Recent field work at the Egg Mountain locality, a dinosaur-nesting
site in the Upper Cretaceous Two Medicine Formation of Montana, has
yielded exceptionally well-preserved and largely autochthonous
mammalian fossils. Here, we describe two new specimen blocks. One
contains semi-articulated dental, cranial, and postcranial (distal
humerus, radius, ulna, femur, tibia, fibula) remains, likely of a
single individual of the multituberculate Cimexomys judithae. The
other specimen block contains associated, disarticulated dental,
cranial, and postcranial (ulna, hand) remains of at least three
individuals of the marsupialiform Alphadon halleyi. Study of these
specimens has just begun, but they hold potential to improve our
assessment of the ecologies of these taxa, clarify our understanding
of their phylogenetic relationships, and establish associations among
their dental, cranial, and postcranial elements. Moreover, because Egg
Mountain is situated in the Western Interior of North America among
several intensely studied, often well-dated Late Cretaceous localities
with large fossil sample sizes of isolated remains, these specimens
will inform studies of these other sites.



DEMAR, David G. Jr, Department of Biology, University of Washington,
24 Kincaid Hall, Box 351800, Seattle, WA 98195-1800,
ddemar@u.washington.edu, CONRAD, Jack L., Department of Anatomy, New
York College of Osteopathic Medicine, Old Westbury, NY 11568, HEAD,
Jason J., Earth and Atmospheric Sciences, University of
Nebraska-Lincoln, 228 Bessey Hall, Lincoln, NE 68588-0340, WILSON,
Gregory P., Department of Biology, University of Washington, 24
Kincaid Hall, Box 351800, Seattle, WA 98195-1800, and VARRICCHIO,
David J., Department of Earth Sciences, Montana State University,
Bozeman, MT 59717
Nearly all Mesozoic lizards of North America are known from isolated
and fragmentary bones such as jaws and vertebrae from vertebrate
microfossil localities. Recent field work at the Egg Mountain locality
in the Upper Cretaceous (Campanian) Two Medicine Formation of Montana
has yielded an exceptional collection of well-preserved fossil lizard
jaws, skulls, postcrania, and nearly complete skeletons. This largely
autochthonous assemblage, which includes similarly well-preserved
fossil mammals, dinosaurs and dinosaur egg shells and egg clutches,
and invertebrate trace fossils, offers an excellent opportunity to
reconstruct a vertebrate terrestrial ecosystem from the Late
Cretaceous of North America. Here we present new results of our
morphological and phylogenetic studies of an undescribed lizard based
on two nearly complete skeletons (MOR 6627 and 7042) from the Egg
Mountain locality. High-resolution computed tomography (CT) and
virtual 3D reconstructions revealed morphological details otherwise
hidden by the surrounding matrix. We performed a phylogenetic analysis
of 279 taxa that were scored for 807 morphological characters. The Egg
Mountain lizard is recovered as the basal-most known member of
Scincogekkonomorpha (i.e., stem + crown scleroglossans). Three
unambiguous apomorphies support that node: 1) presence of a
prearticular crest, 2) a proximally expanded clavicle with a notch or
fenestra, and 3) the symphyseal portion of the pubis is more than half
again as long as the tubercular portion. That placement diverges from
our previous results in which the Egg Mountain lizard, represented
solely by MOR 6627, consistently was nested within Iguania. We
primarily attribute that topological difference to our improved
morphological understanding of the Egg Mountain lizard (i.e., MOR 7042
and CT data) but caution that these results are preliminary pending
additional character sampling of both specimens. The presence of a
basal scincogekkonomorph during the Late Cretaceous has important
implications for determining character state polarities nearest the
major dichotomy of the squamate tree (i.e., Scincogekkonomorpha +
Iguanomorpha) and provides important insights into the early evolution
of lizards from North America and globally.



VARRICCHIO, David J., Department of Earth Sciences, Montana State
University, Bozeman, MT 59717, djv@montana.edu, MOORE, Jason R.,
Honors College, University of New Mexico, Albuquerque, NM 87131,
JACKSON, Frankie D., Department of Earth Sciences, Montana State
University Bozeman, PO Box 173480, Bozeman, MT 59717-3480, and WILSON,
Gregory P., Department of Biology, University of Washington, 24
Kincaid Hall, Box 351800, Seattle, WA 98195-1800
Discovered by Jack Horner in 1978, the Egg Mountain locality
represents a small outcrop of the Upper Cretaceous Two Medicine
Formation in Teton County, Montana. Radiometric dates place the site
at just under 75.5 ± 0.40 Ma. Early excavations of its calcareous
mudstones and carbonates produced the first dinosaur eggs and nesting
grounds from North America, as well as dinosaur skeletons, varanoid
lizards, jaws of metatherian mammals, and the most complete Late
Cretaceous multituberculate mammal from the continent. Original
interpretations argued that the thick, calcareous sequence represents
deposition within or along the margins of a shallow, low-diversity
alkaline lake. Recent excavation (2010-2013) of a large (10 x 7 x 1 m)
quarry by the jackhammer removal of successive, 10 cm-thick,
bedding-parallel intervals from the site has exposed specimens in plan
view and led to revised understanding of the locality. New taphonomic,
sedimentologic, and isotopic data favors deposition of floodplain
overbank fines heavily modified by bioturbation, pedogenesis under
subaerial conditions, and subsequent diagenetic overprinting, although
some lacustrine influence cannot yet be completely ruled out. The
diversity and condition of body fossils further supports largely
subaerial conditions. Nearly 70 m3 of quarrying has not produced a
single gar, turtle or crocodile element, some of the most common
skeletal material in Upper Cretaceous formations. Instead, the
assemblage consists only of terrestrial taxa: dinosaurs, mammals, and
lizards, as well as planispiral terrestrial gastropods. Nearly
ubiquitous trace fossil evidence in the form of abundant insect pupae
cases, dinosaur and non-dinosaurian egg clutches, coprolites, and
emetolites (regurgitates) also indicate in situ terrestrial biotic
activity. Palynological data from the area further suggests a
relatively dry paleoclimate. Mammal and squamate remains occur in one
of four modes: (i) isolated elements, (ii) closely associated to
articulated skeletons, (iii) multi-individual aggregations of
predominantly cranial elements, and (iv) concentrations of highly
fragmented and small bony debris indicating a range of taphonomic
histories. Overall, data show that Egg Mountain represents an
exceptional record of Late Cretaceous terrestrial paleoecology.