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SPECIAL ISSUE ARTICLE
Osteology and reassessment of Dineobellator notohesperus,
a southern eudromaeosaur (Theropoda: Dromaeosauridae:
Eudromaeosauria) from the latest Cretaceous of New
Mexico
Steven E. Jasinski
1,2
| Robert M. Sullivan
3
| Aja M. Carter
4
|
Erynn H. Johnson
5,6
| Sebastian G. Dalman
3
| Juned Zariwala
7
|
Philip J. Currie
8
1
Department of Environmental Science
and Sustainability, Harrisburg University,
Harrisburg, Pennsylvania, USA
2
Don Sundquist Center of Excellence in
Paleontology, Johnson City,
Tennessee, USA
3
New Mexico Museum of Natural History
and Science, Albuquerque, New
Mexico, USA
4
Penn Engineering - GRASP Laboratory,
University of Pennsylvania, Philadelphia,
Pennsylvania, USA
5
Department of Earth and Planetary
Sciences, Yale University, New Haven,
Connecticut, USA
6
Paleontological Research Institution,
Ithaca, New York, USA
7
Maharaja Sayajirao University of Baroda,
Vadodara, Gujarat, India
8
Department of Biological Sciences,
University of Alberta, Edmonton, Alberta,
Canada
Correspondence
Steven E. Jasinski, Department of
Environmental Science and Sustainability,
Harrisburg University, Harrisburg, PA
17101-2208, USA.
Email: sejasinski@gmail.com
Funding information
University of Pennsylvania
Abstract
Dromaeosaurids (Theropoda: Dromaeosauridae), a group of dynamic, swift
predators, have a sparse fossil record, particularly at the end of the Cretaceous
Period. The recently described Dineobellator notohesperus, consisting of a par-
tial skeleton from the Upper Cretaceous (Maastrichtian) of New Mexico, is the
only diagnostic dromaeosaurid to be recovered from the latest Cretaceous of
the southwestern United States. Reinterpreted and newly described material
include several caudal vertebrae, portions of the right radius and pubis, and an
additional ungual, tentatively inferred to be from manual digit III. Unique fea-
tures, particularly those of the humerus, unguals, and caudal vertebrae, distin-
guish D.notohesperus from other known dromaeosaurids. This material
indicates different physical attributes among dromaeosaurids, such as use of
the forearms, strength in the hands and feet, and mobility of the tail. Several
bones in the holotype exhibit abnormal growth and are inferred to be patho-
logic features resulting from an injury or disease. Similar lengths of the
humerus imply Dineobellator and Deinonychus were of similar size, at least
regarding length and/or height, although the more gracile nature of the
humerus implies Dineobellator was a more lightly built predator. A new phylo-
genetic analysis recovers D.notohesperus as a dromaeosaurid outside other pre-
viously known and named clades. Theropod composition of the Naashoibito
Member theropod fauna is like those found in the more northern Late Creta-
ceous North American ecosystems. Differences in tooth morphologies among
recovered theropod teeth from the Naashoibito Member also implies D.notohe-
sperus was not the only dromaeosaurid present in its environment.
KEYWORDS
Dinosauria, Dromaeosauridae, late Cretaceous, paleobiology, Theropoda
Received: 1 April 2022 Revised: 11 September 2022 Accepted: 30 September 2022
DOI: 10.1002/ar.25103
Anat Rec. 2022;1–45. wileyonlinelibrary.com/journal/ar © 2022 American Association for Anatomy. 1
1|INTRODUCTION
Dromaeosaurids (Theropoda: Dromaeosauridae) are a
group of small- to medium-sized theropods that lived
during the Cretaceous Period, mainly on the northern
paleocontinent of Laurasia. They have been found in
North America throughout the Cretaceous, from present
day Alaska to Maryland (e.g., Jasinski & Dodson, 2015;
Matthew & Brown, 1922; Turner et al., 2012). However,
their fossil record is poor near the end of the Cretaceous
and the Cretaceous-Paleogene boundary in North Amer-
ica. Early Cretaceous North American dromaeosaurids
include Deinonychus antirrhopus,Utahraptor ostrom-
maysi, and Yurgovuchia doellingi (e.g., Brinkman
et al., 1998; Kirkland et al., 1993; Ostrom, 1969; Senter
et al., 2012). Several other taxa are known from the Late
Cretaceous, but almost all are from the Campanian,
although it is noted that Atrociraptor marshalli comes
from the Maastrichtian (probably early Maastrichtian)
portion of the Horseshoe Canyon Formation
(e.g., Burnham, 2004; Burnham et al., 2000; Currie &
Varricchio, 2004; Longrich & Currie, 2009; Larson
et al., 2010; Jasinski, 2015a; Jasinski & Dodson, 2015;
Jasinski et al., 2015; Matthew & Brown, 1922;
Sues, 1978). Recently, two taxa (Acheroraptor temer-
tyorum and Dakotaraptor steini) were named from the
upper Maastrichtian Hell Creek Formation, but, aside
from these two skeletal fossil specimens, non-tooth mate-
rial of Maastrichtian taxa is rare (e.g., DePalma
et al., 2015; Evans et al., 2013; Jasinski & Dodson, 2015).
Although isolated dromaeosaurid teeth are somewhat
common in Campanian age strata of North America,
these teeth reveal relatively little information about the
paleoecology of this group (Jasinski et al., 2020).
The dromaeosaurid Dineobellator notohesperus was
recently described from the Maastrichtian (latest Creta-
ceous) of New Mexico (Jasinski et al., 2020). The holotype
specimen of D.notohesperus (SMP VP-2430), collected
from the Naashoibito Member of the Ojo Alamo Forma-
tion in the San Juan Basin in northwestern New Mexico,
consists of over 20 identifiable skeletal elements, includ-
ing parts of the skull, axial skeleton, and fore- and
hindlimbs. Since its original publication, additional
observations and reinterpretations have been made and
are presented below, allowing for a more robust under-
standing of its place within Dromaeosauridae. This more
detailed account allows for a reassessment of the phylo-
genetic relationships of D.notohesperus and further pro-
vides insight into the paleoecology of this late surviving
dromaeosaurid in what is now New Mexico at the end of
the Cretaceous.
Institutional abbreviations: AMNH FARB, American
Museum of Natural History, New York, New York; IGM,
Mongolian Institute of Geology, Ulaan Bataar, Mongolia;
IVPP, Institute of Vertebrate Paleontology and Paleoan-
thropology, Beijing, China; MNHN, Muséum National
d'Histoire Naturelle, Paris; MPC, Paleontological and
Geological Center of the Mongolian Academy of Sci-
ences, Ulaan Bataar, Mongolia; OMNH, Oklahoma
Museum of Natural History, Norman, Oklahoma; SMP,
State Museum of Pennsylvania, Harrisburg, Pennsylva-
nia; TMP, Royal Tyrrell Museum of Palaeontology,
Drumheller, Alberta; UALVP, University of Alberta
Laboratory of Vertebrate Palaeontology, Drumheller,
Alberta.
Anatomical abbreviations: ab, abnormal bone growth;
acdl, anterior centrodiapophyseal lamina; al, alveolus; as,
articular surface; avg, accessory vascular groove; bptp,
basipterygoid process; bspr, basisphenoid recess; bt, basal
tubera; capt, capitulum; cg, costal groove; con, contact;
dci, distal (or caudal) indentation; dcs, distal (or caudal)
centrum surface; dpc, deltopectoral crest; eg, extensor
groove; fhc, curvature of femoral head; fm, foramen mag-
num; for, foramen; ft, flexor tubercle; ind, indentation;
lcd, distal lateral condyle; lct, lateral cotyle; ld, m.latissi-
mus dorsi scar; lg, lateral groove; lr, lacrimal recess; mc,
medial crest; mcd, distal medial condyle; mcr, middle
cotylar ridge; mct, medial cotyle; mg, medial groove; na,
neural arch; nc, neural canal; ns, neural spine; oc, occipi-
tal condyle; op, olecranon process; or, orbital rim; pci,
proximal (or cranial) centrum indentation; pcs, proximal
(or cranial) centrum surface; pocdf, postzygapophyseal
centrodiapophyseal fossa; prcdf, prezygapophyseal cen-
trodiapophyseal fossa; prdl, prezygadiapophyseal lamina;
rs, rugose surface; sdf, spinodiapophyseal fossa; spof, spi-
nopostzygapophyseal fossa; sprf, spinoprezygapophyseal
fossa; ss, sutural surface; tp, transverse process; tub,
tuberculum; up, ulnar papillae; ur, ulnar ridge; vg, ven-
tral groove; vr, ventral ridge; zr, zygapophyseal rod.
1.1 |Geologic setting
The holotype of Dineobellator notohesperus (SMP VP-2430)
was discovered and collected a few meters above the base
of the Naashoibito Member of the Ojo Alamo Formation,
San Juan Basin, New Mexico. The specimen was found
weathering out of a relatively poorly consolidated
sandstone (Figure 1).
40
Ar/
39
Ar dates acquired from
detrital sanidines give a maximum depositional age for the
Naashoibito Member at 66.5 ± 0.2 Ma (upper Maastrich-
tian) (Greene et al., 2018; Heizler et al., 2013; Mason
et al., 2013; Peppe et al., 2013; Williamson & Brusatte,
2014). However, biostratigraphic evidence suggests an
early late Maastrichtian age of about 70.0–68.0 Ma
(Fowler, 2017).
2JASINSKI ET AL.
2|MATERIALS AND METHODS
SMP VP-2430 was first reported by Jasinski, Sullivan, and
Lucas (2011), who provided a brief description of some of
the material and identified it as an indeterminate dro-
maeosaurid and possibly a new species. Jasinski et al.
(2020) described the material further while naming the
taxon Dineobellator notohesperus and conducted phyloge-
netic analyses investigating its evolutionary relationships.
Because the description provided by Jasinski et al. (2020)
was relatively short, a more thorough description of this
specimen is warranted and provided here. We also rei-
dentify some of the previously described elements along
with descriptions of newly identified material. This
includes not only the original material of the holotype
specimen that was largely collected in 2008 (see Jasinski
et al., 2020), but also additional elements subsequently
collected from the type locality in 2009, 2015, and
2016. Anatomical terminology utilizes rostral, cranial
(=anterior), and caudal (=posterior). For caudal
FIGURE 1 (a) Geographic map showing Late Cretaceous through Eocene strata of the San Juan Basin, where the type specimen of
Dineobellator notohesperus (SMP VP-2430) was collected (marked by a star). (b) Stratigraphic chart showing significant strata of the San Juan
Basin. It is noted that within the NALMA/NALVA column, most of the ages are the North American Land Mammal Ages, however, the
Kirtlandian was defined by Sullivan and Lucas (2003,2006) as a North American Land-Vertebrate Age based on (mainly) non-mammal
components. Additionally, the age of the Naashoibito Member of the Ojo Alamo Formation has been debated as to whether it is from the
Edmontonian or Lancian (e.g., Jasinski, Sullivan, & Lucas, 2011). Figure pools information from multiple sources, including the Geologic
Map of New Mexico (2003), Sullivan and Lucas (2003,2006), Williamson and Weil (2008a,2008b), Lucas et al. (2009,2016), Jasinski and
Sullivan (2011,2016), Jasinski, Sullivan, and Lucas (2011); Jasinski, Lucas, and Moscato (2011); Koenig et al. (2012), Sullivan and Jasinski
(2012), Williamson and Brusatte (2014,2016), Jasinski et al. (2015,2020), Jasinski and Dodson (2015), and Ksepka et al. (2017). Clarkfork,
Clarkforkian; Ed, Edmontonian; Lanc, Lancian; Maast, Maastrichtian; NALMA, North American Land Mammal Age; NALVA, North
American Land-Vertebrate Age; Sel, Selandian; Tiff, Tiffanian
JASINSKI ET AL.3
vertebrae, we utilize proximal (=anterior or cranial) and
distal (=posterior or caudal) directions or surfaces.
A new phylogenetic analysis, including Dineobellator
notohesperus, was run using the recent dataset of Powers
et al. (2022) to further investigate the evolutionary relation-
ships of dromaeosaurids, with a focus on eudromaeosaurs
(Eudromaeosauria). Our results are compared to those of
Jasinski et al. (2020) in two other datasets [those of Currie
and Evans (2019) and the Theropod Working Group dataset
which was more recently utilized by Cau et al. (2015,2017)
and Turner et al. (2021)] to further compare those relation-
ships within Dromaeosauridae. The Powers et al. (2022)
dataset originally ran 175 characters on 25 operational taxo-
nomic units (24 ingroup OTUs). “Velociraptor sp.”was
removed from their dataset as this is a potentially new taxon
that they are working on further. It was replaced with
Dineobellator notohesperus, resulting in the same number of
characters and OTUs. The Powers et al. (2022) dataset is a
modifiedversionofthedatasetofPowers(
2020), which is a
further modification of that of Currie and Evans (2019). Cur-
rent data were run with TNT version 1.5 (Goloboff &
Catalano, 2016). The dataset was subjected to a New Tech-
nology search (with default parameters for sectorial search,
ratchet, tree drift, and tree fusion). Bootstrap resampling
was done using 100 replicates to compare the results more
closely to those of Powers et al. (2022).
2.1 |Systematic paleontology
Dinosauria Owen, 1842
Theropoda Marsh, 1881
Coelurosauria Huene, 1914
Dromaeosauridae Matthew & Brown, 1922
Dineobellator Jasinski et al., 2020
Dineobellator notohesperus Jasinski et al., 2020
2.1.1 | Holotype
SMP VP-2430 is a disarticulated, associated individual
(Figure 2) consisting of a rostromedial (anteromedial) por-
tion of the right premaxilla, a left maxillary fragment, ?
maxillary tooth, dorsolateral process of the left lacrimal,
left? nasal fragment, incomplete right jugal, incomplete
left basipterygoid, incomplete occipital condyle, isolated
prezygapophyses, isolated vertebral processes, caudal ver-
tebra 1, middle caudal vertebra, three more distal caudal
vertebrae (distal or posterior to mid-caudal vertebra), four
fused distal caudal vertebrae, several vertebral fragments,
nearly complete rib and rib fragments, nearly complete
right humerus, nearly complete right ulna, incomplete
right radius, incomplete right metacarpal III, nearly com-
plete right manual ungual II, nearly complete right? man-
ual ungual? III, fragmentary right pubis, incomplete right
femur, incomplete right metatarsals II and III, right pedal
phalanx I-I, nearly complete right pedal ungual III, and
various other cranial and post-cranial bone fragments.
2.1.2 | Type locality and horizon
The type locality, SMP 410b, Bisti/De-na-zin Wilderness,
New Mexico. Precise locality information is on file at the
FIGURE 2 Skeletal reconstruction of Dineobellator notohesperus (SMP VP-2430) with known elements colored in white. Figured bones
are as follows: Fused distal caudal vertebra (a); distal caudal vertebra (b); middle caudal vertebra (c); caudal vertebra 1 (d); right femur (e);
rib (f); right basipterygoid (g); left lacrimal (reversed) (h); right jugal (i); right humerus (j); right ulna (k); right metacarpal III (l); right
manual ungual II (m); right metatarsal II (n); right metatarsal III (o); right pubic boot (p). Individual scale bars, 2 cm. Figure modified from
Jasinski et al. (2020, figure 2)
4JASINSKI ET AL.
State Museum of Pennsylvania, Section of Paleontology
and Geology, and is available to qualified researchers.
The holotype (SMP VP-2430) was collected in a weath-
ered sandstone a few meters above the base of the Naa-
shoibito Member (Ojo Alamo Formation).
40
Ar/
39
Ar
dates acquired from detrital sanidines give a maximum
depositional age for the Naashoibito Member at 66.5
± 0.2 Ma (upper Maastrichtian; Greene et al., 2018;
Heizler et al., 2013; Mason et al., 2013; Peppe et al., 2013;
Williamson & Brusatte, 2014). Biostratigraphic evidence,
however, suggests an early late Maastrichtian age,
approximately 70.0–68.0 Ma (Fowler, 2017; Jasinski, Sul-
livan, & Lucas, 2011).
2.1.3 | Revised diagnosis
A mid-sized dromaeosaurid theropod that differs from
other eudromaeosaurs by the following characters: offset
of medial and lateral grooves (or blood grooves) on man-
ual ungual; distinct and conspicuous mediodorsal groove
proximally, dorsal to the articular surface of the manual
ungual; sharp angle of distal deltopectoral crest of the
humerus; opisthocoelous proximal caudal vertebrae, with
gently convex proximal (anterior) centrum surface; short
and robust neural spines on proximal caudal vertebrae;
gracile and sub-rectangular transverse processes on proxi-
mal caudal vertebrae; proximal caudal vertebrae with
curved ventral surface and oval to sub-rectangular proxi-
mal and distal (posterior) centrum surfaces; distinct
round concavities on proximal and distal centrum sur-
faces in mid-caudal vertebrae; enlarged flexor tubercles
on manual ungual II and pedal ungual III; and secondary
lateral grooves (or accessory vascular grooves) on pedal
unguals on both the medial and lateral surfaces, with
those on the lateral surfaces more defined and
conspicuous.
2.2 |Descriptions and comparisons
Jasinski et al. (2020) briefly described much of the
material considered here for the holotype specimen of
Dineobellator notohesperus (SMP VP-2430). Here we
provide a more detailed account of the holotype, along
with comparisons to other known dromaeosaurid taxa
and material. Moreover, we have re-identified some of
material described by Jasinski et al. (2020), along with
documenting several elements not mentioned in their
work. This present contribution provides the opportu-
nity to figure and illustrate all the pertinent elements,
thus giving us a clearer picture of this unique dromaeo-
saurid dinosaur.
2.3 |Skull
A few small fragments of SMP VP-2430 are from the skull
of Dineobellator notohesperus. A small, rostromedial frag-
ment of the right premaxilla is preserved bearing two
empty alveoli, which are visible caudomedially
(Figure 3a,b). Rostrally the surface is smooth where the
rostral parts of the left and right premaxillae would con-
tact, roughly parallel to the midline of the skull. The rem-
nants of the alveoli are quite small labially (medially; see
Table 1for all measurements) and closely spaced, similar
to the condition found in other dromaeosaurids. Portions
of the lateral surface of the premaxilla are rugose and
may be pathologic. The fragment implies a more vertical,
rather than sloped, orientation of the premaxilla. This
more vertical orientation would help distinguish Dineo-
bellator from several other dromaeosaurids that tend to
have more sloping premaxillae (Halszkaraptor,Sinor-
nithosaurus,Utahraptor).
The left maxilla is represented by a small, sub-
rectangular fragment (Figure 3c,d). Although a few small,
questionable, randomly distributed foramina are present,
it is otherwise smooth on its lateral surface. Two partial
alveoli are present lingually (medially). The more com-
plete alveolus on the maxillary fragment is larger and this
is more prominent than any preserved on the premaxil-
lary fragment. Regardless, the small alveoli mean the
fragment is from the caudal portion of the left maxilla.
A single tooth, possibly pertaining to the maxilla, is
small and relatively gracile (Figure 3e,f). The apical
length measures 12.0 mm in total, with a crown height of
11.3 mm (Table 2). There are approximately 18–20 denti-
cles per 5 mm on the distal (or posterior) carina (distal
basal denticles), but no denticles on the mesial
(or anterior) carina. The presence or absence of denticles
on the mesial carina (see Smith, 2005; Torices
et al., 2014) is highly variable among dromaeosaurids
but, in addition to Dineobellator, they are absent in Bam-
biraptor feinbergi and several Asian taxa including Lin-
heraptor exquisitus,Tsaagan mangas, and Velociraptor
osmolskae (e.g., Burnham, 2004; Godefroit et al., 2008;
Norell et al., 2006; Xu et al., 2010). The presence or
absence of denticles on carinae can also sometimes vary
along the tooth row in some taxa, particularly in earlier
diverging dromaeosaurids (e.g., Poust et al., 2020), as well
as the potential development of denticles in the later
ontogenetic stages of some theropods (e.g., Carr &
Williamson, 2004; Currie et al., 1990). There are 3.7–4.3
denticles per 1 mm, most easily seen close to the base of
the distal carina where the denticles are best preserved
(Figure 3f). The angle between the lines of 10% and 90%
of the length of the exposed denticles normally falls
between 86
–95for denticles that are not worn down,
JASINSKI ET AL.5
broken, or deformed, with most falling just under 90.
This measurement was done in a similar fashion to that
of Larson (2008) to evaluate denticle shape, with the lines
of 10% and 90% used to remove any irregularities in the
extreme ends of the denticles. The denticles on the distal
carina are mostly rounded off and show no traces of
hooks. Additionally, the denticles tend to be proximodis-
tally (or dorsoventrally) shallow in relation to cranio-
caudal depth. Additional dromaeosaurids possessing
distal (caudal) denticles that are not apically hooked
(and instead are rounded) are Acheroraptor temertyorum
and Tsaagan mangas whereas others, such as Atro-
ciraptor marshalli and Saurornitholestes langstoni, are
apically hooked (Currie & Evans, 2019; Currie &
Varricchio, 2004; Larson, 2008). On the apical end of the
rostral edge of the tooth, there is a wear facet that mea-
sures approximately 7 mm along the curvature of the
tooth from the distal tooth tip where it would occlude
with a dentary tooth. The tooth is not constricted
between root and crown, has a concave-curve caudally,
and would not have been strongly raked in the alveolus
due to the orientation of the alveoli. Raked here refers to
the tooth curving caudally, as in the motion of sweeping
with a rake or broom. This latter aspect of the teeth dif-
fers from those of Atrociraptor,Bambiraptor, and Deinon-
ychus, where the teeth are strongly raked caudally
(e.g., Burnham, 2004; Burnham et al., 2000; Currie &
Varricchio, 2004; Ostrom, 1969).
The right jugal (Figure 4a,b), is represented by a flat,
trapezoidal fragment suggesting it was a deep and plate-like
element. It is slightly curved laterally toward its rostral and
caudal ends. The element is flat and as there is no evidence
of any medial or lateral projections on the preserved por-
tions, it is likely that none were present on the complete ele-
ment as well. The curvature of the dorsal edge of the jugal
indicates the orbit was circular. Most of the margin of the
bone is incomplete, although, in addition to a ventral por-
tion of the orbit, there is also a region caudodorsally where
the thin ventral margin is complete and gracile. The
dorsoventral extent of the caudal portion of the jugal
implies it was relatively deep, like some dromaeosaurids
such as Adasaurus mongoliensis (Barsbold, 1983;Turner
et al., 2012, figure 10a), but distinguishing it from taxa with
shallower jugals such as Bambiraptor and Halszkaraptor
(Burnham, 2004;Cau,2020; Cau et al., 2017). There is also a
partial foramen present rostrally along the broken surface.
This foramen may have been close to the contact between
the jugal and the maxilla, although that is uncertain due to
its poor preservation. It is similar to foramina present on the
lateral surface of the jugal of Linheraptor exquisitus (IVPP V
16923) and Velociraptor mongoliensis (AMNH FARB 6515;
Xu et al., 2010, see figure 2; Xu et al., 2015).
FIGURE 3 Premaxilla,
maxilla, and tooth material of
Dineobellator notohesperus
(SMP VP-2430). (a, b)
Rostromedial fragment of right
premaxilla in rostral (a) and
caudal (b) views. (c, d) left
maxilla fragment in lateral
(c) and medial (d) views. (e, f)
?Maxillary tooth showing full
tooth (e), and magnified image
showing denticle morphology
(f). Scale bars corresponding to
(a–d) and (e) equal 1 cm. Scale
bar for (f) equals 1 mm
6JASINSKI ET AL.
TABLE 1 Anatomical measurements of the holotype of Dineobellator notohesperus (SMP VP-2430)
Selected measurements of Dineobellator notohesperus (SMP VP-2430)
Element
Length
(in mm) Notes
Premaxilla (right)
Length 8.86
a
Depth 12.38
a
Alveolus “a”length 2.28
Alveolus “b”length 1.81
Maxilla
Length (rostrocaudal) 6.34
a
Depth (dorsoventral) 9.09
a
Alveolus “a”length 3.03
?Maxillary tooth
Apical length 12
Crown height 11.3
Fore-aft basal length 7.78
Basal width 4.15
Wear facet length 6.7
Lacrimal (left)
Length 9.00
a
Depth 6.96
a
Nasal (left)
Length 18.51
a
Width 6.71
a
Jugal (right)
Length (craniocaudal) 37.17
a
Depth (dorsoventral) 20.66
a
Maximum preserved depth measured near caudal-most portion of
bone
Basioccipital
Length (rostrocaudal) 14.79
a
Width (mediolateral) 16.04
a
Basipterygoid Process (right)
Length (rostrocaudal) 31.67 Between the basal tubera and the basipterygoid process
Height (dorsoventral) 13.8 Measured posteriorly at the basal tubera
Width A (mediolateral) 22.06 Measured across the caudal portion with the basal tubera
Width B (mediolateral) 11.58 Measured across the middle constriction just rostral to the carotid
canal
Width C (mediolateral) 8.81 Measured across the rostral portion with the basipterygoid process
Anterior Caudal Vertebra #1
Length (proximodistal) 26.4
Height (dorsoventral) 30.32 From ventral edge to dorsal edge of neural spine
Width (mediolateral) 15.9
Proximal centrum surface height (dorsoventral) 12.75
Proximal centrum surface width (mediolateral) 19.3
Distal centrum surface height (dorsoventral) 14.1
(Continues)
JASINSKI ET AL.7
TABLE 1 (Continued)
Selected measurements of Dineobellator notohesperus (SMP VP-2430)
Element
Length
(in mm) Notes
Distal centrum surface width (mediolateral) 21.95
Neural spine height (dorsoventral) 15.3
Midcaudal Vertebra (8to12)
Length (proximodistal) 32.56
Proximal width (mediolateral) 15.23
Distal width (mediolateral) 14.71
Mid-length width (mediolateral) 10.86
Neural arch length (proximodistal) 28.33
Caudal Vertebra (third identified)
Length (proximodistal) 34.4 This is the preserved length as the proximal portion is not
preserved
Caudal Vertebra (fourth identified)
Length (proximodistal) 46.26
Caudal Vertebra (fifth identified)
Length (proximodistal) 22.35 This is the preserved length as the distal portion is not preserved
Proximal centrum surface height (dorsoventral) 7.21
Proximal centrum surface width (mediolateral) 9.96
Distal Caudal Vertebrae
Fused section length (proximodistal) 19.95
a
Fused section height (dorsoventral) 9.5 Maximum height
Caudal vertebra a length (proximodistal) 4.12 This represents one of the two complete distal caudal vertebrae in
the fused section
Caudal vertebra b length (proximodistal) 5.1 This represents one of the two complete distal caudal vertebrae in
the fused section
Rib A Largest incomplete rib
Length (proximodistal) 100.55
a
Width A (craniocaudal) 25.12 At proximal end across the “D”
Width B (craniocaudal) 10.35 At distally preserved end
Humerus (right)
Length (proximodistal) 185.78
a
Shaft diameter 17.25–
18.52
Shaft width 17.1 proximal, just distal to deltopectoral crest
Shaft length 91.27
a
distal to deltopectoral crest
Ulna (right)
Length (proximodistal) 100.96
a
Width 15.71 Maximum width measured across trochlea and olecranon process
Shaft width 12 Average shaft width
Radius (right)
Height (craniocaudal) 15.16 Measured at distal end
Metacarpal III (right)
Length (proximodistal) 72.75
a
8JASINSKI ET AL.
TABLE 1 (Continued)
Selected measurements of Dineobellator notohesperus (SMP VP-2430)
Element
Length
(in mm) Notes
Width (craniocaudal) 16.68
a
Measured at proximal end
Manual Ungual II (right)
Length (proximodistal) 45.64
a
Measured from ventral edge of proximal articulation surface to
preserved distal tip
Length (proximodistal) 46.97
a
Measured from ventroproximal edge of flexor tubercle to preserved
distal tip
Height (dorsoventral) 29.95 Measured at the proximal end (from dorsal edge of articulation
surface to ventral edge of flexor tubercle)
Height (dorsoventral) 16.46 Measured at the midlength of the claw
Height (dorsoventral) 9.1 Measured at the preserved distal tip
Articulation surface height (dorsoventral) 18
Articulation surface width (mediolateral) 8.33
Flexor tubercle height (dorsoventral) 16.75
Flexor tubercle width (mediolateral) 6.7
?Manual Ungual? III (right)
Length (proximodistal) 30.38 Measured from broken proximal surface to distal tip
Height (dorsoventral) 8.16 Measured at proximal broken surface
Height (dorsoventral) 6.71 Measured at midlength of the preserved portion of the claw
Width (mediolateral) 4.01 Measureed at broken proximal surface dorsal to medial groove
Width (mediolateral) 3.61 Measureed at broken proximal surface ventral to medial groove
Pubis (right)
Length (proximodistal) 21.33 Measured along what would be the distal pubic shaft to the
proximodistal-most point of pubic boot
Boot length (craniocaudal) 19.5 Measured along the craniocaudal segment of the pubic boot
Femur (right)
Length (proximodistal) 68.83
a
Width 20.18
a
Metatarsal I (right)
Length (proximodistal) 11.43
a
Width 7.2 Maximum width measured distally
Metatarsal II (right)
Length (proximal section, proximodistal) 46.79
a
Shaft width (proximodistal section) 18.14 Maximum width measured at preserved distal end
Shaft width (proximodistal section) 8.75 Proximal-most shaft width
Length (distal section, proximodistal) 33.3
a
Shaft width (distal section) 11.52 Maximum width measured at distal end
Metatarsal III (right)
Length (proximodistal) 47.14
a
Width 14.04 Maximum width measured at preserved distal end
?Astragalus (left)
Length (proximodistal) 10.6
a
Width 6.82
a
(Continues)
JASINSKI ET AL.9
Another small fragment is tentatively identified as
part of the left nasal (Figure 4c–e). It is sub-rectangular,
with an enlarged medial surface that may be the sutural
surface between the two nasals, and a flat dorsal surface.
If identified correctly, it shows the nasals are flat dorsally,
like in Bambiraptor and Deinonychus (e.g., Burnham,
2004; Burnham et al., 2000; Ostrom, 1969).
A fragment of the left lacrimal is small, robust, and
sub-triangular with a rounded point laterally (Figure 4f,g).
It preserves the lateral process with a small concavity on
the rostroventral portion of the rostrolateral edge (lacrimal
fenestra or lacrimal recess) and a smooth surface along the
caudolateral edge. The element projects rostrally beyond
the extent of the “sub-triangular”form, and the lacrimal
presumably would have been “T”-shaped if complete. The
bone is incomplete with no sutural surfaces preserved.
The braincase is incomplete (Figure 5). The basioccipi-
tal condyle is preserved (Figure 5d). It is subcircular and
the entire element is obliquely twisted. The shape of the
dorsocaudal portion means the foramen magnum was cir-
cular to subcircular, which would distinguish it from the
dorsoventrally tall oval foramen magnum in Tsaagan
mangas (MPC 100/1015). However, the shape in the latter
may be due, at least partially, to post-depositional medio-
lateral deformation (Norell et al., 2006). As only the most
caudal portion of the occipital condyle is preserved, no cra-
nial nerve passages are present.
A portion of the basisphenoid, including the left
basipterygoid process, is preserved (Figure 5a–c). A small,
but prominent, subcircular basipterygoid recess is visible
medially. This recess is subcircular whereas it tends to be
more craniocaudally elongate in other dromaeosaurids
such as Dromaeosaurus (Currie, 1995) and Velociraptor
(Norell et al., 2004). The left basal tuber is robust but is
incomplete medially. The hypophyseal fossa may be pre-
sent but incomplete, as breakage makes its identification
tentative. The basisphenoid extends rostrally with a por-
tion of the well-developed left basipterygoid process
TABLE 1 (Continued)
Selected measurements of Dineobellator notohesperus (SMP VP-2430)
Element
Length
(in mm) Notes
Pedal Ungual III (right)
Length (proximal section, proximodistal) 13.23
a
Height (proximal section, dorsoventral) 21.3
Articulation surface height (dorsoventral) 10.65
Articulation surface width (mediolateral) 4.12
Flexor tubercle height (dorsoventral) 7.1
Flexor tubercle width (mediolateral) 3.53
Length (distal section, proximodistal) 32.03
a
Height (distal section, dorsoventral) 11.95 Measured at preserved proximal end
Height (distal section, dorsoventral) 9.05 Measured at preserved distal end
a
Incomplete element, measurement as preserved.
TABLE 2 Tooth measurements of dromaeosaurid teeth from the late cretaceous of the San Juan Basin, New Mexico
Specimen
number Taxonomic identity
Element
identity
Apical
length*
Crown
height*
Fore-aft basal
length*
Basal
width*
Denticles
per 5 mm
SMP VP-
2430
Dineobellator
notohesperus
?Maxillary
tooth
12 11.3 7.78 4.15 18–20
SMP VP-
2595
Dromaeosauridae
indeterminate
Tooth 14.25 12.59 8.41 4.71 17
NMMNH P-
32814
Dromaeosauridae
morphotype A
Tooth 6.86 5.13 3.46 1.66 25
SMP VP-
1901
cf. Saurornitholestes
sullivani
Tooth 14.85 12.62 6.75 3.36 14–15
Note: *Measurements in mm. Identity of NMMNH P-32814 from Williamson and Brusatte (2014).
10 JASINSKI ET AL.
preserved. The rostral-most edge of this process is directed
rostrolaterally. The caudal surface is smooth and flat, and
the processes are separated by a deep U-shaped notch,
which is partially visible medially. This deep U-shaped
notch further distinguishes Dineobellator from dromaeo-
saurids with a smaller and shorter notch between the
basipterygoid processes such as Dromaeosaurus (AMNH
FARB 5356). Furthermore, the flattened aspect of the cau-
dal surface of the basal tuber further distinguishes it from
Tsaagan mangas (Norell et al., 2006)andVelociraptor
(Norell et al., 2004; Norell & Makovicky, 1999). Dorsome-
dial to this notch lies part of the basipterygoid recess. This
recess is prominent externally, continues as a thin canal
internally, and is directed caudodorsally. Portions of the
carotid canal are present on the medial edge of the basip-
terygoid recess and extend rostrocaudally. Dorsomedially,
the carotid canal contains multiple small foramina. Ven-
trally, the opening for the carotid canal is 6.5 mm long and
oval. It is noted that Jasinski et al. (2020) incorrectly identi-
fied the basisphenoid process as being from the right side,
but their other observations were correct. Several other
problematic bone fragments are tentatively identified as
coming from the skull, but their exact identifications are
uncertain.
FIGURE 4 Lateral and dorsal cranial elements of Dineobellator notohesperus (SMP VP-2430). (a, b) Incomplete right jugal in lateral
(a) and medial (b) views. (c, e) Left ?nasal fragment in dorsal (c), ventral (d), and medial (e) views. (f, g) Dorsolateral process of left lacrimal
in ventrolateral (f) and dorsomedial (g) views. Scale bars corresponding to (a,b), (c–e), and (f,g) equal 1 cm
FIGURE 5 Braincase elements of Dineobellator notohesperus (SMP VP-2430). (a–c) Incomplete basisphenoid, including portions of the
left basipterygoid in ventral (a), dorsolateral (b), and caudal (c) views. (d) Occipital condyle in caudal view. Scale bar equals 1 cm
JASINSKI ET AL.11
2.4 |Vertebrae
Several vertebrae and vertebral fragments are preserved in
SMP VP-2430, although all material identifiable to a particu-
lar part of the vertebral column is part of the caudal series
(Figures 6–9). A nearly complete proximal (anterior) caudal
vertebra is inferred to be the first caudal (caudal vertebra 1;
Figure 6). The centrum of the vertebra is complete, and por-
tions of the prezygapophyses and transverse processes are
preserved. The neural arch and spine are nearly complete
and robust, and the neural spine is dorsoventrally short. The
proximal (anterior) and distal (posterior) centrum surfaces
are both oval and wider than high. The centrum surfaces of
the caudal vertebrae in other dromaeosaurids tend to be
sub-rectangular (e.g., Dakotaraptor,Deinonychus,Sauror-
nitholestes), leading to the more box-like centra of these ver-
tebrae, although some other taxa (e.g., Velociraptor)have
been known to have slightly more rounded proximal verte-
bral centrum surfaces. The dorsal vertebrae of dromaeosaur-
ids tend to have rounded centrum surfaces, so the oval
surfaces in Dineobellator potentially mark part of the transi-
tion between these morphologies in the vertebral column,
although the sacrum may account for more of this transi-
tion. Caudal vertebra 1 is opisthocoelous, with a gently con-
vex proximal surface of the centrum and a concave distal
surface. The proximal caudal vertebrae of dromaeosaurids
are usually acoelous or amphiplatyan, making the opistho-
coelous nature of the vertebra unique among known dro-
maeosaurids, although opisthocoelous proximal caudal
vertebrae have been noted in one other theropod, the cae-
nagnathid theropod Gigantoraptor (Xu et al., 2007). Several
dromaeosaurids with preservedproximalcaudalvertebrae
do not show this condition (e.g., Achillobator giganticus,Dei-
nonychus antirrhopus,Kuru kulla,Pyroraptor olympius,Yur-
govuchia doellingi;Ostrom,1969; Perle et al., 1999; Allain &
Taquet, 2000;Senteretal.,2012;Napolietal.,2021). How-
ever, it is also noted that most dromaeosaurid specimens
with proximal caudal vertebrae are preserved either flat-
tened and in matrix (e.g., Changyuraptor yangi,Halszkarap-
tor escuilliei,Microraptor gui,M.hanqingi,M.zhaoianus,
Tianyuraptor ostromi,Wulong bohaiensis,Zhenyuanlong
suni,Zhongjianosaurus yangi;Hwangetal.,2002;Xu
et al., 2003; Zheng et al., 2010;Gongetal.,2012;Turner
et al., 2012; Han et al., 2014;Cauetal.,2017;Xu&
Qin, 2017;Cau,2020;Poustetal.,2020)and/orarticulated
(e.g., Bambiraptor feinbergi,Buitreraptor gonzalezorum,Lin-
heraptor exquisitus,Mahakala omnogovae,Shri devi,Sinor-
nithosaurus,Velociraptor mongoliensis; Burnham, 2004;
Burnham et al., 2000; Gianechini et al., 2018;Liu
et al., 2004; Lü & Brusatte, 2015; Norell & Makovicky, 1997;
Norell & Makovicky, 1999; Turner et al., 2011;Turner
et al., 2012;Turneretal.,2021;Turner,Pol,etal.,2007;Xu
et al., 2010), so comparative material is limited and this con-
ditionmaybemorewidelyspreadthancurrentlyknown.
Additionally, an isolated vertebra (MNHN BO 016) referred
to Pyroraptor olympius was mentioned by Allain and Taquet
(2000) and described as a proximal caudal vertebra. It was
described with concave centrum surfaces, making it amphi-
coelous. The vertebra figured by Allain and Taquet (2000,
figure 2E), which is mislabeled as MNHN BO 017 in the fig-
ure caption, agrees morphologically with a proximal caudal
vertebra, potentially also the first caudal. Additionally, the
recently named velociraptorine Kuru kulla includes the
description of a proximal caudal vertebra with a “concave
anterior articular surface and weakly concave posterior
articular surface”(Napoli et al., 2021, p. 19), also making it
amphicoelous, implying there is more variation in proximal
caudal vertebrae centrum surfaces in dromaeosaurids than
previously noted.
Laminae are present on the lateral surfaces of the first
caudal vertebra, particularly close to and dorsal to the
transverse process, with more on the right side, probably
due to it being the better preserved of the two sides.
These include the anterior centrodiapophyseal lamina
ventrally and the prezygadiapophyseal lamina dorsally
FIGURE 6 Caudal vertebra 1 of Dineobellator notohesperus
(SMP VP-2430) in dorsal (a), ventral (b), right lateral (c), left lateral
(d), distal (e), and proximal (f) views. Scale bar equals 1 cm
12 JASINSKI ET AL.
(see Wilson, 1999). The ventral surface is mediolaterally
flat but has a distinct craniocaudal (or proximodistal)
curvature when viewed laterally. This curvature,
with the distal portion of the centrum distinctly ventral
to the proximal portion, is distinct among the caudal
vertebrae of dromaeosaurids. This characteristic
morphology is found in the cervicals of dromaeosaurids
(e.g., Deinonychus), where it likely results in a sigmoidal
curvature of the neck (see Ostrom, 1969). Additionally,
while there is some curvature to the ventral surface of
the centrum of the proximal caudal vertebrae in some
dromaeosaurids, the proximal portion lies ventral to the
distal portion (e.g., Velociraptor, IGM 100/985). We infer
the tail of Dineobellator was, therefore, distinct, with the
tail dipping down, at least slightly, at its proximal portion
before probably becoming more straightened and rod-
like, as in other known dromaeosaurids. Dorsal on the
centrum, the transverse processes, particularly the more
complete right side, project laterally more than dorsolat-
erally, are sub-rectangular, short, and gracile, and situ-
ated midway through to just caudal to the midpoint of
the centrum. The proximal or medial portion of the right
transverse process is well preserved but broken distally.
The right transverse process is more gracile and does not
fan out as much as those in the proximal caudals of
Velociraptor (IGM 100/985). The neural canal is marked
by a depression on the dorsal surface of the centrum ven-
tral to the neural spine. A medial depression or ventral
groove on the ventral surface of the centrum has a width
of 5.1 mm. Craniolaterally, there is a shallow depression
or fossa on the right transverse process, likely the prezy-
gapophyseal centrodiapophyseal fossa (see Wilson
et al., 2011), which becomes more inconspicuous laterally
on the process. The spinoprezygapophyseal fossa lies
FIGURE 7 Mid-caudal vertebra of Dineobellator notohesperus (SMP VP-2430) in lateroventral (a), ventral (b), right lateral (with ventral
surface to top of page) (c), dorsal (d), left lateral (e), proximal (f ), and distal (g, h) views. (c) Has the ventral portion toward the top of the
page and the vertebra has been flipped with the distal centrum surface to the left. (g) and (h) are both distal views of the vertebra but using
different lighting to highlight the impression on the distal (or caudal) centrum surface. Scale bar equals 1 cm
JASINSKI ET AL.13
dorsoventrally on the proximal surface of the neural
spine. The neural spine is low, robust, and flares laterally
toward its distal (posterior) portion. Caudally, there is a
deep foramen just dorsal to the neural canal representing
the spinopostzygapophyseal fossa.
Another nearly complete caudal vertebra is probably
from midway through the caudal series (likely eighth
through twelfth caudal vertebra; Figure 7). The centrum is
complete, and a portion of the left neural arch is preserved,
although none of the neural spine is preserved. The neural
arch spans most of the proximodistal (craniocaudal) length
of the centrum. The centrum underwent some shear defor-
mation. It is platycoelous with well-defined and conspicu-
ous circular to subcircular indentations on both the
proximal and distal centrum surfaces (Figure 7f–h). These
concavities are symmetrical, and both lie just dorsal to the
center of the centrum on their respective surfaces. These
subcircular indentations have not been seen in other dro-
maeosaurid caudal vertebrae, and their purpose is uncer-
tain. Both the proximal and distal centrum faces are sub-
rectangular to sub-trapezoidal, and the centrum is thinner
midway between the two centrum faces.
Several other incomplete and fragmentary caudal ver-
tebrae were collected but not reported by Jasinski et al.
(2020) (Figure 8). These include a caudal vertebra that
underwent taphonomic deformation via slight mediolat-
eral compression (Figure 8a–e). The distal portion of the
centrum is preserved while the proximal portion along
FIGURE 8 Caudal vertebrae of Dineobellator notohesperus (SMP VP-2430). (a–e) Caudal vertebra in left lateral (a), distal (b), right
lateral (c), dorsal (d), and ventral (e) views. (f–j) Caudal vertebra in left lateral (f), right lateral (g), dorsal (h), proximal (i), and distal
(j) views. (k–o) Distal caudal vertebra in proximal (i), dorsal (l), left lateral (m), ventral (n), and right lateral (o) views. Scale bar equals 1 cm
14 JASINSKI ET AL.
with the neural arches and spine and processes are not.
While incomplete, the vertebra is longer than the mid-
caudal vertebra described above, and so is probably from
more distal (posterior) in the caudal series. The distal end
of the centrum is ventrally lower than the middle, which
is common among dromaeosaurid caudal vertebrae. The
distal surface is slightly concave, although most of this is
not well-preserved due to deformation but probably was
similar to the platycoelous condition of the more com-
plete mid-caudal vertebra. Ventral ridges and a ventral
groove are preserved and are particularly visible near the
caudal end.
Another caudal vertebra also underwent significant
mediolateral compression (Figure 8f–j), although it is more
complete than the one described above. Ventral portions of
the neural arches are preserved, with more of the left neural
arch preserved, where it spans most of the length of the cen-
trum. The neural arches, particularly the left neural arch,
help distinguish part of the neural canal. The proximal sur-
face of the centrum, while incomplete, preserves part of an
indentation, like the more complete mid-caudal vertebra dis-
cussed above. This means the indentations on the centrum
surfaces of these caudal vertebrae are not taphonomic fea-
tures. The vertebra is platycoelous with the proximal and
distal centrum surfaces gently concave. This caudal vertebra
is also the longest (46.3 mm) of the preserved caudal verte-
brae, although some of the others are incomplete.
Another incomplete caudal vertebra consists of most
of the centrum, although the distal portion is missing
(Figure 8k–o). While the dorsal surface of the vertebra
preserves the broken surface where the neural arch
would have been, the neural arch and spine are missing.
The floor of the neural canal is present between the bro-
ken neural arch bases. Additionally, there is a small
indentation in the concave proximal centrum surface,
similar to those on several of the other caudal vertebrae.
The shorter preserved length of the centrum (22.4 mm)
means this vertebra was located farther distal in the cau-
dal series where vertebra lengths decreased as the overall
dimensions of the vertebral centra also become smaller.
A small section of at least four fused caudal centra is
preserved with SMP VP-2430 (Figure 9a,b). The lateral
surfaces of the vertebrae are generally flat to slightly con-
vex. Lateral ridges represent the contact surfaces between
adjacent caudals. Two of the vertebrae are complete with
lengths of 4.1 and 5.1 mm, respectively. Thin longitudinal
“lines”are present toward the dorsal half of the caudal
section that may represent the zygapophyseal rods found
in various dromaeosaurid caudal sections that help give
the tail added strength. The vertebrae are quite small and
are inferred to be from the more distal (or posterior) part
of the tail. Although the fusion of distal caudal vertebrae
can form a pygostyle in some theropods such as the ovir-
aptorosaur Nomingia (e.g., Barsbold, Currie, et al., 2000;
Barsbold, Osm
olska, et al., 2000), the caudal fusion in
Dineobellator may be pathologic as they do not resemble
a pygostyle and the tail does not seem to be shortened
compared to other eudromaeosaurs. We note, however,
that the sizes of these fused caudal vertebrae are smaller
than would be expected of the individual represented by
SMP VP-2430 given the dimensions of the other ele-
ments, and it is possible they do not belong with SMP
VP-2430. They do not possess any of the features used to
diagnose Dineobellator notohesperus. Several additional
small elements are identified as portions of vertebrae and
agree with the known caudal vertebral morphology of
other dromaeosaurids, including several isolated zygapo-
physeal fragments (Figure 9c–f).
FIGURE 9 Distal caudal vertebrae
and various vertebral fragments of
Dineobellator notohesperus (SMP VP-
2430). (a, b) Caudal vertebrae in left
lateral (a) and ventral (b) views. (c–f)
Prezygapophyseal fragments. Isolated
right prezygapophysis in lateroventral
(c) and mediodorsal (d) views. Isolated left
prezygapophysis in dorsal (e) and medial
(f) views. Scale bar equals 1 cm
JASINSKI ET AL.15
2.5 |Ribs
Several bone fragments are identified as parts of dorsal ribs,
are fairly nondescript, and do not offer much morphological
information. There is one more complete left dorsal rib that
is missing its distal portion, exhibits some folding dorsally,
and has a long, thin costal groove laterally (Figure 10).
Proximal to the costal groove is a ridge that wraps toward
the caudolateral surface and continues to the proximal
edge. The proximal surface is abnormally expanded and has
a“D”, or semi-circular, shape to it (Figure 10d,e). This
abnormal surface incorporates both the capitulum and
tuberculum, with both forming one irregular articular sur-
face with the corresponding vertebra. Just ventrolateral to
this proximal expansion is another expansion of the ele-
ment, which wraps medially to the proximal edge. The rib
preserves several areas of irregular morphology on its sur-
face, with areas of slight expansion or depression along the
rib shaft. This irregular morphology shows bone restructur-
ing and is inferred to be pathologic in origin.
2.6 |Appendicular elements
The nearly complete right humerus (Figure 11)ismissing
parts of both the distal and proximal ends, including parts
of the deltopectoral crest. The preserved portion of the
humerus measures 18.6 cm, with an estimated total length
of 21.5 cm. This is similar in size to Deinonychus (Table 3),
although the humerus of Dineobellator is more gracile in
proportion. This is particularly evident when comparing
the mediolateral width of the humerus (diameter in cranial
or caudal view) around its midlength, which is approxi-
mately 11 mm in Dineobellator and 21 mm in Deinonychus.
The degree to which these widths differ may be exagger-
ated due to some taphonomic deformation in SMP
VP-2430 mediolaterally, resulting in a somewhat oval
cross-section, although this deformation does not account
for the entirety of the differences (i.e., midshaft circumfer-
ence) present and still results in Dineobellator being more
gracile than Deinonychus. Taken along with the morphol-
ogy and size of the ulna described below, Dineobellator had
a relatively elongate humerus and forelimb. The relatively
elongate humerus distinguishes Dineobellator from most
other known eudromaeosaurs except Bambiraptor and
Saurornitholestes, although an elongate humerus is also
present in some microraptorines and unenlagiines. The
proximal end of the right humerus of Dineobellator is thin,
gracile, relatively flat, and is bent somewhat medially. The
shape of the proximal end is distinct from the sigmoidal
shape present in other dromaeosaurids (e.g., Bambiraptor,
Deinonychus,Saurornitholestes).
FIGURE 10 Incomplete pathologic left dorsal rib of Dineobellator notohesperus (SMP VP-2430) in caudal (a), medial/proximal (b), and
cranial (c) views. (d, e) Oblique proximal view in different lighting conditions to highlight the abnormal bone growth on the proximal
section of the rib. Scale bars for (a–c) and (d, e) equal 1 cm
16 JASINSKI ET AL.
The deltopectoral crest is thinner than the shaft, pro-
jects cranially, and lies closer to perpendicular to the long
axis of the humeral head (68in D.notohesperus versus
23in S.langstoni; Figure 11d,f,g). The deltopectoral crest
is relatively elongate at approximately 31% of the total
length of the humerus, making it proportionally longer
in Dineobellator than in several other dromaeosaurids
with preserved humeri (e.g., Bambiraptor,Dakotaraptor,
Deinonychus,Saurornitholestes, Table 3, Figure 12). It is
unknown if the relative length of the deltopectoral crest
changed through ontogeny. The holotype of Bambiraptor
feinbergi (AMNH FARB 30556) likely represents a juve-
nile dromaeosaurid that may indicate a relatively smaller
deltopectoral crest in juvenile dromaeosaurids, which
would further indicate the holotype of Dineobellator
(SMP VP-2430) was at a more advanced ontogenetic age
at the time of its death. The distal edge of the deltopec-
toral crest creates a sharp angle with the shaft of the
humerus. This sharp-angled curvature of the distal por-
tion of the deltopectoral crest is unique among
FIGURE 11 Humerus in dromaeosaurids. (a, b) Nearly complete right humerus of Dineobellator notohesperus (SMP VP-2430) in lateral
(a) and medial (b) views. (c) Outline drawing of the complete left humerus of Saurornitholestes langstoni (TMP 1988.121.0039), in medial
view. Bone has been reflected for easier comparison with that of D.notohesperus. (d, e) Schematic drawing of the distal deltopectoral crest;
(d) angles between the distal border of the deltopectoral crest and the long axis of the humerus in medial view, and (e) hypothetical
orientation of the muscle bodies and fibers (e.g., m.brachialis) from its origin marked with an arrow. The arrows are perpendicular to the
distal border of the deltopectoral crest. (f, g) Highlighting the distal angle of the deltopectoral crest in the dromaeosaurids Dineobellator
notohesperus (SMP VP-2430) (f) and Saurornitholestes langstoni (TMP 1988.121.0039) (g) with the dashed arrows showing approximately
equivalent points separating the deltopectoral crest from the humerus shaft, and solid arrows showing hypothetical angles of muscle bodies
with the deltopectoral crest. Dn,Dineobellator notohesperus;Sl,Saurornitholestes langstoni. Scale bar for (a–c) equals 2 cm. (f–g) are not to
scale
JASINSKI ET AL.17
dromaeosaurids, although the gentle curvature of the
humerus can become sharper farther away from the
humeral shaft (e.g., Dakotaraptor,Deinonychus;Figure12).
Furthermore, the orientation and thin structure of the del-
topectoral crest (in relation to the humeral shaft) also help
distinguish Dineobellator from other dromaeosaurids, par-
ticularly from members of Unenlagiinae.
The muscle scar of the m.latissimus dorsi is present
proximally on the lateral surface of the humerus. The
medial depression near this muscle attachment is
pronounced and continues distally from the proximal por-
tion for approximately 1/3 of the humerus length. On the
lateral surface, and cranial to the depression, lies a ridge
that runs longitudinally down the bone. The raised ridge
on the proximolateral surface of the bone is approximately
9.3 cm long. It terminates just beyond the distal extent of
the deltopectoral crest. There is a slight bend midway
along the humeral shaft that is inferred to be, at least par-
tially, due to taphonomic deformation. Distal to the bend,
the shaft is sub-circular to oval in cross-section. Distally,
the humerus expands craniocaudally and there is a depres-
sion running longitudinally up the shaft on the medial sur-
face. The humerus is also hollow in cross-section. There is
slight longitudinal crushing of the shaft toward its middle,
but this is undoubtedly due to the hollow nature of
the bone.
The right ulna is a long, thin, bowed bone (Figure 13).
The distal end is missing, but the proximal portion is
complete. The preserved portion has a total proximodistal
length of 10.1 cm, giving the bone a total estimated length
of approximately 14.0 cm based on the ulnae of Deinony-
chus,Saurornitholestes, and Velociraptor. The ulna has a
shallow trochlea and a diminutive, transversely broad,
olecranon process. The process is nearly complete and
sub-triangular. The ulna flares out mediolaterally just dis-
tal to the olecranon process and the sigmoid notch of the
ulna. The shaft of the ulna is curved and flares becoming
thin and wide distally. There is an uneven texture along
the ventral ulnar ridge that bears at least six protuber-
ances, identified as ulnar papillae or quill knobs
(Figure 13d). This implies approximately 12–14 secondary
remiges. These protuberances start approximately 4.7 mm
from the proximal end. Several dromaeosaurid taxa are
known to possess feathers, or feather-like structures, such
as the Barremian–early Aptian Changyuraptor (Han
et al., 2014), the Aptian Sinornithosaurus (L