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Temporal range extension and evolution of the chasmosaurine ceratopsid ‘Vagaceratops’ irvinensis (Dinosauria: Ornithischia) in the Upper Cretaceous (Campanian) Dinosaur Park Formation of Alberta

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Abstract and Figures

The Dinosaur Park Formation (DPF) has a diverse assemblage of chasmosaurines currently represented by Chasmosaurus belli, C. russelli, Vagaceratops irvinensis, and Mercuriceratops gemini, and may also include remains possibly referable to Spiclypeus shipporum. Two skulls, YPM 2016 and AMNH 5402, previously referred to C. belli, both have a straight posterior parietal bar with five epiparietals present (YPM 2016) or inferred (AMNH 5402) on each side – the combination of which is unique to V. irvinensis. Based on our new morphological observations and interpretations of these two skulls, we recover V. irvinensis as a species of Chasmosaurus (C. irvinensis), although the interrelationships between C. irvinensis, C. belli, and C. russelli remain unclear. We refrain from formerly assigning YPM 2016 and AMNH 5402 to C. irvinensis, however, as their parietal fenestrae are significantly larger and their epiparietals are significantly shorter than those of C. irvinensis; instead, we reassign these two skulls to Chasmosaurus sp. Given the low stratigraphic position of YPM 2016 (unknown in AMNH 5402) relative to C. irvinensis, we believe this specimen to represent a basal member of the lineage leading to C. irvinensis. If our assessment is correct, this would indicate that the C. irvinensis lineage has a large degree of stratigraphic overlap with that of C. belli and C. russelli. The close phylogenetic relationship and supposed stratigraphic separation for these three taxa reported in previous studies were used to suggest that they may represent an anagenetic lineage, whereby C. russelli evolved into C. belli, and C. belli evolved into, and was entirely replaced by, the latter. However, the lack of stratigraphic separation between these three taxa indicates that they instead arose via cladogenesis.
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Vertebrate Anatomy Morphology Palaeontology 7:83–100
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INTRODUCTION
e Campanian Dinosaur Park Formation (DPF) of
southern Alberta and Saskatchewan is characterized by a
diverse assemblage of both chasmosaurines and centro-
saurines, the former of which includes Chasmosaurus belli
Temporal range extension and evolution of the
chasmosaurine ceratopsid ‘Vagaceratopsirvinensis
(Dinosauria: Ornithischia) in the Upper Cretaceous
(Campanian) Dinosaur Park Formation of Alberta
James A. Campbell1,2, Michael J. Ryan2, Claudia J. Schröder-Adams2,
Robert B. Holmes3, and David C. Evans4
1Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, Alberta, Canada,
T2N 1N4; email: james.campbell2@ucalgary.ca
2Department of Earth Sciences, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario, Canada, K1S 5B6;
email: michaelpjryan@gmail.com, claudia.schroderadams@carleton.ca
3Department of Biological Sciences, University of Alberta, CW 405 Biological Sciences Building, Edmonton,
Alberta, Canada, T6G 2E9; email: holmes1@ualberta.ca
4Department of Natural History, Royal Ontario Museum, 100 Queens Park, Toronto, Ontario, Canada, M5S 2C6;
email: d.evans@utoronto.ca
Published August 8, 2019
*corresponding author. © 2019 by the authors; submitted February 4, 2019; revisions received July 29, 2019; accepted July
30, 2019. Handling editor: Jordan Mallon. DOI 10.18435/vamp29356
Abstract: e Dinosaur Park Formation (DPF) has a diverse assemblage of chasmosaurines currently represented
by Chasmosaurus belli, C. russelli, Vagaceratops irvinensis, and Mercuriceratops gemini, and may also include re-
mains possibly referable to Spiclypeus shipporum. Two skulls, YPM 2016 and AMNH 5402, previously referred to
C. belli, both have a straight posterior parietal bar with ve epiparietals present (YPM 2016) or inferred (AMNH
5402) on each side – the combination of which is unique to V. irvinensis. Based on our new morphological obser-
vations and interpretations of these two skulls, we recover V. irvinensis as a species of Chasmosaurus (C. irvinen-
sis), although the interrelationships between C. irvinensis, C. belli, and C. russelli remain unclear. We refrain from
formally assigning YPM 2016 and AMNH 5402 to C. irvinensis, however, as their parietal fenestrae are signicantly
larger and their epiparietals are signicantly shorter than those of C. irvinensis; instead, we reassign these two skulls
to Chasmosaurus sp. Given the low stratigraphic position of YPM 2016 (unknown in AMNH 5402) relative to C.
irvinensis, we believe this specimen to represent a basal member of the lineage leading to C. irvinensis. If our assess-
ment is correct, this would indicate that the C. irvinensis lineage has a large degree of stratigraphic overlap with that
of C. belli and C. russelli. e close phylogenetic relationship and supposed stratigraphic separation for these three
taxa reported in previous studies were used to suggest that they may represent an anagenetic lineage, whereby C.
russelli evolved into C. belli, and C. belli evolved into, and was entirely replaced by, C. irvinensis. However, the lack
of stratigraphic separation between these three taxa indicates that they instead arose via cladogenesis.
(Lambe, 1902), C. russelli Sternberg, 1940, Vagaceratops
irvinensis (Holmes et al., 2001), and Mercuriceratops gemini
Ryan et al., 2014, and may also include material referable
to Spiclypeus shipporum Mallon et al., 2016.
Vagaceratops irvinensis was originally described by Holmes
et al. (2001) as Chasmosaurus irvinensis on the basis of a
Vertebrate Anatomy Morphology Palaeontology 7:83-100
84
relatively complete skull and associated skeleton (CMN
41357, holotype), and two referred partial skulls (TMP
1987.045.0001 and TMP 1998.102.0008) from Alberta
(Figs. 1, 2). Since their initial description, two additional
partial skulls (TMP 2009.034.0009, Longrich 2010; TMP
2011.053.0046, Campbell et al. 2018) have been assigned
to this taxon. Holmes et al. (2001) assigned this species to
Chasmosaurus (C. irvinensis), as their phylogenetic analysis
recovered it as the sister taxon to C. belli. Holmes et al.
(2001:1424), in distinguishing C. irvinensis from C. belli
and C. russelli, noted its possession of a “transversely broad
snout; nasal horn core short and transversely broad; brow
[= postorbital] horn [core] absent, its normal position occu-
pied by a low, raised, rugose boss, in one specimen bearing
a large, smooth surfaced, hemispherical resorption pit; jugal
notch on anterior squamosal broadly rounded and open
(not parallel-sided); squamosal tapers little posteriorly, sub-
rectangular in outline, and projects almost directly laterally
... [p]osterior parietal bar straight in anterior and dorsal
aspects, projects only slightly posterior to the squamosal;
maximum diameter of parietal fenestra less than length
of preorbital region of the skull ... [t]en epoccipitals [=
epiossications] on posterior parietal bar, lateral ... [epiossi-
cation] low and shield-shaped, the remaining eight nearly
indistinguishably coossied together, and composed of
attened posteroventral laminae that wrap around the back
of the bar, and larger laminae that curve strongly dorsally
and anteriorly over the bar.
Sampson et al. (2010) described Kosmoceratops richard-
soni (UMNH VP 17000, holotype) from the Campanian
Kaiparowits Formation of southern Utah as also having
ve pairs of epiossications on the posterior frill margin.
However, based on the location of the parietal-squam-
osal suture, they identied the three medialmost pairs as
epiparietals, the fourth pair as epiparietosquamosals, and
the fth pair as episquamosals for this taxon. As the pari-
etal-squamosal suture is dicult to discern in the holotype
of C. irvinensis, likely as a result of advanced age for this in-
dividual (Holmes 2014), Sampson et al. (2010) concluded
that it probably lies below the fourth epiossication, as in
Figure 1. Regional map of localities producing ‘Vagaceratopsirvinensis specimens (solid black stars; CMN 41357, TMP
1987.045.0001, TMP 1998.102.0008, and TMP 2011.053.0046) and ‘V. irvinensis-like Chasmosaurus sp. specimens (empty black
stars; AMNH 5402, TMP 2009.034.0009, and YPM 2016). AMNH 5402 was collected “in Township 21, Range 12, about 1 mile
below Steveville, on the left bank of the river” (Lull 1933:12); the general area this encompasses is shown in light grey.
Campbell et al. — Temporal range of ‘Vagaceratops
85
proof
K. richardsoni. Due to their reinterpretation of C. irvinensis,
they recovered it as the sister taxon to K. richardsoni in their
phylogenetic analysis, and, accordingly, placed C. irvinensis
into a new genus, Vagaceratops.
Longrich (2014) identied ten epiparietals on the
holotype of V. irvinensis (sensu Holmes et al. 2001) and
recovered this species as the sister taxon to C. belli in his
phylogenetic analysis. Although he referred to the former
species as C. irvinensis, he did not formally reassign this
species to Chasmosaurus.
Campbell et al. (2016) later identied ve pairs of epipari-
etals on a skull previously referred to C. belli (YPM 2016),
in which the parietal-squamosal suture is visible. ey also
interpreted the ve pairs of epiossications in V. irvinensis
as either representing ve pairs of epiparietals (i.e., CMN
41357), or four pairs of epiparietals and one pair of epipa-
rietosquamosals (i.e., TMP 1987.045.0001). In their speci-
men-based phylogenetic analysis, they recovered a weak-
ly-supported clade containing V. irvinensis (CMN 41357
and TMP 1987.045.0001), YPM 2016, and AMNH 5402
(another skull previously referred to C. belli), which had an
unresolved relationship with other Chasmosaurus speci-
mens (Fig. 3A). Although Chasmosaurus and Vagaceratops
specimens formed a single, larger clade, their unresolved
relationship made it dicult to say whether these genera
were synonymous or distinct. Campbell et al. (2016) tenta-
tively concluded that the frill of Vagaceratops is suciently
distinct from that of Chasmosaurus to merit its own genus.
ey also tentatively retained YPM 2016 and AMNH
5402 within C. belli, but noted that the similarities be-
tween YPM 2016, AMNH 5402, and V. irvinensis speci-
mens would be discussed in a future publication. ese two
specimens are the subject of the present study.
Geology and Biostratigraphy of the Dinosaur
Park Formation
e Belly River Group is a predominantly terrestrial
sedimentary sequence deposited along the western margin
of the Western Interior Seaway, and includes, in ascending
stratigraphic order, the Foremost, Oldman, and Dinosaur
Park formations (Eberth 2005). e contact between the
Oldman and Dinosaur Park formations is diachronous, due
to the wedge-shaped geometries of these two units. e
DPF is 70 m thick in Dinosaur Provincial Park (DPP), but
thins moving southwards, and is approximately 20 m thick
in Onefour, Alberta (Eberth and Hamblin 1993; Eberth
2005). As a result, the upper sediments of the Oldman
Formation in Onefour are time-equivalent to the lower
to middle DPF in DPP. Alluvial and paralic sediments of
the DPF document an overall transgression, transitioning
from sandy to muddy to coaly (Lethbridge Coal Zone;
LCZ) intervals, and overlain by fully-marine shales of the
Bearpaw Formation.
e DPF has also been subdivided into three distinct
faunal zones, with each one characterized by a unique
assemblage of centrosaurine and lambeosaurine taxa (Ryan
and Evans 2005; Ryan et al. 2012; Fig. 2). ese Dinosaur
Park faunal zones are, in ascending stratigraphic order:
Centrosaurus-Corythosaurus Zone (0–30 m above the
Oldman Formation in DPP), Styracosaurus-Lambeosaurus
lambei Zone (30–50 m above the Oldman Formation in
DPP), and Lambeosaurus magnicristatus-pachyrhinosaur
Zone (50–70 m above the Oldman Formation in DPP).
Chasmosaurus russelli, C. belli, and V. irvinensis were also
thought to be constrained to these three zones, respective-
ly (Ryan and Evans 2005; Ryan et al. 2012). However,
Campbell et al. (2016) recently demonstrated that skulls
previously referred to C. russelli span all three zones,
as the holotype was actually collected from the upper
(Lambeosaurus magnicristatus-pachyrhinosaur) zone.
ABBREVIATIONS
Anatomical Abbreviations: es, episquamosal; es lc,
episquamosal locus; ltf, lateral temporal fenestra; nhc, nasal
horncore; ns, nares; orb, orbit; p, epiparietal; p lc, epipari-
etal locus; pa, parietal; paf, parietal fenestra; p-es, epipari-
etosquamosal; pohc, postorbital horncore; pom, postorbital
mound; sq, squamosal.
Institutional Abbreviations: AMNH, American
Museum of Natural History, New York, NY, U.S.A.;
CMN, Canadian Museum of Nature, Ottawa, ON,
Canada; ROM, Royal Ontario Museum, Toronto, ON,
Canada; TMP, Royal Tyrrell Museum of Palaeontology,
Drumheller, AB, Canada; UMNH VP, Utah Museum of
Natural History Vertebrate Paleontology Collections, Salt
Lake City, UT, U.S.A.; YPM, Yale Peabody Museum, New
Haven, CT, U.S.A.
REDESCRIPTION OF YPM 2016 AND
AMNH 5402
YPM 2016 (Figs. 2, 4I, J, 5E, F) was collected by C.M.
Sternberg (Geological Survey of Canada) as eld speci-
men 2-1919 in 1919 (Campbell et al. 2016). Sternberg
(1919:3) noted that this specimen was collected “about 65
ft below Pierre Shale on the south side of the west branch
of Little Sand Hill Creek within about 3/4 of a mile from
where the badlands give way to grass-covered slopes.” Lull
(1933:12) provided a less detailed and miscopied account
of Sternberg’s notes, writing that YPM 2016 was collected
“on the south side of the west branch of Little Sandhill
Creek, 60 feet below the overlying Pierre shales.” Sometime
between 1935 and 1936, Sternberg revisited the site and
marked it with a stake, and this site is now known as
Vertebrate Anatomy Morphology Palaeontology 7:83-100
86
Campbell et al. — Temporal range of ‘Vagaceratops
87
proof
Quarry 110 (Sternberg 1936; Currie and Russell 2005).
e stratigraphic elevation of Quarry 110 was reported by
Godfrey and Holmes (1995) as being 31.4 m above the
base of the DPF, and amended by Campbell et al. (2016) as
being 26.5 m above the base of the DPF.
e stratigraphic elevation of YPM 2016, as reported by
Lull (1933), is inconsistent with Godfrey and Holmes
(1995) reported elevation of Quarry 110. Lull (1933)
reported the elevation of the specimen as being 65 feet
(approximately 18.3 m) below the Pierre Shale, which,
in southern Alberta, is actually the shales of the Bearpaw
Formation. is would place the specimen somewhere
between 50 and 60 m above the base of the DPF, which
is approximately 20 m higher than Godfrey and Holmes
(1995) reported elevation of Quarry 110.
However, Sternbergs (1919) more detailed locality
description is consistent with the location of Quarry 110
(Currie and Russell 2005). Quarry 110 is located west of
the core area of DPP, in a privately-owned area of bad-
lands. As one moves westwards from the core area of DPP,
the upper portion of the DPF becomes progressively less
exposed, such that neither the LCZ nor the overlying
Bearpaw Formation are exposed in the broad area of
badlands surrounding Quarry 110 (MJR, pers. obs.). is
suggests that Sternberg’s (1919) estimation of the elevation
of YPM 2016 below the Bearpaw Formation was based on
distantly exposed outcrops of that formation and is not
reliable. We therefore believe that Quarry 110 is indeed the
source of YPM 2016 (Currie and Russell 2005), and that
this quarry lies approximately 26.5 m above the base of the
DPF (Campbell et al. 2016).
AMNH 5402 (Figs. 4K, 5G, H) was collected by P.C.
Kaisen and B. Brown (AMNH) in 1913, “in Township 21,
Range 12, about 1 mile below Steveville, on the left bank of
the [Red Deer] river” (Lull 1933:12). e Red Deer River
ows southward in this latter area, and, to the perspective
of someone who is facing downstream, the east bank would
be to the left. Lull (1933:12) also stated that AMNH 5239
(holotype of Monoclonius exus, now a referred specimen of
Centrosaurus apertus) was collected by the AMNH in 1912
“about 1 mile below Steveville, [also] on the left bank of the
[Red Deer] river.” AMNH 5239 was collected by Barnum
Brown from Quarry 57 in Dinosaur Provincial Park (Currie
and Russell 2005), which is situated on the east side of the
Red Deer River. We therefore interpret that AMNH 5402
was collected on the east side of the Red Deer River. About
one mile downstream of Steveville, the east side encompasses
a laterally and stratigraphically extensive area of outcrop,
informally known as the ‘Steveville badlands’ (Fig. 1; Farke et
al. 2011). AMNH 5402 was most likely collected from the
DPF, as chasmosaurines have not yet been recorded from the
Oldman Formation within the DPP area (Ryan and Evans
2005). A chasmosaurine skull (Chasmosaurus sp.) is known
from sediments of the uppermost Oldman Formation in
the Onefour area of southeastern Alberta, although these
sediments are time-equivalent with the DPF as exposed in
DPP, and signicantly younger than the Oldman Formation
as exposed in DPP (Campbell et al. 2018).
YPM 2016 and AMNH 5402 were both previously re-
ferred to C. belli, based on their possession of a relatively
straight posterior parietal margin – a feature considered
to be diagnostic of this species within Chasmosaurus
(Lull 1933; Godfrey and Holmes 1995; Maidment and
Barrett 2011; Campbell et al. 2016). However, instead
of having three, evenly-spaced epiparietals on each
side of the posterior parietal bar, as per Chasmosaurus
(e.g., CMN 2280, CMN 8800, ROM 843, TMP
1983.021.0001, TMP 1999.055.0292), Campbell et
Opposite Page
Figure 2. Stratigraphic positions of ‘Vagaceratopsirvinensis (solid black stars), ‘V.irvinensis-like Chasmosaurus sp. (empty
black stars), C. belli (triangles), C. russelli (inverted triangles), and Chasmosaurus sp. (diamonds) specimens from the Dinosaur
Park Formation (DPF), and age-equivalent sediments (i.e., CMN 8802, denoted by asterix), of Alberta. Stratigraphic data from
Campbell et al. (2016, 2018), except for CMN 41357, TMP 1998.102.0008, and TMP 2009.034.0009 (see below). Specimens
above the regional disconformity (0 m) separating the Dinosaur Park and Oldman formations (error bars ±5 m). Specimens
from the Onefour/Manyberries area (i.e., CMN 8800, CMN 8802, TMP 1998.102.0008, and TMP 2011.053.0046) are placed
in section using their estimated elevation below the Lethbridge Coal Zone (LCZ), which is thought to be an approximate
chronostratigraphic datum across southern Alberta (Eberth 1996). CMN 8802 was collected below the LCZ, from the
uppermost Oldman Formation near Onefour, which is time-equivalent to the upper half of the DPF as exposed in Dinosaur
Provincial Park (Campbell et al. 2018). CMN 41357 was likely collected from a horizon between 0 and 10 m below the base
of the LCZ (MJR, pers. obs.), but the precise horizon is unknown. TMP 1998.102.0008 was collected near Onefour from the
basal lag bonebed in Complex Mud-Filled Incised Valley No. 1, which lies approximately 3 m above the base of the LCZ (Eberth
1996: g. 12); however, due to the depth of the incision cut (approximately 16 m), this specimen may be much younger.
TMP 2009.034.0009 was collected from a horizon approximately 33.5 ±5 m above the Oldman Formation (D. Eberth, pers.
comm.). Parietosquamosal frills of select ‘V.’ irvinensis and ‘V.irvinensis-like Chasmosaurus sp. skulls are shown in dorsal view
on right, in ascending stratigraphic order; dashed line in CMN 41357 marks estimated sutural boundary between parietal and
squamosal; plaster reconstruction in CMN 41357 and YPM 2016 = white.
Vertebrate Anatomy Morphology Palaeontology 7:83-100
88
al. (2016) identied ve on the right side of YPM 2016
(Fig. 4I, J) as per the holotype of V. irvinensis (CMN
41357, Fig. 4A, B). Dierences from the Vagaceratops
condition include: the four medialmost epiparietals of
YPM 2016 are short and do not overhang the posterior
parietal bar; they are not coalesced at their bases; and,
the parietal fenestra length-to-width ratio of YPM 2016
(1.03; Fig. 2) is larger than that of CMN 41357 (0.72;
Fig. 2), but not as large as those of other Chasmosaurus
skulls (ROM 843 = 1.09 to AMNH 5656 = 1.89;
Campbell et al. 2016); the ratio for AMNH 5402 is
1.04 (Campbell et al. 2016: g. 21).
Campbell et al. (2016) identied three epiparietals on
the better-preserved left side of AMNH 5402 (Fig. 4K, L).
However, they noted that their arrangement is unusual,
with the rst and second medialmost epiparietal being
separated by a relatively wide gap. ey also identied
Figure 3. Specimen-based phylogenetic analyses of Chasmosaurus and ‘Vagaceratops’ specimens. A) Strict consensus tree
of Campbell et al. (2016: g. 5D, modied), excluding Bravoceratops, Eotriceratops, Judiceratops, and specimens missing
the diagnostic posterior parietal region (AMNH 5401, CMN 1254, ROM 839, TMP 1981.019.0175, and UALVP 40); 5410 most
parsimonious trees (MPTs), tree length (TL) = 276 steps, consistency index (CI) = 0.64, retention index (RI) = 0.76). B) Strict
consensus tree with same taxa and specimens excluded, except for Judiceratops, and with revised recodings for AMNH 5402
(see text); 1530 MPTs, TL = 291 steps, CI = 0.63, RI = 0.76). Bootstrap replicate frequency and Bremer support (bold) values
are shown below each node; only Bootstrap values of 50% or higher are given. ‘Vagaceratopsirvinensis (solid black stars), ‘V.’
irvinensis-like Chasmosaurus sp. (empty black stars), C. belli (triangles), and C. russelli (inverted triangles) specimens.
Opposite Page
Figure 4. Posterolateral corner of parietosquamosal frills
of Chasmosaurus irvinensis (solid black stars) and C. irvinen-
sis-like Chasmosaurus sp. (empty black stars) in dorsal view.
(A–B) CMN 41357 (C. irvinensis holotype, cast; left side); (C–D)
TMP 1987.045.0001 (left side); (E–F) TMP 1998.102.0008
(left side); (G–H) TMP 2009.034.0009 (right side, reected);
(I–J) YPM 2016 (right side, reected); (K–L) AMNH 5402 (left
side). Brackets delimit size of epiossications; arrows denote
inferred epiparietal attachment loci (low-relief undulations);
dashed lines inferred reconstructed bone; dashed line in (B)
marks estimated sutural boundary between parietal and
squamosal; plaster reconstruction = white.
Campbell et al. — Temporal range of ‘Vagaceratops
89
proof
Vertebrate Anatomy Morphology Palaeontology 7:83-100
90
two low-relief parietal undulations along this gap, and in
the equivalent region of the right side of the frill, but did
not provide an explanation to account for their presence.
e spacing between epiossications in a ceratopsid frill is
relatively uniform, suggesting that the wide gap in AMNH
5402 was once occupied by epiparietals, but were un-
fused and fell o post-mortem. ese undulations are also
similar to the partly exposed epiparietal attachment locus
underlying the left medialmost epiparietal (epiparietal 1).
We therefore interpret the parietal undulations of AMNH
Figure 5. Skulls of Chasmosaurus irvinensis (solid black stars) and C. irvinensis-like Chasmosaurus sp. (empty black stars) in lat-
eral view. (A–B) CMN 41357 (C. irvinensis holotype, cast; right side, ipped); (C–D) TMP 1987.045.0001 (left side); (E–F) YPM
2016 (left side); (G–H) AMNH 5402 (left side). Note that postorbital horncores are present on AMNH 5402, whereas rugose,
postorbital mounds are present in all other skulls. Plaster reconstruction = white.
Campbell et al. — Temporal range of ‘Vagaceratops
91
proof
5402 as attachment loci for two additional, similarly-sized
epiparietals, for a total of ve epiparietals on each side. e
preserved epiparietals in AMNH 5402 (Fig. 4K, L) occupy
homologous positions as epiparietals 1, 4, and 5 in CMN
41357 (Fig. 4A, B) and YPM 2016 (Fig. 4I, J), and are
identied as such in this study.
PHYLOGENETIC ANALYSIS
A phylogenetic analysis was performed using the matrix of
Campbell et al. (2016). is matrix consists of 155 char-
acters and 40 operative taxonomic units (OTUs), the latter
of which includes 23 ceratopsian taxa, and 17 specimens
previously referred to Chasmosaurus and Vagaceratops. e
phylogenetic analysis of Campbell et al. (2016) was re-run
using the same settings as follows, and the above revised
codings for AMNH 5402 (see Appendix 1) were included.
e analysis was performed using the tree bisection recon-
nection search algorithm, starting with Wagner trees, with a
random seed of one, with 10 trees saved per replication (n =
1000), and with Leptoceratops assigned as the outgroup. All
characters were treated as unordered. e analysis (strict con-
sensus tree) and corresponding tree statistics (Bootstrap and
Bremer support) were conducted in TNT 1.1 (Golobo et
al. 2003, 2008). Bootstrap values were calculated using 1000
replicates. Consistency (CI) and retention (RI) indices were
obtained in PAUP 4b10 (Swoord 2002) using the matrix
assembled in Mesquite v.2.75 (Maddison and Maddison
2011). e matrix is provided in Appendix 2.
e analysis produced a strict consensus tree with a
mostly well-resolved Chasmosaurinae clade. Specimens
of Chasmosaurus and Vagaceratops form a monophyletic
clade, with the clade (YPM 2016 + (CMN 41357 + TMP
1987.045.0001)) forming a polytomy with all other speci-
mens except for AMNH 5401 (Chasmosaurus sp.), which
forms an outgroup. Resolution within the Chasmosaurinae
clade was slightly improved with the subsequent exclusion
of the fragmentary taxa Bravoceratops and Eotriceratops
(sensu Campbell et al. 2016). e further exclusion of the
fragmentary Judiceratops had no eect on the resolution
of the Chasmosaurinae clade and was retained in later tree
iterations. In an attempt to improve the resolution within
the (Chasmosaurus + Vagaceratops) clade, the specimens
missing their diagnostic posterior parietal regions (AMNH
5401, CMN 1254, ROM 839, TMP 1981.019.0175, and
UALVP 40) were excluded (sensu Campbell et al. 2016).
is greatly improved the resolution within the clade of
this tree (Fig. 3B; 1530 most parsimonious trees, tree
length = 291 steps, CI = 0.63, RI = 0.76), yielding the cla-
de (CMN 8800 + (AMNH 5402 + (YPM 2016 + (CMN
41357 + TMP 1987.045.0001)))), an unresolved sister
clade including specimens previously referred to C. belli
(CMN 0491, CMN 2245, NHMUK R4948, and ROM
843); the remaining specimens are specimens previously re-
ferred to C. russelli (AMNH 5656, CMN 2280, and TMP
1983.025.0001), which form a polytomic relationship.
e (Chasmosaurus + Vagaceratops) clade and clades
therein are weakly supported, with Bootstrap values all
below 50%, and Bremer values range from 0 to 2 (Fig.
3B). e best supported clades are the (Chasmosaurus +
Vagaceratops), (CMN 41357 + TMP 1987.045.0001), and
(AMNH 5402 + (YPM 2016 + (CMN 41357 + TMP
1987.045.0001))) clades, with Bremer values of 2; the
latter two clades are better supported than in the analysis of
Campbell et al. (2016; Fig. 3A), which recovered Bootstrap
values of 1. e most weakly supported clade is the one
containing specimens previously referred to C. belli, with a
Bremer value of 0.
DISCUSSION
Campbell et al. (2016) did not refer YPM 2016 or
AMNH 5402 to Vagaceratops irvinensis, but instead ten-
tatively attributed the source of their unusual features to
individual variation within C. belli. ese specimens either
have (YPM 2016) or are inferred to have had (AMNH
5402) ve epiossications on the posterior parietal margin,
as well as a straight posterior parietal margin. is com-
bination of characters is unique to V. irvinensis, suggesting
that these two specimens are closely related, if not referable
to, this species. However, YPM 2016 and AMNH 5402
are also similar to C. belli and C. russelli skulls, in that
they possess postorbital horncores, their epiparietals are
relatively short and not coossied with each other at their
bases, and their parietal fenestrae are relatively long. e
intermediate morphologies of YPM 2016 and AMNH
5402 makes their species-level assignment problematic.
While it could be argued alternatively that YPM 2016 and
AMNH 5402 belong to a new species, we believe that they
most likely represent stratigraphically-basal members of
the V. irvinensis clade (see below). Given their intermediate
morphology, however, we tentatively assign YPM 2016 and
AMNH 5402 to Chasmosaurus sp. TMP 2009.034.0009 is
a poorly preserved and fragmented specimen, although the
preserved epiparietals (interpreted herein as epiparietals 1,
2, and 3; Fig. 4G, H) are relatively short, similar to those of
YPM 2016. Given the similarity of these latter two skulls,
we also reassign TMP 2009.034.0009 to Chasmosaurus sp.
One study (Sampson et al. 2010) has suggested that V.
irvinensis is actually more closely related to Kosmoceratops,
and as such, should be moved to the new genus,
Vagaceratops. Subsequent studies have also recovered
Kosmoceratops and Vagaceratops as sister taxa (Mallon et
al. 2011; Wick and Lehman 2013; Mallon et al. 2014;
Vertebrate Anatomy Morphology Palaeontology 7:83-100
92
Campbell 2015; and Brown and Henderson 2015), but the
character-taxon matrices used in these studies are modied
from that of Sampson et al. (2010) and retain the original
coding of three epiparietals per side (Character 93, state 1
of Sampson et al. 2010) for both of these genera. Mallon
et al. (2016) modied the Brown and Henderson (2015)
matrix, and recoded Vagaceratops as having ve epiparietals
per side (sensu Campbell et al. 2016; Character 93, state
1 of Campbell et al. 2016), and C. belli as having both
three and ve per side (sensu Campbell et al. 2016; states
0 and 1, respectively); the polymorphic state for C. belli
was done to account for the condition in YPM 2016 (sensu
Campbell et al. 2016). Mallon et al. (2016) also recoded
Vagaceratops as lacking a concave median embayment on
the posterior parietal margin (sensu Campbell et al. 2016;
Character 66, state 1 of Sampson et al. 2010), unlike the
embayed condition of Kosmoceratops, and recoded C. belli
as having both an embayed and non-embayed condition
(sensu Campbell et al. 2016; states 0 and 1); the poly-
morphic state for C. belli was done to account for the con-
dition in YPM 2016 and AMNH 5402 (sensu Campbell
et al. 2016). Despite these recodings, the phylogenetic
analysis of Mallon et al. (2016) still retained a sister-taxon
relationship between Kosmoceratops and Vagaceratops.
In contrast, the specimen-based phylogenetic analyses
of Campbell et al. (2016) and the present study recover
Chasmosaurus and V. irvinensis as forming a monophy-
letic clade (Fig. 3). Our revised character codings for
AMNH 5402 improved the resolution within this clade,
resulting in V. irvinensis specimens (CMN 41357 and
TMP 1987.045.0001) forming a clade that is well-nested
among Chasmosaurus specimens (Fig. 3B). e topology of
our (Chasmosaurus + Vagaceratops) clade resembles that of
Holmes et al. (2001: g. 12), in which they recovered a (C.
russelli + (C. belli + C. irvinensis)) clade. However, in our
analysis, the placement of C. russelli specimens has a more
scattered distribution, with the holotype (CMN 8800) as
an outgroup to V. irvinensis specimens, YPM 2016, and
AMNH 5402, and other C. russelli specimens as forming
an unresolved polytomy at the base of the (Chasmosaurus +
Vagaceratops) clade. e well-nested position of V. irvin-
ensis within Chasmosaurus in our study (Fig. 3B) suggests
that Vagaceratops should be subsumed into Chasmosaurus,
although this well-nested position is only weakly sup-
ported, with a Bremer value of 1 for the clade containing
all Chasmosaurus and Vagaceratops specimens except for
AMNH 5656, CMN 2280, and TMP 1983.025.0001
(Fig. 3B). As such, we tentatively reassign V. irvinensis to
Chasmosaurus (sensu Holmes et al. 2001). Future phylo-
genetic analyses including more specimens are needed to
corroborate or refute this hypothesis.
Temporal range extension of Chasmosaurus
irvinensis
YPM 2016 was collected approximately 26.5 ±5 m above
the top of the Oldman Formation (Campbell et al. 2016),
corresponding to the upper part of the Centrosaurus-
Corythosaurus Zone (Fig. 2; Ryan and Evans 2005). is
horizon is approximately 25.5 m below the previously
known stratigraphic range of C. irvinensis – a narrow interval
between 52 ±5 m (TMP 2011.053.0046) and ≥58 ±5 m
(TMP 1998.102.0008) above the Oldman Formation,
in the Lambeosaurus magnicristatus-pachyrhinosaur Zone
(Campbell et al. 2016, 2018). e precise stratigraph-
ic position of the C. irvinensis holotype (CMN 41357)
is unknown, but it was collected below the LCZ, from a
horizon likely between 0 and 10 m below the base of the
LCZ (i.e., between 45 and 55 m above the base of the
DPF, as exposed in DPP; Holmes et al. 2001; MJR, pers.
obs.). TMP 1998.102.0008 was collected near Onefour
from the basal lag bonebed in Complex Mud-Filled Incised
Valley No. 1, which lies approximately 3 m above the base
of the LCZ (Eberth 1996: g. 12; Fig. 2); however, due to
the depth of the incision cut (approximately 16 m), this
specimen may be much younger. TMP 2009.034.0009 was
collected from a horizon approximately 33.5 ±5 m above the
Oldman Formation, in the lower part of the Styracosaurus-
Lambeosaurus lambei Zone (Fig. 2; D. Eberth, pers. comm.).
e low stratigraphic positions of YPM 2016 and TMP
2009.034.0009 could account for the morphological
dierences between these skulls and those of C. irvinensis.
If the morphologies exhibited by YPM 2016 and TMP
2009.034.0009 are precursors to the condition seen in
C. irvinensis, as we suggest, this would indicate that the
acquisition of ve posterior epiossications (either ve
epiparietals, or four epiparietals and one epiparietosquam-
osal) occurred prior to the last occurrence of C. belli (CMN
2245) or C. russelli (CMN 8800) (Fig. 2). is indicates
that the lineage leading to C. irvinensis has a large degree
of stratigraphic overlap with that of C. belli and C. russelli
(Fig. 2). Morphological dierences between YPM 2016,
TMP 2009.034.0009, and C. irvinensis specimens may be
due to evolutionary changes including a reduction in the
parietal fenestra length-to-width ratio, a lengthening of the
epiparietals, and a coalescence of the epiparietals at their
bases (Fig. 2). ese inferred evolutionary changes are dif-
cult to test, however, given the lack of specimens between
these two stratigraphic intervals.
e lack of stratigraphic separation between the lineage
leading to C. irvinensis and other species of Chasmosaurus
contradicts previous reports that these taxa formed a faunal
succession, corresponding to the upper (Lambeosaurus
magnicristatus-pachyrhinosaur Zone ), and lower to
middle (Centrosaurus-Corythosaurus and Styracosaurus-
Campbell et al. — Temporal range of ‘Vagaceratops
93
proof
Lambeosaurus lambei zones) units of the DPF, respectively
(Holmes et al. 2001; Ryan and Evans 2005). e strati-
graphic ranges of these two taxa cannot be explained by an
anagenetic model, whereby C. belli or C. russelli evolved
into, and was entirely replaced by, C. irvinensis over time.
e alternative evolutionary model of cladogenesis must
therefore be accepted. is also indicates that the presence
of Chasmosaurus skulls exhibiting ve posterior epiossi-
cations per side (i.e., C. irvinensis and C. irvinensis-like
skulls) should no longer be used as a unique component
of the faunal assemblage of the Lambeosaurus magnic-
ristatus-pachyrhinosaur Zone. ere may also be strati-
graphic overlap between Chasmosaurus and Mercuriceratops
(Ryan et al. 2014) in the lower DPF and age-equivalent
sediments of the Judith River Formation. e close strati-
graphic clustering of the centrosaurines Albertaceratops
(Ryan 2007), Medusaceratops (Ryan et al. 2010; Chiba et
al. 2018), and Wendiceratops (Evans and Ryan 2015) in the
lower Oldman Formation and age-equivalent sediments
of the Judith River Formation suggests that these taxa also
lived contemporaneously.
e presence of postorbital horncores in
Chasmosaurus irvinensis
Holmes et al. (2001) noted that the postorbital dorsal
surface in their referred specimens of C. irvinensis (CMN
41357, TMP 1987.045.0001) were characterized by a
rugose, pitted mound, instead of a horncore (Fig. 5A–D).
ey interpreted this as evidence that C. irvinensis never
possessed postorbital horncores and incorporated this char-
acter into their diagnosis of this taxon. However, they did
acknowledge that the pitted surface may instead represent
the base of a resorbed horncore.
YPM 2016 also has rugose postorbital mounds (Fig. 5E, F),
while the osteologically less mature skull AMNH 5402 has
short (approximately 70 mm; Godfrey and Holmes 1995)
postorbital horncores with pointed, unmodied apices (Fig.
5G, H). If these two skulls represent basal members of the
lineage leading to C. irvinensis, this may suggest that the
postorbital mounds in this taxon are a result of ontogenetic
remodelling, as has also been suggested for C. belli and C.
russelli (Campbell et al. 2016). Alternatively, this may be
indicative of the evolutionary loss of postorbital horncores
in C. irvinensis. e nasal horncore of AMNH 5402 also has
an unmodied, pointed apex (Fig. 5G, H), unlike those of
other C. irvinensis specimens, which have rounded apices,
and likely also underwent remodelling (Fig. 5A–F).
SYSTEMATIC PALAEONTOLOGY
Suborder CERATOPSIA Marsh, 1890
Clade NEOCERATOPSIA Sereno, 1986
Family CERATOPSIDAE Marsh, 1888
Subfamily CHASMOSAURINAE Lambe, 1902
Genus Chasmosaurus Lambe, 1914b
Generic diagnosis (emended from Campbell et al. 2016):
Chasmosaurus is diagnosed based on the following unique
combination of characters: (1) premaxillary ange along
entire anterior margin of external naris; (2) postorbital horn-
cores, when present, curve posteriorly along their length;
(3) squamosal dorsal border laterally adjacent to dorsal
temporal fenestra straight in prole, anteriorly at level with
base of postorbital horncore, and sloping posteroventrally at
a shallow angle before ascending farther posteriorly to form
lateral border of parietal fenestra; (4) medial margin of squa-
mosal, where it articulates with the lateral bar of the parietal,
straight; (5) frill broadens posteriorly to form rectangular to
triangular-shaped shield with maximum width more than
twice the skull width at orbits; and (6) parietal fenestrae
large, occupying most of the parietal.
Type species: Chasmosaurus belli (Lambe, 1914b).
Specic diagnosis (emended from Campbell et al.
2016): Medial margin of posterior parietal bar nearly
straight or shallowly embayed with the left and right halves
meeting at an angle of not less than 136°.
Distribution (emended from Campbell et al. 2016):
Middle beds of the Dinosaur Park Formation [DPF;
Styracosaurus-Lambeosaurus lambei Zone of Ryan and Evans
(2005)] of Alberta [Dinosaur Provincial Park (DPP)], Canada.
Synonymies: Monoclonius belli (Lambe, 1902); Ceratops
belli (Hatcher et al., 1907); Protorosaurus belli (Lambe, 1914a).
Type specimen: CMN 0491, a partial parietal. Although
fragmentary, the holotype is diagnostic based on the
combination of generic character 6 and specic character 1
(shallow posterior embayment), a combination not ob-
served in any other chasmosaurine.
Assigned specimens: CMN 2245, NHMUK R4948,
and ROM 843.
Chasmosaurus russelli (Sternberg, 1940)
Specic diagnosis (from Campbell et al. 2016): Medial
margin of posterior parietal bar moderately to deeply em-
bayed, with the two halves of the bar forming an angle of
between 89° and 128° at the midline.
Distribution: Lower to upper beds of the DPF
[Centrosaurus-Corythosaurus, Styracosaurus-Lambeosaurus
lambei, and Lambeosaurus magnicristatus-pachyrhinosaur
zones of Ryan and Evans (2005)] of Alberta (DPP, Hilda,
Manyberries, Onefour) and Saskatchewan (Saskatchewan
Landing Provincial Park), Canada.
Synonymies: Mojoceratops perifania Longrich, 2010.
Type specimen: CMN 8800, a mostly complete skull
Vertebrate Anatomy Morphology Palaeontology 7:83-100
94
lacking the lower jaws and part of the rostral, part of the ju-
gals from both sides, part of the right quadrate, squamosal,
and parietal.
Assigned specimens: AMNH 5656, CMN 2280,
CMN 8803, CMN 41933, TMP 1983.025.0001, TMP
1997.132.0002, and TMP 1999.055.0292.
Chasmosaurus irvinensis Holmes et al., 2001
Specic diagnosis (emended from Holmes et al. 2001):
Chasmosaurus irvinensis is diagnosed based on the following
combination of characters: (1) transversely broad snout; (2)
nasal horncore short and transversely broad; (3) jugal notch
on anterior squamosal broadly rounded and open (not par-
allel-sided); (4) squamosal tapers little posteriorly, subrect-
angular in outline, and projects almost directly laterally; (5)
posterior parietal margin straight in dorsal view, bearing no
median emargination; (6) each side of the posterior parietal
margin bears either ve epiparietals or four epiparietals and
one epiparietosquamosal; (7) epiparietals 1–4 triangular
and oriented anterodorsally, and epiparietal 5 or epipari-
etosquamosal triangular, straight and oriented posterolat-
erally in the plane of the frill; and (8) dorsal margin of the
posterior parietal bar underlying epiparietals 1–4 curved
anterodorsally, forming a dorsoventrally-thickened ‘ridge’.
e ridge on each side of the posterior parietal bar are
connected medially.
Distribution: Uppermost beds of the DPF [Lambeosaurus
magnicristatus-pachyrhinosaur Zone of Ryan and Evans
(2005)] of Alberta [DPP, Hilda (South Saskatchewan River),
Irvine, Manyberries, Onefour], Canada.
Type specimen: CMN 41357, a mostly complete skull
and skeleton.
Assigned specimens: TMP 1987.045.0001, TMP
1998.102.0008, and TMP 2011.053.0046.
Chasmosaurus sp.
e following specimens are referable to Chasmosaurus,
but cannot be assigned to species as they do not preserve
the diagnostic medial margin of the posterior parietal bar:
AMNH 5401 (holotype: Chasmosaurus kaiseni Brown, 1933),
CMN 1254 (holotype: Monoclonius canadensis Lambe, 1902;
Ceratops canadensis (Hatcher et al. 1907); Eoceratops canadensis
(Lambe 1915); Chasmosaurus canadensis (Lehman 1990)),
CMN 8801, CMN 8802, CMN 34829, CMN 34832, ROM
839 (holotype: Chasmosaurus brevirostris Lull, 1933), TMP
1979.011.0147, TMP 1981.019.0175, TMP 1993.082.0001,
and UALVP 40. e following specimens are also referable
to Chasmosaurus sp., as their posterior parietal margin and
epiparietals are intermediate between C. belli and C. irvinensis:
AMNH 5402, TMP 2009.034.0009, and YPM 2016.
Distribution: Chasmosaurus sp. specimens with known
stratigraphy were collected from the lower (Centrosaurus-
Corythosaurus Zone; CMN 8801, TMP 1979.011.0147,
TMP 1981.019.0175, UALVP 40, YPM 2016), middle
(Styracosaurus-Lambeosaurus lambei Zone; ROM 839,
TMP 2009.034.0009), and upper (Lambeosaurus magnic-
ristatus-pachyrhinosaur Zone; TMP 1993.082.0001) units
of the DPF. CMN 8802 was collected from the upper-
most Oldman Formation of southern Alberta (Milk River
region), below the Lethbridge Coal Zone, and is likely
age-equivalent to the middle or upper unit of the DPF
(Campbell et al. 2018); all other Chasmosaurus sp. speci-
mens were collected from DPP.
SUMMARY
In this study, we redescribe two skulls previously re-
ferred to C. belli (AMNH 5402 and YPM 2016). ese
two skulls have (YPM 2016) or are inferred to have had
(AMNH 5402) ve posterior epiparietals, as well as a
straight posterior parietal margin – the combination
of which is unique to V. irvinensis. Based on our new
morphological observations and interpretations of these
skulls, we recover V. irvinensis as a species of Chasmosaurus
(C. irvinensis), although the interrelationships of C.
irvinensis, C. belli, and C. russelli remain unclear. We
refrain from formerly assigning YPM 2016 and AMNH
5402 to C. irvinensis, however, as their epiparietals are
signicantly shorter than those of C. irvinensis; instead,
we reassign these two skulls as Chasmosaurus sp. Given
the low stratigraphic position of YPM 2016 (unknown
in AMNH 5402) relative to C. irvinensis, we consider
the morphology of YPM 2016 to be a precursor to that
of C. irvinensis. If our assessment is correct, this would
indicate that the lineage leading to C. irvinensis has a large
degree of stratigraphic overlap with that of C. belli and C.
russelli. e close phylogenetic relationship and supposed
stratigraphic separation for these three taxa reported in
previous studies were used to suggest that they may rep-
resent an anagenetic lineage, whereby C. russelli evolved
into C. belli, and C. belli evolved into, and was entirely
replaced by, the latter. However, the lack of stratigraphic
separation between these three taxa indicates that they
instead arose via cladogenesis. is suggests that dinosaur
faunal turnover rates in the DPF were not as pronounced
as previously thought.
ACKNOWLEDGEMENTS
We would like to thank the following people for providing
collections access at their respective institutions: M. Norell
and C. Mehling (American Museum of Natural History),
K. Shepherd, M. Currie, and C. Kennedy (Canadian
Campbell et al. — Temporal range of ‘Vagaceratops
95
proof
Museum of Nature), B. Strilisky and G. Housego (Royal
Tyrrell Museum of Palaeontology), and C. Norris and
D. Brinkman (Yale Peabody Museum). ank you to C.
Brown, K. Chiba, D. Eberth, M. Loewen, J. Mallon, and
D. Tanke for insightful discussions. Financial support was
provided by an Ontario Graduate Scholarship to JAC.
We would also like to thank reviewers D. Fowler and S.
Maidment, and editor J. Mallon for their comments and
for improving the quality of this paper.
LITERATURE CITED
Brown, B. 1933. A new longhorned Belly River ceratopsian.
American Museum Novitates 669:1–3.
Brown, C.M., and D.M. Henderson. 2015. A new horned
dinosaur reveals convergent evolution in cranial ornamentation
in Ceratopsidae. Current Biology 25:1–8. DOI: 10.1016/j.
cub.2015.04.041.
Campbell, J.A. 2015. A reassessment of the horned dinosaur
Judiceratops tigris (Ornithischia: Ceratopsidae) from the Upper
Cretaceous (Campanian) of Montana, USA. Canadian Journal
of Earth Sciences 52:85–95. DOI:10.1139/cjes-2014-0172.
Campbell, J.A., M.J. Ryan, R.B. Holmes, and C.J. Schröder-
Adams. 2016. A re-evaluation of the chasmosaurine ceratopsid
genus Chasmosaurus (Dinosauria: Ornithischia) from the Upper
Cretaceous (Campanian) of western Canada. PLoS ONE
11:e0145805. DOI:10. 1371/journal.pone.0145805.
Campbell, J.A., M.J. Ryan, C.J. Schröder-Adams, D.C. Evans,
and R.B. Holmes. 2018. New insights into chasmosaurine
(Dinosauria: Ceratopsidae) skulls from the Upper Cretaceous
(Campanian) of Alberta, and an update on the distribution
of accessory frill fenestrae in Chasmosaurinae. PeerJ 6:e5194.
DOI:10.7717/peerj.5194.
Chiba, K., M.J. Ryan, F. Fanti, M.A. Loewen, and D.C.
Evans. 2018. New material and systematic re-evaluation of
Medusaceratops lokii (Dinosauria, Ceratopsidae) from the
Judith River Formation (Campanian, Montana). Journal of
Paleontology 92:272–288. DOI:10.1017/jpa.2017.62
Currie, P.J., and D.A. Russell. 2005. e geographic and strati-
graphic distribution of articulated and associated dinosaur
remains, pp. 537–570 in P.J. Currie and E.B. Koppelhus (eds.),
Dinosaur Provincial Park: A Spectacular Ancient Ecosystem
Revealed. Indiana University Press, Bloomington, Indiana.
Eberth, D.A. 1996. Origin and signicance of mud-lled incised val-
leys (Upper Cretaceous) in southern Alberta, Canada. Sedimentology
43:459–477. DOI:10.1046/j.1365-3091.1996.d01-15.x.
Eberth, D.A. 2005. e geology, pp. 54–82 in P.J. Currie and
E.B. Koppelhus (eds.). Dinosaur Provincial Park: A Spectacular
Ancient Ecosystem Revealed. Indiana University Press,
Bloomington, Indiana.
Eberth, D.A. and A.P. Hamblin. 1993. Tectonic, stratigraphic,
and sedimentologic signicance of a regional disconformity in
the upper Judith River Group (Belly River wedge) of south-
ern Alberta, Saskatchewan, and northern Montana. Canadian
Journal of Earth Sciences 30:174–200. DOI:10.1139/e93-016.
Evans, D.C., and M.J. Ryan. 2015. Cranial anatomy of
Wendiceratops pinhornensis gen. et sp. nov., a centrosaurine cera-
topsid (Dinosauria: Ornithischia) from the Oldman Formation
(Campanian), Alberta, Canada, and the evolution of ceratopsid
nasal ornamentation. PLoS ONE 10:e0130007. DOI:10.1371/
journal.pone.0130007.
Farke, A.A., M.J. Ryan, P.M. Barrett, D.H. Tanke, D.R. Braman,
M.A. Loewen, and M.R. Graham. 2011. A new centrosaur-
ine from the Late Cretaceous of Alberta, Canada, and the
evolution of parietal ornamentation in horned dinosaurs.
Acta Palaeontologica Polonica 56:691–702. DOI: 10.4202/
app.2010.0121.
Godfrey, S.J., and R. Holmes. 1995. Cranial morphol-
ogy and systematics of Chasmosaurus (Dinosauria:
Ceratopsidae) from the Upper Cretaceous of western Canada.
Journal of Vertebrate Paleontology 15:726–742. DOI:
10.1080/02724634.1995.10011258.
Golobo, P.A., J.S. Farris, and K.C. Nixon. 2003. TNT: Tree
analysis using new technology. Program and documentation
available from the authors and at http://www.lillo.org.ar/phy-
logeny/tnt.
Golobo, P.A., J.S. Farris, and K.C. Nixon. 2008.TNT: a free
program for phylogenetic analysis. Cladistics 24:774–786.
Hatcher, J.B., O.C. Marsh, and R.S. Lull. 1907. e Ceratopsia.
US Geological Survey Monograph 49:1–300.
Holmes, R.B. 2014. e postcranial skeleton of Vagaceratops
irvinensis (Dinosauria, Ceratopsidae). Vertebrate Anatomy
Morphology Palaeontology 1:1–21. DOI: 10.18435/B5159V.
Holmes, R.B., C. Forster, M. Ryan, and K.M. Shepherd. 2001. A
new species of Chasmosaurus (Dinosauria: Ceratopsia) from the
Dinosaur Park Formation of southern Alberta. Canadian Journal
of Earth Sciences 38:1423–1438. DOI: 10.1139/e01-036.
Lambe, L.M. 1902. On Vertebrata of the mid-Cretaceous of
the Northwest Territory, Part 2. New genera and species from
the Belly River Series (mid-Cretaceous). Canadian Geological
Survey, Contributions to Canadian Paleontology 3:25–81.
Lambe, L.M. 1914a. On the fore-limb of a carnivorous dinosaur
from the Belly River Formation of Alberta, and a new genus
of Ceratopsia from the same horizon, with remarks on the
integument of some Cretaceous herbivorous dinosaurs. Ottawa
Naturalist 27:129–135.
Lambe, L.M. 1914b. On Gryposaurus notabilis, a new genus and
species of trachodont dinosaur from the Belly River Formation
of Alberta, with description of the skull of Chasmosaurus belli.
Ottawa Naturalist 27:145–155.
Lambe, L.M. 1915. On Eoceratops canadensis, gen. nov., with
remarks on other genera of Cretaceous horned dinosaurs.
Geological Survey of Canada Museum Bulletin 12:1–49.
Lehman, T.M. 1990. e ceratopsian subfamily Chasmosaurinae:
sexual dimorphism and systematics, pp. 211–229 in K.
Carpenter and P. Currie (eds.), Dinosaur Systematics:
Vertebrate Anatomy Morphology Palaeontology 7:83-100
96
Perspectives and Approaches. Cambridge University Press, New
York, New York.
Longrich, N.R. 2010. Mojoceratops perifania, a new chasmosaur-
ine ceratopsid from the late Campanian of western Canada.
Journal of Paleontology 84:681–694. DOI: 10.1666/09-114.1.
Longrich, N.R. 2014. e horned dinosaurs Pentaceratops and
Kosmoceratops from the upper Campanian of Alberta and
implications for dinosaur biogeography. Cretaceous Research
51:292–308. DOI: 10.1016/j.cretres.2014.06.011.
Lull, R.S. 1933. A revision of the Ceratopsia or horned dino-
saurs. Yale Peabody Museum Memoir 3, 175 pp.
Maddison, W.P., and D.R. Maddison. 2011. Mesquite: a mod-
ular system for evolutionary analysis. Version 2.75. Available:
http://mesquiteproject.org.
Maidment, S.C.R., and P.M. Barrett. 2011. A new specimen of
Chasmosaurus belli (Ornithischia: Ceratopsidae), a revision of
the genus, and the utility of postcrania in the taxonomy and
systematics of ceratopsid dinosaurs. Zootaxa 2963:1–47. DOI:
10.11646/zootaxa.2963.1.1.
Mallon, J.C., R. Holmes, D.A. Eberth, M.J. Ryan, and J.S.
Anderson. 2011. Variation in the skull of Anchiceratops
(Dinosauria, Ceratopsidae) from the Horseshoe Canyon Formation
(Upper Cretaceous) of Alberta. Journal of Vertebrate Paleontology
31:1047–1071. DOI:10.1080/02724634.2011.601484.
Mallon, J.C., R. Holmes, J.S. Anderson, A.A. Farke and D.C.
Evans. 2014. New information on the rare horned dinosaur
Arrhinoceratops brachyops (Ornithischia: Ceratopsidae) from
the Upper Cretaceous of Alberta, Canada. Canadian Journal of
Earth Sciences 51:618–634. DOI: 10.1139/cjes-2014-0028.
Mallon, J.C., C.J. Ott, P.L. Larson, E.M. Iuliano and D.C.
Evans. 2016. Spiclypeus shipporum gen. et sp. nov., a bold-
ly audacious new chasmosaurine ceratopsid (Dinosauria:
Ornithischia) from the Judith River Formation (Upper
Cretaceous: Campanian) of Montana, USA. PLoS ONE
11:e0154218. DOI: 10.1371/journal.pone.0154218.
Marsh, O.C. 1888. A new family of horned dinosaurs from the
Cretaceous. American Journal of Science, series 3, 36:477–478.
Marsh, O.C. 1890. Description of new dinosaurian reptiles.
American Journal of Science, series 3 39:81–86.
Ryan, M.J. 2007. A new basal centrosaurine ceratop-
sid from the Oldman Formation, southeastern Alberta.
Journal of Paleontology 81:376–396. DOI:10.1666/0022-
3360(2007)81[376:ANBCCF]2.0.CO;2.
Ryan, M.J. and D.C. Evans. 2005. Ornithischian dinosaurs, pp.
312–348 in P.J. Currie and E.B. Koppelhus (eds.), Dinosaur
Provincial Park: A Spectacular Ancient Ecosystem Revealed.
Indiana University Press, Bloomington, Indiana.
Ryan, M.J., A.P. Russell, and S. Hartman. 2010. A new chasmo-
saurine ceratopsid from the Judith River Formation, Montana,
pp. 181–188 in M.J. Ryan, B.J. Chinnery-Allgeier and D.A.
Eberth (eds.). New Perspectives on Horned Dinosaurs. Indiana
University Press, Bloomington, Indiana.
Ryan, M.J., D.C. Evans, P.J. Currie, and M.A. Loewen. 2014. A
new chasmosaurine from northern Laramidia expands frill dis-
parity in ceratopsid dinosaurs. Naturwissenschaften 101:505–
512. DOI: 10.1007/s00114-014-1183-1.
Ryan, M.J, D.C. Evans, P.J. Currie, C.M. Brown, and D.B.
Brinkman. 2012. New leptoceratopsids from the Upper
Cretaceous of Alberta, Canada. Cretaceous Research 35:69–80.
DOI: 10.1016/j.cretres.2011.11.018.
Sampson, S.D., M.A. Loewen, A.A. Farke, E.M. Roberts, C.A.
Forster, J.A. Smith, and A.L. Titus. 2010. New horned dino-
saurs from Utah provide evidence for intracontinental dino-
saur endemism. PLoS ONE 5:1–12. DOI: 10.1371/journal.
pone.0012292.
Sereno, P.C. 1986. Phylogeny of the bird-hipped dinosaurs (order
Ornithischia). National Geographic Research 2:234–256.
Sternberg, C.M. 1919. Field notes, Summer 1919. Unpublished
eld notes archieved at the Canadian Museum of Nature,
Ottawa, Canada.
Sternberg, C.M. 1936. Preliminary map 969A, Steveville sheet,
Alberta. Geological Survey of Canada Paper 36–18.
Sternberg, C.M. 1940. Ceratopsidae from Alberta. Journal of
Paleontology 14:468–480.
Swoord, D.L. 2002. PAUP: Phylogenetic Analysis Using
Parsimony. Version 4.0b10. Sinauer Associates, Inc.,
Sunderland, Massachusetts.
Wick, S.L. and T.M. Lehman. 2013. A new ceratopsian
dinosaur from the Javelina Formation (Maastrichtian) of
West Texas and implications for chasmosaurine phylogeny.
Naturwissenschaften, 100:667–682. DOI:10.1007/s00114-
013-1063-0.
Campbell et al. — Temporal range of ‘Vagaceratops
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proof
Appendix 1. Revised character state codings for AMNH 5402
(93) Epiparietals, number per side (Holmes et al. 2001, character 28, modied by Campbell et al. 2016):
(0) – three.
(1) – four or more.
AMNH 5402 was changed from ‘0’ to ‘1’.
(100) Epiparietal, P2 shape (Sampson et al. 2010, character 100, modied by Campbell et al. 2016):
(0) – low D-shaped process.
(1) – elongate, attened process or spike.
(2) – strongly recurved triangular or recurved, low rugose triangular process.
(3) – well-developed triangular process.
(4) – elongate low process.
AMNH 5402 was changed from ‘0’ to ‘?’.
(101) Epiparietal P2 curvature (Sampson et al. 2010, character 101, modied by Campbell et al. 2016):
(0) – straight.
(1) – medially or laterally curved in the plane of the frill.
(2) – recurved onto dorsal surface of frill.
AMNH 5402 was changed from ‘0’ to ‘?’.
(102) Epiparietal P3 shape (Sampson et al. 2010, character 102, modied by Campbell et al. 2016):
(0) – low raised D-shaped process.
(1) – elongate spike.
(2) – strongly recurved triangular or recurved, low rugose triangular process.
(3) – well-developed triangular process.
(4) – elongate, low process.
AMNH 5402 was changed from ‘0’ to ‘?’.
(153) Epiparietal P4 shape (Campbell et al. 2016, character 153):
(0) – low raised D-shaped process.
(1) – strongly recurved triangular or recurved low gnarled triangular process.
(2) – well-developed triangular process.
(3) – elongate, low process.
AMNH 5402 was changed from ‘?’ to ‘0’.
(154) Epiparietal, P4 orientation (Campbell et al. 2016, character 154):
(0) – epiparietal oriented in the plane of the frill.
(1) – directed anterodorsally.
AMNH 5402 was changed from ‘?’ to ‘0’.
(155) Epiossication in P5 position, shape (Campbell et al. 2016, character 155):
(0) – low raised D-shaped process.
(1) – well-developed triangular process.
(2) – elongate low process.
AMNH 5402 was changed from ‘?’ to ‘1’.
Vertebrate Anatomy Morphology Palaeontology 7:83-100
98
Appendix 2. Data matrix used in phylogenetic analysis.
‘Lepto_grac’
100??0???0??0??010001?001?0??000000??????000?0000000000?00??000000?00000000??????000???????????????????000?000000000000000
0001?000000000000?0?000000(0 1)?0????
‘Proto_andrew’
000??0???0??0??01000110000100000000??????000?0000000000?0100110000?00000100000000000???????????????????000000000000000
0000000100000000000000000000000?0????
‘Zuni_christ’
111000???0??0??0?010000?100??0?1111000102111011?0??11?0???????0????????01?01000????0????????????????????11?1???1?0011011??001???
?1100?????????01?0??1??????
‘Turano_tardarb
???????????????????????0?0????????1?01102???????????1?0???????????????????????????????????????????????????????????0???????1(0 1)11????????????????????????
?????
Alberta_nesmoi’
?111?0???0??0??????01?1011110??11?1?00112110?11112111???1100111001011?101111001111110?0???101000?????10??1?1???1?11011?
1???111???????????????????????00?000
‘Centro_apertus’
011110?0?0??0??111001?1111110101111000022110?1111211111011001110010110101111031111110?0000101001113210011111
1111111011111111111111110111111111011111(0 1)000000
‘Pachy_lakust’
011110?0?0??0??111001?111112010111111????111111112?111101100111001011010111103111111??0???1?1000???211010111111?
1110111111111111?1?10??11111110111??(0 1)00?000
‘Kosmo_rich’
1110011111001100001000111111000111110111111111011011110111120010112211101110001001(0 1)1111321110101213222
1????????11?011?111?1?11????????1?????????????1000???
‘Aguja_maris
111001010110100000111?11111100011111011001111101101111??111?1011112?11??1110?20111011?111?0???01???????111111???1
10?1111??1?111111110????111?11111??1000???
‘Utah_gettyi’
11100101110?11000011001111110001111111022111110110?1111111111011112111101110120111011112210?00013133030???1
111?111011111111111???1?10??????1??11111?1000???
‘Penta_stern’
1110010111111100001100111111000111110011211111(0 1)11111111111111011112211101110120111011112210?0001313303
0?11111111110111111111111111110?1111111111?11??000???
‘Coahuila_magna’
11100?1??10????00??1??11111110??1?11??11?1???????????????11??01?1??????01?1??2011101??1?????????????????????????1?0111111???11?????10
???????????????1?00???
Anchi_ornatus’
1110011(0 1)1110110001001?11111100011111111111111101101111111112101110?11110111100(0 1)10101111220(0 1)2(0 1)0
013233030111111111?1?01?11???111??????????????????????000020?
Arrhino_brachy’
1110011??1?0100001?01?1111110001111?111111111101101111(0 1)1111110111(0 1)0111101111001101011?111012000140040
401111111111110111111??111?1??1????????????????0001???
Campbell et al. — Temporal range of ‘Vagaceratops
99
proof
‘Ojo_fowl’
11??0??????????????0??????111??1??????????111????????????1120?101?????????1100???1011?1110??0011400??40????????111011?111???11??????0?
??????????????1?00???
Toro_latus
1110010??111???0010?1?111111100111111(0 1)112111110112111?(0 1)11111101110?(0 1)12101011031201011?11100?10014004
040111111111?1????????1111???1?10????????????????(0 1)00302
Toro_utah
?????????????????????????????????11?10112111110112?1??1??11?101110?012101011031201011?11111210114004040????????111?11111??1
?111?11??????????????????1???302
‘Eotri_xerin’
11100100?11011000??0??111111??011?111?1121?111?110???????11?1???1????????????????1011?1???12????????????????????????????????1111?????
??????????????????1???
‘Nedo_hatch’
11100100?11111100?0?1?111?1110011?1?10112?11110?12?1?11111111?101???021?1111031101011?11101????1??????????111???????????
?????1????????????????????????00???
Tri_horr’
11100100?111111001001?11111110011111101121111101121111111111101010?00211001??????1011?1110120011400404011111
11111101111111111111111111111111111111111(0 1)00???
Tri_pror’
11100100?111111001001?11111110011111101121111101121111011111101010?00211001??????1011?1110120011400404011111
1111110111111111111111??1??????????????11(0 1)00???
‘AMNH_5401’
1110010101001000001000111?110011111?01102111111110111111111110?11???12101110?00111011?1?100?????????????11?1?1?????
?????????11???????????????????????000???
‘AMNH_5402’
1110010101?010000?101?111?110011111?000?2111111112111111111110?110??12101110000211010?1?100?1001000???0?11?1?1?
1110?111111??11??????????????????????1000001
‘AMNH_5656’
??????????????????????????????1??????????????1??121???1?111110?1112112?01110010111011?1?10??000130030?0?????1???????????????11??????????
??????????????0????
‘CMN_0491’
?????????????????????????????????????????????????????????????????11????01?10010?1101??????????01010?????????????????????????????????????????????????
???????
‘CMN_1254’
?1??0??????????????0??????1100?11?11001021111???????1111?11110111???1??01???????1101???????????????????????????11???1?11111??????????????
???????????1??????
‘CMN_2245’
??????????????????????????11???1111?0002211111111?11111111111011111112101110010111010?11100?0001?1???30111?????111011111
111111111111001??1?1?1??11111000???
‘CMN_2280’
1110010101?0100000101?111111001111110000211111111211111111111011112110101110010111011?11100?00013103030?11?
??1?1110?11111111111111110?1??11111111???1000???
‘CMN_8800’
1110010101?010000?1?00111?11001111110????1111??1???11111111110?1112112101110010111011?11100?00010100030??????1????
?????????????????????????????????????0???
Vertebrate Anatomy Morphology Palaeontology 7:83-100
100
‘CMN_41357’
111001?1010010000010??1?1111001111???????111111?121111111111101110??12?01110000011011?11100?11012132221??????1?11
101111111?1111111?10?1111???11??11?1000111
‘NHMUK_R4948’
1110010101?010000??0??11111100?111110????11111111211111?11111011111112?01?10010111011?11100???????????????1??1??110???
11??1?11111111?01????1????111??000???
‘ROM_839’
111001010100100000101?1111110011111?00002111111110111111111110111???12101110010111011?11100??0?????????111?111?
111011111111111??????????????????????1000???
‘ROM_843’
?1100??1????????00101?1111110011111?0????11111111011111111111011111210101110010211011?11100?00010103?30?11?111?11
???111111111111?1?1001111?1?111111?1000???
‘TMP_81.19.175’
111001010100100000101?11111100111111010?2111111112111111111??0111???1?10111??10?11010?1????????????????111?111????????
????1111???????????????????????000???
TMP_83.25.1’
?1?????????????????????????????11111011?211111111211111111111011112110101110020111010?11100?00013003030?????????????????????
?????????????????????????00????
TMP_87.45.1’
111001?1010010000??01?11111100?11????????111111112111111111110111???12101110???011011?111012????????????11???1???????????
??111???????????????????????000111
‘UALVP_40’
111001010100100000101?1111110011111?0100211111111211111?111??0111???1??0111??????1010?1????????????????111?1?1??110?1?1
1??1111??????????????????????1000???
YPM_2016’
11100111010010000?101?111111001111110????1111111121111111111101110??12101110010211011?11100?10010100001111?1?
1????????????1111???????????????????????000011
‘Judi_tigris’
??????????????????????????????????1101?02?11??1?1???1????1111?11?0?0???01?11041??1011?1??????????????????????????????????????????????????????????
??????????
‘Bravo_poly’
?1????????????????????????111?????111?1???????0?111?????111???1?1???1??01?1??30111011?1???????1??2?????1111???????????11??????????????????????
??????1110???
... russelli + C. belli) is recovered as separated from (Vagaceratops + Kosmoceratops) , despite Vagaceratops (Chasmosaurus) irvinensis being originally recovered as the most derived member of a Chasmosaurus clade by Holmes et al. (2001), and the existence of morphological intermediates between C. belli and V. irvinensis (e.g., cf. C. belli specimen YPM 2016; Lehman 1998;Campbell et al., 2019). Subsequent analyses by Mallon et al. (2011Mallon et al. ( , 2014 using an altered version of the data matrix from ) recovered cladograms (Fig. S2) that appear "upside down", with the early Maastrichtian taxa Anchiceratops and Arrhinoceratops occurring in a basal polytomy, and some of the stratigraphically oldest taxa forming the most derived clade (middle to late Campanian (Chasmosaurus belli + Chasmosaurus russelli)); a configuration that would require considerable ghost lineages for many clades. ...
... The most significant result of reanalysis 1 is the unification of a Chasmosaurus clade with (Vagaceratops + Kosmoceratops). This is similar to the original description of Vagaceratops (Chasmosaurus) irvinensis (Holmes et al., 2001), where the taxon was considered the most derived (and stratigraphically youngest) form of Chasmosaurus, a relationship also recovered in the phylogenetic analyses of Longrich (2014) and Campbell et al. (2016Campbell et al. ( , 2019. ...
... The holotype of Chasmosaurus russelli (CMN 8800) requires redescription, and will likely need to be moved out of Chasmosaurus and coded separately from other referred specimens (Longrich, 2015;Campbell et al., 2016;Fowler & Freedman Fowler, 2017). Chasmosaurus belli referred specimen YPM 2016 has been redescribed (Campbell et al., 2019), and will need to be coded separately into our new matrix as a morphologic intermediate between C. belli specimens and Vagaceratops. Finally, some recently described chasmosaurine taxa (e.g., Judiceratops; Mercuriceratops; Regaliceratops, and Spiclypeus; Longrich, 2013; Ryan et al., 2014;Brown & Henderson, 2015;Campbell, 2015;Mallon et al., 2016) have yet to be coded into the revised matrix, although new taxa known from fragmentary remains may require some reassessment which is beyond the scope of this current work. ...
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Background: The chasmosaurine ceratopsid Chasmosaurus is known from the Upper Cretaceous (Campanian) Dinosaur Park Formation of southern Alberta and Saskatchewan. Two valid species, Chasmosaurus belli and C. russelli, have been diagnosed by differences in cranial ornamentation. Their validity has been supported, in part, by the reported stratigraphic segregation of chasmosaurines in the Dinosaur Park Formation, with C. belli and C. russelli occurring in discrete, successive zones within the formation. Results/conclusions: An analysis of every potentially taxonomically informative chasmosaurine specimen from the Dinosaur Park Formation indicates that C. belli and C. russelli have indistinguishable ontogenetic histories and overlapping stratigraphic intervals. Neither taxon exhibits autapomorphies, nor a unique set of apomorphies, but they can be separated and diagnosed by a single phylogenetically informative character-the embayment angle formed by the posterior parietal bars relative to the parietal midline. Although relatively deeply embayed specimens (C. russelli) generally have relatively longer postorbital horncores than specimens with more shallow embayments (C. belli), neither this horncore character nor epiparietal morphology can be used to consistently distinguish every specimen of C. belli from C. russelli. Status of kosmoceratops in the dinosaur park formation: Kosmoceratops is purportedly represented in the Dinosaur Park Formation by a specimen previously referred to Chasmosaurus. The reassignment of this specimen to Kosmoceratops is unsupported here, as it is based on features that are either influenced by taphonomy or within the realm of individual variation for Chasmosaurus. Therefore, we conclude that Kosmoceratops is not present in the Dinosaur Park Formation, but is instead restricted to southern Laramidia, as originally posited.
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