New Dromaeosaurids (Dinosauria: Theropoda) from the
Lower Cretaceous of Utah, and the Evolution of the
Dromaeosaurid Tail
Phil Senter1*, James I. Kirkland2, Donald D. DeBlieux2, Scott Madsen2, Natalie Toth3
1 Department of Biological Sciences, Fayetteville State University, Fayetteville, North Carolina, United States of America, 2 Utah Geological Survey, Salt Lake City, Utah,
United States of America, 3 Rio Tinto Center, Utah Museum of Natural History, Salt Lake City, Utah, United States of America
Abstract
Background: The Yellow Cat Member of the Cedar Mountain Formation (Early Cretaceous, Barremian? – Aptian) of Utah has
yielded a rich theropod fauna, including the coelurosaur Nedcolbertia justinhofmanni, the therizinosauroid Falcarius
utahensis, the troodontid Geminiraptor suarezarum, and the dromaeosaurid Utahraptor ostrommaysorum. Recent excavation
has uncovered three new dromaeosaurid specimens. One specimen, which we designate the holotype of the new genus
and species Yurgovuchia doellingi, is represented by a partial axial skeleton and a partial left pubis. A second specimen
consists of a right pubis and a possibly associated radius. The third specimen consists of a tail skeleton that is unique among
known Cedar Mountain dromaeosaurids.
Methodology/Principal Findings: Y. doellingi resembles Utahraptor ostrommaysorum in that its caudal prezygapophyses are
elongated but not to the degree present in most dromaeosaurids. The specimen represented by the right pubis exhibits a
pronounced pubic tubercle, a velociraptorine trait that is absent in Y. doellingi. The specimen represented by the tail
skeleton exhibits the extreme elongation of the caudal prezygapophyses that is typical of most dromaeosaurids. Here we
perform a phylogenetic analysis to determine the phylogenetic position of Y. doellingi. Using the resulting phylogeny as a
framework, we trace changes in character states of the tail across Coelurosauria to elucidate the evolution of the
dromaeosaurid tail.
Conclusions/Significance: The new specimens add to the known diversity of Dromaeosauridae and to the known diversity
within the Yellow Cat paleofauna. Phylogenetic analysis places Y. doellingi in a clade with Utahraptor, Achillobator, and
Dromaeosaurus. Character state distribution indicates that the presence of intermediate-length caudal prezygapophyses in
that clade is not an evolutionarily precursor to extreme prezygapophyseal elongation but represents a secondary
shortening of caudal prezygapophyses. It appears to represent part of a trend within Dromaeosauridae that couples an
increase in tail flexibility with increasing size.
Citation: Senter P, Kirkland JI, DeBlieux DD, Madsen S, Toth N (2012) New Dromaeosaurids (Dinosauria: Theropoda) from the Lower Cretaceous of Utah, and the
Evolution of the Dromaeosaurid Tail. PLoS ONE 7(5): e36790. doi:10.1371/journal.pone.0036790
Editor: Peter Dodson, University of Pennsylvania, United States of America
Received February 1, 2012; Accepted April 11, 2012; Published May 15, 2012
Copyright: ß 2012 Senter et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: The authors have no support or funding to report.
Competing Interests: The authors have declared that no competing interests exist.
* E-mail: psenter@uncfsu.edu
VP 21751) found near it. The third specimen (UMNH VP 20209)
is a tail skeleton.
Dromaeosauridae is a diverse family of predatory dinosaurs
with a plethora of species that have been discovered within the last
two decades [5–26] and a few that were known previously [27–
31]. The family is known from the Lower and Upper Cretaceous
of North and South America [5,6,11,16,19,24,27,29,30] and Asia
[10,12,14,15,17,18,20–22,25,28,31] and from the Upper Cretaceous of Europe [8,13], Africa [32], and Madagascar [7]. A wide
range of body sizes is known in the family, with the smallest about
the size of a mockingbird [12] and the largest about the size of an
emu [5]. Dromaeosaurids are remarkable for the presence of an
enlarged, recurved claw on the second toe that may have
functioned as a predatory weapon [33], a weapon for intraspecific
aggression [34], a climbing aid [35], a digging tool [34], or a
combination of functions. Specimens are known that are covered
Introduction
A diversity of theropods is found in the fauna of the Cedar
Mountain Formation (Lower Cretaceous) of Utah. A large
carnosaur similar to Acrocanthosaurus is known from fragmentary
material from the Ruby Ranch Member [1]. The Yellow Cat
Member has yielded the coelurosaur Nedcolbertia justinhofmanni [2],
the therizinosauroid Falcarius utahensis [3], the troodontid Geminiraptor suarezarum [4], and the large dromaeosaurid Utahraptor
ostrommaysorum [5]. Here we describe three new theropod
specimens from the Yellow Cat Member, all of which are
members of Dromaeosauridae. One specimen, UMNH (Natural
History Museum of Utah, Salt Lake City, Utah, United States of
America) VP 20211, includes several vertebrae and part of a pubis;
we designate this specimen the holotype of a new genus and
species: Yurgovuchia doellingi. Another specimen is represented by a
pubis (UMNH VP 21752) and possibly also by a radius (UMNH
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New Dromaeosaurids from Utah
of the tail into two segments is present [45,52–58]. The term
should therefore not be used in such cases.
in birdlike feathers [14,15], and because of their close relationship
with birds [19,21,36] dromaeosaurids are important in studies of
the origin of avian flight [15,37].
In most members of the family the centra of the tail are encased
in a bundle of bony rods that lie parallel to each other across the
lengths of several centra, binding the tail into a rod [18,29,38,39].
These bony rods consist of bifurcating prezygapophyses and
bifurcating left and right cranial processes of hemal arches. It is
hypothesized that this bundle of rods increased tail stiffness and
that this is functionally related to the use of the tail as a dynamic
stabilizer [29]. The term ‘‘caudotheca,’’ from the Latin cauda (tail)
and theca (case, covering), was recently introduced [36] for the
sheath of elongated processes from prezygapophyses and chevrons
that encase the tail. The term is not taxon-specific and can be used
in reference to the similar structure that is present in basal
pterosaurs [40].
There are exceptions to the presence of the caudotheca in
Dromaeosauridae. It is absent in the basal dromaeosaurid
subfamily Unenlagiinae [7,19]. An intermediate state is present
in the large, closely related dromaeosaurids Achillobator and
Utahraptor. In both cases, distal caudal vertebrae have elongated
prezygapophyses, but the prezygapophyses are not known to
extend much farther than the length of one caudal centrum [5,9].
Here, we introduce the term ‘‘hemicaudotheca’’ for this condition.
To facilitate understanding of the results of this study, we must
address the definitions of three relevant terms: Microraptoria,
Eudromaeosauria, and transition point. The name Microraptoria
was introduced in 2004 for the clade of dromaeosaurids more
closely related to Microraptor than to Velociraptor or Dromaeosaurus
[41]. In some subsequent studies the clade has been called
Microraptorinae [19,21,24,36], but that name is a junior synonym
of Microraptoria. The name Eudromaeosauria was recently
introduced as the least inclusive clade containing Saurornitholestes
langstoni, Deinonychus antirrhopus, Dromaeosaurus albertensis, and Velociraptor mongoliensis [24]. This clade is the sister taxon to Microraptoria [19,24,36].
Russell introduced the term ‘‘transition point’’ in 1972 in
reference to ornithomimid tails [42], but the term has since
become routinely applied to dromaeosaurids and other theropods.
Russell defined the term as the point in the tail ‘‘between the last
vertebra bearing transverse processes and the first with distinctly
elongate prezygapophyses’’ and made it clear that the term was
meant to refer to a point of abrupt change in vertebral
morphology that divides the tail into two distinct segments [42].
The term is occasionally used in reference to theropods in which
the caudal series does not exhibit two distinct, abruptly divided
segments [43–45], but if the term is used as originally intended it is
inapplicable to such taxa. Among theropods, abrupt division of the
tail into two distinct segments is present only in Ornithomimidae
and Paraves. In the former, the division is marked not only by loss
of transverse processes and the elongation of prezygapophyses but
also by the gain of an cranial process on each hemal arch so that
the hemal arches are shaped like an inverted T [46,47]. The term
‘‘type 1 transition point’’ was recently introduced for this condition
[36]. In Paraves the division is marked by loss of transverse
processes, extreme reduction in neural spines, elongation of caudal
centra, and the gain of an inverted T shape in the hemal arches,
but not by prezygapophyseal elongation [7,48–51]. The term
‘‘type 2 transition point’’ was recently introduced for this condition
[36]. In contrast, along the caudal series in other coelurosaurs
(Tyrannosauroidea, Compsognathidae, Therizinosauroidea, and
Oviraptorosauria), changes in morphology (reduction in transverse
process and neural spine size, prezygapophyseal elongation, and
hemal arch shape change) are gradual, so that no distinct division
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Geological Setting
All three specimens described here are from the Yellow Cat
Member of the Cedar Mountain Formation, which is divided into
upper and lower parts (Fig. 1). The upper Yellow Cat Member has
been dated as about 124 Ma (Lower Cretaceous: Aptian) based on
detrital zircons [59]. This is close to the cutoff between the
Barremian Stage and the Aptian Stage [60], suggesting that the
lower Yellow Cat Member may be Barremian in age. Both
the upper and lower Yellow Cat have recently yielded several
significant fossil specimens [3,4,6–63].
The holotype of Yurgovuchia doellingi and the isolated pubis
(UMNH VP 21752) and radius (UMNH VP 21751) are from a
portion of the Doelling’s Bowl bone bed (Gr 300v) that is
designated as Don’s Place (Fig. 2, 3). Initial discovery of the site
occurred in 2005 when Don DeBlieux found the vertebrae and
associated pubis of Y. doellingi, while Scott Madsen was simultaneously investigating some large skeletal elements a few tens of
meters to the north and Jim Kirkland was excavating a
polacanthine ankylosaur spine at his initial 1991 tooth and scute
locality [63], a site approximately two hundred meters to the west.
All of these sites were later found to be portions of the same
extensive bone bed.
The identification of the stratigraphic position of the Doelling’s
Bowl bone bed necessitated a reevaluation of the stratigraphic
position of the Jurassic-Cretaceous boundary and the base of the
Cedar Mountain Formation in this area [63]. For a number of
years a widespread multistoried paleosol (calcrete) had been used
to define the base of the Cedar Mountain Formation [61,64–67].
That marker bed is now placed in the middle of the Yellow Cat
Member of the Cedar Mountain Formation and is used to split the
Yellow Cat into a lower and upper part in its type area along the
north side of Arches National Park (Fig. 1). The lithology and
fauna of the lower Yellow Cat are typical of the Cedar Mountain
formation and differ markedly from the underlying Brushy Basin
Member of the Morrison Formation [59,63]. There is no
radiometric date available yet for the lower Yellow Cat.
The lower Yellow Cat Member is characterized by mottled
paleosols with matrix-supported chert pebbles. Its lower contact is
placed at the first occurrence of matrix-supported chert pebbles
above smectitic mudstones characteristic of the Upper Jurassic
Brushy Basin Member of the Morrison Formation and is often
characterized by iron staining and iron-rich nodules. The
Doelling’s Bowl Dinosaur bone bed is centimeters to decimeters
above an interval of distinctive chert layers that form a local
marker ‘‘zone’’ in this area around Arches National Park [63].
Common in the Doelling’s Bowl dinosaur bone bed and the
underlying chert interval are silicified, horizontally oriented,
winding roots, whose rarely preserved internal structure is similar
to that of the ‘‘pseudo-trunk’’ of the Early Cretaceous aberrant
fern Tempskya [68,69,70]. The presence of these horizontally
oriented, ‘‘fern-like,’’ root traces suggests that the bone bed
represents a wet environment. Within the bone bed, these root
traces have been found to be most abundant in the Don’s Place
area, where some of the root traces followed along the surfaces of
bones suggesting that these roots were leaching nutrients out of the
bones.
The Doelling’s Bowl dinosaur bone bed extends over tens of
acres with mostly scattered teeth, ankylosaur ossicles, and isolated
bones in the western exposures and better preserved and much
more abundant skeletal remains in the eastern exposures. The
preserved dinosaurs are dominated by iguanodonts (at least ten
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New Dromaeosaurids from Utah
Figure 1. Revised stratigraphic section for type area of Yellow Cat and Poison Strip Members of the Cedar Mountain Formation
along the east side of the Yellow Cat Rd. south of Exit 193 on Interstate 70. Arrows indicate the placement of the Jurassic-Cretaceous
boundary by previous authors. Tan writing indicates the relative stratigraphic position of a number of important dinosaur localities in the area
[61,63,99,100].
doi:10.1371/journal.pone.0036790.g001
individuals) and polacanthine ankylosaurs (at least three individuals) [60]. Other identified dinosaur remains include the type
specimen of Y. doellingi, one or possibly two associated sauropod
skeletons, a hypsilophodont-grade ornithopod jaw, and teeth from
a large carnosaur. Additionally, teeth and a few crocodilian bones
have been recognized.
The bone bed is a relatively low diversity, multitaxic bone bed
of associated, if not articulated, skeletons, and while there is some
orientation of long bones the close association of elements from the
same individuals suggests low energy [70]. The distribution of
skeletal elements (Fig. 3), together with the iron-rich, ‘‘hydromorphic gley soils’’ suggest a wet, perhaps boggy, environment for the
Doelling’s Bowl dinosaur bone bed, unlike the drier settings
interpreted for many other Cedar Mountain dinosaur localities.
The new dromaeosaurid tail skeleton (UMNH VP 20209) is
from Andrew’s Site (Gr 290v), a small but highly significant
dinosaur site near the top of the Yellow Cat Member of the Cedar
Mountain Formation (Fig. 4, 5). The site has yielded several
significant fossil specimens. These include the skulls of an
iguanodont, a terrestrial crocodilian, and a new species of
mammal [61–63].
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Methods
Phylogenetic Analysis
For this analysis we used the phylogenetic data matrix of a
recent study [36], with the following improvements. Two new
characters (characters 301 and 307) relating to the pelvic girdle
have been added, and character 306 (pubic orientation) has been
re-coded for some taxa according to new insights published here in
the Discussion. The Scipionyx Operational Taxonomic Unit (OTU)
and other compsognathid OTUs have been updated with new
information from a recent study [71]. The Chirostenotes OTU has
been updated by removal of data that came from the holotype of
the newly recognized genus Epichirostenotes [72], a specimen that
was originally described as a specimen of Chirostenotes [73]. The
Ornithomimus OTU has been updated with information from a
recent study [74]. In that study, a small opening ventral to the
maxillary fenestra was called the promaxillary fenestra [74].
However, the absence of that opening in basal ornithomimosaurs
suggests that its appearance in advanced ornithomimosaurs is
neomorphic. Therefore, the phylogenetic data matrix used here
does not recognize the presence of the promaxillary fenestra in
Ornithomimus and other advanced ornithomimosaurs.
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New Dromaeosaurids from Utah
Figure 2. Detailed stratigraphic correlation of the lower Yellow Cat Member of the Cedar Mountain Formation at its type section
with the stratigraphic section at Doelling’s Bowl five kilometers to the east, showing the stratigraphic position of the Doelling’s
Bowl dinosaur bone bed.
doi:10.1371/journal.pone.0036790.g002
the dromaeosaurid tail, using as a phylogenetic framework the
results of the phylogenetic analysis performed here.
The data matrix for the phylogenetic analysis is given in
Appendix S1, and the character list is given in Appendix S2.
Phylogenetic analysis was performed with PAUP 4.0 for
Windows [75]. A heuristic search with 1000 random additionsequence replicates was performed, with no limit to ‘‘maxtrees.’’
The decay index (Bremer support) of each clade was found with
the same software after insertion of a command line that was
created using the program MacClade 3.08a [76]. The analysis was
performed a second time after deletion of several deinonychosaurian taxa known only from fragmentary material, to see whether
this would influence tree topology or statistics.
Nomenclatural Acts
The electronic version of this document does not represent a
published work according to the International Code of Zoological
Nomenclature (ICZN), and hence the nomenclatural acts
contained in the electronic version are not available under that
Code from the electronic edition. Therefore, a separate edition of
this document was produced by a method that assures numerous
identical and durable copies, and those copies were simultaneously
obtainable (from the publication date noted on the first page of this
article) for the purpose of providing a public and permanent
scientific record, in accordance with Article 8.1 of the Code. The
separate print-only edition is available on request from PLoS by
sending a request to PLoS ONE, 1160 Battery Street, Suite 100,
San Francisco, CA 94111, USA along with a check for $10 (to
Tail Evolution Scenario
We used specimens and literature to compare caudal character
states across Coelurosauria for taxa in which articulated tail
skeletons are known or for which enough of the caudal series is
known to be able to deduce the relevant character states (Table 1).
We then used these data to create a scenario for the evolution of
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New Dromaeosaurids from Utah
Figure 3. A small portion of the Doelling’s Bowl dinosaur bone bed at Don’s Place showing the disposition of bones assigned to the
type specimen of Yurgovuchia doellingi.
doi:10.1371/journal.pone.0036790.g003
cover printing and postage) payable to ‘‘Public Library of
Science’’.
In addition, this published work and the nomenclatural acts it
contains have been registered in ZooBank, the proposed online
registration system for the ICZN. The ZooBank LSIDs (Life
Science Identifiers) can be resolved and the associated information
viewed through any standard web browser by appending the LSID
to the prefix ‘‘http://zoobank.org/’’. The LSID for this
publication is: urn:lsid:zoobank.org:pub:4D1838FD-10BB-47548127-9B881D33D004.
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Results
Yurgovuchia Doellingi: Systematic Paleontology
Systematic hierarchy:
Dinosauria Owen, 1841 [77]
Saurischia Seeley, 1887 [78]
Theropoda Marsh, 1881 [79]
Coelurosauria von Huene, 1914 [80]
Dromaeosauridae Colbert and Russell, 1969 [27]
Yurgovuchia gen. nov.
urn:lsid:zoobank.org:act:110C8550-8718-40C6-8AA88A534A33535B
Yurgovuchia doellingi sp. nov.
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New Dromaeosaurids from Utah
Figure 4. Stratigraphic data for Andrew’s Site. Stratigraphic section of the Cedar Mountain Formation in the type area of the Yellow Cat
Member [61], with major dinosaur localities [62,63] in area noted and detail of section spanning the locality (Andrew’s Site, Gr v290) from which the
dromaeosaur tail was collected.
doi:10.1371/journal.pone.0036790.g004
urn:lsid:zoobank.org:act:8C781C52-96FF-4377-A33782FC875DC24E
Holotype. The holotype specimen is UMNH VP 20211. It
includes cervical, dorsal, and caudal vertebrae; and the proximal
end of a left pubis.
Etymology. The genus name honors the Ute Tribe of
northeastern Utah. It is derived from the Ute word yurgovuch,
meaning ‘‘coyote,’’ a predator of similar size to Y. doellingi that
currently inhabits the same region.
The species name honors Helmut Doelling in recognition of his
50-plus years of geological research and mapping of Utah for the
Utah Geological Survey. The Doelling’s Bowl dinosaur sites were
first discovered as a result of his providing taped-together color
photocopies of his then-unpublished geological maps of the Arches
National Park region [81,82] to JIK in 1990.
Locality and horizon. The specimen comes from Don’s
Place, part of the Doelling’s Bowl bone bed in Grand County,
Utah (Fig. 3). The bone bed is in the lower Yellow Cat Member
(Barremian?) of the Cedar Mountain Formation (Fig. 2).
Diagnosis. Dromaeosaurid theropod; centrum of axis with a
single pneumatopore on each side; cranial end of centrum of third
cervical vertebra not beveled; cervical prezygapophyses flexed;
epipophyses of cervical vertebrae above postzygapophyseal facets;
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cervico-dorsal vertebrae with hypapophyses and without pneumatopores; cranial faces of centra of proximal caudal vertebrae
round; caudal prezygapophyses elongated distal to transition
point, but not over the length of a centrum. Pubis without pubic
tubercle.
Yurgovuchia Doellingi: Specimen Description and
Comparisons
Below, specimen numbers in parentheses indicate personal
observation by PS of features not recorded in the literature.
Preserved vertebrae and parts of vertebrae include the left
neural arch of the atlas, a nearly complete axis, three postaxial
cervical vertebrae, partial neural arches of two more postaxial
cervicals, two cervico-dorsal vertebrae, the neural arch of one
dorsal vertebra, and seven caudal vertebrae (Fig 6). In all
preserved vertebrae, neurocentral sutures are obliterated by
coossification. This indicates that the specimen is an adult [83].
It is therefore not a juvenile specimen of Utahraptor ostrommaysorum
but instead represents a much smaller species. Measurements are
given in Table 2.
The postzygapophysis of the atlantal neural arch is bulbous
(Fig. 7A). A deep fossa is present on the medial surface between the
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New Dromaeosaurids from Utah
Figure 5. Quarry map of Andrew’s Site.
doi:10.1371/journal.pone.0036790.g005
Bambiraptor (AMNH FR 30556), the centrum of the axis lacks the
beveling that is characteristic of dromaeosaurid mid-cervical
centra.
One cervical vertebra is completely preserved except that its
neural spine is broken off (Fig. 7C). On the basis of comparison
with the holotype of Tsaagan mangas, the first ten cervicals of which
were found articulated in situ [20], we identify it as the first
postaxial vertebra (cervical 3) because the diapophyses and
parapophyses are not prominent. This is also true of the fourth
cervical of T. mangas, but the shapes of the postzygapophyses and
the laminae connecting them to the prezygapophyses are more
similar to those of the third than the fourth cervical of T. mangas.
The cranial surface of its centrum is not strongly beveled as are
those of most other coelurosaurs, including other dromaeosaurids
base of the arch and the postzygapophysis. The dorsal process that
extends medially toward the right neural arch is shorter and
stouter than in Deinonychus [29].
The intercentrum and odontoid process of the axis (Fig. 7B)
resemble those of Deinonychus [29] and Bambiraptor (AMNH
[American Museum of Natural History, New York City, New
York, United States of America] FR 30556). The neural spine is
laterally compressed and was at least as tall as the centrum. Its tip
and the diapophyses and parapophyses are eroded off. A single
pneumatopore is present at mid-length on each side of the
centrum, as in Deinonychus [29] and Bambiraptor (AMNH FR
30556). A pneumatopore is absent in the axis of Tsaagan [20]. The
cranial surface of the intercentrum is flat, and the caudal end of
the centrum is shallowly concave. As in Deinonychus [29] and
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New Dromaeosaurids from Utah
Table 1. Data from tails of coelurosaurian theropods.
Taxon and references
Table 1. Cont.
NC
TP
E
PZ
C
26
TrPt
Gorgosaurus libratus [52]
31 (+4)
13
2
2
2
No
No
Tyrannosaurus rex [56]
.34
16
2
2
2
No
No
Tyrannosauridae:
.25
17
2
2
2
No
No
Sinocalliopteryx gigas [58] 49
16
2
2
2
No
No
Sinosauropteryx prima [54] .64
17
2
2
2
No
No
TP
E
PZ
C
26
TrPt
Velociraptor mongoliensis
[38,83]
approx. 30 11
6
10
6
No
Yes
UMNH VP 20209
?
?
.8* .7* ?
?
?
proximal caudals are
missing (see text)
26= mid-caudal centra at least twice as long as proximal caudal centra.
E = cranialmost caudal centrum with suddenly marked elongation (length/
height) as compared to more proximal caudal centra. NC = number of caudal
vertebrae. PZ = cranialmost caudal contributing to caudotheca. C = cranialmost
caudal contacted by caudotheca. TP = distalmost caudal with transverse process
as a distinct process (not just a low ridge). TrPt = Abrupt transition point
present. Numbers in parentheses under ‘‘NC’’ indicate estimated number of
additional vertebrae beyond those preserved in the specimen. Hyphens
indicate inapplicability. For cases in which data were collected directly from a
specimen or cast, the specimen number is given. Institutional abbreviations:
AMNH = American Museum of Natural History, New York City, New York, United
States of America. IGM = Mongolian Institute of Geology, Ulaan Baatar,
Mongolia. IVPP = Institute of Vertebrate Paleontology and Paleoanthropology,
Beijing, People’s Republic of China. MPCA = Museo Carlos Ameghino, Cipolletti,
Rio Negro Province, Argentina. UA = Université d’Antananarivo, Antananarivo,
Madagascar. UMNH = Utah Museum of Natural History, Salt Lake City, Utah,
United States.
doi:10.1371/journal.pone.0036790.t001
Ornithomimosauria:
Gallimimus bullatus [41]
36–39
14
2
2
2
No
Yes
Harpymimus okladnikovi
[95]
.34
12
2
2
2
No
Yes
Shenzhousaurus orientalis
[47]
.16
11
2
2
2
No
Yes
Therizinosauroidea:
Alxasaurus elesitaiensis [96] .19
13
2
2
2
No
No
?
2
2
2
No
No
Neimongosaurus yangi [55] 22 (+3 to 8).12 2
Nothronychus graffami [97] 23 (+3)
Beipiaosaurus inexpectus
[57]
NC
*under the assumption that
at least four
Compsognathidae:
Huaxiagnathus orientalis
[45]
Taxon and references
30
2
2
No
No
12
2
2
2
No
No
2
2
2
2
No
No
Khaan mckennai (IGM 100/ 26 (+2)
1127)
21
2
2
2
No
No
Nomingia gobiensis [53]
24
18
2
2
2
No
No
Archaeopteryx sp. [49]
22
5
6
2
2
Yes
Yes
Epidendrosaurus
ningchengensis [50]
22 (+5?)
2
?
2
2
Yes
Yes
Jeholornis prima [51]
24–27
2
3
2
2
Yes
Yes
Anchiornis huxleyi [48]
20 (+6?)
3
5
2
2
Yes
Yes
Sinornithoides dongi [98]
27
9
9
2
2
Yes
Yes
5
8
2
2
Yes
Yes
6
6
2
2
Yes
Yes
?
5
?
4
Yes
Yes
Yes
Oviraptorosauria:
Caudipteryx sp. (IVPP V
12430)
9
[29,84]. This suggests that this part of its neck was held in less of
an S-curve than in other coelurosaurs. It is amphiplatyan. Its right
side is better preserved than the left and bears two short,
horizontal grooves, one dorsal to the other, immediately ventral to
the diapophysis. The more dorsal groove may be a pneumatopore;
obscuration by matrix prevents evaluation of whether it is a
foramen. The prezygapophyses are well separated and flexed. The
epipophyses are distally placed and slightly overhang the
postzygapophyses.
Two nearly complete posterior cervical vertebrae are present.
The more cranial of the two (Fig. 7F) has been obliquely flattened
so that its dorsal parts are caudally displaced. Its centrum is
amphiplatyan and lacks beveling. No pneumatopores are discernible. Small parapophyses that protrude only slightly are present on
the ventrolateral edge of the cranial rim of the centrum, the left
more clearly visible than the right. The neural spine is broken off.
The epipophyses do not reach the tips of the postzygapophyses
and are located above the postzygapophyseal articular facets.
The diapophyses are connected to and extend farther laterally
than the prezygapophyses. A small part of the neural arch from the
Avialae
Troodontidae:
Dromaeosauridae
(Unenlagiinae):
Buitreraptor gonzalezorum .14
(cast of MPCA 245)
Rahonavis ostromi (cast of .13
UA 8656)
Dromaeosauridae
(Microraptoria):
Cryptovolans pauli [14]
28–20
Microraptor gui [15]
approx. 26 ?
4–6 ?
?
Yes
Microraptor zhaoianus [12] 24–26
6
6
6
3
Yes
Yes
Tianyraptor ostromi [25]
.25
?
7
?
3
Yes
Yes
Bambiraptor feinbergorum .23
6
10
9
6
Yes
Yes
9
.10 8
No
Yes
.10 6
No
Yes
Dromaeosauridae
(Eudromaeosauria):
(AMNH FR 30556 and [11])
Deinonychus antirrhopus
[29]
36 (+4)
10
Tsaagan sp. [26]
.20
.12 .8
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Figure 6. Skeletal reconstruction of Yurgovuchia doellingi, with
anachronistic house cat to show its size.
doi:10.1371/journal.pone.0036790.g006
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Table 2. Measurements of vertebrae preserved in the holotype of Yurgovuchia doellingi.
Figure
TH
TL
TW
CL
CHCr
CHCd
CWCr
CWCd
7A (atlantal neural arch)
13.35
12.69
27.43
2
2
2
2
2
7B (axis)
41.97
45.92
2
2
2
2
21.9
17.55
7C (cervical vertebra)
45.95*
53.65
40.29
45.1
2
2
24.35
2
7D (cervical neural arch)
2
48.6
2
2
2
2
2
2
7E (cervical neural arch)
2
5.09*
2
2
2
2
2
2
7F (cervical vertebra)
55.80*
2
69.73*
24.89*
21.27*
2
30.81*
2
7G (cervical vertebra)
46.39*
2
2
40.95*
2
19.58*
2
26.13*
7H (cervico-dorsal vertebra)
47.80*
2
2
26.42*
25.75*
23.39*
2
23.18*
7I (cervico-dorsal vertebra)
79.36*
2
2
32.04
25.96
22.73
2
22.25
7J (dorsal neural arch)
51.73*
22.90*
76.64
2
2
2
2
2
8A (caudal vertebra)
47.89*
44.63*
23.06*
40.17
22.11
27.69
24.11
22.2
8B (caudal vertebra)
45.95*
55.59*
37.32*
45.95
25.16
23.29
19.54
17.57
8C (caudal vertebra)
42.23*
58.74*
44.09*
48.03
23.35
21.64
20.78
18.54
8D (caudal vertebra)
43.2
66.92
2
52.91
22.80*
21.03*
2
16.62*
8E (caudal vertebra)
47.62*
75.81*
2
2
24.73*
23.60*
2
2
8F (caudal vertebra)
43.47*
91.32*
2
55
18.59
18.41
14.47
15.83
8G (caudal centrum)
25.07*
48.34*
2
48.34*
16.97
20.82*
19.24
2
Measurements are in mm. Asterisks indicate measurements that are correct for the vertebra in its current state but are significantly altered from the original state
because relevant part(s) of the vertebra are broken, distorted, or missing. Fig. = figure in which vertebra is illustrated. CHCd = centrum height (caudal face).
CHCr = centrum height (cranial face). CL = centrum length (as preserved). CWCd = centrum transverse width (caudal face). CWCr = centrum transverse width (cranial
face). TH = total height of vertebra (or preserved part). TL = total length of vertebra (or preserved part). TW = total transverse width of vertebra (or preserved part).
doi:10.1371/journal.pone.0036790.t002
succeeding vertebra is preserved in articulation with the caudal
end of this vertebra above the neural canal.
The other nearly complete posterior cervical vertebra is missing
the neural spine, the left cranial part of the neural arch, and the
left dorsolateral part of the centrum (Fig. 7G). The centrum lacks
beveling and has no discernible pneumatopores. Only the right
parapophysis is preserved. It is ovoid in lateral view, with its
cranial end more ventral than its caudal end. The parapophysis is
much larger than its counterpart on the other posterior cervical.
As with the other posterior cervical, the epipophyses are above the
postzygapophyseal facets and do not reach the tips of the
postzygapophyses, and the diapophyses are connected to and
extend farther laterally than the prezygapophyses.
Partial neural arches from two other cervical vertebrae are
present. On one (Fig. 7D) the left prezygapophysis, the horizontal
lamina connecting it with the left postzygapophysis, the base of the
right prezygapophysis, and the base of the neural spine are
preserved. The prezygapophysis is flexed. On the other (Fig. 7E)
the left postzygapophysis and the base of the left prezygapophysis
are preserved.
Two cervico-dorsal vertebrae are preserved, each with a
hypapophysis. Neither has pneumatopores and both are amphiplatyan. In both vertebrae the parapophysis is on the anterodorsal
edge rather than the anteroventral edge of the centrum, which
indicates that both are from the caudal section of the series of
vertebrae with hypapophyses. The vertebra with the larger
hypapophysis is therefore the more cranial of these two vertebrae.
The more cranial of the two (Fig. 7H) is missing the right
prezygapophysis and parapophysis and all but the base of the
neural spine. Its hypapophysis is about half as high as the centrum.
Its parapophyses are ovoid in lateral view and slanted as in the
cervical vertebra described in the preceding paragraph. They stick
out farther laterally than on the cervical vertebra and are on short
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stalks. The one preserved prezygapophysis extends much farther
laterally than the postzygapophyses and is slanted at about 45u,
unlike the cervical prezygapophyses, which are not slanted. The
diapophysis is about midway between the pre- and postzygapophyses. It extends much farther laterally than the zygapophyses
and is about twice as long transversely as it is wide sagittally. It
slants at about 30u, with its tips higher than its base.
The more posterior cervico-dorsal vertebra is missing the
diapophyses, the prezygapophyses, the right postzygapophysis, and
all but the bases of the parapophyses (Fig. 7I). Its hypapophysis is
about one-third the height of the centrum. The postzygapophyses
are much more closely spaced than in the other cervico-dorsal and
the cervicals, with only a narrow notch between them. The left
postzygapophysis is slanted about 45u. The neural spine is at least
as tall as the centrum. Its tip is eroded away.
The neural arch of the dorsal vertebra appears to be broken off
the vertebra rather than simply unfused to the centrum, because of
the rough texture of its ventral surfaces. It is missing all four
zygapophyses (Fig. 7J). The neural spine is broken but the height
of its preserved portion is similar to that of the more posterior
cervico-dorsal. The transverse processes are of similar dimensions
and slant at about the same angle as those of the more posterior
cervico-dorsal.
The cranial six of the seven preserved caudal vertebrae appear
to form a consecutive series (Fig. 8). All are amphiplatyan and lack
pneumatopores. In all six the postzygapophyses are more closely
spaced than the prezygapophyses, and both the pre- and
postzygapophyses are progressively more closely spaced in more
posterior vertebrae. In the first vertebra of the series, the cranial
and caudal faces of the centra are round, and the centra are round
in cross-section. This resembles the condition in Achillobator [9]. It
is unlike the condition in other dromaeosaurids, in which the
proximal caudal centra are subquadrangular in cross-section,
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New Dromaeosaurids from Utah
Figure 7. Cervical and dorsal vertebrae of Yurgovuchia doellingi (UMNH VP 20211). (A)–Left neural arch of atlas. (B)–Axis. (C)–Third cervical
vertebra. (D)–Partial cervical neural arch. (E)–Partial cervical neural arch. (F)–Posterior cervical vertebra. (G)–Posterior cervical vertebra. (H)–Cervicodorsal vertebra. (I)–Cervico-dorsal vertebra. (J)–Dorsal vertebral neural arch. Scale bar = 50 mm. Numbers on sub-figures refer to cranial (1), caudal (2),
left (3), right (4), dorsal (5), and ventral (6) views. Such numbers joined by an ampersand indicate that cranial and dorsal (1&5) or caudal and ventral
(2&6) surfaces are simultaneously visible, due to deformation. Scale bar = 50 mm.
doi:10.1371/journal.pone.0036790.g007
[29,38]. The more distal caudal vertebrae of Y. doellingi have
subquadrangular central faces.
The first (most proximal) caudal vertebra in the series (Fig. 8A)
is from the transition point in the tail. In it and the next two
vertebrae the transverse processes are elongate, subhorizontal, and
slightly backswept, as in the proximal caudals of other dromaeosaurids [29,85]. The transverse processes are reduced to ridges on
the next three vertebrae. In the first vertebra of the series the left
transverse process has broken at the base and twisted around the
break in the frontal plane. The left transverse processes of the
second and third vertebrae are broken off at the base.
The prezygapophyses are vertical on the first vertebra of the
series and upswept in lateral view (Fig. 8A) but are not vertical on
the next three vertebrae (Fig. 8B – D). The zygapophyses of the
last two vertebrae in the series (Fig. 8E, F) taper quickly into
narrow rods that extend far forward; their tips are broken off, but
tapering suggests that they extended very little further than the
broken tips. The postzygapophyses extend farther caudally than
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the centra in all six vertebrae. The neural spines are broken off just
above the base in the first four vertebrae of the series. In the first
vertebra the base of the neural spine begins about halfway down
the length of the centrum (Fig. 8A). It begins progressively farther
cranially on the following vertebrae and begins at the cranial
margin of the neural arch in the last two vertebrae, in which the
entire neural spine is preserved and is merely an extremely low
ridge that extends caudally between the postzygapophyses.
On the fifth caudal vertebra in the series (Fig. 8E), a prong of
bone extends vertically from between the bases of the prezygapophyses. However, it is not certain that this prong is part of the
vertebra. It is likely a fragment from another bone that is currently
held in place by matrix. Such a prong is absent in the caudal
vertebrae of other dromaeosaurids.
One other caudal vertebra is preserved (Fig. 8G). It is
significantly shorter than the posterior three caudal vertebrae of
the series and is therefore probably from close to the tip of the
tail. Its neural arch is missing except for the bases of the
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New Dromaeosaurids from Utah
Figure 8. Caudal vertebrae of Yurgovuchia doellingi (UMNH VP 20211). (A – F)–Six consecutive caudal vertebrae from anterior and middle
section of tail. (G)–Centrum of a distal caudal vertebra. Meanings of numbers on sub-figures same as in previous figure. Scale bar = 50 mm.
doi:10.1371/journal.pone.0036790.g008
bones, and the radius (UMNH VP 21751) was about halfway
between the two (Fig. 3).
The shaft and proximal end of the right pubis are preserved
(Fig. 9B). The preserved length of the pubis is 222 mm. The
craniocaudal length of the proximal end of the pubis, perpendicular to the shaft, is 54.28 mm. The distal tip of the pubis is missing.
The iliac margin of the pubis is perpendicular to the shaft. The
caudal margin of the ischial peduncle is subparallel to the pubic
shaft. A prominent, cranially rounded, transversely compressed
tuber is present along the cranial edge of the pubis approximately
30 mm from the proximal extremity. This feature, the pubic
tubercle, is a muscle and ligament attachment site [87]. It is
similarly prominent and similarly shaped in the velociraptorine
dromaeosaurids Velociraptor [38] and Tsaagan (cast of holotype of
‘‘Linheraptor exquisitus,’’ IVPP [Institute of Vertebrate Paleontology
and Paleoanthropology, Beijing, People’s Republic of China] V
16923). A pubic tubercle as a discrete, prominent process is absent
in other dromaeosaurids [6,7,9,10,15,29,86].
The pubic shaft is craniocaudally flattened. As in other
dromaeosaurids [6,26,29,85], the pubic apron is present in the
distal half of the pubis. The shaft is straight, as in most other
dromaeosaurids [7,11,25,29,38,85] and unlike the pubis of some
microraptorians, which is kinked backward at mid-shaft
prezygapophyses. On the caudal end of its ventral surface is a sulcus.
A shallower sulcus in the same location is present on the
posteriormost two of the vertebrae in the caudal series. A ventral
depression is also present in the distal caudal centra of Velociraptor [85].
In unenlagiine and microraptorian dromaeosaurids the middle
and distal caudals are at least twice the lengths of those cranial to the
transition point [7,15,25,78]. In eudromaeosaurs the middle caudals
are longer than but less than twice as long as the proximal caudals,
and the distal caudals are shorter than the proximal caudals
[26,29,85]. In these respects Yurgovuchia exhibits the eudromaeosaurian condition. In Velociraptor prezygapophyseal elongation
begins with the tenth vertebra [84]. If the same is true for
Yurgovuchia, then the series of six caudals consists of caudals 6–11.
The proximal end of the left pubis is preserved (Fig. 9A). The
pubic shaft is perpendicular to the iliac surface of the pubis. Part of
the pubic apron is preserved in the distal part of the bone. As in
most dromaeosaurids [6,7,9,10,15,29,86], but in contrast to
velociraptorines [38], a pubic tubercle is absent.
New Pubis and Radius
These two bones specimen were found at Don’s Place, in the
same layer as the holotype of Y. doellingi. The pubis (UMNH VP
21752) was at the opposite end of the quarry from the Y. doellingi
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Figure 9. Appendicular bones of new dromaeosaurids. (A)–Left pubis of Y. doellingi (UMNH VP 20211) in medial (above) and lateral (below)
views. (B)–Velociraptorine right pubis (UMNH VP 21752) in (left to right) medial, lateral, cranial, and caudal views. (C)–Possible velociraptorine
radius(UMNH VP 21751) in four views. Scale bar = 50 mm.
doi:10.1371/journal.pone.0036790.g009
light gray sandstone layer at Andrew’s Site in Grand County, Utah
(Fig. 2, 3). The site is part of the upper Yellow Cat Member
(Aptian) of the Cedar Mountain Formation. The specimen’s
stratigraphic position is equivalent to that of the Gaston Quarry,
which is approximately 2 km to the south-southeast (Fig. 1). The
Gaston Quarry yielded the holotype of the eudromaeosaur
Utahraptor ostrommaysorum. We do not consider the new tail skeleton
to represent U. ostrommaysorum, because the latter exhibits a
hemicaudotheca, whereas the new tail skeleton exhibits a
caudotheca.
The proximal caudal vertebra (Fig. 10D – I) has a centrum
45 mm long. It is amphiplatyan with a cranial surface 27 mm
high617 mm wide and a caudal surface 30 mm high620 mm
wide. Including the neural arch, the total height of the vertebra is
58 mm and its total length is 57 mm. Its prezygapophyses do not
extend farther forward than the cranial surface of the centrum.
The neural spine is backswept; it is present in the cranial half of
the centrum only as a low ridge between the bases of the
prezygapophyses. The postzygapophyses emanate as small facets
from the caudal edge of the neural spine at the same height as the
tips of the prezygapophyses. On the left side of the centrum is a
pathological bony spur. No trace of a transverse process is present
on either side. Immediately dorsal to the tiny ridge on the left is a
longitudinal sulcus. Such a sulcus is also present at the same height
on the right side.
The distal section of tail is sharply bent at approximately a right
angle, 218 mm from its cranial end (Fig. 10A). The tail is twisted
at the bend so that cranial to the bend the tail is preserved in
dorsal view, and caudal to it the tail is preserved in right lateral
view. The caudotheca has unraveled somewhat, and some hemal
arches are displaced. Cranial to the bend at least five centra are
present, judging from the lengths of the measurable centra caudal
[10,14,15,24]. It lacks the lateral tab at mid-shaft that is present in
some microraptorians [24,88]. The maximum transverse width of
the pubic apron is 24.74 mm. The transverse width of the pubic
shaft proximal to the apron and approximately halfway between
the proximal end of the pubis and the proximal extremity of the
apron, is 12.16 mm.
This pubis definitely comes from an individual other than the Y.
doellingi holotype. The pubis of the latter is much larger and lacks
the pubic tubercle.
The discrete pubic tubercle and the close morphological match
between the pubis and those of velociraptorines [38] (cast of IVPP
V 16923) indicate that the pubis is velociraptorine. If so, the
dimensions of the radius are consistent with its having come from
the same individual. In velociraptorines [26,84] the radius is much
shorter relative to its diameter than it is in most other
dromaeosaurids [7,9,10,14,15,29]. The radius described here is
short relative to its length (Fig. 9C), as in velociraptorines. As
preserved, it is 109.40 mm long and 10.31 mm wide at midshaft.
Both ends are expanded (widths: 19.33 mm and 20.26 mm), but
little can be said about their morphology because both tips are
missing and may have been chewed off before burial.
New Tail Skeleton
UMNH VP 20209 consists of a proximal caudal vertebra
(Fig. 10D) and a section approximately 458 mm long from a more
distal section of the tail (Fig. 10A – C). The vertebrae of the latter
section are bound together by a caudotheca. The bone material is
nearly the same color as the matrix under natural lighting, which
makes it difficult to see (Fig. 10). We have therefore included a
photo of the specimen under ultraviolet light (Fig. 11) to elucidate
the locations of the bones in Fig. 10. The specimen was found in a
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New Dromaeosaurids from Utah
Figure 10. New dromaeosaurid tail skeleton (UMNH VP 20209). (A)–The tail in situ, with boxes indicating areas enlarged in B and C. (B)–Detail
of A (the rectangle on the left in A). (C)–detail of A (the rectangle on the right in A). (D – I)–Isolated proximal caudal vertebra of same specimen in left
lateral (D), right lateral (E), caudal (F), cranial (G), dorsal (H), and ventral (I) views. In B, anatomical anterior (cranial) is toward the bottom of the page; in
C, anatomical anterior (crania) is to the left. Scale bar for D – I is 40 mm. 1–5 = ‘‘centra 1–50 (see text), bh = body of hemal arch, ns = neural spine,
poz = postzygapophysis, cp = caudal process of hemal arch, prz = prezygapophysis, sbc = space between centra.
doi:10.1371/journal.pone.0036790.g010
Centra 3–5 are estimated to be 40, 43, and 46 mm long
respectively. All are of similar height.
In a few cases elongated prezygapophyses can be traced to their
respective vertebrae. Their lengths cannot be measured with
certainty because their tips may be broken off. The longest visible
section of a prezygapophysis is from centrum 5. It is bifurcated at
its base, and the two tines remain close to each other, nearly
appressed, through half their preserved lengths. The longer (as
preserved) of the two tines extends 122 mm beyond the centrum
to the bend. The caudotheca is absent cranial to the third vertebra
in this series and surrounds that vertebra and all vertebrae caudal
to it. Enough is visible of the prezygapophyses of the second
vertebra in this series to ascertain that they do not extend farther
forward than the centrum (Fig. 10B).
Caudal to the bend the caudal end of a centrum (hereafter
called centrum 1) and four more consecutive centra (hereafter
called centra 2–5) are visible. Only centrum 2 can be measured
with certainty. It is 41 mm long and is cranially 16 mm tall.
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Figure 11. New dromaeosaurid tail skeleton (UMNH VP 20209) under ultraviolet (above) and visible (below) light.
doi:10.1371/journal.pone.0036790.g011
(approximately 2.7 times the length of the centrum). One tine of a
prezygapophysis is traceable to centrum 3. As preserved, it extends
106 mm beyond the centrum. In contrast, the postzygapophysis of
centrum 3 extends only approximately 17 mm beyond the
centrum. That of centrum 4 extends only approximately 11 mm
beyond the centrum.
A detached hemal arch lies on the right side of the tail, with its
body on the anterodorsal corner of centrum 3 (Fig. 10C). It has
been turned around so that its caudal process extends cranially.
That process extends 30 mm beyond the body and is not
bifurcated at the tip. There are two cranial projections, neither
of which is itself bifurcated, the bases of which are joined at the
body of the hemal arch. The longer (as preserved) of these two
projections extends 82 mm from the body of the bone.
In the new specimen, all the proximal caudals with transverse
processes are missing. Using a conservative estimate of four
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missing caudals with transverse processes, we see that the first
caudal vertebra contributing to the caudotheca is no farther
cranial than the eighth caudal vertebra and the caudotheca
extends no farther forward than the seventh.
Phylogenetic Analysis
The phylogenetic analysis recovered 1217 most-parsimonious
trees with 1304 steps. For these trees, the consistency index is
0.3758, the homoplasy index is 0.6242, the retention index is
0.8124, and the rescaled consistency index is 0.3053.
The phylogeny of Coelurosauria recovered here (Fig. 12A)
matches that found using the previous version of the phylogenetic
data matrix [36]. Within Paraves, it differs from some recent
phylogenetic analyses in the following ways. Here, Xiaotingia is
placed at the base of Dromaeosauridae, whereas a previous
analysis placed it with Anchiornis and Archaeopteryx in a clade that
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Figure 12. Phylogeny of Coelurosauria, as found by this study. Numbers at base of each clade are decay indices (Bremer support). (A)–
Phylogeny recovered when fragmentary deinonychosaurian OTUs are included. (B)–Paravian portion of the phylogeny recovered when several
fragmentary deinonychosaurian OTUs are deleted.
doi:10.1371/journal.pone.0036790.g012
formed the sister taxon to Deinonychosauria [89]. Here, Shanag is
placed at the base of the sister clade of Unenlagiinae, whereas
previous analyses placed it at the base of Unenlagiinae itself
[21,22]. Here, Mahakala is placed within Unenlagiinae, whereas a
previous analysis placed it at the base of Dromaeosauridae [21].
Yurgovuchia is found to be part of a clade within Dromaeosaurinae that includes Utahraptor, Achillobator, and Dromaeosaurus but
excludes Deinonychus. Relationships within this clade are uncertain.
Synapomorphies of Deinonychosauria and its sub-clades that are
confirmed to be present on Yurgovuchia are given in Table 3.
When deinonychosaurian OTUs known only from fragmentary
material are deleted from the analysis, the analysis yields 54 mostparsimonious trees of 1265 steps. For these trees, the consistency
index is 0.3866, the homoplasy index is 0.6134, the retention index
is 0.8083, and the rescaled consistency index is 0.3125. Decay
indices for several deinonychosaurian clades are increased, in
some cases dramatically, in comparison to the analysis that
included fragmentary taxa (Fig. 12B). The topology of the strict
consensus tree is nearly identical to that produced without deletion
of fragmentary taxa. The only change is that Bambiraptor is no
longer at the base of Eudromaeosauria in the consensus tree but is
part of an unresolved trichotomy with Eudromaeosauria and
Microraptoria.
between Microraptoria and Eudromaeosauria in the location of
the first caudal vertebra with processes that contribute to the
caudotheca, and (6) a difference between Microraptoria and
Eudromaeosauria in the location of the cranialmost extent of the
caudotheca.
In Microraptoria transverse processes are present only up to Cd
(caudal vertebra) 6, the first caudal vertebra contributing to the
caudotheca is no farther cranial than Cd 6, and the caudotheca
extends forward to Cd 3 or 4. In Eudromaeosauria transverse
processes are present up to Cd 10, the first caudal vertebra
contributing to the caudotheca is no further cranial than Cd 10,
and the caudotheca extends no farther forward than Cd 6. The
new specimen described here that is represented only by a tail
skeleton exhibits the eudromaeosaurian condition.
Discussion
The three new dromaeosaurid specimens described here add to
the known dinosaurian diversity of the upper and lower Yellow
Cat Member of the Cedar Mountain Formation. The therizinosauroid Falcarius utahensis [3] and the small, predatory theropod
Geminiraptor suarezarum [4] have previously been described from the
lower Yellow Cat. To that theropod paleofauna we now add
Yurgovuchia doellingi and the velociraptorine dromaeosaurid represented by the new pubis. From the upper Yellow Cat the large
dromaeosaurid Utahraptor ostrommaysorum has previously been
described [5], as has the small theropod Nedcolbertia justinhofmanni
[2]. To that theropod paleofauna we now add the new, unnamed
eudromaeosaur represented by the new tail skeleton UMNH VP
20209.
According to our phylogenetic results, Y. doellingi and U.
ostrommaysorum are both members of the subfamily Dromaeosaurinae. The new pubis represents the subfamily Velociraptorinae.
During the Late Cretaceous Asia was also simultaneously
inhabited by dromaeosaurines (Achillobator) [9] and velociraptorines (Tsaagan, Velociraptor) [20,28]. In addition, microraptorian
dromaeosaurids are known from the Lower Cretaceous of Asia
[10,12,14,15,18,25,88] and the Upper Cretaceous of North
Tail Evolution Scenario
Comparison of data from a phylogenetically broad spectrum of
coelurosaurian theropod taxa (Table 1) reveals several evolutionary changes in the coelurosaurian tail (Fig. 13). Several of these
changes include reversals within Dromaeosauridae. The changes
are: (1) a decrease in the number of caudal vertebrae early in
coelurosaurian phylogeny, followed by an increase in Eudromaeosauria, (2) a decrease in the number of caudals bearing transverse
processes in Paraves, followed by an increase in this number in
Eudromaeosauria, (3) elongation of middle caudal vertebrae to
over twice the length of the first few caudals in Paraves, followed
by a reversal in Eudromaeosauria, (4) acquisition of a caudotheca
in Microraptoria + Eudromaeosauria, followed by its replacement
by a hemicaudotheca in Dromaeosaurinae, (5) a difference
Table 3. Synapomorphies of Deinonychosauria and its sub-clades that are confirmed to be present in Yurgovuchia doellingi.
Clade
Character
State number and description
Deinonychosauria
160
0: Cervical epipophyses above zygapophyseal facets
Dromaeosauridae
174
1: Posterior trunk parapophyses distinctly projected on pedicels (ACCTRAN only)
Unenlagiinae + (Shanag + (Microraptoria + 174
(Eudromaeosauria)))
1 (DELTRAN only)
Microraptoria + Eudromaeosauria
0: Anterior dorsal transverse processes long and thin
180
165
0: Cervical carotid processes absent (ACCTRAN only)
Velociraptorinae + Dromaeosauridae
165
0: (DELTRAN only)
193
2: Mid-caudal centra between 1.36 and 26 as long as proximal centra
Yurgovuchia + Achillobator + Utahraptor +
Dromaeosaurus
162
0: Anterior cervical centra subcircular or square in cranial view
195
3: Prezygapophyses of distal caudal vertebrae extended in length but not longer than several centra
Character and state numbers are as given in Appendix S1. Unless otherwise mentioned, in each case the state is a synapomorphy of the clade under both accelerated
and delayed transformation. ACCTRAN = accelerated transformation. DELTRAN = delayed transformation.
doi:10.1371/journal.pone.0036790.t003
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New Dromaeosaurids from Utah
Figure 13. Changes in character states of the tail, mapped onto coelurosaurian theropod phylogeny.
doi:10.1371/journal.pone.0036790.g013
birds Jeholornis, Sapeornis, Confuciusornis, and Yanornis; the troodontids Anchiornis, Sinusonasus, Mei, and Sinornithoides; and the
dromaeosaurids Buitreraptor, Sinornithosaurus, Microraptor zhaoianus,
M. gui, Bambiraptor, Tsaagan, Velociraptor, Deinonychus, and Utahraptor.
We therefore consider the matrix used here particularly reliable
for placement of paravian taxa and therefore doubt the placement
of Archaeopteryx, Xiaotingia, and Anchiornis in a clade of their own.
The results of the phylogenetic analysis with fragmentary OTUs
deleted yields a high decay index for Avialae (with Archaeopteryx
therein), which indicates strong support for a close relationship
between Archaeopteryx and other birds (Fig. 12B). It also yields a
high decay index for Deinonychosauria (with Anchiornis and
Xiaotingia therein), which indicates strong support for phylogenetic
separation of Archaeopteryx from Anchiornis and Xiaotingia (Fig. 12B).
America [24]. This shows that transcontinental dispersal events
occurred during the Cretaceous Period for all three dromaeosaurid clades.
Another important aspect of the phylogeny recovered here is
the phylogenetic separation between Archaeopteryx (at the base of
Aves), Xiaotingia (at the base of Dromaeosauridae), and Anchiornis
(at the base of Troodontidae). The analysis that placed these three
genera together in a clade of their own [89] used a modified
version [48] of a phylogenetic data matrix that was published in
2007 [90]. That matrix lacked two sets of updates that were added
later; one set of updates was included in a 2010 version of the
matrix [91] and a further set of updates was included in a 2011
version of the matrix [36], in both cases due to recent examination
of specimens by PS. Among the taxa with significant amounts of
changed data due to post-2007 examination of specimens are the
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New Dromaeosaurids from Utah
Coding of character states of the new pubis inspired a
reevaluation of the orientation of dromaeosaurid pubes. Previous
authors have considered the pubis to be retroverted in Velociraptor
and other eudromaeosaurs [38]. However, in Paraves the pubic
surface of the pubic peduncle of the ilium is horizontal
[7,9,29,38,49,50]. This means that if the iliac surface of the pubis
is perpendicular to the pubic shaft, then the pubic shaft was
vertical. PS has confirmed this in the dromaeosaurids Rahonavis
and Unenlagia by manual articulation of originally disarticulated
pelves. The iliac surface of the pubis is perpendicular to the pubic
shaft in the eudromaeosaurs Velociraptor [85] and Achillobator [9]
and the basal microraptorian Tianyuraptor [25]. Their pubes were
therefore vertical, not retroverted. The retroversion of their pubes
in articulated specimens [25,38,85] is due to disarticulation of the
pubes from the ilia and subsequent rotation of the pubes. A similar
situation is present in Archaeopteryx. Its pubes have become
disarticulated from the ilia and rotated into a retroverted position
in most specimens [49,92,93]; the pubes are vertical in the one
specimen of Archaeopteryx in which they retain articulation with the
ilia [94]. The morphology of the pubis of Yurgovuchia and the new
velociraptorine specimen described here indicates that they, too,
were vertical. Advanced microraptorians are the only dromaeosaurids in which the pubes are retroverted. In advanced
microraptorians the pubic shafts are at a strong angle to the iliac
surface of the pubis [10,15], and an articulated specimen
demonstrates that this causes their pubes to be retroverted [15].
The morphological dichotomy between the tails of microraptorians and eudromaeosaurs relate to a difference in the location of
the transition point between the two clades. The transition point
occurs farther caudally in the tail in Eudromaeosauria than it does
in Microraptoria, so that the proximal segment of the tail contains
a larger number of vertebrae in Eudromaeosauria. This allows the
proximal segment of the tail to swing through a greater arc in
Eudromaeosauria if the zygapophyseal orientations of the
proximal tail segment are uniform between the two clades.
Typically, eudromaeosaurs are larger and have more robust
skeletons than microraptorians, and it is plausible that the smaller
range of motion of the microraptorian tail was insufficient to
accommodate the greater body mass of the eudromaeosaurs
during sudden changes of direction during fast locomotion or
other vigorous activity. That is, the small microraptorians could
accommodate having a very stiff tail, but at larger body sizes
dromaeosaurids needed greater tail flexibility to maintain balance.
Although a hemicaudotheca looks like an intermediate condition in the evolution of a caudotheca, the results of the
phylogenetic analysis show that this is not so. The clade exhibiting
a hemicaudotheca is nested within the caudothecate group and has
four successive caudothecate sister groups: Deinonychus, Velociraptorinae, Bambiraptor, and Microroaptoria (Fig. 12). This indicates
that the caudotheca appeared first and then became reduced into
a hemicaudotheca in advanced dromaeosaurines (Fig. 13).
It is plausible that a hemicaudotheca allowed more tail flexibility
than a caudotheca because of reduction in the lengths of the bony
processes enclosing the caudal centra. If, as postulated above,
larger dromaeosaurids required greater tail flexibility to maintain
balance during vigorous activity, then a more-flexible hemicaudotheca would be more advantageous than a less-flexible
caudotheca to the largest dromaeosaurids. As it happens, the
largest dromaeosaurids, Utahraptor and Achillobator, exhibit a
hemicaudotheca. This supports the hypothesis that the reduction
of the caudotheca into a hemicaudotheca was a prerequisite for
the evolution of large size in Eudromaeosauria.
Supporting Information
Appendix S1 Character List for Phylogenetic Analysis of
Coelurosauria.
(DOC)
Appendix S2 Phylogenetic Data Matrix for Phylogenetic
Analysis of Coelurosauria.
(DOC)
Acknowledgments
We would like to thank Mariah Cuch of the Public Relations Department
of the Ute Tribe, who helped with the translation of ‘‘coyote.’’ We also
thank Mike Laine for his help with the ultraviolet photo. We would also
like to thank the large number of volunteers including those from Utah
Friends of Paleontology who helped with the excavations at Andrew’s Site
and Doelling’s Bowl. Excavation of Andrew’s Site Dinosaur Quarry was
conducted under Bureau of Land Management excavation permit # UTEX-05-031 in 2005 under the supervision of Jennifer Cavin. The locality
(Gr 290v) was discovered by Andrew R. C. Milner. Excavation of the
Doelling’s Bowl bone bed has been conducted under Bureau of Land
Management excavation permit # UT06-035E. We would also like to
thank two anonymous reviewers whose suggestions improved this
manuscript.
Author Contributions
Conceived and designed the experiments: PS JIK NT. Performed the
experiments: PS JIK NT. Analyzed the data: PS JIK NT. Contributed
reagents/materials/analysis tools: JIK DDD SM. Wrote the paper: PS JIK
NT.
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May 2012 | Volume 7 | Issue 5 | e36790
Figure 5
modern
drainage
1m
Holotype
Hippodraco
scutodens
dromaeosaur
tail
large
iguanodontian
crocodilian
basal
ornithopod
scapula
mammal
skull