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Sullivan, R.M. and Lucas, S.G., eds., 2015, Fossil Record 4. New Mexico Museum of Natural History and Science Bulletin 67.
A NEW DROMAEOSAURID (THEROPODA: DROMAEOSAURIDAE) FROM THE
LATE CRETACEOUS OF NEW MEXICO
STEVEN E. JASINSKI
The State Museum of Pennsylvania, Section of Paleontology and Geology, 300 North Street, Harrisburg, PA 17120-0024;
University of Pennsylvania, Department of Earth and Environmental Science, Philadelphia, PA 19104-6316;
Don Sundquist Center of Excellence in Paleontology, Johnson City, TN 37614-1709; -email: jasst@sas.upenn.edu
Abstract— A left frontal from the Upper Cretaceous Kirtland Formation (De-na-zin Member), San Juan Basin,
New Mexico, is diagnosed as Saurornitholestes sullivani n. sp., a new species of dromaeosaurid (Theropoda:
Dromaeosauridae). The frontal is similar to Saurornitholestes langstoni in being triangular in shape, not basined
between the median suture and the orbital rim, and having the caudal portion of the frontal well-rounded and
slightly inated, without evidence of a frontoparietal crest. It is distinct from S. langstoni in being more constricted
anteriorly, possessing less prominent nasal facets, possessing a less prominent anterior projection between the
nasal and lacrimal facet regions, having a deeper and less strongly demarcated orbital rim, possessing a deeper
and more prominent olfactory bulb surface, possessing a more pronounced and longer ventrally-directed ridge
between the olfactory bulb surface and the cerebral hemisphere surface, possessing a more robust frontal-frontal
sutural surface, and while being slightly smaller in overall size, still being more robust than S. langstoni. The
enlarged olfactory bulb surface is believed to convey a greater olfactory sense in this dinosaur, in particular in
comparison to S. langstoni, and may have been important for its predatory behavior. Saurornitholestes sullivani
represents the only known dromaeosaurid from the Late Cretaceous of southern Laramidia, and specically
the San Juan Basin of New Mexico, and shows geographic and temporal differences between the two currently
recognized species of Saurornitholestes.
INTRODUCTION
Late Cretaceous vertebrates from the San Juan Basin of New
Mexico have undergone a tremendous amount of revision over the
last few decades. This revision has included numerous newly named
taxa over the last 22 years. Newly named species from the Fruitland,
Kirtland, and Ojo Alamo formations include the nanhsiungchelyid
turtle Basilemys gaffneyi (Sullivan et al., 2013); the ?azhdarchid
pterosaur Navajodactylus boerei (Sullivan and Fowler, 2011); and
several dinosaurs including the tyrannosaurid Bistahieversor sealeyi
(Carr and Williamson, 2010); the dromaeosaurid Saurornitholestes
robustus (Sullivan, 2006); the caenagnathid Ojoraptorsaurus boerei
(Sullivan et al., 2011); the hadrosaurine hadrosaurids Anasazisaurus
horneri and Naashoibitosaurus ostromi (Hunt and Lucas, 1993); the
ankylosaurids Nodocephalosaurus kirtlandensis (Sullivan, 1999),
Ziapelta sanjuanensis (Arbour et al., 2014); and Ahshislepelta minor
(Burns and Sullivan, 2011); the nodosaurids Edmontonia australis
and Glyptodontopelta mimus (Ford, 2000); the ceratopsid Ojoceratops
fowleri (Sullivan and Lucas, 2010); and the pachycephalosaurids
Sphaerotholus goodwini (Williamson and Carr, 2002) and Stegoceras
novomexicanum (Jasinski and Sullivan, 2011). Newly named genera for
existing species include Denazinemys for the baenid turtle D. nodosa
(Lucas and Sullivan, 2006); Scabremys for the baenid turtle S. ornata
(Sullivan et al., 2013); and Denazinosuchus for the goniopholidid
mesoeucrocodylian D. kirtlandicus (Lucas and Sullivan, 2003).
Dedicated collecting efforts by several institutions, namely The State
Museum of Pennsylvania and the New Mexico Museum of Natural
History and Science, have been key to nding and describing these new
taxa.The Fruitland through Ojo Alamo formations span the Upper
Campanian through the end of the Cretaceous. The Ojo Alamo
Formation actually has Paleocene sediments as well (Jasinski et al.,
2011), although these younger strata are not believed to contain in-situ
dinosaur fossils (Lucas et al., 2009; Koenig et al., 2012; contra Fassett
and Lucas, 2000; Fassett et al., 2002, 2011; Fassett, 2009). Nevertheless,
the majority of the recently named taxa have come from the Upper
Campanian Fruitland and Kirtland formations, as these are also
more richly fossiliferous than the younger Maastrichtian Naashoibito
Member of the Ojo Alamo Formation (Jasinski et al., 2011).
Sullivan and Lucas (2000) described a left frontal (SMP VP-
1270) from the De-na-zin Member of the Kirtland Formation from
a dromaeosaurid and attributed it to Saurornitholestes langstoni.
Saurornitholestes langstoni was named by Sues (1978) and was
reviewed by Norell and Makovicky (2004), who concluded it
belonged to the Dromaeosauridae based, in part, on its possession of a
“T-shaped frontal with large postorbital processes”. Sullivan and Lucas
FIGURE 1. Map showing the type locality of Saurornitholestes.
A, Location of Saurornitholestes langstoni (TMP 1974.010.0005,
holotype) from the Judith River Formation in Dinosaur Provincial Park,
south-central Alberta; B, Location of Saurornitholestes sullivani (SMP
VP-1270, holotype) from the Kirtland Formation (De-na-zin Member)
in the San Juan Basin, north-west New Mexico.
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FIGURE 2. Saurornitholestes sullivani (SMP VP-1270, holotype), nearly complete left frontal. A, dorsal view; B, ventral view; C, medial view;
D, anterior view; E, left lateral view; and F, posterior view. A and B, anterior is up; C, anterior to right; and E, anterior to left. Abbreviations:
ch, cerebral hemisphere surface; cs, convex surface between olfactory bulb surface and cerebral hemisphere surface; laf, lacrimal facet; naf, nasal
facet; nf , nutrient foramen (or foramina); obs, olfactory bulb surface; or, orbital rim ; pop, postorbital process (peduncle); pp , parietal process
(peduncle); and sas, sagittal articular surface. Bar scale = 1 cm.
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FIGURE 3. Saurornitholestes sullivani (SMP VP-1270, holotype), illustrations of nearly complete left frontal. A, dorsal view; B, ventral view;
C, medial view; D, anterior view; E, left lateral view; and F, posterior view. A and B, anterior is up; C, anterior to right; and E, anterior to left.
Abbreviations: ch, cerebral hemisphere surface; cs, convex surface between olfactory bulb surface and cerebral hemisphere surface; laf, lacrimal
facet; naf, nasal facet; nf , nutrient foramen(a); obs, olfactory bulb surface; or, orbital rim ; pop, postorbital process (peduncle); pp , parietal
process (peduncle); and sas, sagittal articular surface. Bar scale = 1 cm.
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FIGURE 4. Anterior portion of left frontals illustrated in ventral view. A, Saurornitholestes sullivani (SMP VP-1270, holotype); B, S. langstoni
(TMP 1974.010.0005, holotype). Olfactory bulb surface is highlighted in grey to better focus on the structure and show that S. sullivani has a larger
olfactory bulb surface both relatively and in actual size/dimensions. Bar scale = 1 cm.
(2000) concluded that SMP VP-1270 was morphologically similar
to the holotype of S. langstoni (TMP 1974.010.0005), and referred
it to that taxon, marking the rst occurrence of Saurornitholestes in
the Late Cretaceous of New Mexico (Fig. 1). Later, Sullivan (2006)
described a second specimen of Saurornitholestes from the De-na-zin
Member (SMP VP-1955, left frontal); however, he felt this frontal was
distinct enough from S. langstoni to warrant naming a new species,
S. robustus. Material previously attributed to S. langstoni from the
Upper Cretaceous strata of the San Juan Basin in New Mexico was then
attributed to S. robustus (Sullivan, 2006). Saurornitholestes robustus
was later reviewed, along with many other dromaeosaurids, by Turner
et al. (2012), who concluded that S. robustus (SMP VP-1955) was a
nomen dubium and did not preserve any of the synapomorphies of
Saurornitholestes, and potentially of Dromaeosauridae. More recently,
Evans et al. (2014a) found the holotype of S. robustus (SMP VP-1955)
to represent an indeterminate troodontid. The conclusion by Turner et
al. (2012), however, does not take into account the taxonomic afnities
of the frontal (SMP VP-1270) earlier referred to S. langstoni. Indeed,
Evans et al. (2014a) mention that, unlike SMP VP-1955, SMP VP-
1270 appears to represent a dromaeosaurid. While Turner et al. (2012)
mention the need for descriptions of further material of S. langstoni to
fully understand this Late Cretaceous dromaeosaurid, this paper will
carefully examine the frontal (SMP VP-1270) described by Sullivan
and Lucas (2000) and discuss its implications for dromaeosaurids from
the Late Cretaceous of New Mexico.
Institutional abbreviations: AMNH, American Museum of
Natural History, New York, New York; GIN (IGM), Mongolian
Institute of Geology, Ulan Bataar; HIII, Henan Geological Museum,
Zhengzhou; IVPP, Institute of Vertebrate Paleontology and
Paleoanthropology; Beijing, China; MPCA, Museo Carlos Ameghino,
Cipolletti, Rıo Negro Province, Argentina; SMP, State Museum of
Pennsylvania, Harrisburg, Pennsylvania; TMP, Royal Tyrrell Museum
of Paleontology, Drumheller, Alberta, Canada; UALVP, University of
Alberta Labortory for Vertebrate Paleontology, Edmonton, Alberta,
Canada.
SYSTEMATIC PALEONTOLOGY
DINOSAURIA Owen, 1842
SAURISCHIA Seeley, 1888
THEROPODA Marsh, 1881
DROMAEOSAURIDAE Matthew and Brown, 1922
VELOCIRAPTORINAE Barsbold, 1983
SAURORNITHOLESTES Sues, 1978
Saurornitholestes sullivani, n. sp.
Fig. 2-3, 4A
Holotype: SMP VP-1270, nearly complete left frontal.
Type Locality: SMP loc. No. 311 (head of the east branch of
Hunter Wash [southeast]), Hunter Wash, San Juan Basin, New Mexico.
Precise GPS coordinates available to qualied researchers.
Formation/Age: Kirtland Formation (De-na-zin Member), Late
Campanian (late Kirtlandian Land Vertebrate Age or LVA) (Sullivan
and Lucas, 2003, 2006).
Etymology: The species name honors Robert M. Sullivan,
who discovered the holotype specimen, and whose work in the Late
Cretaceous of the San Juan Basin, New Mexico has been instrumental
in furthering knowledge of this key region for understanding the Late
Cretaceous of North America.
Diagnosis: A member of the Dromaeosauridae based on a
demarcated postorbital process (based on the portion that is preserved),
a somewhat sigmoidal ridge on the postorbital process, and a sinuous
demarcation of the supratemporal fossa (as discussed by Currie,
1995 and Turner et al., 2012). Saurornitholestes and Bambiraptor are
differentiated by a rostromedial projection and of the frontals and a
long orbital rim in the latter, and a shallow basin situated rostrocaudally
and a posterolateral basin near the postorbital process in the former.
Additionally the overlap of the lacrimal on the frontal is more
pronounced in Bambiraptor than in Saurornitholestes. A member of
Saurornitholestes based on characters listed by Sues (1978), including
“Frontal triangular, not basined between the median suture and the
orbital rim. Posterior of frontal well rounded and slightly inated,
without frontoparietal crest.” Distinguished from Saurornitholestes
langstoni by (1) being more constricted anteriorly (as noted by
Sullivan, 2000); (2) possessing less prominent nasal sutures (facets);
(3) possessing less prominent anterior projection between the nasal and
lacrimal facet regions; (4) having a deeper and less strongly demarcated
orbital rim; (5) having a deeper and more prominent olfactory bulb
surface; (6) possessing a more pronounced and longer ventrally-directed
ridge between the olfactory bulb surface and the cerebral hemisphere
surface; (7) possessing a more robust frontal-frontal sutural surface;
and (8) while slightly smaller, still being more robust than S. langstoni.
Description: The holotype (SMP VP-1270) is a nearly complete,
slightly water-worn, left frontal (Fig. 2). Despite its condition, SMP VP-
1270 preserves key features that allow it to be distinguished from other
dromaeosaurid taxa. The frontal is 42.8 mm long along the midline, has
a maximum width of 27.8 mm and a minimum width of 14.1 mm (see
Table 1). Thus, viewed dorsally, the bone is far longer than wide and
has a triangular shape dominated by the long, concave-lateral orbital
rim (Figs. 2A, 3A).
The anterior end of the frontal is water-worn, but preserves two
small furrows on its dorsal edge near the medial margin. These furrows
are the sutural surface (facet) for the left nasal. Lateral to these is an
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TABLE 1. Comparisons of dromaeosaur (Dromaeosauridae) frontals. Measurements were taken from specimens and various previous studies,
including those of Currie (1995), Barsbold and Osmólska (1999), Burnham et al. (2000), Xu and Wu (2001), Burnham (2004), Makovicky et al.
(2005), Lü et al. (2007), Turner et al. (2012) and Xu et al. (2015). All specimens are holotypes except GIN 100/25, which is a referred specimen
of Velociraptor mongoliensis (see Barsbold and Osmólska, 1999). Make note that ‘Saurornitholestes’ robustus is now considered an indeterminate
troodontid (see Evans et al., 2014a), and Luanchuanraptor henanensis, which was originally thought to be a dromaeosaurid by Lü et al. (2007), has
since been considered a member of the Averaptora rather than the Dromaeosauridae by Agnolín and Novas (2013). Measurements in millimeters.
Abbreviations: l:t, midline length minus nasal + lacrimal-frontal sutural surface/maximum thickness at posterior portion of the frontal; maxw,
maximum width; minw, minimum width; mll, midline length minus nasal + lacrimal-frontal sutural surface; mmll, maximum midline length; obs,
olfactory bulb surface dimensions; orl, orbital rim length in dorsal view (note this measurement deals with the portion of the frontal that makes up
part of the orbital rim and not the entire orbital rim length); >, greater than; *, measurement is incomplete due to breakage or lack of preservation
of a specimen; -, measurement unavailable or unknown.
irregular surface incised below the dorsal surface of the bone. An
arcuate, anteroposteriorly-oriented edge delimits this incised surface,
which is where the lacrimal overlaps the dorsal surface of the frontal.
The dorsal surface of the frontal is smooth (Figs. 2A, 3A). In
dorsal view the orbital rim is 28.4 mm long (note this refers to the
portion of the orbital rim surrounded by the frontal and not the entire
orbital rim). The orbital rim is a convex-dorsal, raised surface of bone
with a slightly concave dorsolateral edge. Medial to the orbital rim,
the dorsal surface of the frontal is slightly concave to form a shallow
anteroposterior sulcus. The bone then becomes convex posterodorsally
along its median half.
The entire posterior edge that contacts the parietal is water-
worn and marks the frontoparietal suture. The frontoparietal suture is
distinguished, in part, by two blunt, irregular, sub-rounded processes
(a lateral process, or peduncle, for the postorbital, and a median
parietal process) that project posteriorly and are divided by a concavity.
This, the articular surface for the parietal and postorbital, forms the
anterior margin of the supratemporal fenestra. Although the left
lateral process that joins with the postorbital is slightly water-worn,
the portion that is preserved does not appear as pronounced as in
Velociraptor mongoliensis or Saurornitholestes langstoni, and instead
is more similar to that feature in Bambiraptor feinbergi (Burnham
et al., 2000; Burnham, 2004), and some species of troodontid (e.g.,
Stenonychosaurus inequalis (=Troodon formosus) of Currie [1985]).
The ventral surface of SMP VP-1270 (Figs. 2B, 3B) is dominated
by three features: (1) the concave and arcuate orbital rim laterally;
(2) a narrow, ovoid sulcus anterolaterally (olfactory bulb surface in
the frontal); and (3) a much larger, subtriangular-shaped (widening
posteriorly) surface for the cerebral hemisphere. A blunt (water-
worn), somewhat sigmoidal and concave-lateral ridge separates the
orbit from the endocranial surfaces. However, the olfactory bulb and
cerebral surfaces are partially separated by a shallow, convex ventrally-
projecting surface.
Viewed laterally, SMP VP-1270 (Figs. 2E, 3E) is wedge-shaped,
as it is taller posteriorly than anteriorly. Almost the entire lateral surface
makes up the dorsomedial wall of the orbit, which has a dorsal margin
that overhangs a concave lateral surface. A row of six, anteroposteriorly-
oriented foramina is present near the greatest point of curvature of the
orbit. These foramina probably represent nutrient foramina, but may
represent neurovascular foramina as well. Three similar foramina are
also present near the posterodorsal margin of the orbit.
The medial (sagittal) articular surface (Figs. 2C, 3C) is grooved,
water-worn and slants laterally. There are a number of small nutrient
foramina, some concomitant with the grooves, which extend
intermittently for the entire length of the frontal. A pronounced,
ventrally-directed ridge is present between the anterior edge of the
cerebral surface and the posterior edge of the olfactory surface, marking
the limits between these two regions. This constriction is slightly greater
than in the holotype of S. langstoni (TMP 1974.010.0005).
Less information can be gathered from the frontal in anterior
and posterior views. In anterior view, the nasal and lacrimal facets
are prominent, along with some nutrient foramina within the orbital
rim (Figs. 2D, 3D). Anteriorly the deep basin of the olfactory bulb
impression can be seen medially deep to the nasal facet. Posteriorly, the
frontal appears to exhibit greater curvature for the cerebral hemisphere
and further nutrient foramina are present within the orbital rim (Figs.
2F, 3F).
DISCUSSION
Currie (1987, p. 52) noted that “the frontal is one of the more
useful isolated bones of theropods as there is only a single pair in
any individual, they tend to be found relatively frequently and they
are diagnostic at the species level.” It is noted that while troodontid
material is known from the Late Cretaceous San Juan Basin, New
Mexico (e.g. Jasinski et al., 2011; Evans et al., 2014a), SMP VP-1270
is not referable to this family. Compared to SMP VP-1270, the frontals
of troodontids tend to have less strongly concave orbital rims (in dorsal
aspect), more strongly tapered postorbital processes distally, and less
prominent depressions for the olfactory bulb surface (in ventral aspect)
(e.g. Russell, 1969; Currie, 1985). In these respects, Saurornitholestes
sullivani (SMP VP-1270) agrees more strongly with dromaeosaurids
than troodontids, and as such is considered a member of the former.
The left frontal of Saurornitholestes sullivani is similar to those
of S. langstoni, except for several features discussed above (see Table
1). As was mentioned above, ‘Saurornitholestes’ robustus has been
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considered a nomen dubium (see Turner et al., 2012). Additionally,
Evans et al. (2014a) found that SMP VP-1955 (‘S.” robustus holotype)
represented a member of the Troodontidae, and conservatively referred
it to an indeterminate troodontid. Nevertheless, comparisons between
S. sullivani (SMP VP-1270) and ‘S.’ robustus (SMP VP-1955) are
warranted as they both represent small theropods from the same strata
(De-na-zin Member of the Kirtland Formation). Some of the characters
mentioned by Turner et al. (2012) that characterize dromaeosaurids,
and some of the features that they mentioned that SMP VP-1955 (‘S.’
robustus holotype) did not possess are present in SMP VP-1270 (S.
sullivani holotype), including a demarcated postorbital process and a
somewhat sigmoidal ridge on the postorbital process. This is despite the
fact that a portion of the postorbital process is not preserved on SMP
VP-1270 (S. sullivani holotype). Even so, SMP VP-1270 (S. sullivani
holotype) agrees more strongly with TMP 1974.010.0005 (S. langstoni
holotype) and dromaeosaurids than SMP VP-1955 (‘S.’ robustus
holotype). Compared to SMP VP-1955 (‘S.’ robustus holotype), SMP
VP-1270 (S. sullivani holotype) is smaller and less robust, with the ratio
of length measured along the midline to the thickness at the posterior
portion of the frontal being 6:1 in the former and 7:1 in the latter. Both
are more robust than TMP 1974.010.0005 (S. langstoni holotype), in
which the ratio is approximately 10:1. Additionally, in contrast to SMP
VP-1955 (‘S.’ robustus holotype), SMP VP-1270 (S. sullivani holotype)
has a more concave orbital rim, a more gracile anterior facet region,
less strongly pronounced nasal facets, a slightly more pronounced
depression along the mid-length of the frontal, a deeper depression
on the postorbital process, a deeper and more prominent olfactory
bulb surface, a relatively smaller cerebral hemisphere surface, a more
sigmoidal ventral orbital rim surface, and a more prominent and deeper
orbital surface.
In comparison to other dromaeosaurs, some, particularly basal
members such as Mahakala omnogovae, possess anteroposteriorly
elongate, thin, and gracile frontals (Turner et al., 2007, 2012), which
is distinct from Saurornitholestes sullivani (SMP VP-1270) (see Table
1). Saurornitholestes sullivani is distinguished from Sinornithosaurus
millenii by a more elongate anterior facet region and a medial
constriction of the orbital rim of the frontal in the former (Xu et al.,
2001). Additionally, the triangular to sub-triangular shape of the
frontal (in dorsal view) distinguishes Saurornitholestes langstoni
and S. sullivani (SMP VP-1270) from Dromaeosaurus albertensis
(AMNH 5356) as discussed by Currie (1995). As discussed above,
the slight basin, along with the presence of the posterolateral basin,
helps distinguish S. sullivani from Bambiraptor feinbergi, Linheraptor
exquisitus, Tsaagan mangas, and Velociraptor mongoliensis (e.g.,
Barsbold and Osmólska, 1999; Burnham et al., 2000; Burnham,
2004; Norell et al., 2006; Xu et al., 2010; 2015). However, based on
the character list used in the phylogenetic analysis of Turner et al.
(2012), four characters are derived from dromaeosaur frontals, and
S. sullivani is not distinguished from numerous other dromaeosaurs,
including S. langstoni. Indeed, this subset of characters would need
to be expanded to further distinguish dromaeosaur taxa with known
frontals, particularly Adasaurus mongoliensis, Bambiraptor feinbergi,
Buitreraptor gonzalezorum, Deinonychus antirrhopus, Dromaeosaurus
albertensis, Linheraptor exquisitus, Saurornitholestes langstoni, S.
sullivani, Tsaagan mangas, and Velociraptor mongoliensis.
Sullivan and Lucas (2000) discussed the differences between
Saurornitholestes langstoni and Velociraptor mongoliensis based on
preserved frontals from a specimen referred of V. mongoliensis (IGM
100/976). This specimen was described by Norell and Makovicky
(1999). Sullivan and Lucas (2000), in comparing the frontals of S.
langstoni and V. mongoliensis, found that the frontals of the latter:
(1) are more gracile; (2) sub-rectangular; and in ventral aspect have
(3) a weakly-developed olfactory bulb depression; (4) have a weakly-
developed cerebral hemisphere depression; (5) have a less concave
orbital surface (in ventral aspect); and (6) have a weakly-developed
posterior lateral wing. Saurornitholestes sullivani in these aspects agrees
with Saurornitholestes langstoni rather than with V. mongoliensis. Of
note is that while the concave olfactory bulb surface is more prominent
in S. langstoni than in V. mongoliensis, it is also more prominent and
deeper in S. sullivani than in S. langstoni (Fig. 4). This implies that S.
sullivani may have had a better sense of smell than either of the other
taxa, and this sense may have been more important for this dinosaur
during predation. Indeed, the dimensions of the olfactory bulb surface
in S. sullivani (SMP VP-1270) is approximately 6.4 mm by 13.5 mm,
while that of S. langstoni (TMP 1974.010.0005) is approximately
4.7 mm by 7.4 mm, with the former having a distinct basin while the
latter is not as distinctly dened (see Fig. 4). This is in addition to S.
langstoni being larger (54.5 mm long along the midline frontal suture,
33.4 mm maximum width, 15.3 mm minimum width) while S. sullivani
is smaller (42.8 mm long along the midline frontal suture, 27.8 mm
maximum width, 14.1 mm minimum width). Indeed, this means that, in
addition to having a more denitive, basin-like olfactory bulb surface,
S. sullivani also has both a relatively and absolutely larger surface. It
is also of note that the position of minimum width of the frontals also
differs with that in S. langstoni being anterior and that in S. sullivani
being more posterior across the orbital rim.
Many of the signicant aspects that Sullivan and Lucas (2000)
listed for Saurornitholestes langstoni, and later Sullivan (2006) listed
for ‘S.’ robustus are now applicable to Saurornitholestes and to S.
sullivani. This new species becomes the second known valid species of
Saurornitholestes, along with S. langstoni. Saurornitholestes sullivani
FIGURE 5. Stratigraphic schematic of the dromaeosaurids from the
Late Cretaceous Fruitland, Kirtland, and Ojo Alamo formations, San
Juan Basin, New Mexico. The numbers on the left side of the lithology
schematic refer to millions of years ago. Ash dates show for the Fruitland
and Kirtland formations are from Fassett and Steiner (1997), and the
66.5 Ma date (base of the Naashoibito Member) is from Mason et al.
(2013a; 2013b). Abbreviations: Di, indeterminate dromaeosaurids;
Dnew, new dromaeosaurid taxon; Ss, Saurornitholestes sullivani. It is
noted that indeterminate dromaeosaurids have also been found in the
De-na-zin Member, although these may be referable to S. sullivani, or
another taxon.
85
is known from the De-na-zin Member of the Kirtland Formation,
which is from the late Kirtlandian LVA. Fassett and Steiner (1997)
found that the De-na-zin Member was about 73 Ma based on 40Ar/39Ar
dates. Saurornitholestes langstoni, on the other hand, is known from
the Dinosaur Park and Two Medicine formations, and both are at least
75 Ma (Eberth, 2005). Both species are distinct geographically and
temporally, lending further support to S. sullivani being a distinct taxon.
Sullivan (2006), when naming ‘Saurornitholestes’ robustus,
referred two other specimens to cf. ‘S.’ robustus. These included an
isolated tooth (SMP VP-1901) and an incomplete left second pedal
ungual (SMP VP-1741). Both specimens were also collected from the
De-na-zin Member of the Kirtland Formation. The tooth (SMP VP-
1901) is similar to “Dromaeosauridae Morphotype A” of Williamson
and Brusatte (2014) and the “Saurornitholestinae” morphotype of
Larson and Currie (2013). SMP VP-1901 is also similar in general
shape and denticle morphology to the recently named Acheroraptor
temertyorum (Evans et al., 2014b). Nevertheless, Zanno et al. (2013)
discussed the identity of isolated dromaeosaurid teeth and felt that their
referral to distinct species was unwarranted. As remaining conservative
as Dromaeosauridae indeterminate. The left second pedal ungual (SMP
VP-1741) is similar to those referred to S. langstoni, and differs from
those of Velociraptor mongoliensis, as it is dorsoventrally deeper
if this referral is correct, this may be another distinction between
Saurornitholestes and Velociraptor; regardless, further study is needed.
However, without the proximal portion and articular surface preserved
FIGURE 6. Life reconstruction of Saurornitholestes sullivani depicting a possible scene from the late Campanian (approximately 73 Ma) in the
San Juan Basin New Mexico. A pair of S. sullivani are shown attacking a subadult Parasaurolophus tubicen. Illustration by Mary P. Williams.
2007). Regardless SMP VP-1741 is herein conservatively referred to
the ungual of a Dromaeosauridae indeterminate.
Saurornitholestes sullivani represents the only valid dromaeosaurid
known from the Late Cretaceous (Late Campanian-Late Maastrichtian)
strata of the San Juan Basin, New Mexico (Fig. 5). Moreover, S.
sullivani currently represents the only named dromaeosaurid from
the Late Cretaceous of southern Laramidia. In addition to some of
the studies that have mentioned dromaeosaurids and dromaeosaurid
teeth from the Late Cretaceous of the San Juan Basin (e.g., Lehman,
1981; Lucas, 1981; 1993; Lucas et al., 1987; 2000; Sullivan, 2000;
2006; Jasinski et al., 2009; 2011), Williamson and Brusatte (2014)
recently reviewed the theropod teeth from these strata, and found there
to be at least two dromaeosaurid taxa based on tooth morphotypes.
Indeterminate dromaeosaurids are also known from teeth from the Late
Cretaceous of Utah (e.g., Hutchison et al., 1997; Eaton, 1999; Eaton et
al., 1999a, 1999b; Parrish, 1999; Kirkland, 2001; Zanno et al., 2005;
2010; 2013; Gates et al., 2010). Dromaeosaurid remains have also been
found in the Late Cretaceous of Texas (e.g., Standhardt, 1986; Rowe
et al., 1992; Sankey, 2001; 2008; 2010; Sankey et al., 2005), although
these also are based on teeth and should be attributed to indeterminate
dromaeosaurids as well. Additionally, dromaeosaurid teeth have been
found in Late Cretaceous strata in Mexico as well (e.g., Rivera-Sylva et
al., 2006; Torres-Rodríguez et al., 2010; Rivera-Sylva and Frey, 2012);
however, these are best referred to indeterminate dromaeosaurids just as
those above are. Moreover, some fragmentary non-tooth dromaeosaurid
remains are known from the Late Cretaceous of Utah (Zanno et al.,
2010; 2013) and Texas (Sankey, 2010), although these are also not
diagnostic and considered to be from indeterminate dromaeosaurids
as well. Now that ‘S.’ robustus has been considered a nomen dubium
86
and/or a troodontid, other dromaeosaurid material from this stratum is
attributed to indeterminate dromaeosaurids. However, dromaeosaurid
material from the Naashoibito Member of the Ojo Alamo Formation
was considered a new taxon by Jasinski et al. (2011) and is currently
under further study. Nevertheless, S. sullivani helps further dene the
distinct nature of the Late Cretaceous fauna of the San Juan Basin and
southern Laramidia (Fig. 6).
ACKNOWLEDGMENTS
I would rst like to thank Robert Sullivan for nding the specimen,
for his previous work on the dinosaurs of the San Juan Basin and for
his work on the specimens described herein, and for all the help and
guidance he afforded me. I thank Mark Norell (American Museum
of Natural History) for the cast of the skull roof of Velociraptor
mongoliensis (lGM 100/ 976) used, in part, for comparative purposes.
Phil Currie allowed the study of the holotype, and referred material,
of Saurornitholestes langstoni under his care at the Royal Tyrrell
Museum. I thank Carl Mehling and Mark Norell for allowing the
study of the type specimens of Bambiraptor feinbergi and Velociraptor
mongoliensis. James Gardner, Michael Ryan, and D. Spivak provided
additional stratigraphic data on Saurornitholestes material in the TMP
collections. Artist Mary P. Williams provided the reconstruction of
Saurornitholestes sullivani in Figure 6. Peter Dodson reviewed an
earlier version of the manuscript. Denver Fowler (Museum of the
Rockies, Montana State University, Bozeman) and Derek W. Larson
(University of Toronto, Toronto) provided helpful reviews of the
manuscript and provided helpful comments and suggestions as well.
This study was made possible, in part, by a grant from the Jurassic
Foundation (originally awarded to Robert Sullivan), which is gratefully
acknowledged. SMP VP-1270 was collected by Robert Sullivan under
BLM permit SMP-8270-RS/WA/WSA-98-C.
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