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Lucas et al., 2022, Fossil Record 8. New Mexico Museum of Natural History and Science Bulletin 90.
A NEW CHASMOSAURINE CERATOPSID FROM THE UPPER CRETACEOUS (CAMPANIAN)
FARMINGTON MEMBER OF THE KIRTLAND FORMATION, NEW MEXICO
SEBASTIAN G. DALMAN¹, STEVEN E. JASINSKI², and SPENCER G. LUCAS¹
INTRODUCTION
Fossil skeletal remains of ceratopsid dinosaurs from Upper
Cretaceous deposits of the San Juan Basin of northwestern New
Mexico include species of the Chasmosaurinae subfamily (e.g.,
Osborn, 1923; Wiman, 1930; Lull, 1933; Rowe et al., 1981;
Sullivan et al., 2005a, 2011e; Sullivan and Lucas, 2010, 2015;
Jasinski et al., 2011; Longrich, 2011; Fowler and Freedman
Fowler, 2020; Dalman et al., 2022), rare material of centrosaurine
ceratopsids (e.g., Gilmore, 1916; Williamson, 1997; Dalman et
al., 2021), and, farther south, the neoceratopsid Zuniceratops
christopheri (e.g., Wolfe and Kirtland, 1998; Wolfe et al., 2010).
The occurrence of skeletal fossil remains of chasmosaurine
ceratopsids have been known from Upper Cretaceous deposits
in the San Juan Basin since the early 20th century (e.g.,
Osborn, 1923; Wiman, 1930; Lull, 1933). Although numerous
fragmentary chasmosaurine specimens consisting of cranial and
postcranial skeletal elements have been described previously
from the San Juan Basin (e.g., Lehman, 1981, 1993), only ve
species are recognized today: Ojoceratops fowleri (Sullivan
and Lucas, 2010), Pentaceratops sternbergi (Osborn, 1923),
Titanoceratops ouranos (Longrich, 2011), the recently named
Navajoceratops sullivani and Terminocavus sealeyi (Fowler and
Freedman Fowler, 2020).
Sierraceratops turneri (Dalman et al., 2022), the most
recently named chasmosaurine from New Mexico, was
described from outside of the San Juan Basin. The new species
is a member of the Chasmosaurinae and was recovered from late
Campanian deposits in the Hall Lake Formation in southern New
Mexico. Furthermore, Dalman et al. (2022, g. 19) recovered
S. turneri as a member of a potentially new southern clade of
chasmosaurines that include such species as Bravoceratops
polyphemus and Coahuilaceratops magnacuerna in their
phylogenetic analysis. The identication of S. turneri continues
to show high biodiversity of chasmosaurines in the Campanian
(and Late Cretaceous) of North America (Dalman et al., 2022).
The diversity of chasmosaurine ceratopsids during the last
20 million years of the Cretaceous in North America suggests
that their widespread radiation began much earlier throughout
the Western Interior Basin, and most likely took place prior to
the late middle Campanian ~76 Ma (e.g., Longrich, 2013), and
continued into the Maastrichtian (e.g., Brown and Henderson,
2015; Dalman and Lucas, 2017; Dalman et al., 2022).
Here, we report on a new species of chasmosaurine ceratopsid
(Fig. 1) collected in 1975 by a University of Arizona eld party
in the vicinity of Alamo Mesa in the Bisti/De-na-zin Federal
Wilderness area. The fossil material of the new species consists
of a nearly complete skull ([NMMNH P-50000 (formerly UALP
13342)]) and was previously referred to Pentaceratops by Rowe
et al. (1981), Lehman (1993), and Fry (2015).
The skull of the new chasmosaurine exhibits several cranial
pathologies, which were described by Dalman and Lucas (2018)
as bite marks made by a tyrannosaurid. The new chasmosaurine
has an incomplete parietosquamosal frill, an element on which
many chasmosaurine and centrosaurine species have been
diagnosed (e.g., Sampson et al., 2010; 2013; Ryan et al., 2014;
Rivera-Sylva et al. 2017; Dalman et al., 2018, 2021, 2022;
Campbell et al., 2019). However, the new cranial morphological
characters, as well as the stratigraphic and geographic position,
support the taxonomic distinctiveness of this new ceratopsid.
Institutional abbreviations: AMNH FARB, Fossil
Amphibian, Reptile, and Bird Collections, American Museum
of Natural History, New York, New York; CMN, Canadian
Museum of Nature, Ottawa, Ontario, Canada; CPC, Colección
Paleontológica de Coahuila, Saltillo, Mexico; MNA, Museum
of Northern Arizona, Flagsta, Arizona; NMMNH, New
Mexico Museum of Natural History and Science, Albuquerque,
New Mexico; OMNH, Oklahoma Museum of Natural History,
Norman, Oklahoma; PMU, Palaeontological Collections,
Museum of Evolution, Uppsala University, Uppsala, Sweden;
ROM, Royal Ontario Museum, Toronto, Canada; TMM,
Texas Memorial Museum, University of Texas, Austin, Texas;
TMP, Royal Tyrrell Museum of Palaeontology, Drumheller,
Alberta, Canada; UALP, University of Arizona Laboratory of
Paleontology, Tucson, Arizona; UALVP, University of Alberta
Laboratory for Vertebrate Palaeontology, Edmonton, Alberta,
Canada; UMNH, Utah Museum of Natural History, Salt Lake
Abstract—A nearly complete skull of a new ceratopsid dinosaur, Bisticeratops froeseorum, is described
from the Farmington Member of the Kirtland Formation (late Campanian, Upper Cretaceous) of New
Mexico. Bisticeratops is distinguished by several diagnostic cranial characters, including those of
the premaxilla (stepped dorsal margin), maxilla (short jugal process lacking the ventral pocket-like
fossa), jugal (short maxillary process of the jugal), and palpebral ornamentation (short with moderate
ornamentation). It diers from other known chasmosaurines, especially from stratigraphically older
species in the same geographic region, Pentaceratops sternbergi and Titanoceratops ouranos, by a
strongly reduced jugal process of the maxilla and an unusual maxilla/jugal contact, which forms a shallow,
triangular-shaped lateroposteriorly concave sulcus. A phylogenetic analysis recovers Bisticeratops
froeseorum as sister species to the unnamed Almond Formation chasmosaurine and as a member of a
potentially new southern clade of chasmosaurines, outside the Triceratopsini, and distinct from other
southern Laramidian chasmosaurines such as Pentaceratops. The dinosaur fauna of the Farmington
Member is comparatively poorly understood, especially compared to stratigraphically older faunas in
the San Juan Basin. Therefore, the new, presumably rare species Bisticeratops froeseorum, together with
several recently named and described chasmosaurines such as Navajoceratops sullivani, Sierraceratops
turneri, and Terminocavus sealeyi, add to the diversity and disparity of chasmosaurines and provides
further support for latitudinal variation in the ceratopsid fauna during the Late Cretaceous interval in
the Western Interior Basin of North America.
¹New Mexico Museum of Natural History, 1801 Mountain Road N. W. Albuquerque, NM 87104; -email: sebastiandalman@yahoo.com;
²Harrisburg University, Department of Environmental Science and Sustainability, 326 Market Street, Harrisburg, PA 17101
128
City, Utah; USNM, United States National Museum of Natural
History, Washington, DC; UTEP, Centennial Museum of the
University of Texas at El Paso, Texas; YPM, Yale Peabody
Museum of Natural History, New Haven, Connecticut.
Anatomical abbreviations: acca, accessory canal
of premaxilla; acfos/dpp, accessory fossa of the dorsal
premaxillary process; acvf, accessory vascular foramen; alv,
alveoli; a-m/acca, anterior margin of the accessory canal of
premaxilla; amp, anterior maxillary process; ant f, antorbital
fenestra; a-rdg, anterior ridge of the ventral premaxillary
process; bo, basioccipital; bptpr, basipterygoid process; btub,
basal tuber of basioccipital; dc, dentary contact; d, dorsal
aring of the narial strut; dpnc, dorsal projection for the nasal
contact; dpp, dorsal process of premaxilla; dr, dorsal ridge of
the epijugal; drmr, dorsal margin of the rostral bone; dr o,
dorsal ridge of the epijugal orientation; dter, dorsal terminal
end of the dorsal process of rostral bone; ec, ectopterygoid;
en, external naris; eo, exoccipital; epj, epijugal; , ange; fm,
foramen magnum; for, foramen; fos, fossa; gr, groove; gvan,
groove for vein, artery, nerve; itf, intertemporal fenestra; j,
jugal; jcs, jugal contact surface; j/m c, jugal-maxilla contact;
jpm, jugal process of maxilla; l, lacrimal; lc, lateral condyle;
ldc, lacrimal duct; lpr, lateral process of rostral bone; lr, lateral
ridge of the postorbital horncore; m, maxilla; mc, medial
condyle; mcn, maxillary canal; mcs, maxilla contact surface;
n, nasal; nc, nasal contact; n/dpp/c, contact between nasal
and dorsal process of premaxilla; ngr, nutrient groove; nh,
nasal horncore; ns, narial strut; nt, notch; ntnc, notch on the
ventral premaxillary process for nasal contact; o, orbit; ont, otic
notch; pal, suture for palatine; par, paroccipital process; pfo,
palatal fossa; phc, postorbital horncore; pm, premaxilla; p-m/
acca, posterior margin of the accessory canal; pm c, premaxilla
contact; pmf, premaxillary fossa; pm-fn, premaxillary fenestra;
po, postorbital; ppl, palpebral; prf, prefrontal; q, quadrate; qf,
quadrate fossa; qj, quadratojugal; qjf, quadratojugal ange; r,
rostral; rdg, ridge; rim, rim of the nasal; rprf, rugose prefrontal
surface; rug, rugosity; S, episquamosal; sd, supradental plate of
maxilla; sf, septal ange; so, supraoccipital; sq, squamosal; sqc,
squamosal contact on jugal; sqf, squamosal ange of quadrate;
sulc, sulcus; sym, symphysis; tipr, tip of the rostral bone; tp,
triangular process; tp-sulc, sulcus of the triangular process; tr,
tooth row; tr/acfos/ns, triangular accessory fossa of the dorsal
narial strut; vcter, terminal contact end of the ventral process
of rostral bone; vf, vascular foramen; vfos, ventral fossa of the
jugal process of maxilla; vm-o, ventral margin of orbit; vmr,
ventral margin of the rostral bone; vppm, ventral margin of
premaxilla; vpp, ventral process of premaxilla; vpp c, contact
surface for ventral process on maxilla; vp-rdg, ridge of the
ventral premaxillary process; vp-sulc, sulcus of the ventral
premaxillary process; v-sulc, ventral sulcus of the anterior narial
strut; vter, terminal end of the ventral rostral process; IX‒XI,
common opening of cranial nerves IX‒XI; XII, opening for
cranial nerve XII.
GEOLOGICAL SETTING
The chasmosaurine ceratopsid skull described here as the
holotype of the new species (NMMNH P-50000) was collected
in 1975 by a University of Arizona eld party in the vicinity of
Alamo Mesa in the Bisti/De-na-zin Federal Wilderness area. The
fossil derived from the upper part of the Farmington Member
of the Kirtland Formation (Fig. 2). The Farmington Member is
the medial, sandy member of the Kirtland Formation. It consists
of interbedded sandstone, conglomerate and mudstone/siltstone
and is as much as 139 m thick along the San Juan River, but thins
southward (Hunt and Lucas, 1992). The Farmington Member
is of Kirtlandian age (late Campanian), and radioisotopic
dating of ash beds above and below the Farmington Member
indicate it is about 74 Ma (see Sullivan et al., 2005b; Fowler
and Freedman Fowler, 2020), which indicates that Bisticeratops
is approximately 2 million years younger than Pentaceratops
sternbergi, “Pentaceratops? fenestratus,” and Titanoceratops
ouranos (Sullivan and Lucas, 2015). Furthermore, Bisticeratops
is younger by 1 million years than the recently named
Navajoceratops sullivani and 750,000 years than Terminocavus
sealeyi (Fowler and Freedman Fowler, 2020). Additionally,
Bisticeratops is nearly 500, 000 years older than the De-
na-zin Member (uppermost Kirtland Formation) unnamed
chasmosaurines NMMNH P-21100 and NMMNH P-41228. It
is also noted that Bisticeratops occurs approximately 1 million
years before Sierraceratops turneri (Dalman et al., 2022).
MATERIALS AND METHODS
The holotype material (NMMNH P-50000) was recovered
from the Farmington Member of the Kirtland Formation, San
Juan Basin, New Mexico at NMMNH locality 6258. Early
preparation of the fossil was undertaken at the University of
Arizona. Further preparation of the fossil was done at NMMNH
by volunteers and nal preparation was done by the senior author
(SGD). The right postorbital horncore of the skull was initially
present, but disappeared sometime between collection and the
transfer from the University of Arizona to NMMNH (Dalman
and Lucas, 2018).
All measurements of the specimens were taken using a
standard metric ruler. To assess the phylogenetic position of
Bisticeratops froeseorum, a phylogenetic analysis was run on
the character dataset of Dalman et al. (2022), which was, in
turn, based on the analysis of Longrich (2014) and Brown and
Henderson (2015) (Appendix 1). The dataset includes a total of
40 operational taxonomic units (OTUs) and 213 total characters.
See Dalman et al. (2022) for further information. The analysis
was run in TNT version 1.5 (Golobo and Catalano, 2016). The
dataset was subjected to a New Technology search (with default
parameters for sectorial search, ratchet, tree drift, and tree
fusion). Tree statistics reported include the consistency index
(CI) and retention index (RI).
Nomenclatural Acts
The electronic edition of this article conforms to the
requirements of the amended International Code of Zoological
Nomenclature, and hence the new names contained herein
are available under that Code from the electronic edition of
this article. This published work and the nomenclatural acts it
contains, have been registered in ZooBank, the online registration
system for the ICZN. The ZooBank LSIDs (Life Science
Identiers) can be resolved and the associated information
viewed through any standard web browser by appending the
LSID to the prex “http://zoobank.org/.” The LSID for this
publication is: urn:lsid:zoobank.org:pub:01864AA5-C3CF-
47DF-BA73-31892914B10A. The electronic edition of this
work was published in a journal with an ISSN, and has been
archived and is available from the following digital repositories:
LOCKSS (http://www.lockss.org); PubMed Central (http://
FIGURE 1. Skull and skeleton reconstruction of Bisticeratops
froeseorum gen. et sp. nov., (NMMNH P-50000). Highlighted
elements in blue are preserved.
129
www.ncbi.nlm.nih.gov/pmc).
SYSTEMATIC PALEONTOLOGY
ORNITHISCHIA Seeley, 1888
CERATOPSIA Marsh, 1888
NEOCERATOPSIA Sereno, 1986
CERATOPSIDAE Marsh, 1888
CHASMOSAURINAE Lambe, 1915
Bisticeratops, new genus
urn:lsid:zoobank.org:act:4D6BE9D5-DDAA-4124-993B-
C6A1EA4F4C42
Etymology: Bisti, in reference to the Bisti/De-na-zin
Wilderness Area, the area from which the specimen came;
“ceratops,” meaning a “horned-face” in Latinized Greek.
Diagnosis: As for type species, by monotypy.
Bisticeratops froeseorum, new species
urn:lsid:zoobank.org:act:E48D29DF-5C70-4649-8FF3-
7AB3608F6DEC
(Figs. 2, 3, 5A, 6A, 7A, 8, 9A, 10A, 11A, 12, 13, 14, 15, 16,
17A, 18A, 19, 21, 22A, 23, 26, 27)
Etymology: The specic epithet honors the late Edgar
Froese, the founder of the instrumental music band Tangerine
Dream, and his son Jerome Froese, the former member of
Tangerine Dream and the founder and leader of the instrumental
music band Loom.
Diagnosis: Chasmosaurine ceratopsid characterized by
the following autapomorphies: (1) the snout in lateral view
has a characteristic stepped margin; whereas, in Pentaceratops
sternbergi the stepped margin is absent; (2) premaxilla with
deeply inserted narrow sulcus located between the base of the
triangular process and the posteroventral process of premaxilla;
(3) the posteroventral process of the premaxilla well-developed
and robust with strongly laterally protruding ridge; (4) posterior
end of the posteroventral process of the premaxilla with two
distinct projections separated from each other by a deep notch;
the dorsal projection is narrow and peg-like; whereas, the
ventral projection is transversely expanded and ange-like; (5)
narial strut with diminutive posterior ange; (6) naris posteriorly
expanded over (dorsal to) the maxillary tooth row; (7) the
maxilla with two short anterior processes separated by a deep
notch; (8) maxilla with a strongly reduced jugal process; (9)
absence of pocket-like fossa between the ventral jugal process
of the lateral surface of the maxilla; (10) lateral surface of the
maxilla with two elongated, low ridges that parallel each other
and underline the antorbital fenestra; (11) maxilla with two
small antorbital fenestrae; (12) maxilla anterodorsal margin
containing single accessory foramen; (13) lateroventral surface
of the maxilla strongly uted with large accessory mental
foramina-like structures; (14) the anterior process of the maxilla
for contact with the ventral process of premaxilla is short and
FIGURE 2. Geographic and stratigraphic position of the type locality of Bisticeratops froeseorum gen. et sp. nov., (NMMNH
P-50000) in northwestern New Mexico during the late Campanian. Paleobiogeographic reconstruction by Ron Blakey, Colorado
Plateau Geosystems.
130
only slightly extends beyond the anterior end of the tooth row;
(15) palpebrals are short with moderate ornamentation; (16) the
postorbital horncore is strongly anteriorly-curved.
Holotype: NMMNH P-50000, a nearly complete skull,
missing the parietal, left squamosal, postorbital horncores (only
the cast of the right postorbital horncore is preserved), left jugal,
left quadrate, predentary, and both dentaries.
Type locality: Bisti/De-na-zin Wilderness Area, San Juan
Basin, northwestern New Mexico (NMMNH locality 6258).
Exact map coordinates on le at the New Mexico Museum of
Natural History and Science, Albuquerque.
Horizon and Age: The specimen was recovered from the
Kirtlandian (late Campanian) strata of the upper Farmington
Member (~74 Ma), Kirtland Formation (see Fowler and
Freedman Fowler, 2020).
DESCRIPTION
General Skull Morphology
The length of the preserved skull of NMMNH P-50000 is
175 cm from the tip of the rostral bone to the broken end of the
right squamosal (Figs. 3, 4, Table 1). Most of the paired bones
are present in the skull, whereas other cranial bones such as the
left jugal with the corresponding epijugal and quadratojugal,
the left quadrate, the right and the left postorbital horncores
(however, a cast of the original right postorbital horncore was
made before the horn disappeared; the cast is available for
study), the left squamosal and the entire parietal, the predentary,
and both dentaries are missing. The right side of the skull is
more complete and better preserved than the left side.
External bone texture of some of the cranial bones is slightly
porous and striated, including the maxilla and jugal; whereas
bones that are fully fused have a smooth texture, including the
premaxillae, maxillae, nasal, and lacrimals, which most likely
represent a subadult bone texturing (e.g., Brown et al., 2009).
The skull has been distorted laterally, and some of the bones in
the skull are not well preserved. Posterior to the nares the snout
is ared in a similar way to larger, more mature chasmosaurine
skulls (e.g., Pentaceratops sternbergi AMNH FARB 1624).
Although the skull is crushed, the preserved right jugal and
the jugal regions are splayed laterally, so that the preserved
right jugal is visible in dorsal view in a way similar to mature
chasmosaurines.
The right, incomplete squamosal is preserved. The anterior
portion of the right squamosal is horizontally oriented and
convex dorsally; whereas, the remaining part is nearly vertically
oriented, resulting in a distinct, saddle-like shape; however,
if complete, the parietosquamosal frill would not be as short
as in juvenile chasmosaurines (e.g., Currie et al., 2016), but
elongate, as in subadult and adult chasmosaurines (e.g., Godfrey
and Holmes, 1995; Sampson et al., 2010; Longrich, 2011).
Compared to mature chasmosaurines, the nares, orbits, the
intertemporal fenestrae, and otic notch are relatively large in
NMMNH P-50000 (Figs. 3, 4). Some of the cranial sutures are
visible, such as those between the premaxilla and maxilla (these
two elements are not fused together); whereas, others are more
difcult to detect, such as the postorbital contact with the frontal
and lacrimal and jugal with the epijugal and quadratojugal. This
further suggests that NMMNH P-50000 was relatively mature
when it died.
Snout: The snout is proportionally elongate (Fig. 5A). This
is particularly true compared to some other chasmosaurines
such as the unnamed Almond Formation chasmosaurine
(AMNH FARB 3652) (Fig. 5B). The snout is also not as deep
in NMMNH P-50000 compared to the unnamed Almond
Formation chasmosaurine (AMNH FARB 3652), although Farke
(2004) noted that the depth of the latter may be exaggerated
due to taphonomic crushing. In contrast, the snout of NMMNH
P-50000 is not as long relative to depth as in some fully grown
chasmosaurines such as Chasmosaurus belli (Lambe, 1902), C.
russelli (Sternberg, 1940), Pentaceratops sternbergi (Osborn,
1923), “Pentaceratops? fenestratus,” (Wiman, 1930), and
Titanoceratops ouranos (Longrich, 2011).
Rostral bone: The rostral bone is laterally compressed,
wedge-shaped and in general outline it diers from the rostral
bone of Pentaceratops sternbergi by having a stepped dorsal
margin that leads to the premaxilla (Fig. 6). The lateral surface
of the rostral bone is pitted and grooved, as in other ceratopsians,
suggesting that in life the bone had a keratinous covering. The
anterior margin of the rostral bone is convex, whereas the
posterior and ventral margins are concave. The rostral bone
is tightly fused to the premaxillae. In lateral view the rostral
bone is curved, so that its anteroventral tip forms a hook that
nearly parallels the dorsal process of the rostrum for contact
with the premaxilla. However, the rostral bone is not as strongly
hooked as in some other chasmosaurines, such as Agujaceratops
mariscalensis, Anchiceratops ornatus, Chasmosaurus russelli,
and Spiclypeus shipporum (e.g., Forster et al., 1993; Godfrey
and Holmes, 1995; Mallon et al., 2016; Lehman et al., 2017),
but is similar to the degree seen in the Almond Formation
chasmosaurine (Fig. 5B). Chasmosaurine species with weakly
hooked rostral beaks include Arrhinoceratops brachyops,
Chasmosaurus belli, Kosmoceratops richardsoni, Pentaceratops
sternbergi, Titanoceratops ouranos, and Utahceratops gettyi
(e.g., Osborn, 1923; Godfrey and Holmes, 1995; Sampson et al.,
2010; Longrich, 2011).
The posterior margin of the rostral bone has long dorsal and
ventral processes, which are characteristic of chasmosaurines
(e.g., Dodson et al., 2004). In NMMNH P-50000, the processes
are missing their terminal ends; however, if complete they
FIGURE 3. Holotype skull of Bisticeratops froeseorum gen.
et sp. nov., (NMMNH P-50000) A, right lateral view; B, line
drawing of the skull in right lateral view showing various cranial
morphological features. See anatomical abbreviations section
for abbreviations.
131
Pentaceratops is also present in other specimens referred to
Chasmosaurus (CMN 2280, 8801, ROM 839, 843, UALVP 40)
(e.g., Campbell et al., 2016).
Premaxilla: The premaxillae are well preserved, tightly
adpressed and rmly co-ossied along the midline, forming the
thickened dorsal margin of the snout, and the anterior margin of
the external naris (Fig. 8). The right and left premaxillae closely
approach each other, forming a transversely narrow snout, which
to some degree may have been caused by the lateral crushing
of the skull. The premaxillae have characteristic chasmosaurine
morphology in being slightly longer (48 cm) than tall (31 cm). In
lateral views the premaxilla has a characteristic stepped margin,
which is situated at the posterior end of the dorsal process of
the rostral bone. The premaxillae have two processes: dorsal
and ventral. Both processes are inclined posterodorsally at a 35°
angle, so that in lateral view the processes parallel each other.
The lateral surface of the dorsal process is smooth throughout
its length; whereas, near the sutural contact with the nasal the
dorsal surface of the process is slightly rugose, consisting of
several shallow pits, which extend onto the rostral process of the
nasal. This condition of the dorsal premaxillary process contrasts
markedly with the strongly rugose dorsal premaxillary process
in the subadult (NMMNH C-3175) and adult (AMNH FARB
6325) Pentaceratops sternbergi, and appears to be unique to
Bisticeratops froeseorum (NMMNH P-50000).
In NMMNH P-50000 the premaxillae are strongly arched
dorsally, a condition similar to that of the holotype specimen
of Pentaceratops sternbergi (AMNH FARB 6325), but are
distinct from those of the subadult P. sternbergi (NMMNH
C-3175), in which they are only slightly arched dorsally. In
other chasmosaurines such as Agujaceratops mariscalensis,
Chasmosaurus belli, Vagaceratops (“Chasmosaurus”)
FIGURE 4. Holotype skull of Bisticeratops froeseorum gen.
et sp. nov., (NMMNH P-50000) A, left lateral view; B, line
drawing of the skull in left lateral view showing various cranial
morphological features. See anatomical abbreviations section
for abbreviations.
FIGURE 5. Ceratopsid skulls in right lateral view, A,
Bisticeratops froeseorum gen. et sp. nov., (NMMNH P-50000);
B, unnamed Almond Formation chasmosaurine (AMNH FARB
3652) from Wyoming. See anatomical abbreviations section for
abbreviations.
appear to have been subequal in length, which is typical
chasmosaurine morphology (e.g., Dodson et al., 2004). The
processes are ared in the anterior region, but appear to have a
uniform dorsoventral depth throughout their respective lengths.
In contrast, in a subadult Pentaceratops sternbergi specimen
(NMMNH C-3175), with a skull as large as that of NMMNH
P-50000, the dorsal process is short and narrow in the posterior
region and strongly ared in the anterior region, a condition
that is also seen in the holotype specimen of P. sternbergi
(AMNH FARB 1624) (Fig. 7B). Furthermore, the posterolateral
margin of the rostral bone in NMMNH P-50000 lacks the
characteristic lateral process, which is pronounced and present
in the subadult of Pentaceratops (NMMNH C-3175) (Fig.
6B); whereas, in the skull of an adult Pentaceratops (AMNH
FARB 1624) the process is also present, but is not as extensive,
suggesting that this process is an ontogenetic feature (Fig. 7B).
It is noted here that Pentaceratops aquilonius was named by
Longrich (2014) from fragmentary material collected in Alberta,
Canada, with additional material referred to Pentaceratops cf.
P. aquilonius from the Williams Park Formation of Colorado.
Mallon et al. (2016) considered it very similar to Spiclypeus
shipporum, but due to the fragmentary preservation considered
it a nomen dubium. We agree with this assessment and consider
Pentaceratops monospecic in the present study.
The dorsal process of the rostral bone of NMMNH P-50000
is inclined posterodorsally, but does not reach the level of the
premaxillary fossa; however, the ventral process of the rostral
bone extends posteriorly and if complete would terminate
directly at the level of the narial strut, a condition similar to that
of the reconstructed rostral bone of Chasmosaurus belli (ROM
843) (e.g., Godfrey and Holmes, 1995). In contrast, in juvenile
and adult specimens of Pentaceratops the ventral process of
the rostral bone terminates anterior to the narial strut (Figs.
7B, C). A condition similar to that of C. belli (ROM 843) and
132
irvinensis, Spiclypeus shipporum, Titanoceratops ouranos, and
Utahceratops gettyi (e.g., Lehman, 1989; Godfrey and Holmes,
1995; Lucas et al., 2006; Sampson et al., 2010; Longrich, 2011;
Mallon et al., 2016; Campbell et al., 2016, 2019) the premaxillae
arch dorsally in a way similar to P. sternbergi (AMNH FARB
6325, NMMNH C-3175) (Fig. 7B–C). However, the exceptions
are Chasmosaurus sp. (“Kosmoceratops sp.” CMN 8801), and
Kosmoceratops richardsoni (UMNH VP 17000) (e.g., Sampson
et al., 2010; Longrich, 2014; Campbell et al., 2016).
The premaxillary septum is shallowly excavated laterally
by an oblong premaxillary fossa, which is not perforated by
an interpremaxillary fenestra. There is a small opening in the
premaxillary septum, however this is not a morphological
feature but simply a missing bone fragment as the bone in this
region is > 1 cm thick. In contrast, in the subadult (NMMNH
C-3175) and adult (AMNH FARB 6325) specimens of
Pentaceratops the premaxillary septum is perforated by a large
interpremaxillary fenestra, a condition that is also present in
some other chasmosaurines such as Anchiceratops ornatus,
Vagaceratops (“Chasmosaurus”) irvinensis, Kosmoceratops
richardsoni, Regaliceratops peterhewsi, Torosaurus latus,
Triceratops prorsus, and Utahceratops gettyi (e.g., Mallon and
Holmes, 2010; Sampson et al., 2010; Longrich and Field, 2012;
Brown and Henderson, 2015).
In NMMNH P-50000 the posterior margin of the
premaxillary septum thickens signicantly to form a narial strut
that is vertically oriented. The narial strut does not extend to
FIGURE 6. Rostral bone in left lateral view, A, Bisticeratops
froeseorum gen. et sp. nov., (NMMNH P-50000); B,
Pentaceratops sternbergi (NMMNH C-3175). See anatomical
abbreviations section for abbreviations.
TABLE 1. Measurements of the holotype skull of Bisticeratops
froeseorum gen. et sp. nov., (NMMNH P-50000). Note: Values
in cm.
Measurement Values
1 Postorbital horncore length (rectilinear) from
dorsal rim of orbit to apex 67.0
2 Postorbital horncore length (curvilinear) from
dorsal rim of orbit to apex 70.0
3 Postorbital horncore anteroposterior length at
base 14.7
4 Postorbital horncore mediolateral width at
base 12.7
5 Postorbital horncore circumference about base 39°
6 Nasal horncore height from base to apex
(excluding nasal bridge) 11.0
7 Nasal horncore transverse width at base 5.4
8 Nasal horncore anteroposterior length at base 9.0
9 Rostral-orbit length 73.0
10 Posterior margin of external naris-orbit
length 22.0
11 Rostral-posterior margin of nasal horncore 52.0
12 Epijugal-orbit length (along surface) 37.0
13 Lateral temporal fenestra-orbit length 10.0
14 Orbit anteroposterior length 13.5
15 Orbit dorsoventral height 12.0
16 Maximum orbit diameter 43.0
17 Minimum distance from jugal notch to
medial margin of squamosal 18.0
18 Minimum distance from lateral margin of
anteriormost episquamosal to medial margin
of squamosal
33.0
19 Rostral-epijugal (rectilinear) 87.0
20 Rostral-posterior edge of maxillary tooth row 82.0
21 Basal skull length (rostral-occipital condyle) 98.5
the nasal. The dorsal terminal end of the narial strut that merges
with the ventral surface of the dorsal premaxillary process is 7
cm posteriorly to the sutural nasal contact. This characteristic
condition is present in all known Campanian chasmosaurines
(e.g., Campbell et al., 2016), except for Titanoceratops in which
the narial strut contributes to the nasal (Fig. 7D), a condition
that is characteristic of the Triceratopsini clade, including
Eotriceratops xerinsularis, Torosaurus latus, and Triceratops
prorsus, except for Regaliceratops peterhewsi (Wu et al., 2007;
Longrich and Field, 2012; Brown and Henderson, 2015). It is
noted that Mallon et al. (2016) did not recover Regaliceratops
as a triceratopsin.
In NMMNH P-50000, the bone surface where the dorsal
end of the narial strut merges into the premaxilla is smooth. In
contrast, in this region in subadult (NMMNH C-3175) and adult
Pentaceratops (AMNH FARB 6325) there is a characteristic
large accessory foramen (Fig. 9B–C). In Titanoceratops
ouranos (OMNH 10165), in the dorsal region of the narial
strut is a shallow triangular fossa-like structure which occupies
nearly half the length of the narial strut (Fig. 9D). Therefore, we
133
accessory canal is present, whereas the vertical sulcus is absent
(Fig. 11E). The accessory canal is also present in the premaxillae
of Chasmosaurus sp. (UALVP 40) and Spiclypeus shipporum
(CMN 57081) (Figs. 11C, F). Similarly, in the premaxillae of
Agujaceratops mariscalensis (UTEP P.37.7.067) (Fig. 11B)
there is also a large accessory canal that directly parallels the
dorsal margin of the premaxillary fossa in the same way as in S.
shipporum (CMN 57081). The accessory fossa is also present in
the premaxilla of A. mavericus (TMM 45922-37; Lehman et al.,
2017, g. 2). In Kosmoceratops richardsoni (UMNH VP 17000)
(Fig. 11D), and in Titanoceratops ouranos (OMNH 10165) (Fig.
11G), the accessory canal is small, deeply inserted in the bone,
and obscured laterally by the anteroventral margin of the narial
strut.
In NMMNH P-50000, directly ventral to the premaxillary
fossa is a characteristic sulcus, which extends from the contact
of the rostral bone to the posterior end of the triangular process of
the premaxilla. The surface of the sulcus is gently concave. The
transition from the premaxillary fossa to the sulcus is smooth
and uninterrupted by the lateral ridge, a feature that is present
in subadult Pentaceratops (NMMNH C-3175), but absent in at
least one adult Pentaceratops (AMNH FARB 6325); however,
the ridge is present in another adult Pentaceratops (AMNH
FARB 1624). The ridge is absent in Titanoceratops ouranos
suggest that the accessory foramen of the narial strut represents
a unique morphological feature, thus far recorded only in
Pentaceratops. Similarly, the triangular fossa-like structure is a
unique morphological feature of Titanoceratops.
In NMMNH P-50000 in the ventral region where the narial
strut merges into the premaxilla the bone surface is smooth,
sloping gently anteroventrally around a characteristic ovoid
accessory canal, which pierces through the bone (Figs. 8A,
10A, 11A). The lateral bone surface that encloses the accessory
canal is strongly convex, and its dorsal margin is thin, forming
a characteristic sharp ridge. Directly posterior to the accessory
canal is a characteristic concavity, which separates the medial
surface of the bone that surrounds the accessory canal from the
anteroventral corner of the narial strut. In contrast, in subadult
Pentaceratops sternbergi (NMMNH C-3175) the ventral region
of the narial strut transitions into a long, pronounced ridge (Figs.
7C, 10B). Furthermore, in NMMNH C-3175 the accessory canal
is absent, and instead there is a deep and extensive vertical
sulcus that is situated directly anterior to and is deeply inserted
between the narial strut and the interpremaxillary fenestra (Fig.
10B). In contrast, in the holotype of Pentaceratops sternbergi
(AMNH FARB 6325) the vertical sulcus and the accessory
canal in the premaxillae are absent (Fig. 9B). However, in
another adult skull of P. sternbergi (AMNH FARB 1624) the
FIGURE 7. Comparisons of chasmosaurine premaxillae in right lateral view, A, Bisticeratops froeseorum gen. et sp. nov., (NMMNH
P-50000); B, Pentaceratops sternbergi (AMMNH FARB 1624); C Pentaceratops sternbergi (NMMNH C-3175); D, Titanoceratops
ouranos (OMNH 10165). See anatomical abbreviations section for abbreviations.
134
FIGURE 8. Premaxillae of Bisticeratops froeseorum gen. et sp.
nov., (NMMNH P-50000) in A, right lateral view; B, left lateral
view; C, ventral view. See anatomical abbreviations section for
abbreviations.
FIGURE 9. Comparisons and the position of the narial strut with respect to the nasal and the base of the nasal horncore, A,
Bisticeratops froeseorum gen. et sp. nov., (NMMNH P-50000); B, Pentaceratops sternbergi (AMNH FARB 6325); C, Pentaceratops
sternbergi (NMMNH C-3175); D, Titanoceratops ouranos (OMNH 10165). See anatomical abbreviations section for abbreviations.
(OMNH 10165) (Fig. 7D) and in most other chasmosaurines,
including members of the Triceratopsini clade.
In subadult (NMMNH C-3175) and adult Pentaceratops
(AMNH FARB 1624) there are four foramina situated dorsal to
the lateral ridge of the premaxilla, forming a single line (Figs.
7B-C). In NMMNH P-50000 there are no foramina in this region
of the premaxilla.
The lateral premaxillary sulcus in NMMNH P-50000 is
obscured in the posteroventral region by the ventral premaxillary
process. The sulcus is deeply excavated in the posteroventral
region between the triangular process and posteroventral
process of the premaxilla. In contrast, in subadult (NMMNH
C-3175) and adult Pentaceratops (AMNH FARB 1624, 6325),
as well as Titanoceratops (OMNH 10165), the region between
the triangular process and ventral process is wide open, so
that the posteroventral margin of the triangular process is
fully exposed. In other chasmosaurines such as Agujaceratops
mariscalensis, Vagaceratops (“Chasmosaurus”) irvinensis,
Chasmosaurus belli, C. russelli, Chasmosaurus sp. (UALVP
40), Kosmoceratops richardsoni, Spiclypeus shipporum, and
Utahceratops gettyi, the posteroventral margin of the triangular
process is exposed (e.g., Lehman, 1989; Godfrey and Holmes,
1995; Sampson et al., 2010; Mallon et al., 2016).
As in other chasmosaurines, the premaxillae of NMMNH
P-50000 contribute to the median septal anges. However, the
septal anges are diminutive, only present in the ventral portion
of the anterior narial margin, and anterodorsally inclined. The
135
septal anges are visible in three aspects: lateral, posterior, and
medial. Lateral to the septal ange in both premaxillae is a large
plate-like triangular process, which extends into the anteroventral
quadrant of the external naris. The general shape of this process is
similar to those of most chasmosaurines except Kosmoceratops
richardsoni, Pentaceratops sternbergi, Titanoceratops ouranos,
and Utahceratops gettyi in which the posterodorsal corners of
the processes are elongate in the derived triangular condition
(Lehman, 1993; Sampson et al., 2010; Longrich, 2011). In lateral
view the dorsal surface of the triangular process in NMMNH
P-50000 is concave, whereas the posterior surface of the process
is nearly straight. The posterodorsal tip of the triangular process
is at the level of the terminal end of the dorsal process of the
premaxilla. In contrast, in subadult (NMMNH C-3175) and
adult specimens of Pentaceratops (AMNH FARB 1624, 6325)
the posterodorsal tip of the triangular process extends slightly
beyond the level of the anterior end of the dorsal premaxillary
process (Figs. 9B–C, 11E).
In NMMNH P-50000, the ventral process of the premaxilla
is robust and short. It projects posteriorly, twisting strongly
along its length as it curves laterally, then medially, and ascends
posterodorsally. The result of this twist is the formation of a
pronounced and robust lateral ridge. The ridge originates at the
level near the midlength of the triangular process. It continues
posteriorly along the lateral surface of the ventral process of the
premaxilla and terminates ~10 cm from the nasal contact surface.
The ridge is ventral to the long axis of the ventral process and its
terminal end merges with the lateroventral surface of the process.
The bone surface of the ventral process directly posterior to
the terminal end of the ridge is slightly convex, smooth, and
dorsoventrally expanded, resulting in a pronounced ange-like
structure situated at the ventral margin of the bone.
The terminal end of the ventral process has two projections
that parallel each other and are separated by a triangular notch.
The dorsal projection is transversely narrow and small; whereas,
the ventral projection is signicantly larger and ange-like. In
lateral view the dorsal margin of the ventral process is nearly
straight, whereas the ventral margin is sinuous. In contrast, in
subadult (NMMNH C-3175) and adult Pentaceratops (AMNH
FARB 1624, 6325) the terminal end of the ventral process has
a single projection. A single projection at the terminal end of
the ventral process is present in most chasmosaurines (e.g.,
Agujaceratops, Anchiceratops, Arrhinoceratops, Chasmosaurus,
Kosmoceratops, Titanoceratops). In some other chasmosaurines
such as Spiclypeus shipporum and Utahceratops gettyi the ventral
premaxillary process has two terminal projections. However,
the terminal projections of the ventral premaxillary process in
both these species dier from that of Bisticeratops (NMMNH
P-50000). In Spiclypeus the dorsal projection is signicantly
larger than the ventral projection, and the posterior margin of the
dorsal projection has a characteristic step. Furthermore, in the
reconstructed skull of Spiclypeus the notch between the dorsal
and ventral projections does not form the accessory antorbital
fossa. Similarly, in Utahceratops the dorsal projection of the
ventral process is larger and projected farther posteriorly than
the ventral projection.
Sampson et al. (2010, g. 3B) suggested that in Utahceratops
the notch between the dorsal and ventral projections in the
ventral premaxillary process is a part of the accessory antorbital
fossa. However, when examining the available cranial elements
of Utahceratops we did not nd the accessory antorbital fossa
in this region of the skull. In general, the ventral surface of the
ventral premaxillary process in chasmosaurines contacts the
dorsal margin of the maxilla and is not a part of the accessory
antorbital fossa. In Vagaceratops (“Chasmosaurus”) irvinensis,
and species of Chasmosaurus, [C. belli, C. russelli, and
Chasmosaurus sp. (UALVP 40)] (e.g., Godfrey and Holmes,
1995; Konishi, 2015) the accessory antorbital fossa is situated
between the lacrimal/maxilla contact, invading the posterodorsal
portion of the maxilla in a similar way to NMMNH P-50000.
In contrast, in the adult holotype specimen of Pentaceratops
(AMNH FARB 6325) the accessory antorbital fossa is obscured
by the bone in the posterior region and does not open into the
lacrimal contact (Fig. 9B). The morphology of this fossa is
described in the section on the maxilla.
In NMMNH P-50000, directly ventral to the anterior half of
the ridge on the ventral premaxillary process is a deep and well-
dened sulcus that, in lateral view, forms a ange-like structure.
The posterior end of the ange contacts the maxilla anteriorly.
The contact surface for the maxilla forms a deep groove, which
is short anteroposteriorly and narrow transversely (Fig. 8A). The
groove terminates directly at the level of the posterior terminal
end of the ange-like structure. Dorsal to this groove is a small
circular fossa that connects with the maxilla anterodorsally.
Following the fossa dorsally there is a narrow ridge that separates
it from a large, continuous groove for the articulation with the
maxilla (Fig. 8A). This groove contacts the maxilla dorsally and
extends along the entire ventral surface of the ventral process.
The palatal surface of the premaxillae has two parasagittally
aligned fossae, which are aligned with the posterior margin
of the rostral bone. The premaxillae diverge from the midline
farther posteriorly and medially contact the anterior processes
of the maxillae.
The external nares: The external nares in NMMNH
P-50000 are large, occupying a mid-portion of the snout.
The shape of the external nares is nearly circular with the
anteroposterior length only slightly longer than the dorsoventral
depth. As in other chasmosaurines, the ventral margin of the
external nares is enclosed by the dorsal margin of the ventral
premaxillary process; whereas, the nasal and the dorsal process
of the premaxilla form the dorsal margin of the external naris,
and the narial strut forms the anterior margin. The posterior
margin of the naris is concave, but the anterior margin has an
FIGURE 10. Comparisons of chasmosaurine premaxillae in
dorsolateral view, A, Bisticeratops froeseorum gen. et sp. nov.,
(NMMNH P-50000); B, Pentaceratops sternbergi (NMMNH
C-3175). See anatomical abbreviations section for abbreviations.
136
anteriorly vertical prole. Furthermore, the posterior margin
of the external naris is formed by the nasal and the posterior
portion of the premaxillary ventral process. This characteristic
morphology of the posterior margin of the external naris is present
in most known chasmosaurines such as Anchiceratops ornatus
(TMP 1983.001.0001), Arrhinoceratops brachyops (ROM
796), the unnamed Almond Formation chasmosaurine (AMNH
FARB 3652), Chasmosaurus belli (ROM 843), Chasmosaurus
sp. (“Kosmoceratops” sp.) (CMN 8801), Vagaceratops
(“Chasmosaurus”) irvinensis (CMN 41357), juvenile C. belli
(UALVP 52613), Eotriceratops xerinsularis (TMP 2002.57.5),
Kosmoceratops richardsoni (UMNH VP 17000), Pentaceratops
sternbergi (AMNH FARB 1624, 6325), Titanoceratops ouranos
(OMNH 10165), Torosaurus latus (ANSP 15192), Spiclypeus
shipporum (CMN 57081), Triceratops horridus (AMNH FARB
5116), T. prorsus (YPM VP 1822), and Utahceratops gettyi
(UMNH VP 16784). The skulls of Bravoceratops polyphemus
(TMM 46015-1), and Coahuilaceratops magnacuerna (CPC
276) are largely incomplete; therefore, it is not known if
the posterior margin of the external nares was concave. The
degree of concavity of the posterior margin of the external
nares diers among chasmosaurine species. In some other
chasmosaurine species such as Agujaceratops mariscalensis
(UTEP P.37.7.067), Chasmosaurus sp. (UALVP 40), C. russelli
(ROM 839), Mojoceratops perifania (AMNH FARB 5401), and
Regaliceratops peterhewsi (TMP 2005.055.0001) the posterior
FIGURE 11. Comparisons of the morphology and position of the accessory canal in the premaxillae of chasmosaurines in right
lateral view, A, Bisticeratops froeseorum gen. et sp. nov., (NMMNH P-50000); B, Agujaceratops mariscalensis (UTEP P.37.7.067);
C, Chasmosaurus sp. (UALVP 40); D, Kosmoceratops richardsoni (UMNH VP 17000); E, Pentaceratops sternbergi (AMNH
FARB 6325); F, Spiclypeus shipporum (CMN 57081); G, Titanoceratops ouranos (OMNH 10165). See anatomical abbreviations
section for abbreviations. Not to scale.
137
margin of the external naris is nearly vertical and lacks the
characteristic concavity.
Nasal horncore: The nasal horncore is small and nearly
complete, missing only a small portion of the tip (Fig. 12). The
base of the nasal horncore is fused to the nasal bone, and no
sutures can be detected. The nasal horncore has an oval cross-
section, with the long axis oriented anteroposteriorly, as in
Agujaceratops mariscalensis (UTEP P.37.7.067), Chasmosaurus
belli (ROM 843), C. russelli (CMN 2280), Pentaceratops
sternbergi (AMNH FARB 1624, 6325), Spiclypeus shipporum
(CMN 57081), the unnamed Almond Formation chasmosaurine
(AMNH FARB 3652), and Titanoceratops ouranos (OMNH
10165). In contrast, in Arrhinoceratops brachyops (ROM 796)
the anterior surface of the nasal horncore is at and nearly vertical;
whereas, in Anchiceratops ornatus (TMP 1983.001.0001), and
Regaliceratops peterhewsi (TMP 2005.055.0001) the nasal
horncore is teardrop-shaped in cross-section.
In NMMNH P-50000 the external surface of the nasal
horncore has several anteroposteriorly oriented ridges and
grooves paralleling each other, which are pitted by several
trending vascular sulci that are visible on the bone surface (Fig.
12). There is a distinctive bony rim on the anteroventral surface
of the nasal horncore. In life, this ridge probably anchored a
keratinous sheath that covered the horncore. A similar bony
rim is present and distinctively pronounced in Chasmosaurus
belli (ROM 843), and Regaliceratops peterhewsi (TMP
2005.055.0001), and is also present and equally pronounced in
some centrosaurines such as Styracosaurus albertensis (AMNH
FARB 5372).
In NMMNH P-50000 the nasal horncore is centered over
the external naris, so that its tip is nearly aligned with the tip of
the triangular process of the premaxilla. In lateral view the nasal
horncore is triangular. The anterior surface is vertical; whereas,
the posterior surface is anterodorsally inclined.
The nasal horncore in NMMNH P-50000 (Fig. 9A) is
centered over the external naris as in Titanoceratops ouranos
(OMNH 10165) (Fig. 9D), Anchiceratops ornatus (TMP
1983.001.0001), Arrhinoceratops brachyops (ROM 796),
Regaliceratops peterhewsi (TMP 2005.055.0001), and
Vagaceratops (“Chasmosaurus”) irvinensis (CMN 41357).
In contrast, in subadult Pentaceratops (NMMNH C-3175)
the nasal horncore is located over the posterior margin of the
external naris, as in Chasmosaurus and Utahceratops. In adult
Pentaceratops sternbergi (AMNH FARB 1624, 6325) the nasal
horncore is more centered over the external naris.
In NMMNH P-50000 the nasal horncore does not overhang
the sutural contact between the nasal process and the dorsal
process of the premaxilla. Similarly, in adult Pentaceratops
sternbergi specimens (AMNH FARB 1624, 6325) the tip of
the nasal horncore also does not overhang the sutural contact
between the anterior nasal process and the dorsal process of
the premaxilla; however, here the tip is directly anterior to the
FIGURE 12. Nasal horncore of Bisticeratops froeseorum
gen. et sp. nov., (NMMNH P-50000) in A, right lateral view;
B, left lateral view. See anatomical abbreviations section for
abbreviations.
FIGURE 13. Right maxilla of Bisticeratops froeseorum gen. et
sp. nov., (NMMNH P-50000) in A, lateral view; B, lingual view;
C, dorsal view; D, ventral view (tooth row); E, posterior view.
See anatomical abbreviations section for abbreviations.
138
posterodorsal tip of the triangular process of the premaxilla.
In contrast, Titanoceratops ouranos (OMNH 10165) lacks the
rostral nasal process, and instead the rostroventral portion of the
nasal horncore strongly overlaps the posterodorsal surface of the
dorsal process of the premaxilla.
Maxilla: The right and left maxillae are preserved with
the right better preserved and more complete than the left
(Figs. 13–15). The better-preserved right maxilla is triangular
in lateral and lingual outline. The anterior end of the maxilla
is inclined posterodorsally at a 39° angle relative to the tooth
row. The maxilla measures approximately 40 cm along the
ventral margin. The maximum depth of the maxilla measured
from the contact surface for the lacrimal is 22.5 cm; whereas, the
minimum dorsoventral depth measured at the anteriormost end
of the bone is 7.5 cm. The tooth row is 30 cm long, extending
throughout most of the ventral length of the maxilla. However,
the tooth row is poorly preserved in places, and a minimum of
two empty double-rooted alveoli can be discerned at the mid
length of the tooth row.
Anterior to the tooth row, the narrow edentulous portion of
the maxilla is laterally covered for the length of 3.5 cm of the
bone surface that contacts the posterior end of the premaxilla.
A large, elongate, accessory vascular foramen is situated in the
anterodorsal region of the maxilla. Directly posterodorsal to the
accessory vascular foramen is another smaller, but distinctive
foramen, and posterodorsal to it is another much larger circular
accessory vascular foramen. Several smaller vascular foramina
are situated on the lateral surface of the maxilla. Some of
the most distinctive vascular foramina are situated in the
posterodorsal region and along the long axis of the maxilla. One
of the foramina situated on the long axis of the maxilla is the
largest in the series; it is ovoid and deeply inserted in the bone. A
grooved surface emerges ventrally from the foramen, extending
anteroventrally onto the lateral surface of the maxilla. Directly
anterior to the accessory vascular foramen the bone surface of
the maxilla is strongly grooved (Fig. 14). These grooves are
interpreted as the grooves for veins, arteries, and nerves (e.g.,
Porter and Witmer, 2019).
The lateral surface of the right maxilla is smooth, but
not at, rather being mostly concave. There are several large
pathologies that pierce through the bone. These pathologies
were described in detail by Dalman and Lucas (2018) as bite
marks made by a tyrannosaurid. Therefore, there is no need to
describe them here again.
The maxilla is concave along the long axis. The concavity
is greater in the posterior region, and is strongly ared
dorsoventrally. The anterodorsal surface of the maxilla is at
for approximately 5 cm but, immediately after, it transitions into
a strong convexity, which extends posteriorly and as a result
it forms a low, but distinct 18.5 cm long ridge in the posterior
region, paralleling the lateral margin of the antorbital fenestra.
Directly ventral to this ridge is a shallow concavity paralleling
the ridge and separating it from another more strongly
developed ridge. This second ridge outlines the posterodorsal
end of the large lateral concavity and is approximately 9.5 cm
long. Both ridges and the concavity mark the lateral surface
of the jugal process of the maxilla; which, compared to other
chasmosaurines, is signicantly short, but its contact surface
for the jugal is extensive; however, it does not extend beyond
the posterior margin of the maxilla. Close examination of the
FIGURE 14. Right maxilla of Bisticeratops froeseorum gen.
et sp. nov., (NMMNH P-50000) in anterolateral view. See
anatomical abbreviations section for abbreviations.
FIGURE 15. Right maxilla of Bisticeratops froeseorum gen. et
sp. nov., (NMMNH P-50000), A, lateral view; B, posterior view.
See anatomical abbreviations section for abbreviations.
FIGURE 16. The skull of Bisticeratops froeseorum gen. et sp.
nov., (NMMNH P-50000) showing the maxilla/jugal contact,
A, right lateral view; B, anterior view (note: the skull in this
picture lies on the left lateral side and the jugal is facing up). See
anatomical abbreviations section for abbreviations.
139
jugal process of the maxilla suggests that the short nature of the
process is not the result of bone damage because the contact
surface of the process ts perfectly with the contact surface
of the maxillary process of the jugal (Fig. 16). In contrast, in
subadult (NMMNH C-3175) and adult Pentaceratops sternbergi
(AMNH FARB 1624, 6325), the jugal process of the maxilla
is well-developed and extends beyond the posterior margin of
the maxilla (Figs. 17B, C). Furthermore, in both subadult and
adult Pentaceratops there is a deeply-inserted fossa between
the ventral margin of the process and the posterolateral surface
of the maxilla; the maxilla of NMMNH P-50000 lacks this
characteristic fossa. This fossa is present in all other Campanian
chasmosaurines, including all members of Triceratopsini.
In NMMNH P-50000 the apex of the maxilla has a at,
horizontally oriented surface to receive the lacrimal, and is
situated 20.5 cm dorsal to the midpoint of the tooth row. A deep
notch is visible laterally, immediately ventral to the apex of the
jugal process of the maxilla, which represents the anterior margin
of the antorbital fenestra. The bone surface between the apex and
the antorbital fenestra is at and smooth. Directly anterior to the
apex is another smaller fenestra, paralleling the dorsal margin
of the maxilla (Fig. 15A). In contrast, all other chasmosaurines,
including Pentaceratops sternbergi (AMNH FARB 1624, 6325),
have a single antorbital fenestra (e.g., Godfrey and Holmes, 1995;
Sampson et al., 2010; Campbell et al., 2016, 2019). Konishi
(2015) identied two antorbital fenestrae in the right maxilla of
Chasmosaurus sp. (UALVP 40), and suggested that the fenestrae
are presumably split from a single antorbital fenestra because
the left maxilla has only one antorbital fenestra. In UALVP 40
the fenestrae open anteroventrally and are aligned parallel to and
dorsal to the supra-alveolar ridge that extends anteroposteriorly
from the maxillary process of the jugal (Konishi, 2015, g. 2B).
However, Konishi (2015) noted that it is uncertain whether the
signicantly smaller antorbital fenestra lies within the maxilla
or not, as the premaxilla–maxilla and nasal–maxilla sutures are
not visible around this fenestra. Alternatively, it is possible that
the anterior fenestra marks the point where those three cranial
bones meet, as in Chasmosaurus sp. (TMP 1981.19.175) (e.g.,
Godfrey and Holmes, 1995, g.2A; Konishi, 2015).
The maxilla tapers posteroventrally to form a tooth-bearing
posteroventral process. The process is elongate and has a
roughened lateral surface at its posterior end, which marks the
contact for the ectopterygoid (Fig. 13). Both maxillae preserve
the ectopterygoids, which are fused with the contact surface of
the posterior end of the maxillae. However, the ectopterygoids
are not well preserved; therefore, the overall morphology cannot
be determined at present. It appears that pterygoids are also
present; however, because of their poor preservation the overall
morphology also cannot be determined.
The lingual surface of the maxilla is poorly preserved;
however, the supradental plate that laterally covers the tooth
row is nearly complete (Fig. 13C). A series of alveolar foramina,
which correspond to the number of tooth positions, extends
along the length of the supradental plate at the base of the tooth
FIGURE 17. Comparison of chasmosaurine maxillae in right lateral view, A, Bisticeratops froeseorum gen. et sp. nov., (NMMNH
P-50000); B, Pentaceratops sternbergi (AMNH FARB 6325; left reversed); C, Pentaceratops sternbergi (MNA V1747); D,
Pentaceratops sternbergi (NMMNH C-3173; left reversed). See anatomical abbreviations section for abbreviations.
140
row.
Along the entire length of the lingual surface is an arcuate
ridge, situated dorsal to the alveolar foramina and extending
to the intermaxillary symphysis, which is expanded lingually
to form the posterior end of the palate. The articulation for
the palate extends along the lingual edge of the ectopterygoid
process, curving anterodorsally along the inner wall of the
broadly open maxillary canal (Fig. 15B). The canal is open on
the lingual surface, occupying the entire jugal process of the
maxilla. Unlike in other chasmosaurines such as Agujaceratops
mariscalensis and Pentaceratops sternbergi, the canal does not
narrow internally, but is expanded dorsoventrally and deep. The
canal exits through a series of several vascular foramina located
on the lateral side, and opens dorsally as a tripartite foramen
in the medial oor of the antorbital fenestra. This portion of
the maxilla is well preserved, and, when associated with the
corresponding cranial elements, it shows the proportional
contribution of the maxilla, jugal, lacrimal and palate to the
margins of the antorbital fenestra (Fig. 16A).
As described before, NMMNH P-50000 has two antorbital
fenestrae, which are separated from each other by a at, plate-
like sulcus (Fig. 15A). This characteristic sulcus forms the
roof of the larger antorbital fenestra. However, none of the
corresponding cranial elements participates in the formation
of both fenestrae. The larger antorbital fenestra is enclosed
medially in the posterior region by the bone that forms the
lateral surface of the fenestra. The smaller antorbital fenestra is
also enclosed in a way similar to the larger antorbital fenestra.
In adult specimens of Pentaceratops sternbergi (AMNH FARB
1624, 6325) the antorbital fenestra is also enclosed by the bone
in the posterior region. In contrast, in subadult P. sternbergi
(NMMNH C-3175) the antorbital fenestra opens in the posterior
region and the corresponding cranial elements, such as the jugal
and lacrimal, participate in its formation. Therefore, we suggest
that this character is ontogenetic in Pentaceratops. Similarly,
the antorbital fenestra in Titanoceratops ouranos (OMNH
10165) is also enclosed by the bone in the posterior region. In
specimens of Chasmosaurus,[ including C. belli, C. russelli, and
Chasmosaurus sp. (UALVP 40)], the antorbital fenestra is open
posteriorly and the corresponding cranial elements, such as the
jugal and lacrimal, participate in its formation.
Currie et al. (2016) identied an antorbital fenestra in
juvenile Chasmosaurus belli (UALVP 52613), which is situated
between the posteroventral margin of the ventral premaxillary
process and the dorsal margin of the maxilla. However, it
appears that the antorbital fenestra in UALVP 52613 is not
a morphological feature, but instead due to a missing bone
fragment. Furthermore, the correct position of the antorbital
fenestra in UALVP 52613 appears to be farther out posteriorly,
as it is in more mature specimens of C. belli and C. russelli (e.g.,
Godfrey and Holmes, 1995; Campbell et al., 2016). Therefore,
this indicates that the position of the fenestra in C. belli and
C. russelli does not change during ontogeny with respect to
other cranial elements. In NMMNH P-50000 this portion of the
maxilla is a thin, dorsoventrally compressed wedge, projecting
anteriorly from the anterior end of the maxilla, and connects
with a corresponding groove (contact surface) of the premaxilla
(Fig. 13B). When associated, the ventral margin of the maxilla is
not aligned with the ventral margin of the premaxilla, but instead
projects signicantly, ~ 5 cm ventrally. A similar condition is not
only present in Pentaceratops sternbergi (AMNH FARB 6325)
and Titanoceratops ouranos (OMNH 10165), but also in most
other chasmosaurines.
The anterior end of the NMMNH P-50000 maxilla has a
FIGURE 18. Comparison of the orbit ornamentation of chasmosaurines in right lateral view, A, Bisticeratops froeseorum gen. et
sp. nov., (NMMNH P-50000); B, Agujaceratops mariscalensis (TMM 43098-1). C-D, Pentaceratops sternbergi (AMNH FARB
6325); E, “Pentaceratops? fenestratus” (PMU 24923); F, Titanoceratops ouranos (OMNH 10165). See anatomical abbreviations
section for abbreviations. Note to scale.
141
short process for articulation with the premaxilla (Figs. 13A,
14, 15A, 17A). Paralleling this process is another short process.
Both processes are separated from each other by a distinctive
“U”-shape notch. In contrast, in subadult (NMMNH C-3175)
and adult Pentaceratops sternbergi (AMNH FARB 1624, 6325)
there is only a single process (Fig. 17B–D), which in comparison
to NMMNH P-50000 is signicantly longer. Therefore, the
presence of two anterior processes on the maxilla separated
by a deep “U”-shape notch further dierentiates Bisticeratops
froeseorum from P. sternbergi and other chasmosaurines.
Circumorbital Region: The bones of the circumorbital
region, including the lacrimal, jugal, postorbital and supraorbital
are fused together on the right side. These elements are described
here as follows:
Orbit: The orbit is circular and large (Figs. 16A, 18A). The
lacrimal forms the anteroventral margin of the orbit; however,
sutures between the lacrimal and other cranial elements cannot
be discerned, because in this region the cranial elements are
strongly co-ossied. The anterior portion of the palpebral
is moderately rugose. The rugosity consists of numerous,
densely spaced, small, bump-like structures and grooves (Figs.
16A, 18A). In contrast, in Pentaceratops sternbergi (AMNH
FARB 1624) (Fig. 18C–D) the rugosity on the palpebral is not
extensive, consisting largely of several low ridges and bump-like
structures more similar to that in Agujaceratops mariscalensis
(Lehman, 1989) (Fig. 18B), Chasmosaurus belli (ROM 843),
and Chasmosaurus sp. (AMNH FARB 5402, CMN 8801,
ROM 839, TMP 1981.19.175, UALVP 40, YPM VP 02016). In
Kosmoceratops richardsoni (UMNH VP 17000) the palpebrals
are moderately rugose and anteroposteriorly narrow, whereas in
Utahceratops gettyi (UMNH VP 16784) the palpebrals exhibit
more extensive rugosity. Furthermore, in “P. fenestratus”
(PMU 24923) and Titanoceratops ouranos (OMNH 10165) the
palpebrals are extensive and strongly rugose, forming a boss-
like structure, protruding anteriorly (Fig. 18E –F).
Postorbital horncore: The postorbital horncores are
missing. However, before the original right postorbital horncore
went missing a cast was made, which was then available for
our study (Fig. 19). The horn core is located anterodorsal to the
orbit, projecting anteriorly. It is 67 cm long, the anteroposterior
length of the base is 14.7 cm, and the maximum circumference
is 39 cm. For most of its length the cross-section of the horncore
is oval, but at the base the medial side is at, so that the basal
cross-section is D-shaped (Fig. 19E). Supraorbital horn size is
variable in other chasmosaurine taxa, but most specically in
specimens referred to Chasmosaurus (Lull, 1933; Godfrey and
Holmes, 1995; Maidment and Barrett, 2011; Campbell et al.,
2016, 2019).
As in other ceratopsids, the postorbital in NMMNH P-50000
forms the posterodorsal margin of the orbit. The postorbital is
thick and extensively rugose; whereas, its lateral surface has
a swollen appearance (Fig. 8A). The postorbital horncore of
FIGURE 19. Right postorbital horncore (cast) of Bisticeratops
froeseorum gen. et sp. nov., (NMMNH P-50000) in A, lateral
view; B, posterior view (or dorsal); C, medial view; D, medial
view; E, base/cross section. See anatomical abbreviations
section for abbreviations.
FIGURE 20. Examples of ceratopsid postorbital horncores in
lateral view, A, unnamed De-na-zin Member chasmosaurine
(USNM V 12741); B, Pentaceratops sternbergi (AMNH FARB
1624); C, Pentaceratops sternbergi (AMNH FARB 6325); D,
“Pentaceratops? fenestratus” (PMU 24923); E, Sierraceratops
turneri (NMMNH P-76870); F, Titanoceratops ouranos (OMNH
10165). See anatomical abbreviations section for abbreviations.
Not to scale.
FIGURE 21. Right jugal of Bisticeratops froeseorum gen. et
sp. nov., (NMMNH P-50000) in A, lateral view; B, anterior
view; C, medial view; D, posterior view; E, ventral view. See
anatomical abbreviations section for abbreviations.
142
NMMNH P-50000 shares this characteristic swollen morphology
with the unnamed chasmosaurine (USNM 12741) from the
De-na-zin Member (Fig. 20A). In contrast, in Pentaceratops
sternbergi (AMNH FARB 1624, 6325), “Pentaceratops?
fenestratus”(PMU 24923), Sierraceratops turneri (NMMNH
P-76870), and Titanoceratops ouranos (OMNH 10165) (Fig.
20B–E) the postorbital has a at lateral surface and is only
slightly rugose. The medial margin of the dorsally-facing
surface of the postorbital extends posteromedially, forming
a dorsoventrally deep, straight, attened facet that contacts
the frontal. As described before, the skull is crushed laterally;
therefore, most of the other morphological features cannot be
distinguished. However, as in other chasmosaurines the attened
facet that contacts the frontal most likely ended in a medially-
facing concave surface that contributed to the frontoparietal
fontanelle (e.g., Godfrey and Holmes, 1995; Maidment and
Barrett, 2011). The suture between the postorbital and the jugal
cannot be seen, but, as in other chasmosaurines, it extends from
the lateral temporal fenestra to the posterior margin of the orbit.
The jugal forms the ventral margin of the orbit and a series of
radial grooves extend across the lateral surface in this area.
Jugal: The lateral side of the “cheek” has a large, lateral
triangular intertemporal fenestra (Figs. 21, 22A). Measured
from the anterior margin to the lower intertemporal fenestra,
the jugal is anteroposteriorly wider than that of the subadult
(NMMNH C-3175) and adult Pentaceratops sternbergi (AMNH
FARB 1624), and “Pentaceratops? fenestratus” (PMU 24923)
(Fig. 22C, E); however, it is comparable in proportions to those
of chasmosaurines in general. The jugal has three large anges:
anteroposterior (ventral margin of the maxillary contact, anterior
(anterior margin of the main body of the jugal), and quadratojugal.
Similar anges are present in most other chasmosaurines,
including the unnamed chasmosaurine (NMMNH P-22858)
from the De-na-zin Member, Sierraceratops turneri (NMMNH
P-76870), Spiclypeus shipporum (CMN 57081), Terminocavus
sealeyi (NMMNH P-27468), Titanoceratops ouranos (OMNH
10165), and Utahceratops gettyi (UNMNH VP 16784) (Fig. 22B,
F, G, H, I, J). The anges extend along the anterior and posterior
margins of the jugal, which increase the transverse width of the
jugal. The anteroposterior ange extends anteroposteriorly along
the ventral margin of the maxillary contact. This ange is present
in subadult and adult Pentaceratops and in most chasmosaurines
(e.g., Dalman et al., 2022). However, in NMMNH P-50000
this ange is more convex than it is in subadult (NMMNH
C-3175) and adult Pentaceratops sternbergi (AMNH FARB
1624); whereas in Sierraceratops turneri (NMMNH P-76870)
and Titanoceratops ouranos (OMNH 10165) the ange is
signicantly short. However, in S. turneri (NMMNH P-76870)
the ange is well developed, strongly convex, and pronounced
(Dalman et al., 2022).
The anterior jugal ange is present in most chasmosaurines;
however, it is absent in “Pentaceratops? fenestratus” and
weakly developed in Pentaceratops sternbergi (AMNH FARB
1624, NMMNH C-3175) (Figs. 22C, D, E). The ange is
especially strongly developed and pronounced in Sierraceratops
turneri (NMMNH P-76870), Terminocavus sealeyi (NMMNH
P-27468), and Titanoceratops ouranos (OMNH 10165) (Figs.
22F, H, I). Furthermore, the anterior jugal ange in NMMNH
P-50000 resembles to some extent the anterior ange of
the unnamed De-na-zin Member chasmosaurine (NMMNH
P-22858) and Utahceratops gettyi (UNMNH VP 16784) (Figs.
22B, J). In contrast, in Spiclypeus shipporum (CMN 57081) the
ange is present but is short and located close to the epijugal
contact suture (Fig. 22G).
The quadratojugal ange represents the posterior extension
of the quadratojugal facet, which is referred to by some workers
(e.g., Currie et al., 2016) as the infratemporal process of the
jugal, a feature that is present in mature chasmosaurines, but
FIGURE 22. Comparison of the jugals and position of the epijugal with respect to the long axis of the jugal of chasmosaurines,
A, Bisticeratops froeseorum gen. et sp. nov., (NMMNH P-50000); B, unnamed De-na-zin Member chasmosaurine (NMMNH
P-22858); C, Pentaceratops sternbergi (AMNH FARB 1624); D, Pentaceratops sternbergi (NMMNH C-3175); E, “Pentaceratops?
fenestratus” (PMU 24923); F, Sierraceratops turneri (NMMNH P-76870); G, Spiclypeus shipporum (CMN 57081); H,
Terminocavus sealeyi (NMMNH P-27468); I, Titanoceratops ouranos (OMNH 10165); J, Utahceratops gettyi (UMNH VP 16784).
See anatomical abbreviations section for abbreviations.
143
lacking in subadult P. sternbergi (NMMNH C-3175) (Fig.
22D). The quadratojugal ange extends into the intertemporal
fenestra and is shorter than the anterior ange. However, it does
not extend far enough posteriorly to contact the squamosal. In
contrast, in mature Chasmosaurus the quadratojugal ange/
infratemporal process is extensive and contacts the squamosal
(see Godfrey and Holmes, 1995, g. 2). In adult Pentaceratops
sternbergi (AMNH FARB 1624) (Fig. 22C) and Titanoceratops
ouranos (OMNH 10165) (Fig. 22I) the quadratojugal ange/
infratemporal process is proportionally smaller than that of
NMMNH P-50000 (Figs. 21, 22A).
The jugal forms the ventral and posteroventral margins of
the orbit, and the posterior margin forms the rostral half of the
intertemporal fenestra (=lower temporal fenestra of Currie et al.,
2016; Dalman et al., 2022). The quadratojugal and quadrate form
most of the posteroventral margin of the intertemporal fenestra.
The jugal is laterally deected and visible in dorsal view. The
lateral surface of the jugal is at, with slight convexity near the
contact with the epijugal, exhibiting long-grained bone texture
(e.g., Brown et al., 2009), which is most pronounced along
the long axis of the jugal and near the contact suture with the
epijugal. However, the grained bone texture is less pronounced
than in juvenile Chasmosaurus belli (UALVP 52613), which
further indicates that NMMNH P-50000 is from a relatively
mature animal.
Epijugal: The right epijugal is nearly complete, missing
only a small portion of the tip (Fig. 21, 22A). The epijugal is not
as extensive as in Sierraceratops turneri (NMMNH P-76870)
and Titanoceratops ouranos (OMNH 10165) (Fig. 22F–I). As in
most chasmosaurines, the epijugal has a pyramidal shape (e.g.,
Sampson et al., 2010; Longrich, 2011; Dalman et al., 2022).
The epijugal has a distinct low dorsal ridge, with a terminal end
that is oriented posteriorly and nearly parallels the posterior
margin of the jugal; the tip of the epijugal is oriented more
anteriorly in a similar way to “Pentaceratops? fenestratus,”
Spiclypeus shipporum, and Utahceratops gettyi (Fig. 22E, G,
J). In Sierraceratops turneri (NMMNH P-76870) the epijugal
is also oriented anteriorly; however, here the anterior position of
the epijugal is far greater than in NMMNH P-50000, including
“Pentaceratops? fenestratus,” S. shipporum, and U. gettyi (e.g.,
Dalman et al., 2022). The anterior and posterior faces of the
epijugal are inclined towards the dorsal ridge, and the ventral
face is at. The dorsal ridge is present in the epijugals in most
chasmosaurines, but is most extensive and well developed in
Anchiceratops ornatus (ROM 796) and T. ouranos (OMNH
10165) (e.g., Mallon et al., 2011; Longrich, 2011). In A. ornatus
the dorsal ridge of the epijugal is aligned with the long axis of
the jugal, but the tip slightly deviates posteriorly (see Mallon et
al., 2011, g. 2A). In T. ouranos (OMNH 10165) the terminal
end of the dorsal ridge of the epijugal is oriented towards the
anterior margin of the jugal. A position of the dorsal ridge similar
to that of T. ouranos (OMNH 10165) is present in the isolated
left jugal of Terminocavus sealeyi (NMMNH P-27468) (Fig.
22G) from the Hunter Wash Member of the Kirtland Formation
and in the unnamed chasmosaurine species (NMMNH P-22858)
from the De-na-zin Member (Fig. 22B). In contrast, in subadult
(NMMNH C-3175) and adult Pentaceratops sternbergi (AMNH
FARB 1624) the dorsal ridge of the epijugal is situated on the
FIGURE 23. Right quadrate of Bisticeratops froeseorum gen.
et sp. nov., (NMMNH P-50000) in A, lateral view; B, close
up of the distal end in lateral view; C, close up of the distal
end in anterior view. See anatomical abbreviations section for
abbreviations.
FIGURE 24. Comparisons of the squamosals of the San Juan Basin chasmosaurines in left lateral views, A, unnamed chasmosaurine
(NMMNH P-41228) from the De-na-zin Member; B, Pentaceratops sternbergi (AMNH FARB 1624); C, Pentaceratops sternbergi
(AMNH FARB 6325); D, “Pentaceratops? fenestratus” (PMU 24923); E, Terminocavus sealeyi (NMMNH P-27468). See anatomical
abbreviations section for abbreviations.
144
long axis of the jugal (Fig. 22C, D).
In NMMNH P-50000 the entire surface of the epijugal is
covered with numerous elongate and closely spaced grooves and
ridges. In general, in chasmosaurines the surface of the epijugals
is covered with grooves and low ridges and small low bump-like
structures.
Quadratojugal: The right quadratojugal is incomplete,
and not well preserved (Fig. 21). However, the portion that is
preserved is strongly co-ossied with the epijugal and jugal.
The orientation of the long axis of the quadratojugal follows
the position of the dorsal epijugal ridge. The lateroventral and
dorsal surfaces of the quadratojugal are smooth and convex. The
length of the quadratojugal is 18.5 cm, and the width is 4 cm.
The quadrate contact is rugose, covered with densely packed
grooves and bump-like structures in a similar way to other
chasmosaurines such as Chasmosaurus belli, Pentaceratops
sternbergi, Torosaurus latus, and Triceratops horridus. The
rugose surface is approximately 10.2 cm long and 5.2 cm wide.
The surface dorsal to the rugose quadrate contact is smooth
and divided by a low ridge, which, in turn, forms two distinct
surfaces, posterolateral and medial. The posterolateral surface
is narrow and enclosed by another low ridge that emerges from
FIGURE 25. Braincase region of Bisticeratops froeseorum gen. et sp. nov., (NMMNH P-50000) in A, posterolateral view; B-C,
occipital view; D, occipital view (note: the skull lies on the right side and the left side is facing up); E, ventral view. See anatomical
abbreviations section for abbreviations.
the lateral margin of the rugose quadrate contact. Both opposing
ridges give the narrower surface a low concavity for the
accommodation of the elongate quadrate process. The medial
surface of the quadratojugal is slightly concave.
In anterior and ventral view the quadratojugal is separated
from the epijugal by a deep rim, which served to anchor a
keratinous sheath in life. The rim does not extend posteriorly,
the contact between epijugal and quadratojugal is uninterrupted,
and the bone surface is smooth in this region.
Quadrate: The right quadrate is preserved, albeit
incomplete, while the left is not present (Fig. 23). Only its distal
end preserves important morphological characters, including the
lateral and medial distal condyles, and the rostral fossa. The distal
lateral portion of the quadrate is covered by the quadratojugal
sheaths and, more rostrally, the quadrate is overlapped by the
jugal. The quadratojugal-jugal suture is not co-ossied. The
height of the quadrate is 27 cm. The quadrate is anteroposteriorly
narrow, and lateromedially wide, resembling the quadrates of
other known chasmosaurines such as Bravoceratops polyphemus
(TMM 46015-1), Eotriceratops xerinsularis (TMP 2002.57.7),
Spiclypeus shipporum (CMN 57081), “Torosaurus? utahensis”
(USNM V-15583), and Utahceratops gettyi (UMNH VP-16784)
145
FIGURE 26. Braincase of Bisticeratops froeseorum gen. et sp.
nov., (NMMNH P-50000) in A, right lateral view showing inside
the orbit; B, interpretive line drawing; C, left lateral side; D,
interpretive line drawing. See anatomical abbreviations section
for abbreviations.
(e.g., Gilmore, 1946; Wu et al., 2007; Sampson et al., 2010;
Mallon et al., 2016). The distal lateral portion of the quadrate
is covered by the quadratojugal sheaths and, more rostrally, the
quadrate is overlapped by the jugal.
The lateral condyle is larger than the medial condyle. The
anterior surface of the quadrate is extensively deformed due to
lateromedial crushing of the bone. However, some morphological
features besides the lateral and medial condyles can be identied.
These features include the quadrate fossa, which separates the
lateral and medial condyles, and the quadratojugal facet for the
articulation with the quadratojugal. Nevertheless, the crushing
of the bone and poor preservation prevent identication of other
important morphological features.
Parietosquamosal Frill: The parietosquamosal frill is
incomplete, and only the right incomplete squamosal is preserved
(Fig. 3). In the reconstructed skull the parietosquamosal frill is
distinctly chasmosaurine in overall form (Fig. 25). Only three
episquamosals are preserved. The anteriormost episquamosal is
strongly elongate and resembles the anteriormost episquamosal
of Pentaceratops sternbergi (AMNH FARB 1624, 6325) (Fig.
24A, B). In contrast, in “Pentaceratops? fenestratus” (PMU
24923) and Terminocavus sealeyi (NMMNH P-27468) (Figs.
24D, E) the anteriormost episquamosal is signicantly smaller
compared to that in NMMNH P-50000 and P. sternbergi
(AMNH FARB 1624, 6325) (Figs. 24B, C). A small anteriormost
episquamosal is also present in the unnamed chasmosaurine
(NMMNH P-41228) from the De-na-zin Member (Fig. 24C).
Alternatively, in Titanoceratops ouranos (OMNH 10165) the
anteriormost episquamosal is lateromedially wide, low, and has
a blunt apex (e.g., Longrich, 2011, g. 4). This characteristic
morphology of the anteriormost episquamosal further separates
Titanoceratops from Pentaceratops to which it has been referred
before by others (e.g., Lehman, 1998; Sullivan and Lucas, 2011).
Furthermore, in NMMNH P-50000 the anteriormost
episquamosal encloses laterally a large otic notch (Fig. 3). The
otic notch is large in the squamosal of the unnamed chasmosaurine
(NMMNH P-41228) from the De-na-zin Member (Fig. 24A),
which closely resembles that of “Pentaceratops? fenestratus”
(PMU 24923) and Terminocavus sealeyi (NMMNH P-27468)
(Figs. 24D, E). However, in these taxa the otic notch is not
as large as in NMMNH P-50000. In contrast, in P. sternbergi
(AMNH FARB 1624, 6325) the otic notch is lateromedially
narrow and the posterior margin forms a narrow concavity (Figs.
24B, C).
In lateral view the squamosal of NMMNH P-50000 is
inclined posterodorsally at a 32° angle relative to its dorsal
portion.
Braincase: The braincase is well exposed in left occipital
view (Figs. 25–26). During the preparation and thorough cleaning
of the skull by the senior author (SGD), the right maxilla and
jugal were removed mechanically, providing the opportunity
to examine and document the right side of the braincase. The
oval occipital condyle has a stout, rectangular pedicel. The
condyle is divided dorsally by a short vertical groove, formed
by the basioccipital and two exoccipitals. The co-ossication of
occipital elements indicates a mature characteristic of the skull.
At the base of the pedicel, the basioccipital is pierced on each
side by a foramen for cranial nerve XII and, ventral to it, by a
foramen for cranial nerves X and XI. As in other ceratopsids, a
foramen for cranial nerve XI served as the exit for cranial nerve
IX; however, the study by Currie et al. (2008) indicates that the
nerves probably exited separately. A pronounced tubera projects
laterally near the base of the pedicel. The foramen magnum is
large, but narrow, forming a dorsoventrally-oriented elliptical
slit. A characteristic depression extends vertically between the
exoccipitals, exposing the supraoccipital, which forms the dorsal
margin of the foramen magnum. The supraoccipital is inset
slightly from the occipital surface forming a lateral tapering
extension between the exoccipital and parietal on the right side
of the skull.
The paroccipital process is fully exposed due to the missing
left squamosal.
As in other chasmosaurines, including juvenile (UALVP 40)
and adult (ROM 843) Chasmosaurus belli, the supraoccipital in
NMMNH P-50000 is excluded from the dorsal margin of the
foramen magnum on the occipital surface (e.g., Tyson, 1977).
The right basipterygoid process of the basisphenoid is articulated
with the pterygoid ventrally. The exoccipital and opisthotic have
co-ossied to form the paroccipital process.
A large portion of the left circumorbital and anterior
temporal regions of the skull were strongly weathered and
broken, exposing the left lateral aspect of the braincase. Although
the left side of the skull is strongly weathered and crushed,
some morphological features of the braincase can be discerned.
The anterolateral surface of the paroccipital process forms the
posteromedial wall of the adductor chamber (Figs. 25–26). Its
dorsal contact with the parietal is visible. The position of this
contact suggests that the parietal extended dorsally to form a
part of the external margin of the chamber in a way similar to
that of Pentaceratops and of other chasmosaurines. The prootic
and laterosphenoid are indistinguishably co-ossied.
PHYLOGENETIC ANALYSIS
To determine the placement of Bisticeratops froeseorum in
a phylogenetic context, the species was included in the dataset of
Dalman et al. (2022), which was, in turn, based on datasets from
Brown and Henderson (2015) and Longrich (2014) (Appendix
A). This analysis was run on 213 characters for 40 OTUs. The
analysis resulted in 485 trees with a Golobo t = 173.28701,
Consistency Index (CI) = 0.5565, and a Retention Index (RI) =
0.7722 (Fig. 27).
The phylogenetic analysis recovered a monophyletic
Centrosaurinae and Chasmosaurinae, with Turanoceratops
tardabilis and Zuniceratops christopheri as non-ceratopsid
neoceratopsians (Fig. 27). Regaliceratops peterhewsi is recovered
inside a monophyletic Triceratopsini, with Arrhinoceratops
146
FIGURE 27. Time-calibrated phylogeny of the inter-relationships of members of the Ceratopsidae, focusing on Bisticeratops
froeseorum gen. et sp. nov., (NMMNH P-50000). Strict consensus phylogenetic analysis resulted in 485 trees with a Golobo t =
173.28701, Consistency Index (CI) = 0.5565, and a Retention Index (RI) = 0.7722. Temporal positions for North American species
are taken from information provided by Fowler (2017) and Dalman et al. (2022a), with others from the original sources of the non-
American species. Red bars refer to species from southern Laramidia (i.e., Colorado, New Mexico, Texas, Utah, Coahuila) and
blue bars refer to species from northern Laramidia (i.e., Montana, North Dakota, South Dakota, Wyoming, Alberta, Saskatchewan).
Black bars refer to species outside North America or from multiple regions.
147
brachyops as sister to this clade. A largely southern clade
of chasmosaurines is recovered as well, including members
from New Mexico (Navajoceratops sullivani, Pentaceratops
sternbergi, Terminocavus sealeyi), Utah (Utahceratops
gettyi), and Colorado (Williams Fork chasmosaurine), with
the fragmentary chasmosaurine P. aquilonius from Alberta,
Canada also recovered in this clade. Other southern Laramidian
species (e.g., Agujaceratops mariscalensis, “A. mavericus,”
Bravoceratops polyphemus, Coahuilaceratops magnacuerna,
Ojoceratops fowleri, Sierraceratops turneri, Titanoceratops
ouranos, “Torosaurus? utahensis,”) are found throughout the
chasmosaurine tree (Fig. 27).
Bisticeratops froeseorum is recovered as sister to the
unnamed Almond Formation chasmosaurine (AMNH FARB
3652) and basal to Triceratopsini. Two other San Juan Basin
chasmosaurines (Ojoceratops fowleri, Titanoceratops ouranos)
are both recovered within the Triceratopsini, within the clade
((((((((Triceratops horridus + T. prorsus) + (O. fowleri) +
Torosaurus? utahensis) + T. latus) + Regaliceratops peterhewsi))
+ (Eotriceratops xerinsularis))) + (Titanoceratops ouranos)).
The most recent named chasmosaurine from New Mexican,
Sierraceratops turneri, was recovered with other southern
chasmosaurines from southern Laramidia outside Triceratopsini,
which potentially form a new southern clade. As mentioned
above, two other recently named New Mexican chasmosaurines
from the Kirtland Formation, Navajoceratops sullivani and
Terminocavus sealeyi, were recovered with Pentaceratops
sternbergi in a clade made up mostly of southern taxa as well
forming another new southern clade.
DISCUSSION
The phylogenetic analysis presented here strongly
supports the placement of Bisticeratops froeseorum in the
Chasmosaurinae. Bisticeratops is younger than Pentaceratops
sternbergi by 2 million years, than Navajoceratops sullivani
by ~1 million years, than Terminocavus sealeyi by ~750, 000
years, and older than Sierraceratops turneri by ~1 million
years. Bisticeratops froeseorum is missing the majority of the
diagnostic parietosquamosal frill. However, as described before,
Bisticeratops can be dierentiated from other chasmosaurines,
especially from its close relative the Almond Formation
chasmosaurine (AMNH FARB 3652) and its more distant
relative Pentaceratops, on the basis of several cranial characters
such as those of the snout, maxilla/jugal contact, postorbital
horncores, and the position of the orbits in the skull with respect
to the nasal.
Navajoceratops and Terminocavus are both diagnosed
based on characters of the parietals, although both include
portions of the squamosal as well (Fowler and Freedman
Fowler, 2020), Bisticeratops, on the other hand, lacks the
parietal, but preserves portion of the right squamosal. As
mentioned above the squamosal of Bisticeratops preserves at
least three episquamosals. The anteriormost episquamosal of
Bisticeratops is characteristically elongated and resembles that
of Pentaceratops and the unnamed chasmosaurine (NMMNH
P-41228) from the De-na-zin Member. The squamosal of
Terminocavus preserves several episquamosals including the
anteriormost, which is signicantly shorter than the anteriormost
episquamosal in Bisticeratops, given that both squamosals are
of approximately the same size.
Bisticeratops shares with “Pentaceratops? fenestratus,”
Sierraceratops turneri, Spiclypeus shipporum, and Utahceratops
gettyi the characteristic position of the epijugal with respect to
the jugal (Figs. 22A, E, F, G, J). In these species the apex of
the epijugal is oriented more anteriorly. In contrast, the apex of
the epijugal in the unnamed De-na-zin Member chasmosaurine
(NMMNH P-22858) and Terminocavus sealeyi is oriented
posteriorly (Figs. 22B, H, I).
Furthermore, Bisticeratops has an extremely short
posterior end of the jugal process of the maxilla, which does
not extend beyond the posterior margin of the maxilla. In other
chasmosaurines, especially in Pentaceratops, the process is well
developed, extending laterally and posteriorly and is separated
from the maxilla by a characteristic pocket-like fossa. In short,
none of these characters provide compelling evidence for
referring Bisticeratops to Pentaceratops or to any other known
chasmosaurine ceratopsid. Instead, the numerous morphological
features Bisticeratops exhibits, along with its stratigraphic and
paleogeographic positions, argue for the distinct taxonomic
nature of this ceratopsid.
One of the common morphological features that
Bisticeratops shares with other chasmosaurines which are more
closely related to Chasmosaurus is the position of the dorsal end
of the narial strut with respect to the nasal and the base of the nasal
horncore. In Bisticeratops and related chasmosaurines, including
Pentaceratops and the Almond Formation chasmosaurine
(AMNH FARB 3652), the dorsal end of the narial strut does not
participate in or contribute to the nasal and the base of the nasal
horncore. The narial strut in Bisticeratops and other closely
related species is separated from the nasal and the base of the
nasal horncore by the dorsal premaxillary process.
Biostratigraphy, Biogeography, Biodiversity
Bisticeratops froeseorum is part of a Kirtlandian-
Edmontonian chasmosaurine group that includes the
better known Pentaceratops sternbergi along with other
southern Laramidian chasmosaurines such as Agujaceratops
mariscalensis, Bravoceratops polyphemus, Coahuilaceratops
magnacuerna, Kosmoceratops richardsoni, Navajoceratops
sullivani, “Pentaceratops? fenestratus,” Sierraceratops
turneri, Terminocavus sealeyi, and Utahceratops gettyi.
These chasmosaurines are characterized by robust skulls
with large parietosquamosal frills, which are larger than the
parietosquamosal frills of the older Judithian chasmosaurines
(e.g., Chasmosaurus belli, Vagaceratops (“Chasmosaurus”)
irvinensis, C. russelli, Spiclypeus shipporum).
The recognition of Bisticeratops results in a substantial
increase in the stratigraphic and paleogeographic range of the
Chasmosaurinae in the Western Interior Basin. Until now, the best
fossil record of chasmosaurines came from northern localities in
Alberta and Montana (e.g., Longrich, 2010; Mallon et al., 2016;
Campbell et al., 2016; 2019). The presence of new chasmosaurine
species in the southern portion of the Western Interior Basin
suggests that, during the Campanian chasmosaurines had a
wide paleogeographic and stratigraphic range. Furthermore, all
major lineages of the Ceratopsidae evolved by the Campanian.
The radiation of the family appears to have taken place more
rapidly, or distinctly earlier, than previously thought, resulting
in high species diversity throughout the Western Interior Basin
(Longrich, 2011; Dalman et al., 2022).
Recent identication of two new southern species,
Navajoceratops sullivani and Terminocavus sealeyi, and their
potential linkage with Anchiceratops ornatus, suggests that
the Pentaceratops lineage extended to the northern parts of the
Western Interior Basin (Fowler and Freedman Fowler, 2020).
This new hypothesis is based on the shared characteristically-
shaped epiparietal (P1). However, our analysis shows that
Anchiceratops shares more morphological features in common
with more northern chasmosaurines such as Arrhinoceratops and
triceratopsins, among others, than it shares with Pentaceratops.
Therefore, the absence of Pentaceratops-like chasmosaurines
in the Campanian deposits in the northern part of the Western
Interior Basin suggests that the lineage was probably
geographically restricted to the southern portion of the Western
Interior Basin. A possible alternative to this is the presence of the
somewhat controversial chasmosaurine P. aquilonius in a clade
148
with other southern chasmosaurines, including P. sternbergi.
However, some (e.g., Mallon et al., 2016) consider P. aquilonius
a nomen dubium, which also suggests the generic placement of
the species is, at best, questionable.
The occurrence of Bisticeratops in the American Southwest
appears to provide further evidence for the existence of distinct
dinosaur faunas in the Late Cretaceous of the Western Interior
Basin. Therefore, it seems likely that the initial evolution of
chasmosaurines in the northwestern and southwestern parts of
the Western Interior Basin occurred in territorial isolation, and
that the family later continued into the Maastrichtian (Brown
and Henderson, 2015).
The identity of Bisticeratops froeseorum as a distinct
species suggests multiple evolutionary lineages of
chasmosaurines in New Mexico in the late Campanian. The
close relationships of Navajoceratops sullivani, Pentaceratops
sternbergi, and Terminocavus sealeyi potentially suggest an
evolutionary progression leading to the unnamed chasmosaurine
(NMMNH P-41228) from the De-na-zin Member. It is also
possible that B. froeseorum is the ancestor of the De-na-zin
Member chasmosaurine (NMMNH P-41228). Therefore, a
forthcoming phylogenetic analysis and study of (NMMNH
P-41228) may reveal its membership in the Chasmosaurinae.
Similar evolutionary progression is well documented in strata
of Judithian, Edmontonian, and Lancian ages in the Dinosaur
Park Formation in Alberta, Canada (e.g., Campbell et al., 2016,
2019; Fowler and Freedman Fowler, 2020) and in the Aguja
and Javelina formations in west Texas (e.g., Lehman, 1989;
Wick and Lehman, 2013; Lehman et al., 2017). Some of the
chasmosaurine species that lived, especially during Campanian
time, were contemporaneous (e.g., Chasmosaurus belli, C.
russelli, Pentaceratops sternbergi, and Utahceratops gettyi).
Wick and Lehman (2013) suggested that endemic
chasmosaurine groups may have emerged independently
and if true then some species are expected to exhibit unique
morphology and their evolutionary progression from less derived
to intermediate to derived forms would not be expected to
precede in a similar way in all paleogeographic areas throughout
the Western Interior Basin. However, contemporaneous
chasmosaurine species are dierentiated primarily on the
basis of their parietosquamosal frill morphologies (e.g.,
Mallon et al., 2016; Campbell et al., 2016, 2019). Contrary to
Wick and Lehman (2013), contemporaneous chasmosaurines
are not remarkably similar to each other as they show many
morphological dierences in their diagnostic cranial elements
such as the overall morphology of the snout, and the postorbital
horncores, in addition to the parietosquamosal frill.
Wick and Lehman (2013) suggested that diversity of
chasmosaurines throughout the Western Interior Basin is likely
the result of periodic exchange that occurred between regional
chasmosaurine populations, and not episodes of population
isolation (i.e., allopatric speciation), and/or northward or
southward radiation events. Furthermore, Wick and Lehman
(2013) suggested that the various chasmosaurine morphotypes
within each group may ultimately be shown to have constituted
regional metapopulations that periodically interbred and
hybridized through time. However, to test the hypothesis
proposed by Wick and Lehman (2013) the paleogeographically
and temporally separated chasmosaurine species need to be
studied in greater details.
Alternatively, the occurrence of dierent species
throughout the Western Interior Basin that are contemporaneous
and the absence of northern species in the southern regions
and vice versa can also be explained by “territoriality.” Two
factors that support this hypothesis include 1) the presence of
competition in other paleogeographic niches throughout the
Western Interior Basin, and 2) adaptation to an environment
(especially its various diseases), which may have prevented the
radiation of some species and lineages (Longrich, 2020 personal
communication). However, Lucas et al. (2016) oer a counter
to this idea, including highlighting dierences in the temporal
occurrences of many species used to support this hypothesis.
The presence of chasmosaurines from southern Laramidia in
several parts of the phylogenetic tree (Fig. 27) also suggests there
was a large amount of migration and movement between northern
and southern Laramidia in the Campanian and Maastrichtian
(Upper Cretaceous). As these southern chasmosaurines,
largely from New Mexico, Utah, and Colorado, do not form a
monophyletic group and are interspersed throughout the tree
with northern species, it is likely that chasmosaurine lineages
were traveling between these northern and southern regions
on a consistent basis. Rather than having distinct northern and
southern dinosaurian faunas that has been discussed by other
authors (e.g., Lehman, 1997, 2001; Sampson et al., 2010), it is
more likely that these correspond to distinct communities on
smaller regional or basin scales. Lucas et al. (2016) discussed
issues with the northern and southern faunal hypothesis and
in particular, discussed a lack of geographic barriers between
the regions, among other things, that would have made
dinosaurs migration more dicult if present. With distinct
species often present in close geographic proximity in the Late
Cretaceous of North America, we hypothesize that high levels
of endemism, particularly present in ceratopsids (especially in
chasmosaurines), may instead be due to adaptations, and high
levels of vicariance, diversication, and speciation within this
group. This would suggest that speciation rates are higher
and species longevity is shorter in dinosaurs, particularly in
chasmosaurine ceratopsids, than in other groups. In particular,
large-bodied dinosaurs have often been compared to larger
mammals for potential analogues. Prothero (2014) suggested a
species longevity (or species duration) of approximately 3.21
million years for large mammals during the Cenozoic. However,
dierences in physiology and genotype between these groups
may make species longevity in mammals a poor analogue
for dinosaurs, even at similar sizes. Fowler and Freedman
Fowler (2020, g. 10) showed temporally fast changes in the
morphology of the parietosquamosal frill in the Pentaceratops
lineage, which can then be inferred to show faster speciation
rates in these dinosaurs. Similar changes in parietosquamosal
frill morphology have been shown in the Chasmosaurus lineage
spanning the upper part of the Belly River Group (e.g., Fowler
and Freedman Fowler, 2020, g. 10). Additionally, as potential
vicariance in chasmosaurines and other dinosaurs would then
likely not be due to geographic barriers, it is more likely that the
diversication and speciation is probably due more to sympatry.
High degrees of genetic polymorphism could have led to faster
speciation rates within chasmosaurines and other dinosaurs.
Indeed, Grin and Nesbitt (2016) discussed high levels of
variation in the postnatal development of some dinosaurs,
although their study focused on theropods. These high degrees
of genetic polymorphism and faster speciation rates (or shorter
species longevity times), in turn, may lead to the high degrees
of endemism seen in chasmosaurines and other dinosaurs.
Therefore, based on the hypotheses of Fowler and Freedman
Fowler (2020, g. 10), the Pentaceratops lineage eventually
moved north through time resulting in Anchiceratops ornatus in
Alberta, while the Chasmosaurus lineage moved south through
time, resulting in Kosmoceratops richardsoni in Utah.
Furthermore, the herbivorous dinosaurs, including
the various chasmosaurine species such as Chasmosaurus,
Pentaceratops, Utahceratops, and especially Bisticeratops could
exploit a range of ecological niches in their respective localities
(e.g., Longrich, 2011). In eect this most likely increased
the food resources available to a population and allowed for
large animals to exist in small areas (Longrich, 2011). This is
furthermore shown by the diets of some herbivorous dinosaurs
149
during the Cretaceous being found to be more selective (e.g.,
nodosaurid ankylosaur Borealopelta, Brown et al., 2020).
The discovery of Bisticeratops also adds to our
understanding of dinosaur diversity. Assuming the phylogeny
presented here is correct would mean that the lineages leading
to Anchiceratops had already diverged during the Campanian
prior to 75 Ma. Many previous and recent phylogenetic analyses
recover Pentaceratops sternbergi + Utahceratops gettyi as sister
species. However, these chasmosaurines can be dierentiated
based on the overall morphology of the snout and, most
signicantly, on the morphology of the parietosquamosal frill
and the postorbital horncores. While we recover these species
in a single clade, they are part of a polytomy that includes
Navajoceratops and Terminocavus as well. Furthermore, while
Pentaceratops and Utahceratops appear to be contemporaneous,
morphologic dierences suggest multiple lineages co-occurring
in relatively close geographic proximity. At least one of these,
therefore, represents a Pentaceratops lineage in New Mexico
that potentially led to Navajoceratops, and Terminocavus.
Additionally, Bisticeratops adds to the high biodiversity of
chasmosaurines in the San Juan Basin during the Campanian–
Maastrichtian, with at least three lineages present. Another
non-triceratopsin lineage includes Bisticeratops potentially
leading to the more derived Sierraceratops lineage, which
may have extended into Maastrichtian. These taxa are close to
each other phylogenetically, although not sister taxa (Fig. 27).
In addition to this these two lineages are two chasmosaurines
recovered as triceratopsins, including the late Campanian
Titanoceratops (e.g., Lehman, 1998; Longrich, 2011) and the
Maastrichtian Ojoceratops (e.g., Sullivan and Lucas, 2010;
Jasinski et al., 2011). These lineages of chasmosaurines would
have at least co-existed in the Late Campanian (~75 Ma), but
the non-triceratopsin chasmosaurines may have at least become
extirpated from this region by the Maastrichtian. Although there
is currently no evidence of non-triceratopsin chasmosaurines
in the Maastrichtian of the San Juan Basin, the phylogenetic
analysis recovers Sierraceratops turneri as a non-triceratopsin,
potentially occurring close to or at the very end of the
Campanian, thus showing that this lineage lasted longer in the
southern Western Interior Basin (Dalman et al., 2022).
The vertebrate fauna of the Farmington Member of the
upper Kirtland Formation is relatively poorly understood.
Many of the specimens previously thought to come from the
Farmington Member are actually from high in the underlying
Hunter Wash Member (see Jasinski and Sullivan, 2011, 2016;
Sullivan and Lucas, 2014). In combination, the Fruitland–
Kirtland formations last around 2.5 million years (~76–73.5
Ma) (see Fowler, 2017), and the more fossiliferous portions of
these formations (Fossil Forest Member of Fruitland Formation
FIGURE 28. Life reconstruction of Bisticeratops froeseorum
gen. et sp. nov. (NMMNH P-50000). (artwork by Sergey
Krasovskiy).
through top of Kirtland Formation) occur for only 2 million
years (~75.5–73.5 Ma). Much of the vertebrate fauna making
up these formations have been studied and non-dinosaurs
include chondrichthyans, osteichthyans, anurans, caudates,
turtles, squamates, crocodylians, pterosaurs, and mammals (e.g.,
Armstrong-Ziegler, 1978, 1980; Flynn, 1986; Hunt and Lucas,
1993; Lucas et al., 2006; Jasinski et al., 2011, 2018; Sullivan
and Fowler, 2011; Sullivan et al., 2011d, 2013; Sullivan and
Jasinski, 2012; Sullivan and Lucas, 2015; Jasinski et al., 2018).
The strata also preserve a diverse dinosaur fauna, including
various theropods, such as caenagnathids, dromaeosaurids,
ornithomimids, oviraptorosaurs, troodontids, tyrannosaurids,
and avians, and herbivores, such as ankylosaurid and
nodosaurid ankylosaurians, chasmosaurine and centrosaurine
ceratopsids, lambeosaurine and saurolophine hadrosaurids,
pachycephalosaurids, and titanosauriform sauropods (e.g.,
Gilmore, 1916; Sullivan, 1999; Sullivan et al., 2000, 2011a,
2011c, 2011e; Lucas et al., 2009, 2016; Carr and Williamson,
2010; Sullivan and Lucas, 2010, 2014, 2015; Jasinski and
Sullivan, 2011; Jasinski et al., 2011, 2020; Koenig et al., 2012;
Sullivan and Jasinski, 2012; Arbour et al., 2014; Jasinski, 2015;
Robinson et al., 2015; Dalman and Lucas, 2018; Gates et al.,
2021). This suggests a thriving dinosaur and vertebrate fauna,
particularly one with high-turnover, leading to high biodiversity
at the end of the Cretaceous in northwestern New Mexico, part
of which included Bisticeratops froeseorum (Fig. 28).
Furthermore, the recognition of Bisticeratops froeseorum
adds to the growing record of chasmosaurine ceratopsids in the
southwest of the United States and provides new information
about the taxonomic diversity of these dinosaurs.
CONCLUSIONS
The recognition of Bisticeratops froeseorum as a new
species provides further evidence for high taxonomic and
morphological diversity within Chasmosaurinae during the
late Campanian in the Western Interior Basin. The holotype
specimen (NMMNH P-50000) was collected from the deposits
of the Kirtlandian (late Campanian) Farmington Member of the
Kirtland Formation (e.g., Hunt and Lucas, 1992; Sullivan and
Lucas, 2015).
The holotype skull (NMMNH P-50000) of Bisticeratops
froeseorum exhibits a combination of character states that
clearly dierentiate it from its close relative Pentaceratops
sternbergi and other chasmosaurines. Diagnostic characters
of B. froeseorum include the morphology of the snout, the
maxilla/jugal contact, and the postorbital horncores. The
parietosquamosal frill is largely incomplete; however, based
on what is preserved the frill of B. froeseorum was fenestrated
and similarly elongated as in Pentaceratops and in other closely
related Campanian chasmosaurine species.
The presence of chasmosaurines from northern and southern
Laramidia (Western Interior Basin) interspersed throughout the
phylogenetic tree argues against distinct northern and southern
dinosaur provinces in North America in the Late Cretaceous. As
chasmosaurines from southern Laramidia are sometimes part
of northern clades or subclades throughout the tree or sister to
some northern taxa, there would have been plenty of migration
and movement in these animals moving between the northern
and southern parts of Laramidia. The high levels of morphologic
variation among chasmosaurine taxa and the perceived high
levels of endemism are more likely due to high levels of genetic
polymorphism and sympatric speciation. The presence of
Bisticeratops froeseorum, another southern taxon, being closely
related to several northern taxa, such as the Almond Formation
chasmosaurine and Anchiceratops ornatus, further supports this
hypothesis, while adding to our knowledge of the biodiversity
of these iconic dinosaurs at the end of the Cretaceous in North
America and the complexity of ecosystems in New Mexico
150
during the Campanian.
ACKNOWLEDGMENTS
We thank Daniel Brinkman for access to specimens in the
collections of the Yale Peabody Museum of Natural History.
Many thanks go to Andy Farke and Nick Longrich for sharing
high quality pictures of various specimens and for the permission
to use them in this work. We thank the reviewers Andy Farke
and Nick Longrich for helpful comments, which improved this
research. Great thanks go to Sergey Krasovskiy for making a
beautiful reconstruction of Bisticeratops froeseorum and for
permission to use it in this work. The senior author (SGD) wishes
to thank the late Edgar Froese and his son Jerome Froese (living)
and the past and current members of Tangerine Dream for the
continuous inspiration, which their music provided through the
years and which inspired this work.
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153
APPENDIX 1
Note: For complete data matrix see Dalman et al. (2022a).
#NEXUS
[written Thu Jul 23 20:23:14 BST 2020 by Mesquite version
3.31 (build 859) at C02VG0GBHTDD/92.242.132.16]
BEGIN TAXA;
TITLE Taxa;
DIMENSIONS NTAX=40;
TAXLABELS
Protoceratops andrewsi, Leptoceratopsidae, Zuniceratops
christopheri, Turanoceratops tardabilis, Diabloceratops eatoni,
Albertaceratops nesmoi, Avaceratops lammersi, Centrosaurus
apertus, Mercuriceratops gemini, Judiceratops tigris,
Chasmosaurus CMN 2280, Chasmosaurus belli, Chasmosaurus
irvinensis, Agujaceratops mariscalensis, Agujaceratops
mavericus, Mojoceratops perifania, Pentaceratops aquilonius,
Williams Fork chasmosaurine, Pentaceratops sternbergi,
Utahceratops gettyi, Navajoceratops sullivani, Terminocavus
sealeyi, Spiclypeus shipporum, Kosmoceratops richardsoni,
Kosmoceratops CMN 8801, Bisticeratops froeseorum,
Almond Formation chasmosaurine, Anchiceratops ornatus,
Arrhinoceratops brachyops, Sierraceratops turneri, Bravoceratops
polyphemus, Coahuilaceratops magnacuerna, Titanoceratops
ouranos, Eotriceratops xerinsularis, Regaliceratops peterhewsi,
Torosaurus latus, Torosaurus utahensis, Triceratops horridus,
Triceratops prorsus, Ojoceratops fowleri.
Bisticeratops froeseorum
1010222021010?0121??10102?0111001?111?11?111021?2100
011??1142?1??1??????1??????0???0????????????????????????
?????????????????????????????????????????????????????????
???????????????????????????????????????????101??
