Report
A New Horned Dinosaur Reveals Convergent
Evolution in Cranial Ornamentation in Ceratopsidae
Graphical Abstract
Highlights
d A new horned dinosaur, Regaliceratops, is described based
on a nearly complete skull
d It exhibits large nasal and small postorbital horns, and large
frill epiossifications
d A derived chasmosaurine, the new animal shows
centrosaurine-like display features
d Evidence for evolutionary convergence in horned dinosaur
display is documented
Authors
Caleb M. Brown, Donald M. Henderson
Correspondence
caleb.brown@gov.ab.ca
In Brief
Brown and Henderson describe a new
horned dinosaur, Regaliceratops
peterhewsi, from a nearly complete skull
characterized by a large nasal horn, small
postorbital horns, and large frill
epiossifications. This new
chasmosaurine shows display features
more similar to centrosaurines and
suggests evolutionary convergence in
display morphology in horned dinosaurs.
Brown & Henderson, 2015, Current Biology 25, 1641–1648
June 15, 2015 ª2015 Elsevier Ltd All rights reserved
http://dx.doi.org/10.1016/j.cub.2015.04.041
Current Biology
Report
A New Horned Dinosaur Reveals Convergent Evolution
in Cranial Ornamentation in Ceratopsidae
Caleb M. Brown1,* and Donald M. Henderson1
1Royal Tyrrell Museum of Palaeontology, Box 7500, Drumheller, AB T0J 0Y0, Canada
*Correspondence: caleb.brown@gov.ab.ca
http://dx.doi.org/10.1016/j.cub.2015.04.041
SUMMARY
Ceratopsid (horned) dinosaurs are an iconic group
of large-bodied, quadrupedal, herbivorous dinosaurs
that evolved in the Late Cretaceous and
were largely restricted to western North America
[1–5]. Ceratopsids are easily recognized by their
cranial ornamentation in the form of nasal and
postorbital horns and frill (capped by epiossifications);
these structures show high morphological
disparity and also represent the largest cranial
display structures known to have evolved [2, 4].
Despite their restricted occurrence in time and
space, this group has one of the best fossil records
within Dinosauria, showing a rapid diversification in
horn and frill morphology [1]. Here a new genus and
species of chasmosaurine ceratopsid is described
based on a nearly complete and three-dimensionally
preserved cranium recovered from the uppermost
St. Mary River Formation (Maastrichtian)
of southwestern Alberta. Regaliceratops peterhewsi
gen. et sp. nov. exhibits many unique
characters of the frill and is characterized by a
large nasal horncore, small postorbital horncores,
and massive parietal epiossifications. Cranial
morphology, particularly the epiossifications, suggests
close affinity with the late Campanian/early
Maastrichian taxon Anchiceratops, as well as with
the late Maastrichtian taxon Triceratops. A median
epiparietal necessitates a reassessment of epiossification
homology and results in a more resolved
phylogeny. Most surprisingly, Regaliceratops exhibits
a suite of cranial ornamentations that are
superficially similar to Campanian centrosaurines,
indicating both exploration of novel display morphospace
in Chasmosaurinae, especially Maastrichtian
forms, and convergent evolution in
horn morphology with the recently extinct Centrosaurinae.
This marks the first time that evolutionary
convergence in horn-like display structures
has been demonstrated between dinosaur
clades, similar to those seen in fossil and extant
mammals [6].
RESULTS
Systematic Paleontology
Dinosauria Owen, 1842, sensu Padian and May, 1993.
Ornithischia Seeley, 1887, sensu Sereno, 1998.
Ceratopsia Marsh, 1888, sensu Dodson, 1997.
Ceratopsidae Marsh, 1888, sensu Sereno, 1998.
Chasmosaurinae Lambe, 1915, sensu Dodson et al., 2004.
Triceratopsini Longrich et al., 2011.
Regaliceratops gen. nov.
Type species: Regaliceratops peterhewsi gen. et sp. nov.
Diagnosis: as per the type and only species.
Regaliceratops peterhewsi gen. et sp. nov.
Etymology
Regaliceratops, from the Latin ‘‘regalis,’’ meaning ‘‘royal,’’ combined
with the Greek ‘‘ceratops,’’ meaning ‘‘horned face.’’ The
adjective ‘‘royal’’ refers to the crown-shaped parietosquamosal
frill and epiossifications and the Royal Tyrrell Museum of
Palaeontology (the ‘‘Royal’’ appellation was bestowed on
the museum in 1990 by Her Majesty Queen Elizabeth II).
The species epithet honors Peter Hews, who discovered the
holotype.
Holotype
The holotype and only known specimen is Tyrrell Museum of Palaeontology
(TMP) 2005.055.0001, a nearly complete cranium
(skull excluding lower jaw) missing only the rostral bone. Palatal
and braincase regions are obscured by matrix.
Type Locality, Horizon, and Age
The holotype was recovered from Upper Cretaceous rocks
along the Oldman River in the area of Waldron Flats, approximately
164 km south of Calgary, Alberta, Canada (Figure 1).
The uppermost St. Mary River Formation and lowermost Willow
Creek Formation are both exposed along the river in this
area. Due to the strongly upthrust and faulted condition of
the bedrock strata in the area and the absence of obvious outcrops
of the Battle Formation and Whitemud Member marker
beds in the quarry area, it has been difficult to determine the
precise stratigraphic position of the specimen in relation to
the contact between the St. Mary River and Willow Creek formations.
Nonetheless, existing geologic maps of the area suggest
that the quarry occurs within the upper 30 m of the
St. Mary River Formation [9]. This stratigraphic position is supported
by the presence of the angiosperm palynomorph Scollardia
trapaformis (D.R. Braman, personal communication) in
the host matrix of TMP 2005.055.0001. S. trapaformis is
diagnostic for upper beds of both the St. Mary River Formation
and the combined Carbon and Whitemud members of the
Current Biology 25, 1641–1648, June 15, 2015 ª2015 Elsevier Ltd All rights reserved 1641
Horseshoe Canyon Formation (southern and central Alberta)
[10, 11]. Carbon Member strata north of Drumheller have
yielded the chasmosaurine Eotriceratops xerinsularis [10: Figure
3] and are assigned an age of 67.5–68.5 mega-annum
(Ma) [10–12]. Given that well-established chronostratigraphic
correlations across southern Alberta equate the upper Horseshoe
Canyon Formation with the upper St. Mary River Formation
(see Figure 9 in [13]), the holotype likely shares this same
middle Maastrichtian age.
A
B
Figure 1. Geographic and Stratigraphic
Occurrence of Chasmosaurinae in Upper
Cretaceous Strata of Southern Alberta
(A) Map of southern Alberta (inset below shows
location of A relative to Alberta and Canada)
showing occurrences of chasmosaurine taxa
(colored circles) and major rivers and cities. Colors
of circles correspond to labeled taxa in the center
panelof(B).Coloredareas ofthemapcorrespond to
stratigraphy of (B) and illustrate the surface expo-
sureofCretaceousformationsintheregion.Position
of TMP 2005.055.0001 is indicated by the yellow
star. ‘‘?’’ indicates purported occurrence of An-
chiceratopsatScabbyButte,northofLethbridge[8].
(B) Stratigraphy of southern Alberta indicating the
occurrence of chasmosaurine taxa in both southwestern
and southeastern regions (incorporating
data from [7]). Colors of formations correspond to
surface exposure in (A).
Diagnosis
Chasmosaurine ceratopsid characterized
by the following autapomorphies (*) and
unique suite of synapomorphies: single,
midline epiparietal ossification (P0) rostrodorsally
offset from plane of frill and
other epiparietals, projecting caudal to
parietal and with a roughly triangular
transverse cross-section*; prominent
midline ridge on parietal confluent with
median epiparietal (P0 locus)*; paired epiparietal
ossifications (P1-2) long, flat, and
roughly pentagonal or spade shaped*;
prominent postorbital ridge running diagonally
from supraorbital horncore to base
of squamosal; parietal fenestrae small
or subequal in size to orbit (shared with
Kosmoceratops); nasal horncore larger
than postorbital horncores (shared with
Chasmosaurus belli and Vagaceratops).
Abbreviated Description
The skull is nearly complete, missing only
the rostral bone and lower jaws, and has a
maximum sagittal length of approximately
1,570 mm. Although the cranium
is nearly complete and three-dimensionally
preserved, it has experienced postdepositional
deformation affecting some
aspects of the cranial morphology,
including rostrocaudal compression of the entire cranium, dorsal
shear of the narial region, and dorsal deflection of the parietosquamosal
frill. For a more complete discussion of the deformation,
see Supplemental Results and Discussion, ‘‘Post-Depositional
Deformation.’’ The description below highlights the most
salient and diagnostic features. For a complete osteological
description, as well as discussion of ontogenetic status, see
Supplemental Results and Discussion, ‘‘Description,’’ ‘‘Ontogenetic
Status of TMP 2005.055.0001,’’ and Table S1.
1642 Current Biology 25, 1641–1648, June 15, 2015 ª2015 Elsevier Ltd All rights reserved
Narial Region
The narial region is completely preserved, with the exception of
the rostral bone and the apex of the nasal horncore. The premaxillary
septum, formed by the appressed premaxillae, is permeated
rostrally by an interpremaxillary fenestra characteristic of
Masstrichtian chasmosaurines (Figure 2). The caudal margin of
the interpremaxillary fenestra is bounded by a narial strut, which
is sinuous in shape (not broad and triangular as in Triceratops
and Titanoceratops [14]) and lacks the thin septal flange seen
in the Campanian chasmosaurines. The caudoventral process
of the premaxilla projects caudodorsally from the laterally flared
ventral aspect of the premaxilla and is of constant thickness. This
process abruptly tapers caudally without forking (Figure 2) and
inserts between the nasal and maxilla laterally, both features
shared with Maastrichtian taxa (e.g., Anchiceratops, Triceratops
[15]) but not Campanian taxa (e.g., Chasmosaurus, Utahceratops
[16, 17]). The external naris extends caudally to overlap the
maxillary tooth row, as seen in other Maastrichtian chasmosaurines
(e.g., Anchiceratops, Anchiceratops, Triceratops [15, 18])
and is not restricted to the area rostral to the tooth row is in
Campanian taxa [16] (Figure 2).
The most obvious feature of the narial region is a large, steeply
sided nasal horncore, which is situated at the caudal margin of
the external naris as in Chasmosaurus [16], in contrast to the
more rostral position seen in Triceratopsini [14, 19] (Figure 2).
The apex of the horncore was lost to erosion (preserved height
is 148 mm) but would have had an estimated height of
240–280 mm, making it one of the tallest nasal horncores in
Chasmosaurinae (see Supplemental Results and Discussion,
‘‘Description: Narial Region: Nasal’’ and Table S2). The nasal
horncore is straight, projects dorsally and slightly rostrally, and
is teardrop shaped in cross-section, with a broad rostral margin
and tapered caudal margin.
Circumorbital Region
The rostrodorsal margin of the orbital rim is characterized by a
prominent antorbital buttress, formed by the rugose, and swollen
palprebral (Figure 2). The postorbital horncores are small relative
to the cranial proportions and are smaller than the nasal horncore
(being 140 mm in height and 110 mm rostrocaudal length at
base). The horncores taper distally, with the apex of each replaced
by a distinct resorption pit (Figure 2). The postorbital
horncores are positioned slightly caudal to the orbit, in contrast
to the more rostral position seen in the short-horned taxa Chasmosaurus
and Kosmoceratops [16, 17], yet share the narrow
base seen in these but not other chasmosaurine taxa (e.g.,
Anchiceratops, Triceratops [18, 19]). The horncores are dorsally
directed and straight in the parasagittal plane (Figures 2C and
2D) and are rostrally procurved (Figures 2A and 2B). A prominent
postorbital ridge, bearing two peaks on each side, extends
caudomedially from the horncores across the postorbital. The
ventrolateral extremity of the jugal is triangular, with the apex
capped by a large, conical epijugal (Figure 2C). The base of
the epijugal is circular to subcircular in cross-section and only
slightly smaller than the postorbital horncore bases.
Parietosquamosal Frill
Although the frill is a nearly perfect semicircle in rostrodorsal
view, it shows signs of post-depositional deformation resulting
in a shortening along the rostrocaudal axis and deflection
dorsally (see Supplemental Results and Discussion, ‘‘PostDepositional
Deformation’’). Similar to Triceratops, the epiossifications
are uniformly spaced along the circumference (Figure
2C), with no medial embayment caudally as seen in
Chasmosaurus and Utahceratops [16, 17]. Relative to other
chasmosaurines, but shared with Triceratops and Nedoceratops,
the frill is short—less than preorbital length and less than
70% basal skull length (but see Supplemental Results and Discussion,
‘‘Post-Depositional Deformation’’).
The dorsal midline of the parietal preserves a prominent
sagittal keel that runs from the rostralmost point of the parietal
to the base of the large midline epiossification (P0) near the
caudal margin. Small, paired parietal fenestrae are situated
entirely within the parietal and do not contact the squamosal
laterally (in contrast to the condition in Chasmosaurus, Agujaceratops,
and Pentaceratops [16, 20]). A single, large epiparietal
(P0) is located at the caudal midline of the parietal, is rostrodorsally
offset from the caudal margin, and projects caudally (Figure
2). This epiossification is confluent with the median ridge of
the parietal and is triangular in cross-section, with a sharp rostral
edge and rounded caudal margin.
The remaining caudolateral periphery of the frill is adorned
with a series of seven flat, distally attenuated epiossifications
on each side, decreasing in size from largest caudomedially to
smallest rostrolaterally. Two paired epiossifications (P1 and P2)
are fused with the caudal parietal exclusively (epiparietals) and
are large (larger than the postorbital horncores) and roughly
pentagonal or spade shaped. These epiparietals represent the
largest (maximum length 201 mm) frill epiossifications in Chasmosaurinae.
Four epiossifications (S1–S4) are fused to the lateral
margin of the squamosal (episquamosals). The rostralmost three
episquamosals (S2–S4) are roughly triangular in shape and
decrease slightly in size rostrally, while the caudalmost (S1) is
pentagonal or spade shaped and distinctly larger than the rostralmost
three. One paired epiossification (PS) articulates along
the parietosquamosal suture (epiparietosquamosal) and is transitional
in both shape and size between the epiparietals and
episquamosals.
DISCUSSION
Homology of Frill Epiossifications
The pattern of homology of the parietosquamosal epiossifications
is integral to an understanding of both taxonomy and phylogeny
of Ceratopsidae. A homology scheme numbering the
epiossifications from medial to lateral was derived initially for
the diverse array of spike- and horn-like epiossifications seen
in centrosaurines [21–24] and was subsequently applied across
Ceratopsidae [25, 26] and modified to include more basal taxa
(K.E. Clayton et al., 2009, 2010, Soc. Vertebrate Paleontol., abstracts).
These studies have shown that for the parietal of Centrosaurinae,
the number of epiossifications is relatively constant,
but with more medial loci showing more variation in development
and more phylogenetic signal than lateral ossifications [22, 27].
Contrasted with Centrosaurinae, epiossification homology in
Chasmosaurinae is less well established and has featured less
prominently in inferring phylogeny. New data derived from the
epiossifications of Regaliceratops have prompted a review of
epiossification homology across Chasmosaurinae, specifically
those taxa with a median epiparietal (Figure S3).
Current Biology 25, 1641–1648, June 15, 2015 ª2015 Elsevier Ltd All rights reserved 1643
A
A’
B
B’
C C’
D D’
Figure 2. Photographs and Interpretive Line Drawings of the Holotype of Regaliceratops peterhewsi gen. et sp. nov.
(A–D) Nearly complete cranium, TMP 2005.055.0001, in right lateral (A), left lateral (B), rostral (C), and dorsal (D) views.
(A0
–D0
) Interpretive drawings of photographed views in (A)–(D).
(legend continued on next page)
1644 Current Biology 25, 1641–1648, June 15, 2015 ª2015 Elsevier Ltd All rights reserved
The median epiparietal of Regaliceratops is similar, and likely
homologous, to the median epiparietal of Triceratops spp., previously
termed P0 (e.g., [28] and K.E. Clayton et al., 2010, Soc.
Vertebrate Paleontol., abstract), in terms of (1) a median position,
Areas in shadow, (C) and (D) left, are fully illustrated at right. Areas in white represent reconstruction (plaster/epoxy putty), and hatched areas indicate matrix. The
following abbreviations are used: cvp, caudoventral process of premaxilla; ej, epijugal; en, external naris; isf, interseptal fenestra; itf, infratemporal fenestra; j,
jugal; jn, jugal notch; m, maxilla; n, nasal; nhc, nasal horncore; ns, narial strut; ob, orbit; p, parietal; pf, parietal fenestra; phc, postorbital horncore; pm, premaxilla;
por, postorbital ridge; pp, palpebral; ps, epiparietosquamosal; P#, epiparietal; s, squamosal; stf, supertemporal fenestra; S#, episquamosal; tp, triangular
process. Scale bar represents 10 cm.
Figure 3. Time-Calibrated Phylogeny of
Chasmosaurinae
Time-calibrated strict consensus tree of five most
parsimonious trees for Chasmosaurinae utilizing
the new epiossification homology scheme (for
tree details, see Figure S1B). For comparison of
results and support indices, see Figure S1. Black
bars indicate confident stratigraphic occurrence,
whereas gray bars indicate less confidence.
Stratigraphic information is derived from [17].
Bottom right: oblique view of the holotype of
Regaliceratops peterhewsi, TMP 2005.055.0001.
(2) being of unpaired morphology, and (3)
projecting caudal to the parietal margin.
Additionally, based on (1) dorsally offset
position from the plane of the frill, (2)
rostrally offset position from the caudal
margin of the frill, and (3) roughly triangular
cross-section, the median epiossification
of Regaliceratops is likely also
homologous with the laterally curved
hooks of Anchiceratops, which have previously
been termed P1 [15]. To test this
homology across Chasmosaurinae, we
shifted the identity of the epiparietals of
Anchiceratops, Pentaceratops, and Utahceratops
one position medially (Figure S3;
see Supplemental Experimental Procedures,
‘‘Phylogenetic Methods’’). The
phylogenetic analysis of this revised homology
scheme for the epiossifications
results in a simpler and better-resolved
evolutionary history (i.e., a shorter, better-resolved
tree), indicating support for
the revised homology hypothesis proposed
here (Figure S1; see Supplemental
Experimental Procedures, ‘‘Phylogenetic
Methods’’).
Regaliceratops and Display
Evolution in Ceratopsidae
The cladistic analysis of relationships
within Chasmosaurinae recovers Regaliceratops
in a polytomy with Eotriceratops
and Ojoceratops, as sister taxa to the remaining
Triceratopsini (Triceratops, Torosaurus,
Nedoceratops, Titanoceratops)
(Figures 3 and S1). This phylogenetic position hypothesized for
Regaliceratops is consistent with its temporal occurrence, being
roughly time equivalent to Eotriceratops (Figure 3). This suggests
that Regaliceratops is part of an evolutionary trend showing both
Current Biology 25, 1641–1648, June 15, 2015 ª2015 Elsevier Ltd All rights reserved 1645
an increase in body size and solidification of the frill, with an
extreme example being the latest Maastrichtian Triceratops.
Despite being recovered within the Triceratopsini, Regaliceratops
shows ornamentation morphology distinct from all other
members of this clade, as well as the more inclusive clade
including Anchiceratops and Arrhinoceratops. Relative to all
other taxa in this clade, Regaliceratops has the smallest postorbital
horncores (Figure S2), as well as the tallest nasal horncore
relative to skull size. Campanian chasmosaurines show plasticity
in the size of the postorbital horncore, with the evolution of short
horncores occurring at least three times (Figure S2). However,
prior to the discovery of Regaliceratops, Maastrichtian chasmosaurine
taxa appeared to have stabilized on a long-horned postorbital,
and this new taxon represents the only evolution of a
short-horned postorbital within Maastrichtian chasmosaurines
(Figure S2).
There has been a historical dichotomy in ceratopsid cranial
ornamentation where individual species tend to emphasize
either (1) the nasal horn and frill epiossification (e.g., Styracosaurus,
Centrosaurus) or (2) the postorbital horns and length of the
frill (e.g., Anchiceratops, Anchiceratops, Pentaceratops), but
not both [5, 29, 30] (Figure 4). These contrasting patterns of cranial
ornamentation have been thought to be evolutionary hallmarks
of two independent evolutionary lineages, Centrosaurinae
(emphasizing nasal horn and frill epiossifications) and ChasmoFigure
4. Plot Illustrating Morphospace
within Ceratopsidae in Reference to Postorbital
Horncore Length against Nasal Horncore
Length
Convex hulls (colored polygons) show morphospace
occupation by Centrosaurinae (red),
Campanian Chamsosaurinae (light blue), and
Maastrichtian Chasmosauridae, excluding Regaliceratops
(dark blue). Diagonal dotted lines indicate
ratio of postorbital horn length to nasal horn
length. Basal centrosaurines (e.g., Albertaceratops,
Diabloceratops) are not plotted. Data are derived
from specimen measurements (C.M.B.) as well as
previously published data; see Table S2.
saurinae (emphasizing the postorbital
horns and length of the frill) [30, 31].
Recent discovery of the basal centrosaurines
Albertacertops [32], Diabloceratops
[33], and Nasutoceratops [34] have illustrated
higher disparity in cranial ornamentation
than previously thought and indicate
that this dichotomy evolved not at
the split between Chasmosaurinae and
Centrosaurinae, but within the Chasmosaurinae
and Centrosaurinae lineages.
Additionally, Sampson et al. [34] reported
the discovery of a clade within Centrosaurinae
(Nasutoceratops and Avaceratops)
showing cranial ornamentation
similar to those of Chasmosaurinae, i.e.,
an emphasis on the size of the postorbital
horns and retention of a less complex frill.
The discovery of Regaliceratops, although well nested within
Chasmosaurinae, shows the reciprocal pattern to the basal
centrosaurines above, where the nasal horn and epiossifications
are exaggerated relative to the postorbital horns and frill
length. A plot of postorbital horncore length as a function of
nasal horncore length results in Regaliceratops falling far
outside the morphospace occupied by other Maastrichtian
chasmosaurines, and within the morphospace of Campanian
centrosaurines (Figure 4). This is an unexpected pattern for
Maastrichtian Chasmosaurinae, and one that is evolutionarily
convergent with Centrosaurinae. Convergent evolution of
horns, or other display/signaling structures, between sister
clades or more distantly related groups has been well documented
in mammals [6, 35, 36] and recently found in hadrosaurid
dinosaurs [37], but this marks the first occurrence within
the diverse clade of horned dinosaurs. Based on disparate
patterns of cranial ornamentation, the use of these horns
and frills as display or sociosexual signaling structures has
been suggested to be distinct between these two subfamilies
of horn dinosaurs [29, 38, 39]. Convergent horn evolution in
mammals often correlates with convergent social behaviors
[6]. It may be hypothesized that Regaliceratops converged
not only morphologically with Centrosaurines but also
behaviorally, following the early Maastrichtian extinction of
Centrosaurinae.
1646 Current Biology 25, 1641–1648, June 15, 2015 ª2015 Elsevier Ltd All rights reserved
Chasmosaurine Evolution
The occurrence of a chasmosaurine ceratopsid with centrosaurine-like
ornamentation following the early Maastrichtian
extinction of the Centrosaurinae illustrates chasmosaurine ornamentation
increasing in disparity and exploration of novel morphospace
previously occupied by the Centrosaurinae (Figure 4).
Prior to this discovery, Maastrichtian-aged ceratopsid and hadrosaurid
taxa exhibited a pattern of lower diversity and longer
duration than Campanian-aged taxa [12, 40, 41] and may also
have exhibited a pattern of lower morphological disparity [42]
and slowing of evolutionary rates. Regaliceratops not only increases
the diversity of Maastrichtian ceratopsids but also
greatly increases the known morphological disparity.
The present study finds cladistic support for a deep split within
the Chasmosaurinae into an older Chasmosaurus clade and a
younger Triceratops clade based on features of the premaxilla
and parietal shape (exclusive of the epiossifications). If supported
by future analyses, this deep split within Chasmosaurinae
has two major implications for chasmosaurine evolution. First,
because these two clades are nearly non-overlapping (the
Chasmosaurus clade being of largely Campanian age, and the
Triceratops clade being of largely Maastrichtian age), a long
(3 Ma) ghost lineage is implied at the base of the Triceratops
clade (Figure 3). A similar (5 Ma) ghost lineage is also implied
for many taxa within the Triceratopsini [14], and these ghost lineages
taken together suggest that there is an undiscovered
diversity of Chasmosaurine taxa in the Campanian and Maastrichtian.
Much of the ghost lineage within the Triceratops clade
is inferred due to Titanoceratops being well nested within Triceratopsini
yet occurring in the Campanian, a combination that is
stratigraphically inconsistent relative to the other taxa.
The second implication is that the Chasmosaurus clade appears
to go extinct in the early Maastrichtian, at approximately
the same time as the extinction of the Centrosaurinae. The dynamics
of the centrosaurine extinction are not well understood,
so whether a common mechanism may be responsible cannot
be determined. We speculate that the extinction of two diverse
clades of horned dinosaurs in the early Maastrichtian may have
allowed for the diversification of the Triceratopsini just prior to
the end-Cretaceous mass extinction.
More than 100 years of fossil collecting and stratigraphic work
on the upper Campanian and Maastrichtian strata of the Red
Deer River Valley, specifically the Horseshoe Canyon and Scollard
formations, has revealed distinct faunal turnovers in ornithischian
taxa through this interval [12]. This is perhaps best illustrated
by the Chasmosaurinae, with Anchiceratops occurring in
the Horsethief, Morrin, and Tolman members; Anchiceratops
occurring in the Horsethief and Morrin members; Eotriceratops
occurring in the Carbon member; and Triceratops occurring in
the Scollard Formation [12]. This high-resolution dinosaur
biostratigraphy, particularly across the Campanian-Maastrichtian
boundary, is in contrast to much of the Upper Cretaceous record
elsewhere in North America, where terrestrial stratigraphic
sections are neither as complete and continuous nor as rich in
dinosaurs (e.g., Figure 6.11 in [43]).
The unexpected discovery of Regaliceratops reinforces the
plasticity in cranial ornamentation expressed in Ceratopsidae
and highlights how much of their true diversity still remains
unknown. Ongoing research will likely continue to reveal both
increased taxonomic diversity and increased morphological
disparity (particularly in cranial ornamentations) within the group
and may continue to blur the suite of ornamentation features
between the two subfamilies.
ACCESSION NUMBERS AND NOMENCLATURE
This published work and the nomenclatural acts it contains have been registered
in ZooBank, the online registration system for the ICZN. ZooBank LSIDs
(Life Science Identifiers) can be viewed by appending the LSID to the prefix
http://zoobank.org/. The LSID for this publication is urn:lsid:zoobank.org:
pub:9D3C353D-4422-49D7-85FD-28FFF489FA6A. The electronic edition of
this work was published in a journal with an ISSN and will be archived and
made available from the following digital repository: CLOCKSS (http://www.
clockss.org/clockss/Home).
SUPPLEMENTAL INFORMATION
Supplemental Information includes Supplemental Results and Discussion,
three figures, two tables, three appendices, and Supplemental Experimental
Procedures and can be found with this article online at http://dx.doi.org/10.
1016/j.cub.2015.04.041.
AUTHOR CONTRIBUTIONS
D.M.H. assisted with collecting the specimen. C.M.B. performed the description
and phylogenetic analyses. C.M.B. and D.M.H. wrote the manuscript.
ACKNOWLEDGMENTS
We thank P. Hews for his many fossil discoveries in Alberta, including the holotype
of Regaliceratops. D. Tanke, J. McCabe, and D. Lloyd assisted in the
excavation and collection of the specimen. K. Thompson and family provided
land access for equipment and excavation. D. Tanke’s technical assistance in
both the field and laboratory, including his patient preparation, was integral to
this research and allowed for the reconstruction and study of the specimen
that would have not been possible otherwise. Access to, and assistance
with, the specimen was provided by B. Strilisky, R. Russell, G. Housego, B.
Sanchez, and T. Courtnay. J. Bancescu provided assistance with map illustration.
D. Braman and D. Eberth provided geological context and discussion,
and B. Borkovic, D. Brinkman, D. Eberth, D. Evans, D. Field, J. Mallon, M.
Ryan, and J. Scannella provided helpful discussion and information. We also
thank F. Maderspacher, M. Loewen, and an anonymous reviewer who provided
comments that improved the manuscript. Funding for this research
was provided by the Royal Tyrrell Museum of Palaeontology and the Royal Tyrrell
Museum Cooperating Society.
C.M.B. would specifically like to highlight the ongoing and unwavering support
of Lorna O’Brien. Lorna, will you marry me?
Received: March 14, 2015
Revised: April 20, 2015
Accepted: April 20, 2015
Published: June 4, 2015
REFERENCES
1. Sampson, S.D., and Loewen, M.A. (2010). Unraveling a radiation: a review
of the diversity, stratigraphic distribution, biogeography, and evolution of
horned dinosaurs (Ornithischia: Ceratopsidae). In New Perspectives on
Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium,
M. Ryan, B.J. Chinnery-Allgeier, and D.A. Eberth, eds. (Indiana University
Press), pp. 405–427.
2. Dodson, P., Forster, C.A., and Sampson, S.D. (2004). Ceratopsidae. In The
Dinosauria, Second Edition, D.B. Weishampel, P. Dodson, and H.
Osmolska, eds. (University of California Press), pp. 494–513.
3. Xu, X., Wang, K., Zhao, X., and Li, D. (2010). First ceratopsid dinosaur from
China and its biogeographical implications. Chin. Sci. Bull. 55, 1631–1635.
Current Biology 25, 1641–1648, June 15, 2015 ª2015 Elsevier Ltd All rights reserved 1647
4. Hatcher, J.B., Marsh, O.C., and Lull, R.S. (1907). The Ceratopsia
(Monographs of the United States Geological Survey XLIX). (United
States Geological Survey).
5. Lull, R.S. (1933). A Revision of the Ceratopsia or Horned Dinosaurs
(Memoirs of the Peabody Museum of Natural History 3). (Yale University
Press).
6. Geist, V. (1966). The evolution of horn-like organs. Behaviour 27, 175–214.
7. Braman, D.R. (2013). Triprojectate Pollen Occurrence in the Western
Canada Sedimentary Basin and the Group’s Global Relationships
(Contribution Series Number 1). (Royal Tyrrell Museum of Palaeontology).
8. Langston, W., Jr. (1975). The ceratopsian dinosaurs and associated lower
vertebrates from the St. Mary River Formation (Maestrichtian) at Scabby
Butte, southern Alberta. Can. J. Earth Sci. 12, 1576–1608.
9. McMechan, M.E., and Stockmal, G.S. (2013). Geology, Maycroft, Alberta
(Geological Survey of Canada Canadian Geoscience Map 25). (Natural
Resources Canada).
10. Wu, X.-C., Brinkman, D.B., Eberth, D.A., and Braman, D.R. (2007). A new
ceratopsid dinosaur (Ornithischia) from the uppermost Horseshoe Canyon
Formation (upper Maastrichtian), Alberta, Canada. Can. J. Earth Sci. 44,
1243–1265.
11. Eberth, D.A., and Braman, D.R. (2012). A revised stratigraphy and depositional
history for the Horseshoe Canyon Formation (Upper Cretaceous),
southern Alberta plains. Can. J. Earth Sci. 49, 1053–1086.
12. Eberth, D.A., Evans, D.C., Brinkman, D., Therrien, F., Tanke, D.H., and
Russell, L.S. (2013). Dinosaur Biostratigraphy of the Edmonton Group
(Upper Cretaceous), Alberta, Canada: Evidence for Climate Influence.
Can. J. Earth Sci. 50, 701–726.
13. Hamblin, A.P.(2004).TheHorseshoe Canyon Formation inSouthern Alberta:
Surface and Subsurface Stratigraphic Architecture, Sedimentology, and
Resource Potential (Geological Survey of Canada Bulletin 578). (Natural
Resources Canada).
14. Longrich, N.R. (2011). Titanoceratops ouranos, a giant horned dinosaur
from the late Campanian of New Mexico. Cretaceous Res. 32, 264–276.
15. Mallon, J.C., Holmes, R., Eberth, D.A., Ryan, M.J., and Anderson, J.S.
(2011). Variation in the skull of Anchiceratops (Dinosauria, Ceratopsidae)
from the Horseshoe Canyon Formation (Upper Cretaceous) of Alberta.
J. Vertebrate Paleontol. 31, 1047–1071.
16. Godfrey, S.J., and Holmes, R. (1995). Cranial morphology and systematics
of Chasmosaurus (Dinosauria: Ceratopsidae) from the Upper Cretaceous
of western Canada. J. Vertebrate Paleontol. 15, 726–742.
17. Sampson, S.D., Loewen, M.A., Farke, A.A., Roberts, E.M., Forster, C.A.,
Smith, J.A., and Titus, A.L. (2010). New horned dinosaurs from Utah provide
evidence for intracontinental dinosaur endemism. PLoS ONE 5, e12292.
18. Mallon, J.C., Holmes, R., Anderson, J.S., Farke, A.A., Evans, D.C., and
Sues, H.-D. (2014). New information on the rare horned dinosaur
Arrhinoceratops brachyops (Ornithischia: Ceratopsidae) from the Upper
Cretaceous of Alberta, Canada. Can. J. Earth Sci. 51, 618–634.
19. Lehman, T.M. (1998). A gigantic skull and skeleton of the horned dinosaur
Pentaceratops sternbergi from New Mexico. J. Paleontol. 72, 894–906.
20. Lehman, T.M. (1989). Chasmosaurus mariscalensis, sp. nov., a New
Ceratopsian Dinosaur from Texas. J. Vertebrate Paleontol. 9, 137–162.
21. Sampson, S.D. (1995). Two new horned dinosaurs from the Upper
Cretaceous Two Medicine Formation of Montana: With a phylogenetic
analysis of the Centrosaurinae (Ornithischia: Ceratopsidae). J. Vertebrate
Paleontol. 15, 743–760.
22. Sampson, S.D., Ryan, M.J., and Tanke, D.H. (1997). Craniofacial ontogeny
in centrosaurine dinosaurs (Ornithischia: Ceratopsidae): taxonomic and
behavioural implications. Zool. J. Linn. Soc. 121, 293–337.
23. Ryan, M.J. (1992). The Taphonomy of a Centrosaurus (Ornithischia:
Ceratopsidae) Bone Bed (Campanian), Dinosaur Provincial Park,
Alberta, Canada. (University of Calgary).
24. Sampson, S. (1993). Cranial Ornamentations in Ceratopsid Dinosaurs:
Systematic, Behavioural, and Evolutionary Implications. (University of
Toronto).
25. Holmes, R.B., Forster, C.A., Ryan, M.J., and Shepherd, K.M. (2001). A new
species of Chasmosaurus (Dinosauria: Ceratopsia) from the Dinosaur Park
Formation of southern Alberta. Can. J. Earth Sci. 38, 1423–1438.
26. Loewen, M.A., Sampson, S.D., Lund, E.K., Farke, A.A., Aguillo´ n-Martı´nez,
M.C., de Leon, C.A., Rodrı´guez-de la Rosa, R.A., Getty, M.A., and Eberth,
D.A. (2010). Horned dinosaurs (Ornithischia: Ceratopsidae) from the Upper
Cretaceous (Campanian) Cerro del Pueblo Formation, Coahuila, Mexico.
In New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum
Ceratopsian Symposium, M.J. Ryan, B.J. Chinnery-Algeier, and D.A.
Eberth, eds. (Indiana University Press), pp. 99–116.
27. Ryan, M.J., Holmes, R., and Russell, A.P. (2007). A revision of the late
Campanian centrosaurine ceratopsid genus Styracosaurus from the
Western Interior of North America. J. Vertebrate Paleontol. 27, 944–962.
28. Longrich, N.R., and Field, D.J. (2012). Torosaurus is not Triceratops:
ontogeny in chasmosaurine ceratopsids as a case study in dinosaur
taxonomy. PLoS ONE 7, e32623.
29. Farlow, J.O., and Dodson, P. (1975). The Behavioral Significance of Frill
and Horn Morphology in Ceratopsian Dinosaurs. Evolution 29, 353–361.
30. Dodson, P. (1993). Comparative craniology of the Ceratopsia. Am. J. Sci.
293, 200–234.
31. Lehman, T.M. (1990). The ceratopsian subfamily Chasmosaurinae: sexual
dimorphism and systematics. In Dinosaur Systematics: Approaches and
Perspectives, K. Carpenter, and P.J. Currie, eds. (Cambridge University
Press), pp. 211–229.
32. Ryan, M.J. (2007). A new basal centrosaurine ceratopsid from the Oldman
Formation, Southeastern Alberta. J. Paleontol. 81, 376–396.
33. Kirkland, J.I., and DeBlieux, D.D. (2010). New basal centrosaurine
ceratopsian skulls from the Wahweap Formation (Middle Campanian),
Grand Staircase-Escalante National Monument, southern Utah. In New
Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum
Ceratopsian Symposium, M.J. Ryan, B.J. Chinnery-Algeier, and D.A.
Eberth, eds. (Indiana University Press), pp. 117–140.
34. Sampson, S.D., Lund, E.K., Loewen, M.A., Farke, A.A., and Clayton, K.E.
(2013). A remarkable short-snouted horned dinosaur from the Late
Cretaceous (late Campanian) of southern Laramidia. Proc. Biol. Sci. 280,
20131186.
35. Goss, R.J. (1983). Deer Antlers: Regeneration, Function and Evolution.
(Academic Press).
36. Geist, V. (1998). Deer of the World: Their Evolution, Behaviour, and
Ecology. (Stackpole Books).
37. Bell, P.R., Fanti, F., Currie, P.J., and Arbour, V.M. (2014). A mummified
duck-billed dinosaur with a soft-tissue cock’s comb. Curr. Biol. 24, 70–75.
38. Farke, A.A. (2004). Horn use in Triceratops (Dinosauria: Ceratopsidae):
testing behavioral hypotheses using scale models. Palaeontol. Electronica
7, 1–10.
39. Farke, A.A., Wolff, E.D.S., and Tanke, D.H. (2009). Evidence of combat in
Triceratops. PLoS ONE 4, e4252.
40. Ryan, M.J., and Evans, D.C. (2005). Ornithischian dinosaurs. In Dinosaur
Provincial Park: A Spectacular Ancient Ecosystem Revealed, P.J. Currie,
and E.B. Koppelhus, eds. (Indiana University Press), pp. 312–348.
41. Mallon, J.C., Evans, D.C., Ryan, M.J., and Anderson, J.S. (2013).
Megaherbivorous dinosaur turnover in the Dinosaur Park Formation (upper
Campanian) of Alberta, Canada. Palaeogeogr. Palaeoclimatol. Palaeoecol.
350–352, 124–138.
42. Campione, N.E., and Evans, D.C. (2011). Cranial growth and variation in
edmontosaurs (Dinosauria: Hadrosauridae): implications for latest
Cretaceous megaherbivore diversity in North America. PLoS ONE 6,
e25186.
43. Roberts, E.M., Sampson, S., Deino, A., Bowring, S.A., and Buchwaldt, R.
(2013). The Kaiparowitz Formation: A remarkable record of Late
Cretaceous terrestrial environments, ecosystems, and evolution in
western North America. In At the Top of the Grand Staircase: The Late
Cretaceous of Southern Utah, A.L. Titus, and M.A. Loewen, eds.
(Indiana University Press).
1648 Current Biology 25, 1641–1648, June 15, 2015 ª2015 Elsevier Ltd All rights reserved