SEDIMENTOLOGY AND TAPHONOMY OF A JUVENILE
ALAMOSAURUS SITE IN THE JAVELINA FORMATION
(UPPER CRETACEOUS), BIG BEND NATIONAL PARK, TEXAS
by
ALAN BLAKE COULSON, B.S.
A THESIS
IN
GEOSCIENCE
Submitted to the Graduate Faculty of Texas Tech University in
Partial FulfiUment of the Requirements for
the Degree of
MASTER OF SCIENCE
Approved
December, 1998
ACKNOWLEDGEMENTS
I wish to thank my advisor, Dr. Thomas Lehman, for allowing me the opportunity
to work on this fascinating project. I also thank my committee members. Dr. James
Barrick and Dr. Sankar Chatterjee, for their advice, help, and insight. For their technical
support in the laboratory, I thank Dr. Haraldur Karlsson, James Browning, and Michael
Gower, without whose assistance the thin section and isotope studies would never have
been done. For their assistance in the field, 1 thank Dr. Thomas Lehman, James
Brovming, Jonathan Wagner, Richard Kissel, Jeff Anglen, Denny Surratt, and all those
who worked at this site before I began this project: their assistance was invaluable.
Lastly, I wish to thank my parents, Philip and Karen Coulson, as well as Jane and Rick
Munsey, for all their support over the years.
n
TABLE OF CONTENTS
ACKNOWLEDGEMENTS ii
ABSTRACT v
LIST OF TABLES vii
LIST OF FIGURES viii
LIST OF ABBREVIATIONS x
CHAPTER
I. BACKGROUND 1
Introduction 1
Regional Geology 2
Previous Geologic Studies 3
Previous Paleontologic Studies 5
II. SEDIMENTOLOGY 9
Javelina Formation 9
General Sedimentology 10
Stratigraphy and Lithology at Field Site 12
Thin Sections 13
Depositional Environment 14
III. PALEONTOLOGY 17
IV. ALAMOSA UR US SANJUANENSIS 21
m
Background 21
Discussion 23
Description of TMM 43621-1 24
Axial Skeleton 26
Appendicular Skeleton 36
Taphonomy 40
Ontogeny 43
Comparison with Other Sauropod Taxa 45
V. STABLE ISOTOPE ANALYSIS 85
Procedure 85
Discussion 87
VI. CONCLUSIONS AND SUMMARY 94
REFERENCES 96
IV
ABSTRACT
A partial skeleton of a juvenile sauropod dinosaur was recovered fi"om an outcrop
of the Javelina Formation in the Grapevine Hills region of Big Bend National Park,
Texas. Paleocene mammals and reptiles were collected a few meters above the sauropod,
making this section the most tightly constrained Cretaceous-Tertiary boundary section in
the Big Bend region. Freshwater gastropods, fi-eshwater fish, and charophyte algal
oogonia suggest the deposits represent a lake.
The sauropod is assigned to Alamosaurus sanjuanensis, based on similarities in
the humerus, and the unique morphology of the ischium. Many skeletal elements
collected were previously unknov^ni for this species. These include six cervical centra and
six cervical neural arches. Other skeletal elements recovered and not previously reported
in the literature are one dorsal centrum, four dorsal neural arches, two distal tibiae, one
complete fibula, and one partial fibula.
An ontogenetic series of six humeri assigned to Alamosaurus sanjuanensis were
measured to investigate changes with growth in this element. Proximal width, distal
width, shaft circumference, and shaft diameter were each compared against length. The
allometric coefficients are all greater than one, indicating that all these measures
increased relatively faster than length, making the humerus more robust with growth.
Taphonomic data suggests that this animal died on its left side, and the skeleton
was disarticulated prior to burial. Scavenging may have been responsible for partial
disarticulation, with the smaller and easily transported elements being winnowed out by
currents that affected the orientation of the remaining bones.
Carbonate nodules were collected along a 192 m section spanning the K/T
boundary at this site. Stable isotope analysis revealed a pattem similar to that obtained
by Ferguson et al. (1991) fi-om nearby exposures. There is a strong correlation between
S CpDB and 6 0pDB values, and the trend resembles an evaporative pattem. A large
negative excursion in both the carbon and oxygen isotope values occurs at or just above
the K/T boundary. This excursion is thought to represent climatic change during the
early Paleocene to cooler and wetter conditions in the Big Bend region.
VI
LIST OF TABLES
1 Measurements of Alamosaurus sanjuanensis Humeri 79
2 Measurements of Alamosaurus sanjuanensis Cervical Centra 80
3 Measurements of Alamosaurus sanjuanensis Cervical Neural Arches 81
4 Measurements of Alamosaurus sanjuanensis Dorsal Neural Arches 82
5 Log-Transformed Measurements for RMA Analysis 83
6 Slope and Intercept Values for RMA Plots 84
7 Carbon and Oxygen Isotope Values 93
Vll
LIST OF FIGURES
1 The Big Bend region 6
2 Paleogeographic map of North America in Masstrichtian time (Lehman, 1987) 7
3 Chart delineating the Tomillo Group, which inadvertently includes the Aguja Formation 8
4 Cross section of the main hill at the field locaHty (after Lehman, field notes) 16
5 Three species ofgastropods collected at the field locality 20
6 Skeletal reconstruction of a sauropod dinosaur by W. Langston, Jr. (1974). Elements belonging to the Alamosaurus specimen described by Gilmore (1946) are shown in black 50
7 Comparison of sauropod ischia 51
8 Alamosaurus sanjuanensis scapula 52
9 Unidentified specimen with juvenile bone texture visible 53
10 Quarry map showing distribution of Alamosaurus bones at the field locality 54
11 The axis 55
12 The third (?) cervical centrum, in dorsal view (scale bar = 5 cm) 56
13 The fourth (?) cervical centrum, in dorsal view (scale bar = 5 cm) 57
14 The fifth (?) cervical centrum 58
15 The sixth (?) cervical centrum, in ventral view (scale bar = 5 cm). 59
16 The seventh (?) cervical vertebrae, in lateral view (scale bar = 5 cm) 60
17 The third (?) cervical neural arch 61
18 The eighth (?) cervical neural arch 62
vni
19 Anterior dorsal neural arch 63
20 Anterior dorsal neural arch, in anterior view (scale bar = 5 cm) 64
21 Posterior dorsal neural arch 65
22 Dorso-sacral vertebrae 66
23 Left coracoid, in lateral view (scale bar = 5 cm) 67
24 Left humerus, in anterior view (scale bar = 5 cm) 68
25 Left ischium, in lateral view (scale bar = 5 cm) 69
26 Left fibula, in medial view (scale bar = 5 cm) 70
27 Distal left tibia 71
28 Orientation of the long axes of /<2mo5awrw5 bones at the field locality 72
29 Bivariate plot of humerus length versus (a) distal width and (b) shaft diameter used forRMA. 73
30 Bivariate plot of humerus length versus (a) proximal width and (b) shaft circumference used for RMA. 74
31 Comparison of sauropod cervical vertebrae in lateral view 75
32 Comparison of sauropod anterior dorsal vertebrae in posterior view 76
33 Comparison of sauropod humeri in dorsal view 77
34 Comparison of sauropod fibulae and tibiae 78
35 Measured section at field locaHty 89
36 6' CpDB versus 6 0pDB values for carbonate nodules collected at the field locality 90
37 S CpDB values throughout the measured section at the field locality 91
38 6 *OpDB values throughout the measured section at the field locality 92
IX
LIST OF ABBREVIATIONS
AMNH American Museum of Natural History
C concretion
ca capitellum
cf coracoid foramen
DC deltopectoral crest
dc distal cup
dip distal process
dp diapophysis
ip ihal peduncle
nc neural canal
ns neural spine
nsr prespinal laminae
op odontoid process
pa pedicel articular surface
pb proximal ball
pd pedicel
pez prezygapophyses
pi pleurocoel
poz postzygapophyses
pp parapophyses
RMA reduced major axis analysis
sa scapular articular surface
TMM Texas Memorial Museum
tu trochlea
XI
CHAPTER I
BACKGROUND
Introduction
A section of continental sedimentary rocks representing Late Cretaceous through
early Eocene time is exposed in the Big Bend region of southwestem Texas. This
stratigraphic section is important because it includes a record of continental
sedimentation across the Cretaceous-Tertiary (K/T) boundary (Lehman, 1990). Also, as
the southernmost such sequence in the United States, these strata provide an opportunity
to discern Late Cretaceous paleoenvironmental and paleoecological information for an
area much farther south than the more extensively studied correlative deposits in Montana
and Alberta (the Lance and Hell Creek Formations; e.g., Sloan, 1969; Lehman, 1987).
The primary goal of this study is to describe a fossiliferous Late Cretaceous site in
Big Bend National Park, Texas. This site is the stratigraphically highest dinosaur-bearing
locality yet known in the region, occurring only a few meters below the K/T boundary.
Data from sedimentology, paleontology, and isotope geochemistry provide information
on the paleoenvironmental conditions, and the fauna that existed at this site. The
secondary goal of this study is to describe a juvenile specimen of the sauropod dinosaur
Alamosaurus sanjuanensis, which was recovered from this site. This study adds to our
knowledge of the anatomy and ontogeny of . sanjuanensis.
Regional Geology
The boundaries of the Big Bend region can be roughly defined as follows:
northem boundary at 29° 30' N, southem boundary at the Rio Grande, northeastem
boundary at the Sierra del Carmen range, and the southwestem boundary at the Terlingua
fault zone (Baker, 1935). During Late Cretaceous time, the area that is now Big Bend
National Park was bounded by the Cretaceous Interior Seaway to the east and an orogenic
belt to the west (Lehman, 1987, 1989a; Fig. 1). During Late Campanian time, the
shoreline of the interior sea began retreating to the northeast, marking the final regression
of the Interior Seaway (Lehman, 1987, 1989a). The Laramide Orogeny began during
Maastrichtian time, which, combined with tectonic-induced accretion along the westem
coast of North America, created a series of uplifts and isolated intermontaine basins
throughout westem North America (Lehman, 1987; Fig. 2). A continental sedimentary
basin called the Tomillo Basin developed in the area that is now Big Bend National Park
(Wilson, 1970; Schiebout, 1987; Lehman, 1991). Bounded on the east by a west-facing
monoclinal uplift and on the west by the Chihuahua Tectonic Belt, the Tomillo Basin was
a site of major sediment deposition during Maastrichtian time (Wilson, 1989; Lehman,
1991). Sediment deposited in the Tomillo Basin originated from erosion of older
Cretaceous rocks uplifted by Laramide tectonism, cannibaHzation of Late Cretaceous
sediments, and volcanic activity in what is now southwestem New Mexico and
southeastem Arizona (Lehman, 1991). These deposits form the Tomillo Group of
Maxwell et al. (1967), which includes the Javelina, Black Peaks, and Hannold Hill
Formations (Fig. 3).
The sedimentary strata of the Tomillo Group were disturbed by late Eocene-
Oligocene igneous activity in the region (Wilson, 1989; Lehman, 1991). Igneous
activity in the area subsided by the early Miocene (Wilson, 1989). This igneous activity
resulted in the emplacement of a large body of volcanic and plutonic igneous rocks in the
Big Bend region. Following this. Basin and Range faulting affected the area. Movement
along northwest-southeast trending faults around the margins of the area led to the
creation of the "Sunken Block," a graben in which Big Bend National Park is now
located (Schiebout, 1987; Wilson, 1989). Erosion of the Tertiary igneous deposits
resulted in the formation of gravel-covered pediment surfaces during the Pleistocene
(Maxwell et al., 1967).
Previous Geologic Studies
A preliminary report on the geology of the Big Bend region was published by
Hill in 1902. Hill, Phillips, and Udden published a map in 1904 that included the rocks
of the Tomillo Group, but no text accompanied their map (Schiebout, 1987). Udden
(1907) conducted a more thorough geologic investigation, although he did not include a
map in his publication. He designated the stratigraphic series of clay-dominated deposits
above the Rattlesnake Beds (now the Aguja formation) as the Tomillo Clays, to which he
assigned a Late Cretaceous age. Wilson (1952, 1967) demonstrated that at least part of
the Tomillo Clays were Tertiary in age, based on their mammalian fossil content. The
most extensive study of Big Bend National Park geology was published by Maxwell et al.
(1967). In this study, the Tomillo Clays were given the stratigraphic rank of group. The
newly formed Tomillo Group was subdivided into the Javelina (Late Cretaceous), Black
Peaks (Paleocene), and Hamiold Hill (early Eocene) formations (Fig. 3). This
nomenclature has been challenged (Lawson, 1972; Schiebout et al., 1987, 1988), based
mainly on the assertion that the formations are too difficult to discem from each other
because they represent different developmental degrees of the same fluvial depositional
system. Their arguments have been disputed by Lehman (1988), who pointed out the
formations have afready been successfiilly mapped, and the deposits are discemable upon
close examination of parameters such as color. Thus, I agree with Lehman (1988) that a
revision of the terminology of Maxwell et al. is not required.
This study will focus on a fossiliferous site in the uppermost part of the Javelina
Formation. Several workers have examined various aspects of the geology of the
Javelina Formation. The stratigraphy and paleoecology of the Tomillo Group was
investigated by Lawson (1972). Lehman (1985) studied the petrography and
sedimentology of the Upper Cretaceous deposits. Lehman (1988) redefined the boundary
between the Javelina Formation and overlying Black Peaks Formation such that it now
approximates the K/T boundary. Most recently. Straight (1996) conducted a survey of
the stratigraphy and paleontology of the upper Javelina Formation and lower Black
Peaks Formation, particularly in the immediate area of the present study.
Previous Paleontologic Studies
The majority of fossil material collected in Big Bend National Park has come
from the Aguja Formation (Brown, 1941; Lehman, 1982; Davies, 1983; Tomlinson,
1997), the Black Peaks Formation (Wilson, 1952, 1967; Schiebout, 1970, 1974;
Standhardt, 1986) and the Hannold Hill Formation (Stovall, 1948; Hartnell, 1980;
Runkel, 1988). However, the Javelina Formation has also yielded much fossil material.
Udden (1907) first reported the presence of "saurian bones" in part of the Tomillo Clays
now included in the Javelina Formation. B. Brown collected sauropod material for the
American Museum of Natural History (AMNH) in 1941. In 1947, W. Langston, Jr. and a
group from Texas Technological College recovered a sauropod femur (Langston et al.,
1989). W. Langston, Jr. and coworkers also excavated a partial skeleton of Alamosaurus
sanjuanensis in the early 1970's, and have recovered a great deal of pterosaur material
belonging to the genus Quetzalcoatlus over the past twenty-five years (Lawson, 1975;
Langston et al., 1989; Straight, 1996). D.A. Lawson (1976) reported the presence of
ceratopsians and theropods in the Javelina Formation. In recent years, field excursions
led by T. Lehman have recovered additional sauropod and ceratopsian material from the
Javelina Formation. Wheeler et al. (1994) reported the discovery of a new genus of
dicotyledonous wood, an important find given the paucity of fossil plant material
recovered from the Javelina Formation, relative to the Aguja and Black Peaks formations.
To date, with the exceptions of Lawson's and Wheeler's publications, none of this
material has been completely prepared and formally reported in the literature.
«0*N
lec-
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Ccrdille Fold end Thrjs!
Be
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( b )
Fig. 1 The Big Bend region: (a) paleogeographic map of North America during Campanian time (Lehman, 1987), when the area was inundated by the Westem Interior Seaway, (b) location of the Big Bend region (Schiebout et al., 1987).
60'N eo'N BO*N 60*N
120" W eo* w
60'W
Fig. 2 Paleogeographic map of North America in Maastrichtian time (Lehman, 1987).
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8
CHAPTER II
SEDIMENTOLOGY
Javelina Formation
The Javelina Formation is the name assigned by Maxwell et al. (1967) to the
lower part of Udden's (1907) Tomillo Clays. The formation was named for Javelina
Creek, which runs across the northeastem part of Tomillo flat. The Javelina Formation is
correlative with the El Picacho Formation to the southwest (Lehman, 1989a, 1991). The
Javelina Formation is assigned a latest Cretaceous age based on its dinosaur fauna and a
preliminary paleomagnetic correlation with chrons C30N and C29R determined by
McFadden (in Standhardt, 1986). The best outcrops of the Javelina Formation occur in a
non-continuous ring around the Tertiary intmsives comprising the Chisos Mountains in
the center of Big Bend National Park (Straight, 1996). Maxwell et al. (1967) mistakenly
assigned two type sections for the Javelina Formation; one at Dawson Creek and another
at Tule Mountain. The Tule Mountain section has since been shovm to contain beds
assigned to the Aguja Formation, and the Dawson Creek section is now considered the
best type section (Lehman, 1985). Few vertically extensive outcrops of the Javelina
Formation exist. The most complete sections are at Dawson Creek (thickness = 150 m)
and McKinney Springs (thickness = 150 m).
General Sedimentology
The Javelina Formation is composed mainly of fine, variegated clays, with
lenticular sand bodies and rare lacustrine limestones distributed throughout (Maxwell et
al., 1967; Standhardt, 1989). The sediments were derived from erosion of Lower- and
Upper Cretaceous marine rocks upHfted by Laramide tectonism to the west (Schiebout,
1987; Lehman, 1989a), and deposited in the Tomillo Basin in Maastrichtian time
(Lehman, 1991). Volcanic material from a magmatic arc to the west was also
incorporated into the Javelina deposits (Udden, 1907; Lehman, 1987, 1989a). This
composition reflects that of all Maastrichtian sediments in the Big Bend region, which are
estimated to contain about 75% mudstone, 25% sandstone, and less than 1% limestone
(Lehman, 1989b).
Uplifts to the west of the Tomillo Basin, attributed to Laramide tectonism, were
responsible for redirecting paleocurrents to the southeast (Lehman, 1989a). Thus, fluvial
systems carried their sediment load into and deposited it within the Tomillo Basin
(Schiebout, 1974; Lehman, 1991). This fluvial origin agrees with other sedimentologic
data, including the stmctureless nature of the clay deposits (Maxwell et al., 1967), poor
sorting of clastic material (Udden, 1907; Maxwell et al., 1967), lenticular geometry of
sand bodies (Maxwell et al., 1967; Lehman, 1985, 1989b), and the development of
paleosols on overbank deposits (Lehman, 1989b, 1990). The presence of lacustrine
limestone (Standhardt, 1989) and freshwater gastropods and bivalves (Lehman, 1989b;
Straight, 1996) indicate that standing bodies of water were present, at least in some areas.
The clays are stmctureless, variegated, and mostly bentonitic in origin (Udden, 1907;
10
Eley, 1938; Maxwell et al., 1967). They are composed almost entirely of smectite
(Lehman, 1985). Typical clay colors include dull shades of red, blue, green, gray, purple,
yellow, and brown, with rare black and white layers. The clays are highly impervious to
water, and thus weather in a "creeping" fashion described by Udden (1907), in which the
top few inches of the clays swell when wetted, then dessicate, crack, and erode via wind,
water, or gravity. Calcium carbonate (CaCOj) nodules are common within the clays in
many areas, forming an armored surface of nodules as the surrounding clay is weathered
and eroded. These nodules typically range in diameter from 2 cm to 7 cm, with some as
large as 20 cm (Maxwell et al., 1967). These concretions are usually gray, yellow, off-
white, or purple in color, with rough exteriors and sometimes display shrinkage cracks
(Udden, 1907).
The amount of sandstone varies among locations. The sandstones are usually
lenticular bodies representing channel deposits. Sand sorting is often poor (Maxwell et
al., 1967), indicating rapid, simultaneous settling of all sediment in an environment of
weak or no currents (Udden, 1907; Maxwell et al., 1967). In some areas, the sands are
conglomeratic (Maxwell et al., 1967). They are typically composed of fine- to medium-
grained sand, are immature to mature, and contain volcanic arenite and plagioclase arkose
with conglomeratic lags of calcium carbonate nodules, and lesser amounts of chert and
quartz (Lehman, 1985). Udden (1907) noted that many of the sandstones in his Tomillo
Clays were very hard due to their cementing agents.
11
Stratigraphy and Lithology at Field Site
Outcrops of the Javelina Formation are present north of the Grapevine Hills
laccolith. Straight (1996) summarized the stratigraphy and paleontology of the Upper
Cretaceous and Lower Tertiary strata exposed in this area. In the Javelina Formation
exposures. Straight noted the presence of four major sandstone ridges. The Javelina
Formation outcrops in the area are dominated by variegated mudstones, with thinner
channel sandstones locally prominent. Straight (1996) noted the presence of a volcanic
ash layer between two sandstone units, and indicated that the middle of the Javelina
Formation, at the level of this ash layer, may have been removed from the section by
faulting. The ash layer is present at the Grapevine Hills locality.
All fossil specimens were collected from below a single small hill (height ca. 19
m following strike with a dip of 36°) in the area north of Grapevine Hills (Fig. 4). The
base of the hill is composed of a dark purple- to maroon-colored mudstone layer
containing some concretions and fossil surface float. Overlying this layer is a dark olive
gray laminated mudstone layer. The main bone horizon is 106 cm above the contact with
the underlying purple to maroon layer. A large number of fossilized burrows were found
in close association with the vertebrate material. Fifty-six cm above the bone horizon,
the dark olive gray mudstone is intermpted by a thin (about 20 cm thick) yellowish
breccia horizon, which contains an abundance of fossiUzed freshwater gastropod shells.
This layer may represent the K/T boundary at this locality. About 2 m higher, a
Paleocene mammal tooth along with turtles and crocodilians were collected, making this
site the best-constrained K/T boundary section in the Big Bend region (previously, the
12
best constrained K/T section was a 30 m section near Dawson Creek, Lehman, 1990).
The mudstone is overlain by a tan to white sandstone, which in turn is overlain by a dark
brown cross-bedded sandstone unit. Straight (1996) measured a 116 m section of the
Javelina Formation in this area, but noted that the middle of the section may have been
intermpted by faulting.
Thin Sections
Samples of the breccia layer, clay matrix of the bone horizon, and burrow casts
were thin sectioned. All three rock types contain charophyte oogonia, bone chips, and
microcrystalline calcite globules that are interpreted to be fecal pellets. These features
are most common in the clay matrix, and are less abundant in the burrow and breccia thin
sections. The bone chips appear as medium-to-dark brown angular grains in plain and
cross-polarized light that range from 0.125-2.0 mm in size, with most between 0.25 and
0.5 mm. The charophyte oogonia are circular stmctures with a rind of radial fibrous
calcite and that are filled with coarse crystalline calcite. The oogonia are 0.25 -0.5 mm in
size. The calcite globules appear as dark gray microcrystalline grains under crossed
polarized light, and most are 0.25-0.5 mm in size, with a few as large as 2.0 mm. The
clay and carbonate cement appear as a variegated, fine-grained micritic texture, with
coarse radial calcite crystals coating the oogonia and some bone chips. No stmcture is
present in any of the thin sections except those of the burrows, which have a rind-like
lining along the edge of the burrow.
13
Depositional Environment
Previous Paleoenvironmental Interpretation
The Javelina Formation sediments were deposited on an inland fluvial floodplain
as evidenced by the terrestrial fossil fauna and the occurrence of extensive fine-grained
overbank deposits and channel sand deposits. Paleosols have been well documented in
the Javelina Formation (Lehman, 1989b; 1990). The presence of petrocalcic horizons
within the paleosol profiles indicates that paleosol development occurred under at least
two sets of climatic conditions (Lehman, 1985, 1989b). However, this does not
necessitate "warm" and "cool" conditions. Growth rings are absent in both fossilized
wood (Wheeler et al., 1994) and dinosaur bones (Lehman, personal communication,
1997) collected in the Big Bend region. The most probable explanation for absence of
growth rings is a lack of pronounced seasonaUty. Without a distinct cold season, growth
in plants and non-continuously growing animals, such as reptiles, continues unabated
year-round.
Stable oxygen isotope studies of the carbonate nodules common in the Javelina
deposits indicate mean annual temperatures above 15° C (Lehman, 1990; Ferguson,
1991). Integration of paleosol studies with amiual rainfall formulas indicate an average
precipitation of 93-96 cm/yr, depending on the equation used (Lehman, 1990), compared
to 183-234 cm in the Paleocene, and about 37 cm in modem times (Maxwell et al., 1967).
Evidence of drier conditions exist in the form of gypsum crystals and pseudomorphs,
which are locally present in the Javelina Formation. It is likely that standing bodies of
14
water, as evidenced by rare limestones, were ephemeral in nature. Thus, these
floodplains apparently underwent alternating periods of humid and semi-arid conditions
(Lehman, 1985).
Interpretation of Field Area
This site is thought to represent a lake deposit. The presence of freshwater
gastropods, freshwater algae, and fine-grained clastic sediments necessitate a standing
freshwater body. That the sauropod bones were buried in a mixture of clay and carbonate
material suggests both biologic and clastic sedimentation were occurring. It is possible
that, during periods of semi-arid conditions, lake sedimentation became chemically
dominated, allowing for fiirther precipitation of calcium carbonate. No gypsum or halite
deposits, suggestive of increased degrees of chemical precipitation, occur in the
immediate vicinity.
15
E a s t West
Top of Hill 56 cm
bone h o r i z o n 106 cm
/
Wi^-ny'
j ^ ^ gray mudstone
purple mudstone
breccia
sandstone
Fig. 4 Cross section of the main hiU at the field locality (after Lehman, field notes).
16
CHAPTER III
PALEONTOLOGY
A variety of fossils has been collected at the field site, though some are
represented by a single specimen. Both macrovertebrate and microvertebrate remains
have been collected, as well as trace fossils and microscopic plant remains. The fauna at
this site is not unusual for the Javelina Formation (Lehman, 1989b). The macrovertebrate
remains are a partial skeleton of a juvenile Alamosaurus sanjuanensis. This specimen
will be discussed in Chapter IV, and the other fossil material will be described here.
Two groups of fish are represented in the collection. A single gar fish scale was
collected from the thin breccia layer. It is a small black parallelogram, 3 mm by 5 mm,
with a characteristic hard, shiny, enamel-like surface. A single vertebra, also from the
breccia layer, belongs to an amiid fish. It is ovate in anterior-posterior view, measuring
2.1 cm across, 1.3 cm in length, and 1.8 cm tall.
Two types of trace fossils have been observed at the site. Two elements may
represent coprolites (Lehman, personal communication, 1998). The other trace fossils are
burrows, which are quite abundant, especially in proximity to the sauropod remains.
These stmctures are cylindrical in shape, have an average diameter of 1-3 cm, and an
average length from 4-6 cm, with the longest specimens approaching 10 cm. In situ, the
burrows tend to be directed straight down, and branch out in proximity to the sauropod
bones. Thin sections of the burrows reveal they are lined and contain bone fragments,
calcite globules that may be fecal pellets, and algal oogonia, all of which are also present
17
in the surrounding matrix. The close association of the burrows with the vertebrate
fossils, along with the presence of bone chips within the burrows, suggests the organisms
that created these stmctures may have been feeding on the remains of the sauropod.
However, the morphology of the burrows most closely matches that of dwelling
stmctures attributed to arthropods, rather than tme feeding stmctures.
Oogonia of charophyte algae are visible in thin sections of the clay matrix and of
the burrows. Oogonia are the reproductive stmctures of charophyte algae, and the only
part of the organism that becomes fossilized, usually via calcification (Adams et al.,
1984). These stmctures, initially hollow spheres, are coated with a radial rind of calcite,
and are filled with coarse crystalline calcite. The radial-fibrous habit of the stmcture,
whose main constituents are normally aragonite and high magnesium calcite, is common
in freshwater deposits formed near the water-sediment contact (Adams et al., 1984).
These algae are indicative of a freshwater environment, and their tendency to precipitate
calcite fits the depositional interpretation of a standing body of freshwater, such as a lake
(Lerman, 1978).
Gastropod fossils are quite common at the field site. Four species have been
recognized in the collection (Fig. 5). Most common are two freshwater species of
viviparid snails, Viviparus retusus and V. trochiformis. Viviparus retusus is a large, low-
spired gastropod with a body whorl diameter of up to 40 mm, and an overall maximum
length of 40 mm. In a random sample of twelve individuals, the two measurements were
always within 2 mm of each other. Viviparus trochiformis has a smooth trochiform shell
that is an average of 10-15 mm long. Curved growth lines are on the shell. A few
18
individuals of Goniobasis tenera were collected in the thin breccia horizon. These are
small (average length 10-15 mm), high-spiraled forms with axial plications on the apical
whorls. Five prominent raised spiral lirae are present on each whorl. The body whorl is
an average of 5-7 mm in diameter. Goniobasis is a member of the Cyclophoridae; this
family contains terrestrial and freshwater species. The fourth species is represented by a
single, tiny (length = 9 mm) individual collected in the breccia layer, and has not been
identified. The presence of these gastropod species indicates that the deposits are not of
marine origin.
A random sample of thirty individuals collected in float revealed Viviparus
trochiformis to be the most abundant (21 individuals), with the remainder of the sample
containing only V. retusus. One complication is the difficulty of telling the two species
apart. As pictured in Russell (1931) and La Rocque (1960), the large body whorl and
very low spiral of V. retusus appears to be easily distinguishable from the mid-sized V.
trochiformis. However, many individuals possess a large body whorl, but also have 2-3
well-defined whorls above. Many of the individuals assigned to Viviparus trochiformis
are much larger than the average 10-15 mm length, being more in the 25-27 mm length
range. The possibility that these two groups represent different growth stages of the same
species should be considered. Unfortunately, there is very little literature pertaining to
Late Cretaceous gastropods.
19
(a) ( b ) ( c )
i <:Lrn I i
CiY\
Fig. 5 Three species ofgastropods collected at the field locality: (a) Viviparus retusus, (b) Viviparus trochiformis, (c) Goniobasis tenebra.
20
CHAPTER IV
ALAMOSA UR US SANJUANENSIS
Background
The systematic taxonomy (sensu Mcintosh, 1990a) of Alamosaurus sanjuanensis
is as follows:
Superorder Dinosauria Owen 1842
Order Saurischia Seeley 1887
Suborder Sauropodamorpha von Huene 1932
Infraorder Sauropoda Marsh 1878
Family Titanosauridae Lydekker 1885
Genus and SpQciQS Alamosaurus sanjuanensis Gilmore 1922
Type Specimen: USNM 10486 (right scapula)
Paratype: USNM 10487 (left ischium)
Referred Specimens: TMM 41541, TMM 41450, TMM 40426, TMM
42495, TMM 41398, TMM 40597
Uncataloged Specimens: TL 95-1, TL 95-4, TLMcS2-3.
The holotype specimen of Alamosaurus sanjaunensis was discovered by J.B. Reeside, Jr.
in 1921 and formally described in 1922 by C.W. Gilmore. The type specimen, United
States National Museum (USNM) 10486, was collected from the Ojo Alamo Sandstone
near Barrel Springs Arroyo, in northem New Mexico (the dinosaur-bearing part of the
21
Ojo Alamo Sandstone has since been reassigned to the Naashoibito Member of the
Kirkland Shale, Kues et al., 1980). The type specimen consists of a left scapula, found
with a right ischium designated a paratype (USNM 10487). The creation of a new taxon
was justified because this specimen was the first sauropod reported from the Late
Cretaceous of North America, and both bones were distinctive from those of other known
sauropods. As noted by Gilmore, the distal process of the ischium is much shorter than in
other sauropods, being subequal in size to the ilial articular peduncle (Fig. 7). This gives
the bone an almost bilaterally symmetrical outline in lateral view. The scapular shaft has
a gradual expansion moving towards the suprascapular end, a condition not seen in any
sauropod known at that time. This, combined with the lack of anterior and/or posterior
expansion of either the proximal or distal end, and the orientation of the spine at ca. 90°
to the scapular shaft, make the scapula unique among sauropods (Fig. 8). Mateer (1976)
pubHshed descriptions of a fragmentary illium, one sacral, and one caudal vertebrae
collected near the type locality. Teeth attributed to A. sanjuanensis were also collected
near the type locality and described by Kues et al. (1980).
In 1946, Gilmore described a more complete specimen from the North Hom
Formation of Utah (Fig. 6). This specimen (USNM 15560) included thirty articulated
caudal vertebrae, 25 chevrons, both ischia, left scapula and coracoid, right forelimb
complete to the metacarpals, 2 sternal plates, and rib fragments (not described) This
remains the most complete specimen ftilly described in the literature. Uncollected
specimens from the McRae Formation in central New Mexico are pictured in Lozinsky et
al. (1984) and Wolberg et al. (1986).
22
D.A. Lawson (1972) described several skeletal elements from the Javelina
Formation of Texas in the Texas Memorial Museum (TMM) collection in his
unpublished thesis. Many additional specimens have been collected from the Javelina
Formation, but not prepared or described. A cervical vertebra was collected by B. Brown
in 1941 for the American Museum of Natural History. W. Langston, Jr. recovered a
femur in 1947, and a partial skeleton in 1972 (Langston et al., 1989; TMM 41541).
Langston recovered additional material near Dawson Creek in 1982 (TMM 42495),
which remains unprepared at Texas Memorial Museum, along with other specimens
(TMM 41398, TMM 40597-2, and TMM 41450-2). In recent years, specimens of at least
three individuals have been collected by T. Lehman.
Discussion
Alamosaurus sanjuanensis is an interesting species for several reasons. It is the
only known titanosaurid from North America, the only known Late Cretaceous sauropod
from North America, and was one of the latest-surviving dinosaurs, existing to the very
end of the Cretaceous. It is the defining member of the Alamosaurus fauna, the group of
large terrestrial vertebrates indigenous to the southwestem United States during the
Maastrichtian (Sloan, 1969; Lucas, 1981; Lehman, 1987). As a titanosaurid living in the
southwestem United States, its presence has been cited as evidence of a land bridge that
connected North and South America in latest Cretaceous time, for titanosaurids were the
dominant group of large herbivores in South America until the end of the Cretaceous
(Sloan, 1969; Calvo and Bonaparte, 1991; McCord, 1997). The absence of sauropods
23
from much of the Cretaceous record in North America has also been explained by the
poor preservation of terrestrial strata deposited during the mid-Cretaceous when the
Cretaceous Interior Seaway flooded much of what is now the Westem Interior. Davies
(1983) suggested that hadrosaur distribution was environmentally controlled, and the
same may have been tme of sauropods. This possibility is bolstered by the strong
correlation of . sanjuanensis to inland deposits (Lehman, 1989b), which also holds for
the Jurassic sauropod remains recovered from the Morrison Formation and contemporary
strata. However, this idea is contradicted by the presence of sauropods in marginal
marine deposits of early Cretaceous age (Lockley, 1986).
Description of TMM 43621-1
The specimen collected at the study site (field number TL 95-1) represents a
juvenile individual. This is indicated by the size of the elements (humems length = 60
cm, versus 136 cm for the humems of USNM 15560, and 84 cm for a subadult specimen
collected by Lehman, unpublished; Table 1), the presence of juvenile striated bone
texture seen on some specimens (e.g., unidentified bone, field label K, Fig. 9), and the
lack of fiision between neural arches and their corresponding centra. The elements
collected and identified from this site to date include six cervical centra, six cervical
neural arches, one partial cervical rib, one dorsal centmm, four dorsal neural arches, left
coracoid, left humems, left ischium, left fibula, partial right fibula, and both distal tibiae.
Two specimens are too fragmentary to be identified with any certainty. A good number
of pieces were collected as surface float. Whereas many of these articulate with other
24
such pieces, only two have so far been identified, a transverse process from a dorsal
vertebrae and a partial cervical neural arch.
The specimens were all collected from the same horizon, a dark, olive gray
mudstone layer located 56 cm below a thin breccia layer that is thought to represent the
K/T boundary in this area (Fig. 4). The specimen was completely disarticulated (Fig. 10),
and most elements had suffered post-fossilization breakage, most likely caused by
compaction or swelling of the surrounding clay. The specimens were cleaned with a
variety of dental tools, an airscribe, dissection picks, small bmshes, and formic acid
washings as described by Rutzky (1994). Butvar was used to strengthen and protect the
bone surfaces. Broken specimens were reassembled with Durro Master Mend Quick Set
Epoxy, although the limb elements were left in two sections for strength and ease of
transport and storage.
The bones were covered in a thin layer of calcite concretion. On many specimens,
this concretion has a radiating fibrous stmcture that flakes off as thin (2-4 mm thick)
plates when prepared with a combination of dilute (3%) formic acid, dental picks, and an
airscribe. Other specimens, however, were coated with microcrystalline calcite
concretion lacking the radial fibrous stmcture. This concretion has proven very difficult
to remove, as the airscribe and formic acid baths have a minor effect. In some cases
enough of this concretion was removed from a specimen to allow for examination of the
bone surface undemeath. On some specimens, the outermost layer of bone was totally
removed prior to preservation, allowing the concretionary material to infiltrate the bone
and thus obscure any clear bone-concretion contact surface (thus explaining the
25
ineffectiveness of the airscribe). Therefore, many specimens have not been fiilly
cleaned. However, even with much of the concretion still intact, most of the elements
lend themselves to easy identification and description. The concretion coating artificially
inflates measurements, but the thickest layers of concretion observed are no more than 5
mm in thickness. Thus, linear measures should be no more than 1-2 cm greater than the
tme measure of the specimen. All measurements were done with a metric tape measure.
Each measurement was taken twice and the results averaged.
The specimen is currently at the Texas Tech University Geology Department.
Once fiilly prepared, it will be reposited with the Vertebrate Paleontology Laboratory at
the University of Texas, where it has been given the number TMM 43621-1.
Axial Skeleton
Cervical Centra
Six cervical centra have been collected. These are arranged for purposes of
description from the axis (cervical 2) through 3, 4, 5, 6, and 7, interpreting position by
gradual increase in length. Overall length ranges from 15.5-29.8 cm. Only one (the
seventh?, field label B) has any significant portion of the neural arch attached to it. The
centra are strongly opisthocoelous and are dorsoventrally compressed. While
compression by the surrounding clay may be responsible, the centra do not appear to be
significantly more compressed than those of other sauropods, such as Camarasaurus
(Osbom and Mook, 1921) and Diplodocus carnegeii (Hatcher, 1901).
26
The centrum of the axis, or second cervical vertebra (field label NGH-11; Fig.
11), was one of the first elements recovered from the site. The centmm appears to have
been in the weathering zone for some time, for the texture of the bone and concretion
resemble the material collected as surface float. It differs from the other centra in being
mediolaterally compressed. It has a well-developed cup for articulation with the
succeeding vertebra. There is an anterior ball, as well as an ovate protmsion of bone
attached to the anterior margin, projecting ventrolaterally. This protmsion is the odontoid
process, which articulates with the preceding atlas (not present) and identifies the
centrum as belonging to the axis. Pleurocoels are visible along the lateral edges. A
shallow channel (for the spinal cord) runs along the midline of the dorsal surface.
Measurements are given in Table 2.
The third (?) cervical centrum (field label Ka; Fig. 12) appears to be complete
except for a ring around the center, which was damaged by acid infiltration. The
pleurocoels are deep (average = 2.3 cm), well-defined, and extend along more than half of
the lateral margins of the centrum. The ventral cup is deep (3.0 cm). When resting flat
on its ventral surface, the dorsal margin of the cup appears to extend farther posteriorly
than the ventral margin. The ventral surface of the centrum is slightly concave. Partial
exposure of the posterior end of the dorsal surface with an airscribe reveals the bone to be
complete, with little concretion infiltration. The articular surface for the neural arch is
also partially visible. Measurements are given in Table 2.
The fourth (?) cervical centrum (field label M2; Fig. 13) was found alongside the
left ischium. The dorsal margin of the posterior cup extends farther posteriorly than the
27
ventral margin does. A burrow cast (maximum diameter 3.6 cm) protmdes up from the
anterodorsal surface, and presumably tunnels into the bone. Measurements are given in
Table 2.
The fifth (?) cervical centmm (field label HI; Fig. 14) appears to be complete.
Part of the ventral border of the posterior cup appears to be missing, but the tme outline
of the cup is too encmsted with concretion to be certain. Two wing-like parapophyses
protmde from the mid region of the ventral margin of the centmm. The proximal ball and
distal cup, for articulation with the preceding and succeeding centra respectively, are well
developed. Measurements are given in Table 2.
The sixth (?) cervical centmm (field label CI; Fig. 15) has not been prepared with
acid washings as of this time. Much of the concretion has a yellow-orange tint, which is
also seen on several dorsal neural arches (E2 and C). This centrum resembles the others
in being complete, dorsoventrally flat, and strongly opisthocoelous, but the ventral
margin of the posterior cup extends farther posteriorly than the dorsal margin. The
pleurocoels are marked by slight indentations on either side, but may be filled with some
concretionary material. This centrum, like the fifth (?) centmm, has two wing-like
parapophyses protmding laterally from the margins of the ventral surface. Measurements
are given in Table 2.
The seventh (?) cervical centmm (field label B; Fig. 16) is the only cervical
centmm that has a portion of the neural arch attached to it. The centmm is mostly
complete, though both articular ends are distorted and the specimen shows the same
dorsoventral cmshing as the other centra. The anterior ball appears to be incomplete, and
28
the posterior cup is covered in concretion, with attached fossilized burrow casts fiirther
distorting it. The parapophyses and diapophyses are present on both sides, enclosing long
(13.0 ± 0.5 cm) and deep (4.0 ±0.5 cm) pleurocoels along the lateral margins of the
centmm. The left pleurocoel is obstmcted by a fossihzed burrow cast (ca. 3.0 cm in
diameter) attached to the overlying diapophysis. The ventral surface is slightly concave,
as in the other specimens. A portion of the right tuberculum appears to still be attached
to the right diapophysis. Of the neural arch, only the base of the neural spine, partial
prezygapophyses, and partial postzygapophyses are preserved. The dorsal surface of the
specimen is in poor condition, apparently having been exposed to the weathering zone.
The breakage surfaces marking the location of the zygapophyses are clean breaks,
indicating recent separation. Unfortunately, the processes have not been identified in any
of the float material collected. Measurements are given in Table 2.
Cervical Neural Arches
Six cervical neural arches have been identified in the collection. At this time,
only one can definitely be paired with one of the cervical centra, as specimen B consists
of a nearly complete centrum and a partial neural arch (see above). Sauropod neural
arches are comprised of thin laminae of bone, thus allowing for strength without adding
weight (Mcintosh, 1990a). Their delicate nature, combined in this case with the
concretion that coats them, makes preparation of these elements difficult.
The cervical neural arches are similar in basic design to most other sauropods,
with prezygapophyses extending anteriorly on finger-like projections, a neural spine that
29
rises posteriorly, and postzygapophyses that are short and attached directly to the
posterior surface of the neural spine. Comparison of overall shape with those of
Camarasaurus (Osbom and Mook, 1921), Apatasaurus louisae (Gihnore, 1936), and
Qs^QcmWy Diplodocus carnegeii (Hatcher, 1901) suggests these are anterior neural arches,
most likely belonging to vertebrae between the third and seventh cervicals. Although
Apatosaurus, Camarasaurus, and Diplodocus belong to different, largely Jurassic
families of sauropods, no titanosaurid cervical series has been described in the literature
that can be cited for comparison (the cervical series described by Powell, 1986, is of a
different morphology pertaining to an unknown titanosaurine).
The smallest and most complete of the cervical neural arches is possibly the third
(field label O; Fig. 17). The neural spine has been distorted such that it leans about 50° to
the right of a tme vertical orientation. This deformation probably occurred after burial
and fossilization, as the neural spine is intact. The prezygapophyses extend forward on
finger-like projections. Their articular surfaces cannot be observed due to concretion.
The postzygapophyses are obscured, but appear to be located on short projections
protruding posteriorly from the posteroventral portion of the neural spine. Measurements
are given in Table 3.
A partial cervical neural arch (possibly the fifth) is preserved in float material
(field label H2). This specimen lacks both prezygapophyses and both postzygapophyses,
and the surface has been weathered. However, the neural spine and body of the neural
arch are intact and articulated, and the specimen seems to be in good condition. The
30
neural spine is distorted 40° right of a tme vertical orientation, and there is no evidence of
a concavity along its posterior edge. The basic dimensions of the specimen are in Table
3.
A fragmentary cervical neural arch comprised only of the anterior half with both
prezygapophyses and the left side of the posterior half may represent part of the sixth
vertebra (field label C2). The neural spine and postzygapophyses are not present, and
only one pedicel can be readily identified. The specimen is covered in the radial-fibrous
calcite concretion, and it was at least partially exposed to the weathering zone as
indicated by the textural difference of the distal part of the ventral surface. No fiirther
preparation is planned unless the specimen can be more completely reassembled from
float material. The specimen has a maximum length of 23.2 cm and a maximum width of
17.3 cm.
The seventh (?) cervical neural arch is the only one attached to a centrum
(possibly the seventh, field label B; Fig. 16). This is a partial specimen, with the
postzygapophyses and a partial neural spinr being all that remains. The neural arch is
distorted such that the left side is slightly elevated relative to right side. The neural spine
is tilted to the right. The postzygapophyses are longer than in the specimens described
above, in accordance with the larger size of this specimen. The neural spine appears to
reach its summit in the middle, rather than at the posterior end, of the neural arch. Such a
change in morphology is seen in the cervical series of many sauropods at the 7* - 9*
position. The change in neural spine morphology, combined with its size relative to the
other cervical neural arches present, places this specimen posterior to the sixth vertebra.
31
The cervical neural arch possibly pertaining to the eighth vertebrae (field label E;
Fig. 18) has been reassembled, but no fiirther preparation has been conducted. The
specimen seems largely complete, with the neural spine, both prezygapophyses, one
postzygapophysis, and both pedicels present. The neural arch has been distorted so that it
leans about 40° left of a tme vertical orientation. The neural spine appears quite massive;
there may be a large amount of concretion attached, thus expanding the neural spine
transversely. Similar to the third (?) cervical neural arch (field label O), the
prezygapophyses protmde anteriorly on finger-like projections, and the one
postzygapophysis present appears to rise near the base of the neural spine via a short
protmsion or lamina of bone. There is also a deep concavity along the posterior midline
of the distorted neural spine. This concavity may have been formed by a lamina of bone
extending from the neural spine ventrally to the postzygapophyses, leaving a depression
along the midline where it bifiircates to extend to both postzygapophyses. Measurements
are given in Table 3.
The largest of the cervical neural arches (field label G) is badly damaged and may
pertain to the ninth vertebra. Overall, the specimen resembles the other cervical neural
arch specimens, with prezygapophyses protmding forward, postzygapophyses short and
near the posterior base of the neural spine, and a neural spine that is massive and leans
about 40° to the right of a vertical orientation, with a deep concavity on its posterior
surface. Maximum length of the specimen is 30.1 cm.
One small partial cervical rib (field label N) was recovered. Its small size
suggests that it pertains to one of the anteriormost cervical vertebrae.
32
Dorsal Centra
One anterior dorsal centmm has been identified in the float material (field label J).
The centmm is dorsoventrally compressed, possibly due to post-burial deformation. A
shallow groove mns along the midline of the dorsal surface, defining the neural canal.
The ventral surface is concave, giving the centmm the "classic" spool-like outline. The
anterior and posterior ends possess ball and cup articular surfaces respectively, as in the
cervicals, but they are not as well developed. Measurements include the following:
maximum length = 11.8 cm; maximum width =14.5 cm; maximum height = 6.4 cm.
Dorsal Neural Arches
Four dorsal neural arches (field labels A, C, E2, and Z) are nearly complete, and
are covered in the radial-fibrous calcite concretion. There is a good deal of variation in
the morphology of these elements, indicating that they come from different areas along
the back. Nomenclature for the morphology of dorsal neural arches is from Mcintosh
(1990a).
An anterior dorsal neural arch (field label E2; Fig. 19) was prepared with acid
washings (total of 35.25 hours submerged). The transverse processes are nearly
complete, with the tip of the left diapophysis broken off The pedicels are slightly
damaged, but otherwise the specimen is complete. There are well-developed fossae on the
lateral surfaces of the pedicel between the centroparapophyseal and centrodiapophyseal
laminae, as well as at the posterior base of the transverse processes between the
centrodiapophyseal and lateroinfrapostzygapophyseal laminae. The neural spine is tilted
33
posteriorly about 40°, and both the prezygapophyses and postzygapophyses are short and
attached directly to the anterior and posterior base of the neural spine, respectively.
Measurements are given in Table 4.
An additional anterior dorsal neural arch (field label C; Fig. 20) is covered in
"fibrous-style" concretion that has not been prepared with acid washings. It possesses a
morphology very similar to the anterior dorsal described above (field label E2), and its
size suggests that it may immediately succeed this specimen in the dorsal series. The
transverse processes and neural spine are complete, but the pedicels are damaged, and the
postzygapophyses are obscured by attached fossihzed burrow casts and the "fibrous-
style" concretion that covers the bone. A large additional unidentified bone mass was
collected with this specimen, and it rests along the right margin of the neural spine and
dorsal surface of the right transverse process. The mass is not part of the regular anatomy
of the neural arch and represents a portion of a different bone. Measurements are given in
Table 4.
A posterior dorsal neural arch (field label Z; Fig. 21) is well preserved. The
neural spine is nearly vertical, and the prespinal lamina running along the midline of the
anterior face of the neural spine has been tilted to the right about 25°. This distortion is
mirrored by a slight twisting of the anterior face to the right as well. The neural canal is
arch-shaped and well-defined by the foot-like pedicels, which are not as tall as in many
other sauropods. Both prezygapophyses are preserved above the pedicels at the base of
the transverse processes. Though mostly filled with concretion, there are depressions
34
between the prezygapophyses and the supradiapophyseal lamina rising to the neural
spine. The prespinal lamina rises from the posterior base of the prezygapophyses and
mns vertically along the midline of the neural spine. The neural spine is simple and
spatulate in anterior view. The transverse processes are directed upward from the base of
the neural spine. They are not equal in size owing to distortion. The parapophysis is
located high up on the precentroparapophyseal lamina. On the posterior surface of the
neural spine, a concave groove begins 7.2 cm below the crest and mns down the length of
the spine to the level of the postzygapophyses, deepening as it goes. There is no
postspinal lamina. The postzygapophyses are inclined laterally, just above the base of
the neural spine. Lateral fossae lie anterior to the postzygapophyses, separating them
from the bases of the transverse processes. Postzygadiapophyseal laminae are not well
developed. Another pair of lateral fossae are located along the sides of the pedicels,
between the precentroparapophyseal laminae and centrodiapophyseal laminae. There are
no hyposphene/hypantmm articulations apparent. Measurements are given in Table 4.
The largest of the dorsal neural arch specimens (field label A, Fig. 22) was one of
the first elements collected, recovered from the weathering zone. The neural arch seems
to be nearly complete, though several edges and comers appear to be wom, and the entire
specimen is covered in "fibrous-style" concretion. The prezygapophyses and
postzygapophyses are present, but obscured by concretion. Their position is the same as
in the other dorsal neural arches. The bone has been distorted such that the pedicels lean
inward, closing off the ventral opening of the neural canal. The posterior portion of the
left pedicel is not present. The neural spine is tilted slightly posteriorly, and the entire ,
35
spine is covered with concretion and attached remnants of burrow casts. The transverse
processes are directed outward from the anterior margin of the base of the neural spine
and extend straight out to either side. No parapophyses are apparent. Fossae occur along
the lateral margins of the pedicels and between the lateroinfrapostzygapophyseal laminae
and the base of the neural spine. Also, a deep excavation lies between the anterior base of
the neural spine and the prezygapophyses. The large size of the specimen, combined with
the orientation of the transverse processes, indicates that this neural arch is one of the
posteriormost in the dorsal series, perhaps the first or second dorso-sacral vertebra. A
similar specimen, comprised only of the neural spine and the supradiapophyseal laminae
is in the Texas Memorial Museum collection (TMM 41398-1) labeled as a posterior
cervical neural spine. However, given the broad lateral extent of the transverse processes
in the Texas Tech specimen, I do not agree with this identification. Measurements are
given in Table 4.
Appendicular Skeleton
Coracoid
The left coracoid (field label NGH-10; Fig. 23) is almost completely free of
concretion. It is mostly complete, except for parts of the anterior and ventral margins.
The convex lateral surface is perforated by the coracoid foramen that passes
posterodorsally through the bone and opens near the dorsal margin of the concave medial
surface. The anterior margin is thin (0.7 cm). This thickness is constant posteriorly
along the margin of the bone, until just below the level of the coracoid foramen. From
36
there, the bone thickens posteriorly, reaching a maximum thickness of 7.0 cm on the
mgose and roughened posterior margin, which forms part of the glenoid cavity (Gilmore,
1946). The dorsal margin is smooth and slightly undulose; the coracoid is fiised to the
scapula along this margin in adult individuals (e.g., USNM 15560; Fig. 8). Other
measurements include the following: maximum length = 19.3 cm; maximum width =
15.3 cm; foramen diameter =1.9 cm.
Humems
The left humems (field label L; Fig. 24) is complete except for a small (6.5 cm by
2.8 cm) section of the proximolateral comer. It resembles the humems described by
Gilmore (1946, USNM 15560) in having a very straight lateral edge, a deep olecranon
groove, and well-defined capitellum and trochlea for articulation with the radius and ulna,
respectively. It differs from USNM 15560 in not having a massive deltopectoral crest.
However, Gilmore mentioned that the deltopectoral crest of USNM 15560 appears to
have been laterally enlarged by post-burial deformation. Also, the deltopectoral crest,
being a muscle attachment site, need not be fiilly developed in juveniles, but can increase
in size as the animal grows. The anterior face of the proximal half of the specimen is
concave, as is the outline of the medial edge of the specimen. Although covered in the
microcrystalline calcite concretion, the processes and crests are easily discemed on this
specimen. Both ends are mgose and roughened, a condition typical of sauropod limb
37
bones. The two to three parallel cracks that mn across the middle of the shaft are thought
to have been caused by compression of the surrounding clay. The shaft is ovate in cross-
section at mid-length. Measurements are given in Table 1.
Ischium
The ischium (field label M; Fig. 25) belongs to the left side of the pelvic girdle. It
has a long flat surface for conjoinment with the right ischium, and a broad surface for
articulation with the left pubis (Gilmore, 1946). The distal extension of the ischium is
very short in Alamosaurus, being subequal in length with the ilial articular peduncle.
This is unlike other sauropods (including titanosaurids), in which the distal process is
subequal to or longer than the shaft and ilial articular peduncle combined. This specimen
matches the descriptions and figures of the ischia of Alamosaurus specimens USNM
10487 (Gihnore, 1922) and USNM 15560 (Gilmore, 1946). The morphology of the
ischium, along with the humems, confirm that this individual belongs to the species
Alamosaurus sanjuanensis. Measurements include the following: total length = 37.1
cm; width at mid-shaft =14 cm; distance from distal end of distal process to
dorsoproximal comer = 34 cm; distance from proximal end of ilial articular peduncle to
ventrodistal comer = 30.2 cm; maximum width of distal end of the shaft = 19.0 cm;
maximum width of proximal end of the shaft =18.6 cm.
38
Fibula
The left fibula (field label E3; Fig. 26) is well preserved. This element was
covered in "fibrous-style" concretion that was ahnost completely removed with acid
treatments and an airscribe, though some concretion remains at either articular end. The
anterior edge of the proximal end is missing, and a short section of burrow cast is
attached to the anterolateral margin. The shaft is roughly circular in cross section near
the distal end, but becomes mediolaterally compressed in the upper half of the specimen,
resulting in an elongate ovate cross section (long axis mnning anterposteriorly).
Measurements include the following: maximum length = 48.7 cm; maximum
anteroposterior width, proximal end = 13.3 cm; maximum anteroposterior width, distal
end = 8.6 cm; minimum shaft circumference = 15.0 cm; minimum shaft diameter = 5.6
cm (shaft is not quite circular at this point, measurement was taken along short axis).
Part of the proximal end of the right fibula is also preserved (field label NGH-12).
This specimen has the same mediolaterally flattened ovate cross section as the left fibula.
It represents the portion of the bone where the proximal end of the shaft meets the antero-
posteriorly expanded head. There is little concretion on the bone, which was collected as
surface float to the south of the main collecting locality. The specimen is 17.2 cm long.
Tibia
The distal portion of the left tibia is preserved, (field label Y; Fig. 27). The distal
end, heavily coated in concretion and burrow casts, is massive and blocky in shape. The
tibia is broken very close to the distal end. At the break, the shaft's cross section is ovate
39
in shape, with a well-defined boundary between cancellous and cortical bone.
Identification was accomplished via comparison to a large Alamosaurus distal tibia
(TMM 42495-4), and a distal tibia assigned to Titanosaurus indicus by von Huene and
Matley (1933, plate 1, Fig. 4). Measurements include the following: maximum length =
ca. 21.0 cm; shaft diameter = 6.0 cm by 4.0 cm; measurements of distal end are inflated
by attached fossilized burrows.
Part of the distal end of the right tibia is also preserved (field label NGH-12).
This specimen is free of concretion and burrow casts, thus, the articular notch for the
astragalus is readily identifiable. This specimen, like the left tibia described above, has a
very circular cross section with a well-defined boundary between cancellous and cortical
bone. The right tibia was recovered to the south of the main collecting locality, alongside
the partial right fibula. Measurements include the following: maximum length =13.5
cm; cross sectional diameter of shaft = 5.8 by 4.1 cm.
Taphonomy
The lack of duplication of elements of ihQ Alamosaurus remains and uniform size
variation of elements suggest the presence of only one individual. The remains were
completely disarticulated prior to burial; the two forehmb elements (humems and
coracoid) are the only specimens that maintained any semblance of their original position
with regards to one another (Fig. 10). All the elements are from the left side of the body
except for the partial tibia and fibula, which were displaced to the south of the main
collection site. The degree of weathering to which the bones were subjected prior to
40
burial cannot be accurately ascertained until the concretion can be more thoroughly
removed. There is no direct evidence, such as bone damage (on the exposed specimens)
or shed carnivore teeth, of scavenging. However, such damage may be obscured by
concretion, and some parts of the body, especially the limbs, may have been carried away
by scavengers. That the carcass was scavenged by burrowing animals is certain, given
the orientation of the pervasive burrows near, and sometimes into, the bones, and the
presence of bone chips within the burrows.
The specimens were broken into many pieces along smooth breaks, with the
pieces remaining in their original position and orientation. Thus, breakage occurred after
burial, and can be attributed to the compaction of the surrounding clay. The remains
were entombed in fine-grained mudstone, indicating burial near the place of death with
little or no transport (Behrensmeyer, 1975). Preservation of the deUcate laminae of the
cervical and dorsal neural spines also indicates that the bones underwent little transport.
However, the disarticulated nature of the remains necessitates that some form of pre-
burial transport occurred.
Voorhies (1969) defined transport groups for mammaHan skeletal elements, based
on relative ease of transport. However, it is difficult to apply these directly to sauropods.
The most obvious difference is in the skull and jaws, which are much larger in proportion
to the rest of the skeleton in mammals than in sauropods. Thus, while mammalian crania
are relatively resistant to transport, it is likely that sauropod crania would be moved easier
than most other skeletal elements. This assertion is supported by the general scarcity of
sauropod skulls, even when most other skeletal remains are present.
41
The orientation of the bones in the field suggests a weak current may ha\'e
affected the remains prior to burial. Figure 28 illustrates a bimodal distribution of bone
orientations, with the two directions perpendicular to each other. Bones unaffected by
weak currents/running water have their long axes oriented parallel to flow, while bones
affected by the currents have their long axes oriented perpendicular to flow. The lack of
small, easily transported elements in the collection also suggests current activity, as such
elements are quickly winnowed out of a site.
The cervical neural arches were all found dorsal side up, and the dorsal neural
arches were all found anterior face up. These positions seem to represent the most stable
orientation for these elements. In the field, the specimens laid along a north-south
transect, tapering to the northwest in the northem area of the site. Specimens in the
southem half of the site are those covered in the "fibrous-style" concretion, while those in
the northem half are covered in microcrystalline calcite concretion.
The animal probably died in a nearshore lake environment, with its body mired on
the left side in mud either in shallow water or just onshore. Exposure of the bones on the
surface for a period of time would result in deterioration of the outer surface of the bone,
as seen on those specimens in which concretionary material has infiltrated the bone.
Although there is no direct evidence of scavenging, it still could account for the missing
limbs and flanks, as well as the disarticulation of the elements not eaten or otherwise
destroyed. Weak currents affected the bones, winnowing out the easily transported
elements and reorienting those that remained. Charophyte algae induce precipitation of
carbonate material during photosynthesis (Lerman, 1978), which may explain the
42
concretion that coats the fossils. It is possible that the lake underwent this cycle, from
periods of ephemeral chemical characterization, to periods of clastic and biologic
deposition, in accordance with oscillations from semi-arid to semi-humid conditions,
which are thought to have occurred in the Big Bend region during the Late Cretaceous.
Ontogeny
Five nearly complete and one partial humeri, including one from the present
specimen, have been attributed to Alamosaurus sanjuanensis, allowing a mdimentary
ontogenetic study of this limb bone to be conducted. Obtaining the allometric coefficient
(k) using Huxley's (1932) equation involves plotting the log-transformed measurements
against one another and taking the slope of the Hne. If, as in the present case (owing to
individual variation), the data do not fit a straight line, mathematical manipulation is
necessary to derive a line as a best-fit line. For this study, the method of reduced major
axes (RMA) was used. The method of least squares requires designation of independent
and dependent variables. RMA avoids this difficulty by deriving the slope and y-
intercept of the appropriate line with the following equations:
slope (a)= [ Z / - y(£y)] [Zx' - x(Sx)]
y-intercept (b)= y - xa
where x and y are the log-transformed values of any two sets of measurements (e.g., total
length X and proximal width y). No statistical tests of significance were applied to this
43
data set. With so few specimens, the data set would likely not prove significant at any
reasonable confidence interval. Lack of specimens is often a problem in such analyses in
vertebrate paleontology. Thus, one must make do with the material available.
Five measurements were taken on the humeri; length, proximal width, distal
width, shaft circumference, and shaft diameter (Table 1, Table 5). It should be noted that
these measurements are defined by extremal points, which are not tme anatomical
landmarks. The measurements were log-transformed, and length was used as the basis
for comparing the other four measurements In each case, the allometric coefficient (a)
was found to be greater than one (Table 6; Fig. 29-30). This signifies that positive
allometric growth occurred; that is, each of the other measurements increased more
rapidly relative to the increase in length. However, the a values are close to 1, indicating
positive allometric growth was not pronounced, and for some measures, the increase was
almost isometric (a=l, measurements changed at the same rate relative to one another).
The results were checked with a best fit line applied to the plots initially made for
analysis via Huxley's equation, which have different slopes and intercepts. Assuming the
best fit line approximates the tme line, the two methods show comparable results (a
versus k values. Table 6). Proximal width has the largest coefficient in both cases. The
values for shaft diameter are both less than shaft circumference, which is expected since
circumference increases as the diameter is multipUed by pi. Distal width is the only
disparate character, with the best fit line resulting in a higher coefficient than the RMA
line. Observation of the specimens reveals that the distal end does not expand nearly as
44
much as the proximal end with grovv^h. This suggests that the RMA value is more
reasonable. Positive allometric grov^h of the proximal and distal transverse measures
illustrates that the larger humeri are more "bow-tie" shaped in outline.
Comparison with Other Sauropod Taxa
The following is a comparison of Alamosaurus sanjuanensis with several other
sauropod taxa reported in the literature. The comparison is limited to the elements
present in Alamosaurus specimen TMM 43621-1, and includes several sauropods that are
well-defined taxa and are known from material suitable for comparison with this
specimen of Alamosaurus.
The cervical centra of sauropods seem typically uniform. They are dorsoventrally
compressed, strongly opisthocoelous, and possess large pleurocoels on their lateral
surfaces, Malawisaurus dixeyi being an exception to the latter (Jacobs et al., 1993). The
general sauropod condition fits that observed in the cervical centra of Alamosaurus (Figs.
11-16).
The cervical neural arches of sauropods show more marked variation (Fig. 31).
Members of the Diplodocidae and Camarasauridae possess bifiircated neural spines. This
bifurcation can begin as far anteriorly as cervical 3 and can continue throughout the
presacral series (e.g., Camarasaurus lewesi, Mcintosh et al., 1996). This bifiircation is
not seen in Alamosaurus or other titanosamids. In lateral outline, Alamosaurus cervical
neural arches are similar to those of many other sauropods, such as Camarasaurus
supremus (Osbom and Mook, 1921), Diplodocus carnegii (Hatcher, 1901), Apatosaurus
45
excelsus, and Apatosaurus louisae (Gihnore, 1936). The cervical neural arches
included in specimen TMM 43621-1 most strongly resemble cervical neural arches 3-9 of
these taxa in having neural spines that are tallest posteriorly, a neural arch that is longer
than it is tall, prezygapophyses that extend forward on finger-like projections, and short
postzygapophyses attached just above the posterior base of the neural spine. In
Apatosaurus, Camarasaurus, and Diplodocus these characters begin to change at
cervicals 7-9, such that the neural spines are taller and often reach their peak more
anteriorly. This has the effect of changing the lateral outline of the neural spine from that
of an ahnost right triangle to a pyramidal form. The partial neural spine attached to the
seventh (?) cervical centrum has this "pyramidal" morphology, indicating its placement in
the cervical series is definitely posterior to cervical 6.
One major exception to the basic sauropod cervical design is found in the
titanosaurid Saltasaurus loricatus. As described and illustrated by Powell (1986, 1992),
the neural spine is highest anteriorly, with postzygapophyses extending backwards on
finger-like projections, while the prezygapophyses are short and attach in front of the
anterior base of the neural spine. The neural spines do get taller in the posterior part of
the cervical series, as do the cervicals of Titanosaurus colberti, the only other titanosaurid
with multiple cervical elements described and illustrated in the literature, though they
have the normal zygapophyses morphology (Jain and Bandyopadhyay, 1997). This
"reversed cervical" condition is also present in Euhelopus zdanskyi {=Helopus zdanskyi,
Wiman, 1929) and two indeterminate specimens assigned to the Titanosaurinae illustrated
in Powell (1986, lamina 13 and 14).
46
Few dorsal vertebrae of titanosaurids have been described in the literature. J.
Powell has announced the recovery of several nearly complete titanosaurid skeletons
from South America, but this material has not been formally described. The anterior
dorsal neural spines of genera such as Apatosaurus, Camarasaurus, and Diplodocus are
bifiircated, the bifiircation extending posteriorly to different degrees in different species.
Posterior dorsal neural spines in these taxa are tall and straight. The dorsal neural spines
of Saltasaurus loricatus (Powell, 1986, 1992), Titanosaurus colberti (Jain and
Bandyopadhyay, 1997), and an unidentified specimen (Titanosaurinae indet., lamina 15,
Powell, 1986) have non-bifiircated neural spines tilted posteriorly, as in the present
Alamosaurus specimen (the condition being strongest in Saltasaurus; Fig. 32). These
taxa (information not available for the indeterminate titanosaurine specimen) also have
transversely wider neural spines in the anterior portion of the dorsal series; those farther
back are more gracile. Following this pattem, in the present specimen E2 and C are
anterior dorsal neural spines, with Z located posterior to them. A is thought to be a
posterior dorsal based on its large neural spine and broad transverse processes. However,
a similar element in the TMM collection (TMM 41398-1), possessing only the neural
spine and the supradiapophyseal lamina, is identified as a posterior cervical or anterior
dorsal neural spine. This interpretation is thought to be invalid.
The ischium of sauropods can be divided into three basic parts. The shaft is the
central, blocky region that articulates with the pubis along its anterior margin. A
peduncle extends posterodorsally from the dorsal margin of the shaft and articulates with
the ilium, and a distal process extends posteroventrally from the ventral margin of the
47
shaft, articulating with the opposite ischium along its ventral border. In most sauropods,
the length of the distal process is equal to or greater than the length of the shaft and ilial
articular peduncle combined. However, this is not the case in Alamosaurus sanjuanensis
(Fig. 7). The ischium of Alamosaurus possesses a distal process that is subequal in
length to the ilial articular peduncle, giving the bone a symmetrical lateral outline unlike
the ischia of other sauropods. In other titanosaurids, such as Malawisaurus dixeyi (Jacobs
et al, 1993), Titanosaurus colberti (Jain and Bandyopadhyay, 1997), and Andesaurus
delgadoi (Calvo and Bonaparte, 1991) the distal process is not as elongate as in non-
titanosaurid sauropods, but is still noticeably longer and broader than the ilial articular
peduncle when seen in lateral view. The distal process of the ischium of Saltasaurus
loricatus figured by Powell (1986, 1992) is incomplete and its length cannot be
determined. The short distal process of Alamosaurus is not an ontogenetic character, as
the ischia of USNM 10487 and USNM 15560 (both adult Alamosaurus individuals) have
the same form. Thus, this trait can be considered autapomorphic for ^. sanjuanensis.
No distinct features have been noted for the coracoid, but the humems is different
from the typical sauropod humems (Fig. 33). In genera such as Apatosaurus,
Camarasaurus, and Diplodocus, the humems has concave lateral and medial margins,
giving the bone a "bow-tie" outline in anterior view. The humems of the present
specimen has a lateral margin that is much less concave in anterior view, being straight
instead. In this aspect, Alamosaurus most closely resembles Brachiosaurus (Janensch,
1914) and Ceteosaurus (= Cetiosaurusl, Phillips, 1874). This trait may be partially
related to the degree of expansion of the humeral head, which expands during growth. In
48
aduh Alamosaurus individuals, the humems of TMM 41541-1 (total length = 150.3 cm)
does have a sHghtly more "bow-tie" outline, but USNM 15560 (total length = 136 cm)
does not.
Being incomplete, the hindlimb elements are difficult to compare in detail (Fig.
34). The left fibula appears to have a form similar to most other sauropod fibulae
(especially Saltasaurus loricatus, Powell, 1986, 1992). The left distal tibia strongly
resembles a distal tibia assigned to Titanosaurus indicus. (von Huene and Matley, 1933).
49
Fig. 6 Skeletal reconstmction of a sauropod dinosaur by W. Langston, Jr. (1974). Elements belonging to the Alamosaurus specimen described by Gilmore (1946) are shown in black.
50
( a ) ( d )
Fig. 7 Comparison of sauropod ischia: (a) Camarasaurus, (b) Apatosaurus, (c) Diplodocus, (d) Alamosaurus (Mcintosh, 1990a).
51
(a) ( b )
Fig.8 Alamosaurus sanjuanensis scapula: (a) USNM 10486, the type specimen, (b) USNM 15560 (a from Gihnore, 1922; b from Gihnore, 1946).
52
Fig. 9 Unidentified specimen with juvenile bone textiu-e visible (field label K,+2+3» scale bar = 5 cm).
53
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55
p a
Fig. 12 The third (?) cervical centrum, in dorsal view (scale bar = 5 cm).
56
p b
Fig. 13 The fourth (?) cervical centmm, in dorsal view (scale bar = 5 cm).
57
Fig. 14 The fifth(?) cervical centrum, in (a) lateral and (b) dorsal views (scale bar = 5 cm).
58
Fig. 15 The sixth (?) cervical centmm, in ventral view (scale bar = 5 cm).
59
Fig. 16 The seventh (?) cervical vertebrae, in lateral view (scale bar = 5 cm).
60
Fig. 17 The third (?) cervical neural arch, in (a) lateral and (b) dorsal views (scale bar = 5 cm).
61
Fig. 18 The eighth (?) cervical neural arch, in (a) posterior and (b) dorsal views (scale bar 5 cm).
62
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Fig. 21 Posterior dorsal neural arch, in (a) posterior, (b) lateral, and (c) anterior views (scale bar = 5 cm).
65
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Fig. 24 Left humems, in anterior view (scale bar = 5 cm).
68
Fig. 25 Left ischium, in lateral view (scale bar = 5 cm).
69
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Fig. 26 Left fibula, in medial view (scale bar = 5 cm).
70
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71
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72
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73
Length versus Proximal Width, Ln Transformed Values
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Fig. 30 Bivariate plots of humems length versus (a) proximal width and (b) shaft circumference used for RMA.
74
(a)
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Fig. 31 Comparison of saurood cervical vertebrae in lateral view: (a) Camarasaurus, (b) Apatosurus, (c) Diplodocus, (d) Saltasaurus (a-c from Mcintosh, 1990a; d from Powell, 1992).
75
(a) ( b )
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Fig. 32 Comparison of sauropod anterior dorsal vertebrae in posterior view: (a) Camarasaurus, (b) Apatosaurus, (c) Diplodocus, (d) Saltasaurus (a-c from Mcintosh, 1990a; d from Powell, 1992).
76
( a ) ( c )
( d ) ( e )
Fig. 33 Comparison of sauropod humeri in anterior view: (a) Camarasaurus, (b) Apatosaurus, (c) Diplodocus, (d) Alamosaurus, (e) Saltasaurus (Mcintosh. 1990a).
77
( a ) ( b ) Tub. la l
( e ) ( f )
Fig. 34 Comparison of sauropod fibulae (a-c) and tibiae (d-e): (a) Camarasaurus, (b) Apatosaurus, (c) Saltasaurus, (d) Titanosaurus, (e) Camarasaurus, (f) Apatosaurus (a, b, e, and f from Mcintosh, 1990a: c from Powell, 1992: d from von Huene and Matley, 1933).
78
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o "^ CN
00 oo »—( • y—(
^ IT) 1—1
1.29
U-i
ON 1—(
OO r-r-» — t
o c> vo
T—1
1
uo ON
J H
vo OO
q » — «
CN CN f-H
CN OO
«n
CN od CO
(N '«t "* •
r--r-CN
<N
vo ^ »—1
o o\ (N
-"i-CN 0\ '"'
o *
00
5-4
C7N hJ H
CN VO CO
""
p CO CN
vo 0C3
vo CN r--
ON t VO . f—i
00
r-^
<
g
<
2
-"f CO t-H
CN
cq
136
o vo
1—1
^ (
C/3
CN CN CO « — 1
q 1—1
cs
o cs oo
vd vo
.66
,
r-«n ""I-
o
i> T—t
o ON wo
r-r-1-H CN
CO
o
1-H 1
»-H
Tf
H
z
< z
< z
< z
< z
< z
^ ^ r-
w-j
g
u o G u t-l .o CH fH
H
U
cir
<a cd x : CO II u 00
l-l (D ••-»
<U
a
<« ed X! CO
II P 00
g
13
X
2 p.
Xi • * - >
. 1 - 1
• « - <
CO •^H
i
83
Table 6 Slope and intercept values for RMA plots
xavg yavg y-intercept slope (RMA) slope (Huxley) LvsPW 1.932 1.503 -0.966 1.278 1.249
LvsDW 1.932 1.426 -0.649 1.074 1.185
LvsSC 1.932 1.5796 -0.645 1.151 1.103
LvsSD 1.932 1.084 •1.118 1.140 1.078
L= length SC= shaft circumference
PW= proximal width SD= shaft diameter
DW= distal width
84
CHAPTER V
STABLE ISOTOPE ANALYSIS
Procedure
Carbonate samples were collected from the Grapevine Hills locality and their
stable carbon and oxygen isotope ratios were analyzed. This was done in order to
compare results with carbonate isotope data collected at other nearby sections. Soil
carbonate nodules were collected along a measured section that spans the K/T boundary
at the field site (Fig 35). The outer rind of the nodules may have experienced weathering
alteration and must be removed. Also, some nodules contain coarse crystalline calcite
that forms in shrinkage cracks within the nodule, which also must be removed. The
nodules were broken apart with a rock hammer in order to recover appropriate material
(not the coarse crystalline or outer rind) for stable carbon and oxygen isotope analysis.
The carbonate samples were prepared following the methodology of McCrea
(1950). First, the samples were cmshed to a fine powder with a mortar and pestle. The
samples were placed in ceramic boats and roasted in a horizontal tube fiimace at 475-500°
C for 30 minutes. This removed any organic carbon in the samples, ensuring the carbon
dioxide derived from the samples comes from the calcium carbonate. Twenty-five to
thirty-five milligrams were weighed out and sealed in reaction vessels, with 30 ml of
100% phosphoric acid solution in the other half of the vessel. The tubes were hooked to a
vacuum line and evacuated for 2 hours. After being closed, the tubes were placed in a
water bath for 15 minutes to stabiHze the samples' temperature at 25.2° C. The tubes
85
were then tilted as to allow the phosphoric acid to begin reacting with the carbonate
sample. The tubes were left in the water bath for 48 hours to allow the sample to react
completely.
The tubes were reattached to the vacuum line in order to recover the evolved
carbon dioxide. The gas was passed through a series of traps containing liquid nitrogen
and dry ice slushes to purify the carbon dioxide. The purified gas was saved in another
sample tube and its carbon and oxygen isotope ratios were analyzed with a mass
spectrometer (SIRA-12 IRNS). Results were calculated using both the SMOW and PDB
standards. All results presented here are given relative to PDB.
Mass spectrometry results show a strong correlation between the carbon and
oxygen isotope content of the nodules (Fig. 36). Analyzed separately, the 6 CpDB and
5 0pDB measurements show similar trends as one moves up through the section (Figs. 37-
38, Table 7). Both values steadily become more positive moving up through the lower 66
m of the section, except for one exceptional negative value at 40.5 m. Above the 66 m
mark, a large negative excursion occurs. The isotope values do not immediately return to
the trend seen lower in the section a few meters higher. Instead, the values start steadily
becoming more positive through the remainder of the section. At the top of the section,
both the carbon and oxygen values are approximately the same as they were at the bottom
of the section.
86
Above the 50 m mark, carbonate nodules become scarce, being only locally
abundant until one reaches the top of the section. There is a 28.5 m interval of covered
section and layers lacking nodules above the 66 m mark. Thus, the negative isotope
excursion cannot be documented until the 94.5 m mark.
A large negative carbon and oxygen isotope excursion has been documented at the
K/T boundary in the Big Bend region (Ferguson et al., 1991). The sections studied by
Ferguson et al. (1991) are on Dawson Creek and at Dogie Mt., where the position of the
K/T boundary cannot be constrained any closer than within about 20 meters. The breccia
layer thought to represent the K/T boundary at the Grapevine Hills locality lies
approximately at the 60 m mark, just below the isotope excursion noted above. The
disparity between the stratigraphic and isotopic placement of the K/T boundary cannot be
quantified due to the absence of nodules between 66 and 94.5 m. Paleontologic evidence
places the K/T boundary no more than a few meters above the breccia layer. Thus, if the
isotope excursion coincides with the K/T boundary, the excursion occurs no higher than
the 70 m mark. If the trend matches that seen higher in the section, the excursion is even
larger than recorded here (ca. 6 % drop in 6' CpDB and ca. 7% drop in S' Opoe)-
Discussion
The trend seen in the delta values on Fig. 36 is typical of that in ancient and
modem lake deposits. This trend is thought to represent enrichment of soil carbonates in
the heavy isotopes via evaporation. This explains why the soil carbonate nodules from
87
the Cretaceous part of the section have higher delta values than the lake sediments
(represented by carbonate samples from the breccia-limestone horizon).
The cause of the drop of the delta values above the K/T boundary is unknown.
Although Ferguson et al. (1991) suggested that a drop in atmospheric carbon dioxide at
the K/T boundary could explain the excursion, another possibility is climatic cooling.
The Early Paleocene is thought to have been a cooler and wetter time in the Big Bend
region, compared to the semi-arid conditions present during the Late Cretaceous. Cooler
conditions could result in a negative isotopic shift.
The paucity of carbonate nodules though the majority of the section may also be
related to climatic change. Cerling (1984) states that soil carbonates readily form in areas
with less than 75 cm of annual precipitation, whereas they rarely form in areas receiving
more than 100 cm of annual precipitation. The rainfall equations of Jenny (1941) and
Arkley (1963) were applied to paleosol data from the Big Bend region by Lehman
(1990). Both equations indicate that annual precipitation in the Big Bend region
increased from about 90 cm during the Late Cretaceous to well over 100 cm during the
Early Paleocene (183 cm with the Jenny equation, 234 cm with the Arkley equation).
This increase is likely the reason carbonate samples are rare in the lower Paleocene part
of the section. Nevertheless, more data points are needed from the interval between 66 m
and 94 m to help constrain the isotope excursion more tightly.
88
150
180
170
160
150
140
130
120
110
100
90
80
70
60 (0
e 40
30
20
10
Y cl >
SI CO 1
C? O G
* - isotope sample
Y = yellow
V = v a r i e g a t e d
G = gray
P =
&3 =
purple
covered
rubble-strewn
fossils
B = brown
} B
Paleocene vertebrate horizon G 0<3 i *
* Sauropod bone horizon
CO
Fig. 35 Measured section at field locality. 89
6"CpDB versus S' Op B values across the K/T boundary
j — . 1 I - t — • r 1 — I - t \ 1 1 1 1 —
5 -14 -13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1
tOrOO-
Lake sediments « Cretaceous soil carbonates
•
• •
/ * • •
Tertiary soil carbonates
• •
S' C
-1.00-
-2.00-
-4.00
-5.00
-6.00
-7.00 +
-8.00
-9.00
-10.00
-11.00
12.00
6'*0 PDB
PDB
Fig. 36 5' CpDB versus 5'*0pDB values for carbonate nodules collected at the field locahty.
90
6''CpDB changes across the K/T boundary
V'ji.iV...-.
• . . '
' ^v^
i
. • ' ' •
•" • .
- . • •
^
•
_ ' * , •
• .
^ • •
<»••
• .
« •
• •
• • '
•
• . :
» •
• •
. ' ' '..< ..'
* •, •
SGO-r
190 •
180 •
• 170 ••
160 •
•• 150 •
140 •
130 •
120 -
1 1 0 -
1 0 0 -
. 90 •
80 •
7 0 -
60
50 •
40 •
30 ••
2 0 ••
10 •
0 -
-16 -14 -12 -10 -8
5' C PDB
-2
height (meters)
Fig. 37 6' CpDB values throughout the measured section at the field locality.
91
5'«0pDB changes across the K/T boundary
(A t-O *.*
PDB
P . . « . . o . ^ « . - . — > - ^ " - " ^ - " " " " - " ""^ "•
92
Table 7 Carbon and oxygen isotope values
Sample ' Cp B "Opoe "O.MOW "'OP™ " O , 'PDB ^SMOW ^PDB ^SMOW
carbonate carbonate 1-lR 1-2R 2-lR 2-2R 3-lR 3-2R 4-lR 4-2R 5-lR 5-2R 6-lR 6-2R 7-lR 7-2R 8-lR 8-2R 9-lR 9-2R 10-lR 10-2R 11-lR 11-2R 12-lR 12-2R 13-lR 13-2R Y-IR Y-2R E2-1R E2-2R C-IR C-2R BL-IR BL-2R
-9.593 -10.389
-9.720 -8.646 -8.930 -8.854
-13.079 -12.748
-8.724 -9.223 -8.402 -8.497 -8.264 -8.657
-14.007 -12.181 -12.101 -12.988 -12.560 -12.852
-10.535 -10.892 -10.621 -10.560
-9.487 -9.563 -8.398
-9.379 -9.85
-9.362 -9.385
5.604 5.574 5.817 6.617 6.144 6.069 3.930 4.069 6.295 6.368 6.919 6.605 6.137 6.379
-1.060 4.136 4.214 3.464 3.729 3.695
3.770 4.277 5.288 3.546 6.190 6.109 1.675
1.473 1.431 6.319 6.345
36.637 36.606 36.857 37.681 37.194 37.116 34.911 35.055 37.349 37.425 37.993 37.668 37.186 37.436
29.967 35.123 35.204 34.43
34.704 34.669
34.746 35.269 36.311 34.515 37.241 37.157 32.586
32.378 32.336 37.374 37.401
-4.59 -4.63 -4.39 -3.59 -4.06 -4.13 -6.26 -6.11 -3.91 -3.84 -3.29 -3.61 -4.07 -3.83
-11.20 -6.05 -5.97 -6.72 -8.66 -8.69
-6.41 -5.91 -4.91 -6.64 -4.02 -4.09 -8.49
-8.69 -8.726 -3.89 -3.87
26.11 26.12 26.33 27.15 26.67 26.59 24.41 24.55 26.82 26.89 27.46 27.13 26.66 29.91
19.32 24.62 24.70 23.93 21.93 21.89
24.25 24.76 25.80 21.74 26.72 26.63 22.11
21.90 21.86 26.85 26.88
93
CHAPTER VI
CONCLUSIONS AND SUMMARY
This paper describes an important locality just below the K/T boundary in the
Grapevine Hills area of Big Bend National Park, Texas. The site, located in the Upper
Cretaceous Javelina Formation, represents a lake deposit as evidenced by the carbonate-
rich clay deposits and fi-eshvv^ater microfauna ofgastropods, fish, and algae. The
vertebrate fossil collection places the Cretaceous-Tertiary boundary within approximately
a 2 m stratigraphic interval, making this site the most tightly constrained K/T boundary
section in the Big Bend region.
Description of a juvenile individual of Alamosaurus sanjuanensis sheds light on
the anatomy of the cervical and dorsal region of this species, which have not previously
been described. Recovery of a juvenile individual allows for ontogenetic information to
be gathered as well, although the small number of Alamosaurus specimens restricts the
application of quantitative analyses. Comparison of this taxon with other sauropod
species indicates that Alamosaurus sanjuanensis is a valid species.
Burial in fine-grained mudstone indicates that this animal died at the site, the
skeletal elements being subjected to little mechanical transport. The disarticulated nature
of the remains is attributed to winnowing of the most easily transported elements by
either rising water level or water currents strong enough to affect some of the remaining
94
elements. Evidence of scavenging is absent, but could have been obscured by later clastic
and biogenic/chemical sedimentation that buried the specimens, coating them in
calcareous concretion.
Analysis of carbonate nodules collected along a 192 m measured section reveals a
large negative excursion in the 6' OpDB and 6' CpDB values at or just above the K/T
boundary. There is a strong correlation between the values of the C and O isotopes,
which likely represents an evaporative trend typical of lake deposits. The delta values are
lower in the Tertiary part of the section than in the Cretaceous deposits. This may be
related to an increase in the relative abundance of the lighter isotopes caused by the
cooler conditions present during Early Paleocene time.
95
REFERENCES
Adam, A., MacKenzie, W., and C. Guilford, 1984. Atias of sedimentary rocks under the microscope. John Wiley and Sons, New York: 104 pp.
Arkley, R.J., 1963. Calculation of carbonate and water movement in soil fi-om climatic data. Soil Sciences, vol. 96: pp. 239-241.
Baker, C.L., 1935. Part 2: major stmctural features of Trans-Pecos Texas. University of Texas Bulletin, no. 3401: pp. 137-214.
Brown, B., 1941. The age of sauropod dinosaurs. Science, vol. 93, no. 2425: pp.594-595.
Calvo, J.O., and J.F. Bonaparte. 1991. Andesaurus delgadoi gen. Et. sp. Nov. (Saurischia-Sauropoda), dinosaurio titanosauridae de la formacion Rio Limay (Albiano-Cenomaniano), Neuquen, Argentina. Ameghiniana, vol. 28 (3-4): pp. 303-310.
Cerling, T.E., 1984. The stable isotopic composition of modem soil carbonate and its relationship to climate. Earth and Planetary Science Letters, vol. 71: pp. 229-240.
Davies, K.L., 1983. Hadrosaurian dinosaurs of Big Bend National Park, Brewster County, Texas. Master's thesis. University of Texas at Austin.: 233 pp.
Davies, K.L., and T.M. Lehman. 1989. The WPA quarries. In Vertebrate Paleontology, Biostratigraphy, and Depositional Environments, Latest Cretaceous and Tertiary, Big Bend Area, Texas. Buseby, A.B. Ill, and T.M. Lehman, eds. pp. 32-42.
Eley, H.M., 1938. The invertebrate paleontology of Big Bend National Park, Marathon, Texas. Master's thesis. University of Oklahoma, Norman: 117 pp.
Ferguson, K.M., Lehman, T.M., and R.T. Gregory, 1991. C- and O- isotopes of pedogenic soil nodules fi-om two sections spanning the K/T transition in west Texas. Geological Society of America Abstract with Program, vol. 23(5): pp. 302.
Gilmore, C.W., 1921. Discovery of sauropod dinosaur remains in the upper Cretaceous of New Mexico. Science, vol. LIV: pp. 274.
1922. A new sauropod dinosaur fi-om the Ojo Alamo formation of New Mexico. Smithsonian Miscellaneous Collections, vol. 72, no. 14: pp. 1-9 (plus 2 plates).
96
1925. A nearly complete articulated skeleton of Camarasaurus, a saurischian dinosaur from the Dinosaur National Monument, Utah. Memoirs Camegie Museum, vol. X, no. 3-4: pp. 347-410.
1936. Osteology of Apatosaurus, with special reference to specimens in the Camegie museum. Memoirs of the Camegie Museum, vol. XL, no. 4: pp. 175-300.
1938. Sauropod dinosaur remains in the upper Cretaceous. Science, vol. 87, no. 2257: pp. 299-300.
1946. Reptihan fauna of the North Hom formation of central Utah. Geological Survey Professional Paper, no. 210-C: pp. 29-51 (plus 10 plates).
Hartnell, J. A., 1980. The vertebrate paleontology, depositional environment, and sandstone provenance of early Eocene rocks on Tomillo flat. Big Bend National Park, Brewster county, Texas. Master's thesis, Louisiana State University, Baton Rouge: 174 pp.
Hatcher, J.B., 1901. Diplodocus (Marsh): its osteology, taxonomy, and probable habits, with a restoration of the skeleton. Memoirs of the Camegie Museum, vol. I, no. I: 63 pp. (plus 13 plates).
1903. The osteology of Diplodocus Marsh. Memoirs of the Camegie Museum, vol. II, no. 6: pp. 225-278.
Hill, B.F., and J.A. Udden, 1904. Geological map portion of a portion of west Texas, showing parts of Brewster, El Paso, Jeff Davis, and Presidio counties, and south of the southem Pacific railroad. The University of Texas Mineral Survey.
Jacobs, L.L., Winkler, D.A., Downs, W.R., and E.M. Gomani. 1993. New material of an early Cretaceous titanosaurid sauropod dinosaur from Malawi. Palaeontology, vol. 36 (3): pp. 523-534.
Jain, S.L., and S. Bandyopadhyay. 1997. New titanosaurid (Dinosauria: Sauropoda) from the late Creetaceous of central India. Joumal of Vertebrate Paleontology, vol. 17: pp.114-136.
Janensch, W., 1914. Ubersicht uber die wirbeltierfauna der Tendagum-Schichten, nebst einer kurzen charakterisierung der neu aufgestellten arten von sauropoden. Archiv fiir Biontologie, vol. 3: pp. 81-110.
Jenny, H., 1941. Factors of Soil Formation. McGraw-Hill, New York: 281 pp.
97
Kues, B.S., Lehman, T.M., and K. Rigby, Jr. 1980. The teeth of Alamosaurus sanjuanensis, a late Cretaceous sauropod. Joumal of Paleontology, vol. 54, no. 4: pp. 864-869.
La Rocque, A., 1960. Molluscan faunas of the Flagstaff Formation of central Utah. The geological Society of America Memoir, no. 78: pp. 86-96.
Langston, W.A., Jr. 1974. Nonmammahan Comanchean tetrapods. Geoscience and Man, vol. 8: pp. 77-102.
Langston, W.A., Jr., Standhardt, B., and M. Stevens, 1989. Fossil vertebrate collectiong in the Big Bend- history and perspectives. In Vertebrate Paleontology, Biostratigraphy, and Depositional Environments, Latest Cretaceous and Tertiary, Big Bend Area, Texas. Busbey, A.B., III, and T.M. Lehman, eds. pp. 11-22.
Lawson, D.A., 1972. Paleontology of the Tomillo Formation, Big Bend National Park. Master's thesis. University of Texas at Austin: 182 pp.
1975. Pterosaur from the latest Cretaceous of west Texas: discovery of the largest flying creature. Science, vol. 187: pp. 947-948.
1976. Tyrannosaurus and Torosaurus, Maastrichtian dinosaurs from Trans-Pecos, Texas. Joumal of Paleontology, vol. 50, no. 1: pp. 158-164.
Lehman, T.M., 1982. A ceratopsian bone bed from the Aguja formation (Upper Cretaceous), Big Bend National Park, Texas. Master's thesis. University of Texas at Austin: 209 pp.
1985, Stratigraphy, sedimentology, and paleontology of late Cretaceous (Campanian-Maastrictian) sedimentary rocks in Trans-Pecos, Texas. Ph.D. dissertation. University of Texas at Austin: 299 pp.
1987. Late Maastrichtian paleoenvironments and dinosaur biogeography in the westem interior of North America. Palaeogeography, Palaeoclimatology, Palaeoecology, vol. 60: pp. 189-217.
1988. Stratigraphy of the Cretaceous-Tertiary and Paleocene-Eocene transition rocks of Big Bend National Park, Texas, a discussion. Joumal of Geology, vol. 96: pp. 627-631.
98
1989a. Overview of late Cretaceous sedimentation in Trans-Pecos Texas, in Vertebrate Paleontology, Biostratigraphy ,and Depositional Environments, Latest Cretaceous and Tertiary, Big Bend Area, Texas. Busbey, A.B. Ill, and T.M. Lehman, eds. pp. 23-27.
1989b. Upper Cretaceous (Maastrichtian) paleosols in Trans-Pecos, Texas. Geological Society of America Bulletin, vol. 101: pp. 188-203.
1990. Paleosols and the Cretaceous?/Tertiary transition in the Big Bend region of Texas. Geology, vol. 18: pp. 362-364.
1991. Sedimentation and tectonism in the Laramide Tomillo basin of west Texas.
Sedimentary Geology, vol. 75: pp. 9-28.
1997. Personal communication, Texas Tech University.
1998. Personal communication, Texas Tech University.
Lerman, A. (ed)., 1978. Lakes: chemistry, geology, physics. Springer-Verlag, New York: 363 pp.
Lockley, M.G., 1986. The paleobiological and paleoenvironmental importance of dinosaur footprints. Palaios, vol. 1: pp. 37-47.
Lozinsky, R.P., Hunt, A.P., and D.L. Wolberg. 1984. Late Cretaceous (Lancian) dinosaurs from the McRae formation, Sierra county. New Mexico. New Mexico Geology: pp. 72-77.
Lucas, S.G., 1981. Dinosaur communities of the San Juan basin: a case for lateral variation in the composition of late Cretaceous dinosaur communities. Advances in San Juan Basin Paleontology. Lucas, S.G., Rigby, Jr., J.K,, and B.S. Kues, eds. University of New Mexico Press, Albuquerque: pp. 337-393.
Lydekker, B., 1885. Introductory observations. Paleontologica Indica, series 4,: pp. v-vi.
Marsh, O.C, 1878. Notice of new dinosaurian reptiles. American Joumal of Science, series 3, vol. 15: pp. 241-244.
Maxwell, R.A., Lonsdale, J.T., Hazzard, R.T., and J.A. Wilson, 1967. Geology of Big Bend National Park, Brewster county, Texas. The University of Texas Publication,no. 6711: 320 pp.
99
Mateer, N.J., 1976. New topotypes of Alamosaurus sanjuanensis Gilmore (Reptilia: Sauropoda). Bulletin of the Geological Institutions of the University of Uppsala, vol. 6: pp. 93-95.
McCord, R.D., 1997. An Arizona titanosaurid sauropod and revision of the Late Cretaceous Adobe Canyon fauna. Joumal of Vertebrate Paleontology, vol. 17(3): pp. 620-622.
McCrea, J.M., 1950. On the isotopic chemistry of carbonates and a paleotemperature scale. The Joumal of Chemical Physics, vol. 18: pp. 819-857.
Mcintosh, J.S., 1990. Sauropoda. in The Dinosauria. Weishampel, D.B., Dodson, P., and H.A. Osmolska, eds. University of Cahfomia Press, Los Angeles, pp. 345-502.
1990a. Species determination in sauropod dinosaurs with tentative suggestions for their classification. In Dinosaur Systematics: Approaches and Perspectives. Carpenter, K., and P.J. Currie, eds. Cambridge University Press, Cambridge: pp. 53-71.
Mcintosh, J.S., Miller, W.E., Stadtman, K.L., and D.D. Gillette, 1996. The osteology of Camarasaurus lewisi (Jensen, 1988). Brigham Young University Geology Studies, vol. 41:73-115.
Osbom, H.F., and CC. Mook, 1921. Camarasaurus, Amphicoelias, and other sauropods of Cope. Memoirs of the American Museum of Natural History, new series vol. Ill, pt. Ill: pp. 251-387 (plus 25 plates).
Owen, R., 1842. Deuxieme rapport sur les reptiles fossiles de la grande-Bretagne. Institut., vol. 10: pp. 11-14.
Powell, J.E., 1992. Osteologia de Saltasaurus loricatus (Sauropoda- Titanosauridae) del Cretacico superior del noroests Argentine. Los Dinosaurios y su Entomo Biotico. Sanz, J., and A. Buscalioni, eds. pp. 166-230.
Runkel, A.C., 1988. Stratigraphy, sedimentology, and vertebrate paleontology of Eocene rocks, Big Bend region, Texas. Ph.D. dissertation, University of Texas at Austin: 310 pp.
Russell, L.S., 1931. Early Tertiary moUusks from Wyoming. Bulletins of American Paleontology, vol. 18, no. 4: pp. 32-37.
100
Rutzky, I.S., Elvers, W.B., Maisey, J.G., and A.W.A. Kelhier., 1994. Chemical preparation techniques. Vertebrate Paleontological Techniques Volume 1. Leiggi, P., and P. May, eds. Cambridge University Press, Cambridge: pp. 155-187.
Schiebout, J. A., 1970. Sedimentology of Paleocene Black Peaks formation, westem Tomillo flat. Big Bend National Park, Texas. Master's Thesis, University of Texas at Austin: 114 pp.
1974. Vertebrate paleontology and paleoecology of Paleocene Black Peaks formation, Big Bend National Park, Texas. Bulletin of the Texas Memorial Museum, no. 24: 88 pp.
Schiebout, J.A., Rigsby, C.A., Rapp, S.D., Hartnell, J.A., and B.R. Standhardt. 1987. Stratigraphy of the Cretaceous-Tertiary and Paleocene-Eoscene transition rocks of Big Bend National Park, Texas. Joumal of Geology, vol. 95: pp. 359-375.
1988. Stratigraphy of the Cretaceous-Tertiary and Paleocene-Eocene transition rocks of Big Bend National Park, Texas, a reply. Joumal of Geology, vol. 96: pp. 631-634.
Seeley, H.G., 1887. On the classification of the fossil animals commonly called the Dinosauria. Proceedings of the royal Society of London, vol. 43: 221-228.
Sloan, R.E., 1969. Cretaceous and Paleocene terrestrial communities of westem North America. Proceedings of the North American Paleontological Convention: pp. 427-453.
Standhardt, B.R., 1986. Vertebrate paleontology of the Cretaceous/Tertiary transition of Big Bend National Park, Texas. Ph.D. dissertation, Louisiana State University, Baton Rouge: 298 pp.
1989. Dawson creek: late Cretaceous and Paleocene vertebrates of Big Bend National Park. Vertebrate Paleontology, Biostratigraphy and Depositional Environments, Latest Cretaceous and Tertiary, Big Bend Area, Texas. Busbey, A.B. Ill, and T.M. Lehman, eds. pp. 27-29.
Stovall, J.W., 1948. Chadron vertebrate fossils from below the Rio rock of Presidio county, Texas. American Joumal of Science, vol. 246: 78-95.
Straight, W.H., 1996. Stratigraphy and paleontology of the Cretaceous-Tertiary boundary. Big Bend National Park, Texas. Master's thesis, Texas Tech University, Lubbock. 102 pp.
101
Swinton, W.E., 1947. New discoveries of Titanosaurus indicus Lydekker. Annals and Magazine of Natural History, series 11, vol. xiv: pp. 112-123.
Tomlinson, S.L., 1997. Late Cretaceous and early Tertiary turtles from the Big Bend region, Brewster county, Texas. Ph.D. dissertation, Texas Tech University, Lubbock: 194 pp.
Udden, J.A., 1907. A sketch of the Geology of the Chisos country, Brewster county, Texas. Bulletin of the University of Texas, no. 93: 101 pp.
von Huene, F, 1932. Die fossile Reptil-Ordung Saurischia, ihre entwicklung und geschichte. Monograph of Geology and Paleontology, series 1, vol. 4: pp. 1-361.
von Huene, F., and CA. Matley, 1933. Figures and descriptions of the organic remains procured during the progress of the geological survey of India. Memoirs of the Geological Survey of India, vol. XXL, memoir no. 1: 41 pp, (plus 24 plates).
Voorhies, M.R., 1969. Taphonomy and population dynamics of an early Phocene vertebrate fauna, Knox county, Nebraska. University of Wyoming Contributions to Geology Special Paper no. 1: 69 pp.
Wheeler, E.A., Lehman, T.M., and P.E. Gasson. 1994. Javelinoxylon, an upper Cretaceous dicotyledonous tree from Big Bend National Park, Texas, with presumed malvalean affinities. American Joumal of Botany, vol. 81(6): pp. 703-710.
Wilson, J. A., 1967. Early Tertiary mammals. Geology of Big Bend National Park, Brewster County, Texas. Maxwell, R.A., Lonsdale, J.T., Hazard, R.T., and J.A. Wilson., eds. University of Texas Bureau of Economic Geology Pubhcation, vol. 6711:157-169.
1989. General geography and geological setting of the Trans-Pecos region. In Vertebrate Paleontology, Biostratigraphy, and Depositional Environments, Latest Cretaceous and Tertiary, Big Bend Area, Texas. Busbey, A.B. Ill, and T.M. Lehman eds, pp. 7-10
Wilson, J.A., Maxwell, R.A., Lonsdale, J.T., and J.H. Quinn, 1952. New Paleocene and lower Eocene vertebrate localities. Big Bend National Park, Texas. University of Texas Bureau of Economic Geology Report, inv. no. 14: pp. 7.
Wiman, C , 1929. Die kreide-dinosaurier aus shantimg. Palaeontologica Sinica, vol. VI: 67 pp. (plus 9 plates).
102
Wolberg, D.L., Lozinsky, R.P., and A.P. Hunt, 1986. Late Cretaceous (Maastrichtian-Lancian) vertebrate paleontology of the McRae formation. Elephant Butte area, Sierra county. New Mexico. New Mexico Geological Survey Guidebook: pp. 227-234.
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