Revision of the sauropod dinosaurs of the Lower Cretaceous Trinity Group, southern USA, with the description of a new genus

Abstract

Early Cretaceous sauropods were among the first dinosaurs discovered in North America, but several aspects of their taxonomy and evolution remain poorly understood. Much of this ambiguity stems from lack of anatomical overlap among taxa and the 125-year-long taxonomic confusion surrounding the sauropods Astrodon and Pleurocoelus. New discoveries have begun to remedy the first problem, but a lack of autapomorphies in their holotypes and skeletal associations among their hypodigms renders Astrodon johnstoni, Pleurocoelus altus and Pleurocoelus nanus nomina dubia. Herein I examine the affinities of sauropods from the Trinity Group of Texas and Oklahoma previously referred to as ‘Pleurocoelus’ or ‘Astrodon’. Some of this material currently comprises the genera Paluxysaurus and Sauroposeidon from laterally equivalent strata in Texas and Oklahoma, respectively. Although representative individuals of Paluxysaurus are only two-thirds the size of Sauroposeidon, bone histology of Paluxysaurus indicates that the individuals from the type locality were not near adult size. The similar provenance, lack of morphological differences, and shared unique features support referral of Paluxysaurus to Sauroposeidon. Other sauropod remains from the Trinity Group are not referable to ‘Pleurocoelus’, ‘Astrodon’ or Sauroposeidon. Some of these remains comprise the holotype of Astrophocaudia slaughteri gen. et sp. nov., a basal titanosauriform diagnosed by a hyposphene–hypantrum system in the caudal vertebrae. A sauropod hind limb previously referred to ‘Pleurocoelus’ is instead referable to Cedarosaurus weiskopfae based on shared features of the pes. Cladistic analysis indicates that Astrophocaudia and Sauroposeidon are members of Somphospondyli, whereas Cedarosaurus is a brachiosaurid. The Trinity Group of Texas and laterally equivalent Antlers Formation of Oklahoma exhibit similar dinosaur faunas at the generic and specific levels to the Cloverly Formation of Wyoming. This homogeneity with respect to latitude stands in marked contrast to the latitudinal variation in dinosaur communities that developed later in the Cretaceous.http://zoobank.org/urn:lsid:zoobank.org:pub:FE82D372-7ADA-4870-9572-3A3F607D39CE

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Revision of the sauropod dinosaurs of the Lower
Cretaceous Trinity Group, southern USA, with the
description of a new genus
Michael D. D’Emic a b
a Museum of Paleontology and Department of Geological Sciences, University of Michigan,
1109 Geddes Avenue, Ann Arbor, MI, 48109–1079, USA
b Department of Geology and Geography, Georgia Southern University, Box 8149,
Statesboro, GA, 30460, USA
Version of record first published: 30 Nov 2012.
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southern USA, with the description of a new genus, Journal of Systematic Palaeontology, DOI:10.1080/14772019.2012.667446
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Journal of Systematic Palaeontology, iFirst 2012, 1–20
Revision of the sauropod dinosaurs of the Lower Cretaceous Trinity Group,
southern USA, with the description of a new genus
Michael D. D’Emic∗
Museum of Paleontology and Department of Geological Sciences, University of Michigan, 1109 Geddes Avenue, Ann Arbor,
MI 48109–1079, USA
(Received 5 December 2011; accepted 6 December 2011)
Early Cretaceous sauropods were among the first dinosaurs discovered in North America, but several aspects of their taxonomy
and evolution remain poorly understood. Much of this ambiguity stems from lack of anatomical overlap among taxa and the
125-year-long taxonomic confusion surrounding the sauropods Astrodon and Pleurocoelus. New discoveries have begun to
remedy the first problem, but a lack of autapomorphies in their holotypes and skeletal associations among their hypodigms
renders Astrodon johnstoni,Pleurocoelus altus and Pleurocoelus nanus nomina dubia. Herein I examine the affinities of
sauropods from the Trinity Group of Texas and Oklahoma previously referred to as ‘Pleurocoelus’or‘Astrodon’. Some of
this material currently comprises the genera Paluxysaurus and Sauroposeidon from laterally equivalent strata in Texas and
Oklahoma, respectively. Although representative individuals of Paluxysaurus are only two-thirds the size of Sauroposeidon,
bone histology of Paluxysaurus indicates that the individuals from the type locality were not near adult size. The similar
provenance, lack of morphological differences, and shared unique features support referral of Paluxysaurus to Sauroposeidon.
Other sauropod remains from the Trinity Group are not referable to ‘Pleurocoelus’, ‘Astrodon’orSauroposeidon. Some of
these remains comprise the holotype of Astrophocaudia slaughteri gen. et sp. nov., a basal titanosauriform diagnosed by a
hyposphene–hypantrum system in the caudal vertebrae. A sauropod hind limb previously referred to ‘Pleurocoelus’ is instead
referable to Cedarosaurus weiskopfae based on shared features of the pes. Cladistic analysis indicates that Astrophocaudia
and Sauroposeidon are members of Somphospondyli, whereas Cedarosaurus is a brachiosaurid. The Trinity Group of Texas
and laterally equivalent Antlers Formation of Oklahoma exhibit similar dinosaur faunas at the generic and specific levels to
the Cloverly Formation of Wyoming. This homogeneity with respect to latitude stands in marked contrast to the latitudinal
variation in dinosaur communities that developed later in the Cretaceous.
http://zoobank.org/urn:lsid:zoobank.org:pub:FE82D372-7ADA-4870-9572-3A3F607D39CE
Keywords: sauropod; titanosauriform; Pleurocoelus;Astrodon; Trinity; Cretaceous
Introduction
Sauropod dinosaurs were common and diverse mega-
herbivores in many Mesozoic ecosystems. Their status
as the largest land animals that ever evolved, as well as
their unique body plan with a long neck and tail set on
an elephantine body, has fuelled studies of their evolution
and palaeobiology (e.g. Wilson 2002; Sander & Clauss
2008; Sander et al. 2010; Mannion et al. 2011). Their
extreme size has also hindered such studies, contributing
to the incompleteness of most fossil sauropod individuals
and the difficulty of working with them (Mannion &
Upchurch 2010). Nonetheless, better fossil material and
many systematic revisions in the last decade have greatly
increased the amount of information available to sauropod
researchers (e.g. McIntosh 2005; Rose 2007; Taylor 2009;
Carballido et al. 2011; Mannion 2011).
∗Present address: Department of Geology and Geography, Georgia Southern University, Box 8149, Statesboro, GA 30460, USA.
Email: mdemic@umich.edu
The first sauropod described from North America was
found in the Arundel Formation of Maryland (Johnston
1859), which was originally thought to be Late Jurassic
in age (e.g. Marsh 1897), but is now recognized as
Early Cretaceous (e.g. Ostrom 1970). The earlier-named
Astrodon Leidy, 1865 and the later-named Pleurocoelus
Marsh, 1888 were based on isolated, incomplete type spec-
imens, to which later-discovered specimens from Maryland
and elsewhere were referred. The validity, hypodigms and
inferred affinities of these two genera have varied widely
since their naming over a century ago (Table 1). Sauropods
from several other regions of the world have been referred
to Pleurocoelus and Astrodon (e.g. Langston 1974), but
new discoveries and analyses have challenged some of these
referrals (e.g. Wedel et al. 2000a; Rose 2007). The contro-
versial or ambiguous taxonomy of many fragmentary Early
Cretaceous North American sauropods and the discovery
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2M.D.D’Emic
Tab le 1. Novel genus–species combinations of Astrodon and Pleurocoelus in order of publication, with taxonomic action taken at the
time of naming.
Author Taxa named Action
Johnston 1859 Astrodon New genus
Leidy 1865 Astrodon johnstoni New species
Marsh 1888 Pleurocoelus nanus,Pleurocoelus altus New genus, two new species
Marsh 1896 Pleurocoelus montanus New species
Lydekker 1890 Pleurocoelus valdensis New species
Marsh 1897 Pleurocoelus suffosus New combination
Hatcher 1903 Astrodon suffosus New combination
Gilmore 1921 Astrodon nanus,Astrodon altus New combinations
de Lapparent & Zbyszewski 1957 Astrodon pusillus,Astrodon montanus New species; new combination
Kingham 1962 Astrodon altithorax,Astrodon atalaiensis,
Astrodon brancai,Astrodon fraasi
New combinations
of substantial new material prompt a comprehensive re-
evaluation of Early Cretaceous North American sauropods.
Cretaceous sauropods of North America
The survival of sauropods into the Cretaceous of North
America was confirmed by Larkin (1910), who reported
the discovery of a sauropod coracoid in the Early Creta-
ceous Antlers Formation of Oklahoma (a lateral equivalent
of the Trinity Group of Texas). Several decades later, more
complete excavations and exploration in the Trinity Group
were undertaken by the Field Museum of Natural History,
Harvard University, and Southern Methodist University.
These excavations yielded the remains of a diverse verte-
brate fauna, including sauropods (Bilelo 1969). Additional
Trinity Group sauropod remains were reported from Texas,
including a hind limb from the Paluxy Formation at Walnut
Creek in Wise County (Bilelo 1969) and a partial skele-
ton from the underlying Glen Rose Formation near Blanco
(Langston 1974; Tidwell & Carpenter 2003).
The Trinity Group sauropods collected by the Field
Museum teams and reported by Bilelo (1969) were referred
to Pleurocoelus sp. by Langston (1974), a taxonomic deci-
sion that was followed by some subsequent authors (e.g.
Gallup 1975, 1989; McIntosh 1990), but not more recent
ones (e.g. Gomani et al. 1999; Upchurch et al. 2004;
Carpenter & Tidwell 2005; Rose 2007). Authors have also
disagreed on the phylogenetic affinities of the Early Creta-
ceous Texan materials referred to Pleurocoelus, with some
referring them to Brachiosauridae, and others regarding
them as more derived (e.g. McIntosh 1990; Salgado et al.
1995). Fig. 1 depicts a cladogram of the major clades
and taxa discussed in this paper based on recent analyses
(Upchurch et al. 2004; Rose 2007).
The Early Cretaceous North American sauropod fossil
record has improved greatly in the last decade as several
more complete skeletons have been described from Early
Cretaceous strata, especially in the Trinity Group and
Antlers Formation of Texas and Oklahoma, respectively
(Fig. 2). Two monospecific genera have been named from
these strata: Sauroposeidon proteles Wedel et al., 2000a
and Paluxysaurus jonesi Rose, 2007. Comparatively little
has been said of the taxonomy or phylogeny of other Trin-
ity sauropod fossils, although a partial sauropod skeleton
reported by Bilelo (1969; SMU 61732) has been mentioned
as a genus distinct from other Early Cretaceous Trinity
sauropods (e.g. Tidwell et al. 1999; Wedel et al. 2000b).
Here I provide a name, diagnosis, description and compar-
isons for this skeleton. I then examine the anatomy and
affinities of the hind limb from the Paluxy Formation
described by Gallup (1975, 1989), and evaluate the validity
and diagnoses of other Early Cretaceous sauropods from
the Trinity Group. Finally, I evaluate the similarity of these
revised Trinity Group faunas to those of similar age, such
as the Cloverly Formation of Wyoming and Montana and
the Cedar Mountain Formation of Utah.
Note on the taxonomy of Astrodon and
Pleurocoelus
The taxonomies of Astrodon and Pleurocoelus have varied
widely according to different authors (Table 1). The type
series of Astrodon johnstoni consists of two teeth (YPM
Figure 1. Simplified cladogram depicting the relationships of
relevant sauropod clades. Based on the phylogeny of Upchurch
et al. (2004).
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Trinity Group sauropods 3
798) from the Arundel Formation in Maryland, USA
(Johnston 1859; Leidy 1865). The type series of P. altus
consists of a left tibia and fibula from one individual
(USNM 4971), and the type series of P. nanus consists
of a cervical (USNM 5678), a dorsal (USNM 4968), a
sacral (USNM 4969) and a caudal (USNM 4970) vertebral
centrum, all of which are unfused to their neural arches and
ribs, and were not recovered with the type series (Marsh
1888; Lull 1911). The type series of Pleurocoelus nanus
is the appropriate size to belong to one individual, but the
exact provenance of each bone is uncertain. These bones
could represent a chimera of individuals or taxa (Hatcher
1903).
ReferralsofnewmaterialtoPleurocoelus and Astrodon
and revisions of the Arundel Formation fauna drastically
changed the taxonomy of its sauropods during the 20th
century. Hatcher (1903: 12) believed that the Arundel
Formation remains were found “... in essentially, and
perhaps identically, the same locality and horizon ...”, and
given the lack of substantial variation among those sauro-
pod remains suggested that only one genus and species,
Astrodon johnstoni, was present. Lull (1911) agreed with
Hatcher (1903) that Astrodon and Pleurocoelus altus repre-
sented the same taxon, but thought that Pleurocoelus nanus
was a different taxon, based on the relative frequency of
small and large sauropod bones in the formation. Gilmore
(1921) reviewed the Arundel Formation fauna and agreed
with former workers that more than one species of sauro-
pod was present, but differed from them in assigning
taxonomic value to the observed differences among the
material, referring all of the specimens to a single genus,
Astrodon, and creating the new species Astrodon nanus
and A. altus. Gilmore’s (1921) taxonomy was preferred for
several decades; for example, subsumation of Pleurocoelus
into Astrodon was followed by the influential work of Romer
(1956). Kingham (1962) also referred all of the Maryland
species to Astrodon; in addition, he referred several species
of Brachiosaurus to Astrodon, creating A. atalaiensis,A.
brancai and A. altithorax. Kingham (1962) also named A.
fraasi; in resurrecting this species, he overturned Janensch’s
(1929) synonomy of Brachiosaurus fraasi with B. brancai.
Kingham’s (1962) assignments have not been followed by
subsequent authors (e.g. McIntosh 1990; Upchurch et al.
2004; Carpenter & Tidwell 2005).
Carpenter & Tidwell (2005) redescribed much of the
Arundel Formation sauropod material and concluded
that the low degree of variability in the available skeletal
elements indicated that only one species was present,
whichwouldbeAstrodon johnstoni based on priority.
They presented 10 autapomorphies in their diagnosis of A.
johnstoni (based on all of the sauropod material from the
Arundel Formation): (1) supraoccipital crest low and wide;
(2) tall, narrow foramen magnum; (3) short, wide camerate
cervical vertebrae with very large pleurocoels; (4) deep
pleurocoels in the dorsal vertebrae; (5) deep pleurocoels
in the sacral vertebrae; (6) posterior sacral vertebrae with
a prominent groove on the ventral surface; (7) anterior
caudal vertebrae with short centra; (8) coracoid thick with
prominent lip; (9) radius with distinct oblique ridge; and
(10) two small posterodistal condyles on the radius. Many
of these features are indistinguishable compared to other
sauropods such as Camarasaurus (characters 1, 2, 7–10;
Osborn & Mook 1921; Ostrom & McIntosh 1966, pls 46,
51; Madsen et al. 1995, fig. 23), and/or are related to the
juvenile nature of the material (characters 1, 3–5; Wedel
et al. 2000b; Curry Rogers & Forster 2004).
None of these autapomorphies deals with teeth or the
crus, which are the holotypic elements of Astrodon john-
stoni and Pleurocoelus altus, respectively. Like Astrodon
and P. altus, the syntype vertebrae of P. nanus bear no
unique features, making all three taxa nomina dubia.
Carpenter & Tidwell (2005) presented an example of the
‘laissez-faire’ approach outlined by Wilson et al. (2009), in
which undocumented field associations are assumed, forc-
ing conspecificity where it might not be present. Employing
this approach in the case of the Arundel Formation involves:
(1) ascribing no taxonomic meaning to the range of varia-
tion in the sample; (2) assuming the penecontemporaneous
nature of the various outcrops of the Arundel Formation;
and (3) inferring ontogenetic transformations among
specimens in the sample. These assumptions are large. For
the taxonomy of Astrodon and Pleurocoelus, I advocate the
opposite viewpoint, the ‘tabula rasa’ approach (Wilson et al.
2009), in which taxa whose holotypes are non-diagnostic
are deemed nomina dubia. I employ this approach in the
Arundel Formation because of the especially fragmentary
and non-diagnostic type species involved, and the paucity
of provenance or quarry data for nearly all specimens.
However, the ventral groove on the sacral vertebra (char-
acter 6 of Carpenter & Tidwell 2005) may be unique (in
the referred specimen USNM 5666, pers. obs. 2010), but
cannot be observed in the syntype specimen of Pleuro-
coelus nanus (USNM 4969). Indeed, other sauropod mate-
rial from the Arundel Formation does bear unique features,
including a groove below the ectopterygoid/palatine articu-
lar facets on the maxilla and laterally curved pedal unguals
(pers. obs. 2010). However, the lack of association among
these materials and/or the holotype of P. nanus and P. altus
limits their systematic utility. Furthermore, some bones in
the sample display marked variation, such as the deeply
divided versus flat distal ends of the first metatarsals (pers.
obs. 2010). Future discoveries may yield associated skele-
tons in the Arundel Formation bearing these or other diag-
nostic features.
Anatomical abbreviations
acdl: anterior centrodiapophyseal lamina; acet: acetabu-
lum; bo: boss; CD: caudal vertebra; cprl: centroprezy-
gapophyseal lamina; haa: hypantrum articulation surface;
hy: hyposphene; ncj: location of fused neurocentral
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4M.D.D’Emic
junction; ng: nail groove; pcdl: posterior centrodiapophy-
seal lamina; pl: pleurocoel; pn fo: pneumatic fossa;
pocdf: postzygapophyseal centrodiapophyseal fossa; podl:
postzygodiapophyseal lamina; posdf: postzygapophyseal
spinodiapophyseal fossa; poz: postzygapophysis; prcdf:
prezygapophyseal centrodiapophyseal fossa; prdl: prezy-
godiapophyseal lamina; prsl: prespinal lamina; prz:
prezygapophysis; sdf: spinodiapophyseal fossa; sprf:
spinoprezygapophyseal fossa; sprl: spinoprezygapophy-
seal lamina; spol: spinopostzygapophyseal lamina; tp:
transverse process; tprl: intraprezygapophyseal lamina; tu:
tubercle wf: wear facet.
Institutional abbreviations
ASDM: Arizona-Sonora Desert Museum, Arizona, USA;
DMNS: Denver Museum of Nature and Science, Denver,
USA; FMNH: Field Museum of Natural History, Chicago,
USA; FWMSH: Fort Worth Museum of Science and
History, Fort Worth, USA; HMN MB. R: Humboldt
Museum f¨
ur Naturkunde, Berlin, Germany; OMNH: Okla-
homa Museum of Natural History, Norman, USA; SMU:
Southern Methodist University, Dallas, USA; TMM: Texas
Memorial Museum, Austin, USA; USNM: United States
National Museum (Smithsonian Institution), Washington,
DC, USA.
Systematic palaeontology
Dinosauria Owen, 1842
Sauropoda Marsh, 1878
Neosauropoda Bonaparte, 1986
Titanosauriformes Salgado et al., 1997
Astrophocaudia gen. nov.
Type species. Astrophocaudia slaughteri sp. nov.
Astrophocaudia slaughteri sp. nov.
(Figs 3–11)
1974 ‘Pleurocoelus’ sp. Langston: 85, figs 5, 6a.
1997 ‘Pleurocoelus’ Salgado & Calvo: 44, fig. 9.
Holotype. SMU 61732 and 203/73655; a tooth (SMU
203/73655), two cervical vertebrae, fragments of dorsal
vertebrae, 24 caudal vertebrae, approximately 20 fragmen-
tary dorsal ribs, two chevrons, a distal scapular blade, part
of a right ilium, and numerous fragments. The two associ-
ated teeth mentioned by Rose (2007) are prezygapophyses
of middle caudal vertebrae; these were glued onto their
vertebrae during preparation in August 2009. The appro-
priate size and lack of duplication of elements suggest that
only one sauropod individual was present in the quarry.
Diagnosis. Autapomorphies include: anterior-middle
caudal vertebrae with planar hyposphene–hypantrum
articulations set off from zygapophyses; anterior-middle
caudal vertebrae with prespinal lamina contacting
intraprezygapophyseal lamina. Unlike Astrophocaudia,
Sauroposeidon proteles (see below) has wide spino-
prezygapophyseal fossae that are bounded by strongly
developed spinoprezygapophyseal laminae in anterior
Figure 2. A, type locality of Astrophocaudia slaughteri in Wise County, Texas, USA (star), with locations of other named Early Cretaceous
North American sauropods (dots); arrow indicates the direction of north during the Albian (taken from www.paleodb.org); scale bar =
500 km. B, stratigraphical position of Astrophocaudia slaughteri relative to other Early Cretaceous North American sauropods; placement
of the abbreviated name indicates the most likely age for the taxon, and the dotted lines represent age uncertainty. Abbreviations: Aby,
Abydosaurus; Arun, Arundel Formation sauropod material, including ‘Astrodon’and‘Pleurocoelus’; As,Astrophocaudia gen. et. sp. nov.;
Blanco, TMM 40435, partial sauropod skeleton from the Glen Rose Formation (Tidwell & Carpenter 2003); Bro,Brontomerus;Ced,
Cedarosaurus; Clo, Cloverly Formation sauropod material (Ostrom 1970); FMNH, FMNH PR 977, hind limb of a sauropod from the
Paluxy Formation referable to Cedarosaurus weiskopfae (Gallup 1989); Plx,Paluxysaurus;Sau,Sauroposeidon (holotype only); Son,
Sonorasaurus. Tooth figures indicate horizons that preserve indeterminate sauropod teeth.
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Trinity Group sauropods 5
Figure 3. Holotypic tooth of Astrophocaudia slaughteri (SMU
203/73655) in: A, labial; B, ?mesial; C, lingual; D, ?distal; E,
occlusal; and F, proximal views. Orientation is uncertain because
of uncertainty in tooth position within the jaw. Scale bar =1cm.
caudal vertebrae. Giraffatitan,Abydosaurus,Venenosaurus
and Cedarosaurus are differentiated from Astrophocaudia
by the presence of sporadically distributed fossae below
the transverse processes in caudal vertebrae and forward-
leaning neural spines in the latter two genera. Sonorasaurus
is differentiated from Astrophocaudia by the reduction of
the spinopostzygapophyseal laminae in the anterior-middle
caudal vertebrae that cause each postzygapophysis to
project far beyond the posterior margin of the neural spine.
The ilium of Astrophocaudia is dissimilar from that of
Brontomerus mcintoshi in its gently curving preacetabular
process in dorsal view.
Derivation of name. A-, non- (Greek); stropho-, twist-
ing or turning (Greek); caud-, tail (Greek). The name is in
reference to the tightly articulating hyposphene–hypantrum
system in the anterior and middle caudal vertebrae, which
Figure 4. Holotypic middle to posterior cervical vertebra of
Astrophocaudia slaughteri (SMU 61732) in lateral view. Dashed
lines indicate missing bone. Scale bar =10 cm.
also resembles a star (astron; Greek) in posterior view. The
generic name is also a reference to Astrodon, the first Early
Cretaceous North American sauropod. The specific name
honours Dr Robert H. Slaughter, who excavated the speci-
men in the 1960s.
Locality, horizon and age. The holotype comes from
Walnut Creek, southeast of Decatur, Wise County, Texas,
33◦09N, 97◦34W (Thurmond 1974; Fig. 2). This locality
has also yielded the semionontid fish Lepidotes (some
scales of which were found in contact with the bones of
Astrophocaudia), a theropod claw (SMU 62723), a thero-
pod squamosal (SMU 61741), and the turtle Naomichelys.
Bilelo (1969) reported the sauropod as coming from
Wall, Texas. There is a city called ‘Wall’ in Texas, but
it is several hundred kilometres from Wise County. Dr
Wann Langston visited the Walnut Creek sauropod site
in 1984 (pers. obs. of field notes housed at SMU, 2009),
and noted the location as occurring “5.6 miles south and
0.9 miles west of Decatur” (which is in Wise County). In
addition, Thurmond (1974, appendix) gave latitude and
longitude coordinates for a “Walnut Creek B local fauna”
that includes a sauropod and is in accordance with the
locality given in Langston’s notes. SMU 61732 comes
from the Trinity Group, uppermost part of the middle unit
of the Paluxy Formation (Thurmond 1974), which is lower
Albian (112.2–106 Ma) in age (Jacobs & Winkler 1998).
Description and comparisons
In the following description, abbreviations for vertebral
laminae and fossae follow Wilson (1999) and Wilson
et al. (2011), respectively. Comparisons are made where
relevant; other comparative information can be found in
the differential diagnosis or Discussion below.
Tooth
SMU 203/73655 (Fig. 3) is missing its enamel, but details
of its morphology and wear are still evident. It is uncer-
tain what part of the jaw the tooth comes from. The tooth
is 17 mm long, 5.6 mm wide labiolingually, and 6.4 mm
wide mesiodistally. It is very slightly spatulate, with a
midline longitudinal groove on its lingual face and a broad
arch across the labial face (Fig. 3). The crown–root junc-
tion is not clearly preserved, precluding precise calculation
of the slenderness index (mesiodistal crown width/crown
height; Upchurch 1998). However, the slenderness index
would be somewhere around 2.7, which is intermediate
between values observed in narrow-crowned diplodocoids
and titanosaurs, and broad-crowned basal titanosauriforms
and more primitive sauropods (Chure et al. 2010, fig.
5). The slenderness index of Astrophocaudia is close to
the average value observed for Abydosaurus (Chure et al.
2010). Its wear facet is nearly planar and is angled either
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6M.D.D’Emic
Figure 5. Selected vertebrae of the holotypic anterior-middle caudal vertebral series of Astrophocaudia slaughteri (SMU 61732) in: A,
left lateral; B, anterior; and C, posterior views. Numbers below each vertebra indicate its likely position in the caudal sequence. The 10th
caudal vertebra is reversed in A. Dashed lines indicate missing bone. Scale bar =10 cm.
mesially or distally, but not labiolingually. There is a very
slight axial twist towards the apex of the tooth, though not
as great as in the upper teeth of Abydosaurus (Chure et al.
2010).
Presacral vertebrae
One partial middle to posterior cervical vertebra and frag-
ments of several posterior cervical or anterior dorsal verte-
brae are accessioned as part of SMU 61732. Little can be
said about the morphology of the more fragmentary verte-
brae, so description will focus on the middle to posterior
cervical vertebra.
The mid-cervical vertebra has been sheared dorsally on
its right side, exposing the ventral face of the centrum in
right lateral view (Fig. 4). Its centrum is 48 cm long, and
the partially fused neurocentral junction is still visible ante-
riorly and posteriorly as well-defined furrows offsetting the
neural arch pedicles. The posterior centrum is 24 cm wide
and 15 cm tall but is sheared, so the actual measurements
would have been closer to 22 ×17 cm. The elongation index
(EI =centrum length/posterior centrum height; Upchurch
1998) cannot be determined reliably due to the deformation
mentioned above, but is between 2.8 and 3.2. The average
EI (aEI =centrum length divided by average of posterior
width and height; Chure et al. 2010) equals 2.5. The aEI
varies along a vertebral column in sauropods; it is gener-
ally highest in the middle cervical vertebrae. The aEI of
this vertebra of Astrophocaudia is intermediate between
the low values observed in basal macronarians (e.g. Cama-
rasaurus) and the high values (above 4.0) observed in many
titanosauriforms (e.g. Giraffatitan,Malawisaurus; Chure
et al. 2010).
The centrum is strongly opisthocoelous and has a flat
to slightly concave bottom that lacks ridges, fossae or
foramina. Pneumaticity is extensive in the centrum and its
lateral face is highly subdivided into pneumatic camerae
and camellae that are about 1–8 cm in their longest dimen-
sion, ramify into decreasingly smaller cavities, and are
separated by 1–3 mm thick bony walls. A sharp ridge
on the dorsolateral face of the centrum delimits the pneu-
matic areas of the centrum from those of the neural arch.
The mid-posterior cervical vertebra appears to possess the
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Trinity Group sauropods 7
Figure 6. Prezygapophyses and hypantra of the 3rd and 6th
preserved caudal vertebrae of the holotype of Astrophocaudia
slaughteri (SMU 61732) in anterolateral view. Dashed lines indi-
cate missing bone. Scale bar =1cm.
Figure 7. Selected vertebrae of the holotypic posterior caudal
vertebral series of Astrophocaudia slaughteri (SMU 61732) in:
A, left lateral; B, anterior; and C, posterior views. Numbers below
each vertebra indicate likely position of the vertebra in the caudal
sequence. Dashed lines indicate missing bone. Scale bar =10 cm.
Figure 8. Holotypic dorsal rib of Astrophocaudia slaughteri
(SMU 61732) in: A, lateral; and B, posterior views. Dashed lines
indicate missing bone. Scale bar =10 cm.
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8M.D.D’Emic
Figure 9. Holotypic chevron of Astrophocaudia slaughteri (SMU
61732) in: A, anterior; B, proximal (line drawing); C, posterior;
and D, lateral views. Dashed lines indicate missing bone. Scale
bar =5cm.
camellate or somphospondylous condition sensu Wedel
(2003), with several generations of sub-centimetre branch-
ing chambers that permeate the centrum. Much of the
neural arch is damaged, and the neural spine is largely
missing. The anterior centrodiapophyseal lamina and prezy-
gapophyseal diapophyseal lamina are well developed, and
the fossa between them (prezygapophyseal centrodiapophy-
seal fossa) is subdivided.
Caudal vertebrae
Langston (1974) listed 21 caudal vertebrae as belonging
to SMU 61732. In addition to these, three vertebrae
were located in a drawer with other materials of SMU
61732, along with a notecard, which reads: “Walnut Creek
Loc. Paluxy Fm. Sauropod Loc. Turtle vertebrae” (pers.
obs. 2009). These caudal vertebrae and the 21 presented
by Langston (1974) are from a single quarry and are
appropriate in morphology, size, and preservation to
represent a single series. With these additional vertebrae,
the holotypic caudal vertebral series includes a total of
24 preserved vertebrae (Figs 5–7). Additional fragments,
including zygapophyses, neural spines, and transverse
processes, were recovered from boxes of fragments from
the site and reattached in August 2009.
Figure 10. Holotypic partial scapula of Astrophocaudia slaugh-
teri (SMU 61732) in lateral view with cross section indicated.
Dashed lines indicate missing bone. Scale bar =10 cm.
All regions of the tail are well represented, aside from the
anteriormost caudal vertebrae. The anteriormost preserved
caudal vertebra is likely the eighth in the series, based on
comparisons with Giraffatitan brancai and Cedarosaurus
weiskopfae. After this, there is a gap of 1–2 vertebrae, and
then a series of five consecutive caudal vertebrae. The rest
of the preserved tail is made up of series of one to six
vertebrae with gaps between. Estimated vertebral positions
are given in Figs 5 and 7. In the description below, vertebrae
will be numbered according to their most likely anatomical
position.
Over the course of the caudal vertebral series, the centra
maintain a width:height ratio of roughly 1:1 (Table 2). In
caudal vertebra eight, the lateral walls of the centrum angle
inwards ventrally and are delimited from the flat ventral
face by a weak ridge. This ridge persists to about caudal
vertebra 25, whereas distal caudal vertebrae are cylindrical
in cross section. There are no fossae on the lateral or ventral
faces of any of the caudal vertebral centra, and all of the
caudal vertebral centra and neural arches have a solid (i.e.
non-camerate or camellate) bone texture. With the neural
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Trinity Group sauropods 9
Figure 11. Holotypic partial right ilium of Astrophocaudia
slaughteri (SMU 61732) in: A, dorsal; and B, lateral views.
Dashed lines indicate missing bone. Scale bar =10 cm.
canal held horizontally, the centrum and neural spines of the
anterior and middle caudal vertebrae are nearly vertically
oriented (Fig. 5).
The anterior face of the first preserved (eighth) caudal
centrum is concave, and the posterior face is irregular in
shape, but overall flat (Fig. 5). The eighth and tenth caudal
vertebral centra have concave anterior faces, and posterior
faces that are flat or weakly concave. In the next vertebra,
both faces are concave, but the anterior concavity is greater
than the posterior. This type of articulation, termed ‘plani-
concave’ by Tidwell et al. (2001) has been proposed as an
autapomorphy of Cedarosaurus. However, this condition
is present in several sauropods, including Camarasaurus
(YPM 1905; pers. obs. 2007), Brachiosaurus altithorax
(FMNH P 25107; pers. obs. 2008) and Sauroposeidon
(FWMSH 93-B; see below; pers. obs. 2009). The rest of
the vertebrae, excepting the last few, have equally weakly
concave anterior and posterior faces (i.e. weakly amph-
icoelous). The last few are a mix of procoelous and biconvex
centra as in some vertebrae referred to Giraffatitan brancai
(HMN MB.R 5000; pers. obs. 2008) and some titanosaurs
(e.g. Trotta et al. 2002; Calvo & Gonz´
alez Riga 2003).
The neural spines of the more anterior caudal verte-
brae are composed anterolaterally of spinoprezygapophy-
seal laminae. In caudal vertebrae 8–15, the prespinal lamina
rugosity reaches all the way to the intraprezygapophyseal
lamina. The spinoprezygapophyseal fossa is narrow and
shallow. In the tenth caudal vertebra in the series, there is
a slight transverse expansion of the neural spine distally.
Tab le 2. Measurements of the holotypic caudal vertebrae of
Astrophocaudia slaughteri (SMU 61732) in cm. e =estimated
measurement; d =measurement influenced by distortion.
Centrum width and height measured at posterior face.
Estimated position
in series
Centrum
length
Centrum
width
Centrum
height
8 ———
10 7.215.6e —
11 ———
12 9.710.2e 10e
13 9.110.39.2
14 8.79.48.9
15 7.410.28.6
19 8.86.87.1
20 9.16.67.4
22 8.66.46.7
23 8.77.4d 5.9d
24 8 6e 6.2
25 7.36.5d 6.3
26 7.26.85.8
27 8.16.45.5
30 7.85.45.2
31 7.25.45.2
33 6.84
.34.3
37 6.9——
38 6.5——
39 5.73.43.1
43 5.1e 2.6e 1.8e
46 4.51.51.6
48 — 1.31.2
In all other caudal vertebrae, the lateral faces of the neural
spine are parallel. In the eighth caudal vertebra of the series,
the neural spine has a ‘saddle’ at its midpoint (Fig. 5), as
in some vertebrae of Venenosaurus (DMNH 40392; pers.
obs. 2010) and Camarasaurus (Ostrom & McIntosh 1966,
pl. 37). Some mid-posterior caudal vertebrae have a slight
anterior projection on the neural spine (Fig. 7). On the
neural arch, there is a small fossa in front of the postzy-
gapophyses that represents a combined postzygapophyseal
spinodiapophyseal fossa plus a postzygapophyseal centro-
diapophyseal fossa. The remnants of this fossa persist as a
subtle depression until caudal vertebra 15.
The zygapophyses and hyposphene–hypantrum articula-
tions undergo dramatic morphological changes along the
caudal vertebral series. In the first caudal vertebra that
preserves zygapophyses (caudal vertebra 10), the pre- and
postzygapophyses are large and subhorizontally oriented,
and the hyposphene is subequal in size to the postzygapoph-
ysis. The postzygapophyses and hyposphene are both planar
and meet at an angle of about 80◦(Fig. 5). More posteriorly
in the caudal vertebral series, the zygapophyseal articu-
lar surfaces decrease in size faster than the hyposphene-
hypantrum articular surfaces. By caudal vertebra 20, the
intervertebral neural arch articulation is represented by a
single, vertical plane, as in other sauropods (e.g. Cama-
rasaurus,Giraffatitan,Mendozasaurus).
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10 M. D. D’Emic
Dorsal ribs
A total of about 20 fragmentary dorsal ribs are present;
none are ‘plank-like’ (cross section more than three times
wider than broad). Some of the preserved ribs approach this
condition (cross sectional ratio 2.8), so Astrophocaudia may
have plank-like ribs as do titanosauriforms (Wilson 2002).
The largest dorsal rib is pneumatic as in Titanosauriformes
(Fig. 8). There is an oval, ridged tubercle on the anterior
half of the proximolateral part of the largest dorsal rib (Fig.
8A). This feature is absent in the only other dorsal rib that
preserves this portion of the shaft.
Chevrons
Langston (1974) reported a single chevron with SMU
61732. In the process of studying the material, a second
was discovered. Both come from the anterior region of the
tail. The more complete chevron is missing only its distal-
most blade (Fig. 9). It is 24.2 cm long and has an open hemal
canal measuring 9.1 cm deep dorsoventrally. On the anterior
face of the blade, there is a flattened oval boss measuring
1.2 ×4 cm that has a texture of ridges and grooves (Fig. 9).
Each arm of the chevron bears a single articular facet with
a medially pointed process.
Scapula
A distal scapular blade (Fig. 10) is preserved, which will be
described as if held subvertically. The blade has complete
anterodorsal and posteroventral margins, and is almost
complete distally. It could represent a left or right scapula,
as the preserved part is symmetrical about its long axis.
The preserved length is 70 cm. Its breadth ranges from
17 to 38.5 cm, giving a minimum/maximum width ratio of
about 2.3. The scapular blade is less than 1 cm thick distally
and about 3 cm thick at the centre of the broken base of
the blade. The base of the blade is flat in cross section as
in Euhelopus and titanosaurs, rather than D-shaped with a
broad lateral ridge as in non-somphospondylans (Wilson
& Sereno 1998). The bone has a texture of subtle, axially
oriented ridges and grooves on the exterior face of the bone.
Ilium
The acetabular region and part of the preacetabular process
of the right ilium are present (Fig. 11). The preacetabular
lobe of the ilium flares outward at about 45◦along a gentle
curve, as in most titanosauriforms (Salgado et al. 1997).
No evidence of pneumaticity exists in the preserved ilium.
A subtle ridge extends anteroposteriorly above the pubic
peduncle on the lateral face of the ilium, as in some other
sauropods (e.g. Camarasaurus; Ostrom & McIntosh 1966).
This ridge helps to delimit a subtle subtriangular fossa just
above and in front of the public peduncle, as in some other
sauropods (e.g. Cetiosaurus; Upchurch & Martin 2003).
The ventral edge of the preacetabular process is crushed
inwards. The total preserved length of the element is
45 cm.
Genus Cedarosaurus Tidwell et al., 1999
Type species. Cedarosaurus weiskopfae Tidwell et al.
1999.
Cedarosaurus weiskopfae Tidwell et al. 1999
(Figs 12–15)
1974 Pleurocoelus sp. Langston: 85, figs 5, 6a.
1989 Pleurocoelus sp. Gallup: 71, figs 1–5.
1997 Pleurocoelus Salgado & Calvo: 44, fig. 9.
1999 Cedarosaurus weiskopfae Tidwell et al.: 22, figs 2–11.
Holotype. DMNH 39045, a partial skeleton consisting of
dorsal and caudal vertebrae, dorsal ribs, chevrons, partial
left and right scapulae, coracoids and sternal plates, a
right humerus, radius, ulna, and metacarpal IV, partial right
and left pubes, ischia, and femora, a right tibia and right
metatarsals I, II and V.
Holotype locality, horizon and age. Early Cretaceous
Yellowcat Member of the Cedar Mountain Formation, Utah,
USA, Barremian–Aptian (Tidwell et al. 1999; Greenhalgh
& Britt, 2007).
Referred material. FMNH PR 977, a partial hind limb
including an incomplete tibia and fibula, an astragalus,
five metatarsals and 11 phalanges. Paluxy Formation,
Aptian–Albian (Jacobs & Winkler 1998), 20 km south of
Decatur, Texas, USA.
Revised diagnosis. Autapomorphies of Cedarosaurus
weiskopfae include: radius with well-developed flange
lateral to ulnar articulation (Tidwell et al. 1999), radius
with tubercle on anterior face of shaft, one-third of the
way from proximal end, metatarsal II with well-developed
medial and lateral tubercles at mid-shaft (pers. obs. 2010).
FMNH PR 977 is referable to Cedarosaurus on the basis of
two additional autapomorphies: metatarsal V only slightly
expanded proximally, and metatarsal V around 1.5 times
longer than metatarsal I. Also, FMNH PR 977 possesses
four well-developed pedal unguals and a phalanx on
metatarsal V, providing two additional autapomorphies for
Cedarosaurus.
Description
The following description focuses on material referred
to Cedarosaurus weiskopfae, which consists of a partial
hind limb described by Gallup (1989). For description and
comparisons of the holotype of Cedarosaurus, see Tidwell
et al. (1999).
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Trinity Group sauropods 11
Figure 12. Metatarsals I–V, referable to Cedarosaurus weiskopfae (FMNH PR 977). in dorsal (top row) and lateral (bottom row) views.
Dashed lines indicate missing bone. Scale bar =10 cm.
Crus and tarsus
About three-quarters of the tibia and fibula are preserved
in several pieces (Gallup 1975). The preserved lengths of
the tibia and fibula are about 71 and 95 cm, respectively.
The tibia is oval in cross section, and its midshaft measures
16.1 cm anteroposteriorly by 8.4 cm transversely. The
fibula is roughly D-shaped in cross section with a slightly
concave medial margin, and its midshaft measures 11.6 cm
anteroposteriorly by 5.7 cm transversely. The astragalus is
extremely crushed dorsoventrally. It resembles the astragali
of most sauropods (e.g. Camarasaurus) in its proportions
and rugose texture. No calcaneum was found with the
specimen.
Metatarsals
Five metatarsals are preserved (Figs 12, 13). Metatarsals
II–IV are incomplete distally, and the second and fifth are
crushed dorsoventrally (Fig. 12). The proximal articular
surface is largest on metatarsal I, and it is slightly smaller
or subequal for metatarsals II–IV. All of the metatarsals have
slightly concave proximolateral faces for the articulation of
the adjacent metatarsal. In dorsal view, the lateral margin
of each metatarsal is more tightly curved than the medial,
as in most sauropods. The metatarsals increase in length
laterally such that metatarsal V is the longest and about 1.8
times longer than metatarsal I. The long axis of the proximal
end of metatarsals I and III is oriented dorsoventrally and
roughly orthogonally with respect to the long axis of their
distal ends, which is oriented mediolaterally (Figs 12, 13).
Metatarsal I is subtriangular in proximal view, coming
to a point dorsally. The articular facet for ungual I.1 is
bevelled dorsomedially (Figs 12, 13). Metatarsals II–IV are
subrectangular proximally. Little can be said about their
distal ends due to deformation and extensive plaster recon-
struction (Fig. 12). Metatarsal V is much broader trans-
versely than dorsoventrally, and is only slightly narrower
transversely at its midshaft than at its distal end (Fig. 12).
Phalanges
Eleven phalanges were preserved with the foot, includ-
ing four unguals (Figs 14, 15). The first digit is the only
one for which an exact phalangeal count (two) is known.
Three are definitively the proximalmost phalanges of digits
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12 M. D. D’Emic
Figure 13. Articulated pes referable to Cedarosaurus weiskopfae
(FMNH PR 977) in: A, proximal; and B, anterodorsal views.
Dashed lines indicate missing bone. Scale bar =10 cm.
Figure 14. Phalanx I.1 referable to Cedarosaurus weiskopfae
(FMNH PR 977) in: A, proximal; B, distal; C, ventral; and D,
medial views. Scale bar =5cm.
Figure 15. Unguals referable to Cedarosaurus weiskopfae
(FMNH PR 977). A, ungual of digit I in proximal, medial and
dorsal views; B, ungual of digit II in proximal, medial and dorsal
views; C, ungual of digit III in proximal, medial and dorsal views;
D, ungual of digit IV in proximal, medial and dorsal views. Scale
bar =10 cm. Dashed lines indicate missing bone.
2–4 based on their large size, and a small phalanx belongs
to metatarsal V because it is too small to be the penul-
timate phalanx on any of the other digits, which bear
unguals. The best-estimate phalangeal formula is 2-3-3-3-1
(Fig. 13), but there is a range of possibilities based on other
sauropods (e.g. 2-(2-3)-(2-4)-(2-4)-1; Gonz´
alez Riga et al.
2008). Phalanx I.1 is wedge-shaped. The remaining non-
terminal unguals are roughly trapezoidal in dorsal view with
constricted midshafts and oval proximal faces. The inner-
most three unguals are about 1.7 times longer than tall and
have dorsally acuminate oval proximal faces (Fig. 15). Each
bears variably developed nail-grooves. The presence of a
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Trinity Group sauropods 13
Figure 16. Bone histology of Paluxysaurus jonesi. A, micropho-
tograph of a thin section of the humerus (FWMSH 93B-10);
B, microphotograph of a thin section of the femur (FWMSH 93B-
10). Thin sections reveal wide vascular canals in primarily laminar
fibrolamellar bone, which indicates that these individuals were not
at adult size at death. Scale bar is the same for A and B.
large claw on metatarsal IV is regarded as an autapomorphy
among eusauropods (Upchurch 1995, 1998; Wilson 2002).
Sauroposeidon Wedel et al., 2000a
Type species. Sauroposeidon proteles Wedel et al., 2000a.
Sauroposeidon proteles Wedel et al. 2000a
(Fig. 16)
2000a Sauroposeidon proteles Wedel et al.: 110, figs 1, 2,
4.
2007 Paluxysaurus jonesi Rose: 5, figs 4–27.
Holotype. OMNH 53062, four middle cervical vertebrae.
Holotype locality, horizon and age. Early Cretaceous
(Aptian–Albian) Antlers Formation of southern Oklahoma,
USA.
Referred material. Referred material (see below) includes
holotypic and referred materials of Paluxysaurus jonesi
Rose 2007: FWMSH 93B-10-1 through FWMSH 93B-
10-51, TMM 42488. Early Cretaceous (Aptian–Albian)
Twin Mountains Formation of north-central Texas, USA.
(Winkler et al. 1990). The Twin Mountains Formation
is laterally equivalent to the Antlers Formation. Some of
the material reported by Ostrom (1970) from the Cloverly
Formation is likewise referable to Sauroposeidon,the
details of which will be dealt with in future work (see also
Wedel & Cifelli 2005).
Revised diagnosis. Extreme elongation of the middle
cervical vertebrae (length/posterior centrum height >6),
middle cervical vertebrae with posterior expansion of the
pneumatic fossa to the cotyle, neural spines perforated in
middle cervical vertebrae, top of neural spine with broad
midline ridge flanked by small fossae at its anterior and
posterior ends, middle and posterior dorsal neural spines
that taper distally, anterior caudal vertebral centra roughly
square in cross section, anterior caudal vertebrae with diver-
gent spinoprezygapophyseal laminae (angle greater than
50◦) forming wide spinoprezygapophyseal fossae, scapula
with two processes at the base of the ventral edge of the
blade, humerus gracile, length/midshaft width >7.5.
Remarks. Sauroposeidon proteles and Paluxysaurus
jonesi are from laterally equivalent units and have been
hypothesized to be closely related to the brachiosaurids
Brachiosaurus and Giraffatitan (Wedel et al. 2000b; Rose
2007). Because of their close spatiotemporal similarity
and proposed phylogenetic affinity, it is possible that
Sauroposeidon and Paluxysaurus represent a single taxon.
Seven autapomorphies were originally proposed to diag-
nose Sauroposeidon proteles (Wedel et al. 2000a, b). Four
of these features characterize a wider group of titanosauri-
forms, including extreme elongation of cervical vertebrae
(e.g. Erketu, Ksepka & Norell 2006; Euhelopus, Wilson
& Upchurch 2009); internal somphospondylous vertebral
pneumaticity (e.g. Chubutisaurus, Salgado et al. 1997;
Euhelopus, Wilson & Upchurch 2009), extremely long
cervical ribs (e.g. Rapetosaurus, Curry Rogers 2009), and
a ‘centroparapophyseal lamina’ (Wedel et al. 2000a, b),
which is similarly developed in some large vertebrae of
Giraffatitan brancai (e.g. Janensch 1950, figs 40, 42; pers.
obs. 2008) and Euhelopus (Wiman 1929, pl. 3; Wilson
& Upchurch 2009). Wedel et al. (2000b) described the
latter feature as differing between Sauroposeidon and Giraf-
fatitan, but existing differences in their development and
orientation are minor when serial variation within Giraf-
fatitan itself is taken into account. Three of the proposed
autapomorphies of Sauroposeidon (Wedel et al. 2000b)
are shared with Paluxysaurus: extremely thin-walled to
perforate neural spines in mid-cervical vertebrae, poste-
rior expansion of the lateral pneumatic fossa of the centrum
(‘pleurocoel’), and the posterior placement of the diapophy-
ses in larger cervical vertebrae (Rose 2007).
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14 M. D. D’Emic
Besides the autapomorphies presented by Wedel
et al. (2000a, b), Rose (2007) proposed three features to
distinguish Sauroposeidon from Paluxysaurus: absence of
an anterior centrodiapophyseal lamina, wider neural arches,
and a wider prezygapophyseal diapophyseal lamina than
Sauroposeidon. However, re-examination of the vertebrae
of both exemplars indicates that these features do not distin-
guish them. There are multiple laminae beneath the arm
of the prezygodiapophyseal lamina (prdl) in both exem-
plars (see Wedel et al. 2000b, fig. 6; Rose 2007, figs 7, 8;
pers. obs. 2009). The anterior centrodiapophyseal lamina
appears unusually large on the sixth cervical vertebra of
Paluxysaurus (Rose 2007, fig. 8) because this vertebra has
been sheared upwards and backwards on its right side.
Despite this shearing, it is apparent that the vertebrae of
the two taxa do not differ in breadth of the centrum or the
width of the prezygodiapophyseal lamina (prdl).
Although there are no substantive morphological
differences between their exemplars, the two taxa differ
substantially in size: the sixth to eighth cervical vertebrae
of Sauroposeidon have centra (including condyles) that are
around 1.25 m long, whereas the largest known vertebra
of Paluxysaurus (FWMSH 93B-10-30) was estimated to
have a centrum length of 0.83 m (Rose 2007). In order to
evaluate the meaning of this size difference, morphological
and histological features relevant to ontogeny are described
below.
Description
The following description focuses on demonstrating the
juvenile nature of exemplars of ‘Paluxysaurus jonesi’in
order to substantiate its referral to Sauroposeidon prote-
les. For description and comparisons of the holotype of
Sauroposeidon proteles, see Wedel et al. (2000a, b), and
for description and comparisons of ‘Paluxysaurus jonesi’
see Rose (2007).
All of the neurocentral sutures of the holotypic cervical
vertebrae of Sauroposeidon are fully fused, suggesting that
it was at or near adult size (Ikejiri 2003). In contrast, some
cervical and dorsal vertebrae referred to Paluxysaurus (e.g.
FWMSH 93B-10-8, -13, -30) have slight furrows repre-
senting their neurocentral sutures near their condyles and
cotyles (pers. obs. 2009). In addition, the last sacral verte-
bra and ilia of one specimen of Paluxysaurus are not fully
fused into the sacrum (pers. obs. 2009), and one of the
coracoids is not fused to a scapula (Rose 2007), provid-
ing evidence that these individuals were not fully skeletally
mature (Schwarz et al. 2007). The femora and humeri in the
Jones Ranch quarry do not differ by more than 10% in size
(Rose 2007), so all of the quarry individuals were likely of
similar ontogenetic age.
In order to more precisely determine the ontogenetic
age of the Paluxysaurus specimens, midshaft samples of a
referred fragmentary humerus (FWMSH 93-B-10-7; Rose
2007, fig. 23, subfigures 8–11) and left femur (FWMSH
93-B-10) were taken with a diamond-tipped drill accord-
ing to the methodology of Stein & Sander (2009). Due to
the impermeable but friable nature of the bones, stabiliza-
tion with glue and extraction of the cores was difficult, and
the outermost few millimetres of bone were lost from one
core. A second sample from the femur preserves the entire
periosteum, but is slightly off-centre and distal relative to
the mid-shaft sample. It is uncertain whether or not the
femur and humerus belonged to a single individual.
Thin sections of the humeral and femoral cores reveal
a cortex composed of fibrolamellar bone, as in most other
sauropods (Fig. 16; Klein & Sander 2008). Most of the bone
texture is parallel-fibred, and vascular canals are relatively
open. Only one line of arrested growth is visible in each
section. The presence of an external fundamental system
is equivocal in the humerus and one of the femoral cores
due to damage, but it was absent in the femoral section
that preserves the periosteum. A few secondary osteons are
present within the outer centimetre of both cortices, but
these do not form a solid remodelling front.
The bone represented in the outer cortex of the humerus
represents types D and E of Klein & Sander (2008), which
approximates to these authors’ histological ontogenetic
stage 8 or 9. This indicates that this individual was not
at adult size. Femora and humeri of Giraffatitan brancai at
histological ontogenetic stage 8–9 can be one-half to three-
quarters the size of the largest known individuals of that
species (see Klein & Sander 2008, fig. 4G).
In summary, lack of substantial morphological or defini-
tive size differences and shared unique features (see diag-
nosis above) suggest that Paluxysaurus jonesi and Sauro-
poseidon proteles represent the same species.
Discussion
Phylogenetic affinities of sauropod remains
from the Trinity Group and Antlers
For ma tion
The proposed phylogenetic affinities of sauropods from
Trinity–Antlers strata have not been as complex as their
taxonomic identities, with all authors agreeing that they
represent basal titanosauriforms or titanosaurs. As shown
above, most of the material making up ‘Pleurocoelus’
from Texas discussed by Salgado et al. (1997) and other
authors (Langston 1974; McIntosh 1990; Upchurch et al.
2004) is instead attributable to Astrophocaudia (SMU
61732), Cedarosaurus (FMNH PR 977) or Sauroposeidon
(FWMSH 93B-10; TMM 42488). Salgado et al. (1995,
1997) suggested that ‘Pleurocoelus nanus’ is the sister
taxon to Titanosauria, and ‘Pleurocoelus sp.’ from Texas
is a basal titanosaur. The characters listed as supporting
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Trinity Group sauropods 15
titanosaur or near-titanosaur affinities – for example, a
single prespinal lamina in dorsal vertebrae – are now
recognized as features characterizing a wider clade than
Titanosauria (Carballido et al. 2011). Sauroposeidon was
described as a brachiosaurid (Wedel et al. 2000a) and
recovered as such (as ‘Paluxysaurus’) in the phylogenetic
analysis of Rose (2007). Upchurch et al. (2004) and Naish
et al. (2004) also suggested that Sauroposeidon was a
brachiosaurid. Referral of material from the Cloverly
Formation to Sauroposeidon (Wedel et al. 2000b; D’Emic
and Foreman in press) augments the available data relevant
to its phylogenetic position. Ostrom (1970) pointed out
some features shared between sauropod material from
the Cloverly Formation (e.g. YPM 5449) and titanosaurs
(such as a robust ulna); these features contrast with the
brachiosaurid–Sauroposeidon links proposed by Wedel
et al. (2000a, b), Naish et al. (2004) and Rose (2007).
The taxonomic revisions presented above augment,
combine and redistribute some apomorphies of the Trinity
Group sauropods. With this new information in hand, a
cladistic analysis of basal titanosauriform relationships
was conducted, including 119 characters and 22 ingroup
taxa. Shunosaurus (Dong et al. 1983), Omeisaurus (He
et al. 1988; Tang et al. 2001) and Jobaria (Sereno
et al. 1999) were used as outgroup taxa. Provenance and
reference information for each terminal taxon is listed
in the Online Supplementary Material. Most characters
were culled from the literature (e.g. Upchurch 1998;
Wilson 2002), and many of these characters are novel. The
character–taxon matrix and character list are presented
in the Online Supplementary Material. Characters were
entered into MacClade (Maddison & Maddison 1992) and
analysed in PAUP∗(Swofford 2000). A branch and bound
search using the tree bisection and reconnection algorithm
yielded 33 equally most parsimonious trees of length 197
steps (Fig. 17; consistency index =0.64; retention index =
0.80). Decay indices for many nodes in the tree were equal
to one but others, such as those supporting Brachiosauri-
dae, Somphpospondyli and Titanosaurifromes, were higher
(Fig. 17).
Both Astrophocaudia and Sauroposeidon are recovered
as members of Somphospondyli more derived than Liga-
buesaurus, in a polytomy with Tastavinsaurus,Chubuti-
saurus,Phuwiangosaurus and Euhelopus. Nine steps are
required to move Sauroposeidon into the Brachiosauridae,
and 10 steps are required to position it within Titanosauria.
Templeton tests (see Larson 1994; Wilson 2002) reject
both titanosaur and brachiosaurid affinities for Sauro-
poseidon (n=36 and p<0.0001 for Titanosauria;
n=21, p=0.03 for Brachiosauridae). Astrophocaudia
Figure 17. Phylogenetic relationships of Astrophocaudia,Sauroposeidon,andCedarosaurus among basal titanosauriforms. Numbers to
the right of each node indicate the decay index; if no number is listed, decay index =1. Abbreviations: CI, consistency index; mpts, most
parsimonious trees; RI, retention index; TL, treelength.
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16 M. D. D’Emic
and Sauroposeidon are recognized as titanosauriforms
based on the presence of camellate presacral vertebrae,
pneumatic dorsal ribs, a flared iliac preacetabular process,
and caudal vertebrae with neural arches situated ante-
riorly. Somphospondylan features of Astrophocaudia
and Sauroposeidon include somphospondylous vertebral
pneumaticity (sub-centimetre cells with sub-millimetre
walls that permeate the vertebra) and a scapular blade with
a flat cross section at its base. Sauroposeidon possesses
numerous other somphospondylan synapomorphies,
including anterior dorsal vertebrae with a single prespinal
lamina and flat, ‘paddle-shaped’ neural spines, a medially
bevelled scapular glenoid, an ischial blade that is shorter
than the pubic blade, and a proximally embracing tibia and
fibula. Cedarosaurus is a brachiosaurid titanosauriform
on the basis of a high humerus-to-femur ratio, gracile
humerus, rounded humeral proximolateral corner, and
anterior and middle caudal vertebrae with sporadically
distributed, shallow fossae in lateral faces of centrum.
Several sauropod remains that are indeterminate to
the genus level have been reported from Trinity–Antlers
strata, including a coracoid (Larkin 1910), ischium (Gallup
1975) and teeth (Gallup 1975; Maxwell & Cifelli 2000).
Langston (1974) mentioned a partial skeleton from the
Glen Rose Formation of Blanco County, Texas (TMM
40435; see also Tidwell & Carpenter 2003). This specimen
is a juvenile based on the lack of neurocentral fusion
in some vertebrae, and the lack of fusion among the
laterosphenoids, prootics, parietals and frontals (pers. obs.
2008). This skeleton represents a titanosauriform based on
the presence of camellate presacral vertebral pneumaticity,
but is not diagnostic at the genus level.
Latitudinal homogeneity in Early
Cretaceous North American dinosaur faunas
The referral of Paluxysaurus and some Cloverly Forma-
tion sauropod material (Ostrom 1970; D’Emic and
Foreman in press) to Sauroposeidon, as well as the refer-
ral of the hind limb from the Glen Rose Formation to
Cedarosaurus, reinforces proposed faunal links among the
Trinity Group, Antlers Formation, Ruby Ranch Member of
the Cedar Mountain Formation, and the Cloverly Formation
(Langston 1974; Winkler et al. 1990; Jacobs & Winkler
1998). Nydam & Cifelli (2002) challenged the temporal
correlation of the Cloverly and Antlers formations on the
basis of their disparate lizard faunas, but noted similar-
ity between the Cloverly and Twin Mountains formations.
However, at the spatiotemporal scale of sampling in these
formations, palaeoenvironmental biases can also explain
the observed differences in faunal compositions, especially
when dealing with small taxa of probable small geographi-
cal range (Winkler et al. 1990).
Though separated by over 15◦of palaeolatitude (1500
km; Fig. 2), four dinosaur genera are shared between
the penecontemporaneous Twin Mountains/Antlers
and Cloverly formations: Tenontosaurus,Deinonychus,
Sauroposeidon and Acrocanthosaurus (D’Emic et al. in
press). The formations also share multiple non-dinosaur
genera, as well as some suprageneric dinosaur taxa such
as Nodosauridae and an unnamed clade of small basal
ornithopods (Jacobs & Winkler 1998). This degree of
faunal similarity over 15◦of palaeolatitude stands in
contrast to the latitudinal variation present in dinosaur
faunas observed in the Late Cretaceous (Lehman 1987,
2001). Decades of exploration and analyses of Late
Cretaceous North American strata have reinforced this
latitudinal variation (Gates et al. 2010; Mannion et al. in
press), whereas increased data and study of Early Creta-
ceous faunas has reinforced its latitudinal homogeneity.
Proposed explanations for Late Cretaceous latitudinal
variation (e.g. climate) could be tested against the more
homogenous pattern observed in the Early Cretaceous.
Conclusions
Historically, Early Cretaceous sauropods from North
America were referred to the genera Pleurocoelus or
Astrodon from the Early Cretaceous Arundel Formation
of Maryland. A lack of associations and non-diagnostic
type specimens means that species of Astrodon and
Pleurocoelus (Table 1) are nomina dubia.
Because these Maryland species are invalid, materials
previously referred to them were re-examined. A single
partial skeleton previously referred to ‘Pleurocoelus sp.’
from the Trinity Group represents a new taxon, Astropho-
caudia slaughteri. Material from the Trinity Group desig-
nated as Paluxysaurus jonesi are morphologically similar
to and bear autapomorphies of Sauroposeidon,haveasimi-
lar spatiotemporal provenance, and were not at their adult
body size. Paluxysaurus is a junior synonym of Sauroposei-
don, which is also represented in the Cloverly Formation of
Wyoming (Ostrom 1970; Wedel et al. 2000b; D’Emic and
Foreman in press). This augmentation makes Sauroposei-
don one of the best-known Early Cretaceous North Amer-
ican sauropods, whereas previously it was one of the most
poorly known. A hind limb from the Trinity Group previ-
ously referred to ‘Pleurocoelus’ (Langston 1974) is referred
to Cedarosaurus weiskopfae on the basis of pedal synapo-
morphies. Cladistic analysis indicates that Cedarosaurus is
a brachiosaurid, whereas Astrophocaudia and Sauroposei-
don are members of the Somphospondyli. The revision of
the taxonomic and phylogenetic affinities of Sauroposeidon
have implications for the affinities of fragmentary sauropod
remains that have been linked to the genus from other land-
masses and geological time periods (e.g. Naish et al. 2004;
You & Li 2009).
The sauropod dinosaurs Sauroposeidon and
Cedarosaurus were widespread in western North America
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Trinity Group sauropods 17
in the Early Cretaceous, reinforcing links among northern
and southern faunas first drawn based on other dinosaurs
(Jacobs & Winkler 1998). This relative homogeneity
suggests that provincialism among North American
dinosaur faunas with respect to latitude developed only
later in the Cretaceous.
Acknowledgements
This paper represents a portion of my doctoral thesis
at the University of Michigan. Thanks go to A. Pan
and L. Ballinger (FWMSH), K. Carpenter (DMNS), D.
Winkler and L. Jacobs (SMU), M. Carrano and M. Brett-
Surman (USNM), R. Cifelli (OMNH), L. Murray and T.
Rowe (TMM), B. Simpson (FMNH), D. Schwarz-Wings
(Humboldt Museum), W. Joyce and D. Brinkman (YPM),
D. Colodner (ASDM), and J. Diffily and the mounting crew
at the Reid workshop in Azle, Texas, for collections access.
D. Winkler is thanked for permission to describe, and infor-
mation pertaining to, Astrophocaudia; A. Pan, L. Ballinger
and D. Colodner (ASDM) for permission to destructively
sample limb bones for histology; M. Sander and K. Stein
(University of Bonn) for helpful technical information
about drilling sauropod bones; D. Fisher (University of
Michigan) for use of thin-sectioning equipment; K. M.
Smith (Georgia Southern University) for assitance; L. Beati
Ziegler (Georgia Southern University) for computing time;
and D. Nixon (FWMSH) for preparation of some bones of
Astrophocaudia. Discussions with T. Ikejiri, P. Mannion,
P. Rose, J. A. Whitlock, D. Winkler and especially J. A.
Wilson greatly improved the paper. T. Baumiller, C. Badg-
ley, T. Ikejiri, J. A. Whitlock and J. A. Wilson are thanked
for helpful comments on earlier drafts of this manuscript. P.
Upchurch, an anonymous reviewer, and editors are thanked
for comments and edits that improved the paper. Funding
was provided by the University of Michigan Scott Turner
Award and a Horace Rackham Graduate Student Research
Grant.
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