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A NEW CERATOPSID DINOSAUR (CENTROSAURINAE: NASUTOCERATOPSINI) FROM THE FORT CRITTENDEN FORMATION, UPPER CRETACEOUS (CAMPANIAN) OF ARIZONA

Authors:
  • New Mexico Museum of Natural History and Science
  • New Mexico Museum of Natural History and Science
  • Maryland-National Capital Park and Planning Commision

Abstract and Figures

A new ceratopsid dinosaur, Crittendenceratops krzyzanowskii, is described from the Fort Crittenden Formation (Upper Cretaceous) of southeastern Arizona, and is based on two individuals consisting of partial cranial material recovered from the same stratigraphic unit. A phylogenetic analysis of ceratopsids recovers Crittendenceratops as a member of Nasutoceratopsini, a subclade of Centrosaurinae defined as the stem-based clade of centrosaurine ceratopsids more closely related to Avaceratops lammersi and Nasutoceratops titusi than to Centrosaurus apertus. Reconstruction of the parietosquamosal frill based on two specimens indicates that C. krzyzanowskii is a unique, nasutoceratopsin taxon. The parietosquamosal frill of C. krzyzanowskii had a broad medial ramus and at least five epiparietal loci situated around the margin of the frill, a typical characteristic of Centrosaurinae. The epiparietals are pronounced triangles that are dorsally concave and ventrally convex. Additionally, two large, triangular hook-like flanges, nearly the size of the epiparietal loci, are situated along the dorsomedial margin of the parietal ramus. The left squamosal has a pronounced dorsal ridge with a single dorsal squamosal process and large episquamosal undulations, a typical characteristic of Centrosaurinae. The presence of C. krzyzanowskii in Arizona indicates that the nasutoceratopsins persisted into the late Campanian. The temporal and paleobiogeographic distribution of Nasutoceratopsini further weakens the hypothesis of distinct northern and southern Laramidian provinces. INTRODUCTION During the Campanian, the centrosaurine ceratopsids exhibited great morphological and taxonomic diversity. Their paleobiogeographic range extends through much of western North America, from Alaska to Mexico (Loewen et al., 2010; Fiorillo and Tykoski, 2012; Rivera-Sylva et al., 2016, 2017). Outside of North America, centrosaurines have also been described from China, with Sinoceratops zhuchengensis (Xu et al., 2010), a lineage which originated in North America and radiated into Asia (Ryan et al., 2017). During the past two decades, several new ceratopsian taxa have been identified in North America (e.g., Ryan, 2007; Sampson et al., 2010, 2013; Longrich, 2011, 2013; Wick and Lehman, 2013; Ryan et al., 2014, 2017; Evans and Ryan, 2015; Brown and Henderson, 2015; Lehman et al., 2016; Mallon et al., 2016; Rivera-Sylva et al., 2016, 2017). The recognition of these new taxa adds to the growing record of taxonomic and morphologic diversity of ceratopsids. Between the mid 1990’s and 2000, a number of new ceratopsian specimens were collected by teams at the Arizona- Sonora Desert Museum (ASDM) and the New Mexico Museum of Natural History and Science (NMMNH) from the upper Campanian Fort Crittenden Formation of Adobe Canyon within the Santa Rita Mountains of southeastern Arizona (Figs. 1-2). These new specimens provide important new information about the morphologic and taxonomic diversity of Ceratopsidae in North America. The NMMNH specimens were briefly described by Heckert et al. (2003), who identified them as belonging to a centrosaurine ceratopsian. This was based on the overall morphology of the left squamosal, which has the characteristic “stepped” squamosal-parietal contact, a feature that is present in all centrosaurines (Ryan, 2007). The ASDM specimens are previously undescribed specimens that are new additions to this study. Here, we re-describe the Fort Crittenden Formation ceratopsian and
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141
Lucas, S.G. and Sullivan, R.M., eds., 2018, Fossil Record 6. New Mexico Museum of Natural History and Science Bulletin 79.
A NEW CERATOPSID DINOSAUR (CENTROSAURINAE: NASUTOCERATOPSINI) FROM THE
FORT CRITTENDEN FORMATION, UPPER CRETACEOUS (CAMPANIAN) OF ARIZONA
SEBASTIAN G. DALMAN¹, JOHN-PAUL M. HODNETT¹˒², ASHER J. LICHTIG¹ and SPENCER G. LUCAS¹
¹New Mexico Museum of Natural History, 1801 Mountain Road NW Albuquerque, NM 87104, -email: sebastiandalman@yahoo.com;
²Maryland-National Capital Parks and Planning Commission, Natural and Historical Resources Division, Archaeology Program,
8204 McClure Road, Upper Marlboro, MD 20772
Abstract—A new ceratopsid dinosaur, Crittendenceratops krzyzanowskii, is described from the Fort
Crittenden Formation (Upper Cretaceous) of southeastern Arizona, and is based on two individuals
consisting of partial cranial material recovered from the same stratigraphic unit. A phylogenetic
analysis of ceratopsids recovers Crittendenceratops as a member of Nasutoceratopsini, a subclade
of Centrosaurinae dened as the stem-based clade of centrosaurine ceratopsids more closely related
to Avaceratops lammersi and Nasutoceratops titusi than to Centrosaurus apertus. Reconstruction
of the parietosquamosal frill based on two specimens indicates that C. krzyzanowskii is a unique,
nasutoceratopsin taxon. The parietosquamosal frill of C. krzyzanowskii had a broad medial ramus and at
least ve epiparietal loci situated around the margin of the frill, a typical characteristic of Centrosaurinae.
The epiparietals are pronounced triangles that are dorsally concave and ventrally convex. Additionally,
two large, triangular hook-like anges, nearly the size of the epiparietal loci, are situated along the
dorsomedial margin of the parietal ramus. The left squamosal has a pronounced dorsal ridge with a single
dorsal squamosal process and large episquamosal undulations, a typical characteristic of Centrosaurinae.
The presence of C. krzyzanowskii in Arizona indicates that the nasutoceratopsins persisted into the late
Campanian. The temporal and paleobiogeographic distribution of Nasutoceratopsini further weakens
the hypothesis of distinct northern and southern Laramidian provinces.
INTRODUCTION
During the Campanian, the centrosaurine ceratopsids
exhibited great morphological and taxonomic diversity. Their
paleobiogeographic range extends through much of western
North America, from Alaska to Mexico (Loewen et al., 2010;
Fiorillo and Tykoski, 2012; Rivera-Sylva et al., 2016, 2017).
Outside of North America, centrosaurines have also been
described from China, with Sinoceratops zhuchengensis (Xu
et al., 2010), a lineage which originated in North America and
radiated into Asia (Ryan et al., 2017).
During the past two decades, several new ceratopsian
taxa have been identied in North America (e.g., Ryan, 2007;
Sampson et al., 2010, 2013; Longrich, 2011, 2013; Wick and
Lehman, 2013; Ryan et al., 2014, 2017; Evans and Ryan, 2015;
Brown and Henderson, 2015; Lehman et al., 2016; Mallon et
al., 2016; Rivera-Sylva et al., 2016, 2017). The recognition of
these new taxa adds to the growing record of taxonomic and
morphologic diversity of ceratopsids.
Between the mid 1990’s and 2000, a number of new
ceratopsian specimens were collected by teams at the Arizona-
Sonora Desert Museum (ASDM) and the New Mexico Museum
of Natural History and Science (NMMNH) from the upper
Campanian Fort Crittenden Formation of Adobe Canyon within
the Santa Rita Mountains of southeastern Arizona (Figs. 1-2).
These new specimens provide important new information about
the morphologic and taxonomic diversity of Ceratopsidae in
North America. The NMMNH specimens were briey described
by Heckert et al. (2003), who identied them as belonging to
a centrosaurine ceratopsian. This was based on the overall
morphology of the left squamosal, which has the characteristic
“stepped” squamosal-parietal contact, a feature that is present
in all centrosaurines (Ryan, 2007). The ASDM specimens are
previously undescribed specimens that are new additions to this
study.
Here, we re-describe the Fort Crittenden Formation
ceratopsian and include it in a phylogenetic analysis.
It is recognized here as a new species and a member of
Nasutoceratopsini, a clade of Centrosaurinae, which includes
the Campanian taxa Avaceratops lammersi, Nasutoceratops
titusi and Yehuecauhceratops mudei. Identity of a new
nasutoceratopsin provides evidence that this clade persisted
throughout Laramidia into the late Campanian.
Institutional Abbreviations: ANSP, Academy of Natural
Sciences, Philadelphia, Pennsylvania; ASDM, Arizona-Sonora
Desert Museum, Sonora, Arizona; CMN, Canadian Museum
of Nature, Ontario, Canada; GPDM, Great Plains Dinosaur
Museum, Malta, Montana; NMMNH, New Mexico Museum of
Natural History and Science, Albuquerque, New Mexico; TMP,
Royal Tyrrell Museum of Palaeontology, Drumheller, Alberta,
Canada.
GEOLOGICAL SETTING
The Upper Cretaceous (Latest Campanian) deposits of
the Fort Crittenden Formation are best exposed in the Adobe
Canyon area of the Santa Rita Mountains in southeastern
Arizona (Stoyanow, 1949; Miller, 1964; Drewes, 1971a,
1971b; Dickinson 1981; Hayes, 1986, 1987; Dickinson et al.,
1989) (Fig. 3). The sediments that formed the Fort Crittenden
Formation were deposited br rivers, in lakes and on lake margins
in faulted basins. Depositional environments of the formation
include subaerial and subaqueous settings consisting of alluvial
fans, alluvial plains, deltas, lakes, and rivers. The thickness of
the formation is 1700 m. The Fort Crittenden Formation has
been divided informally into ve members, in ascending order:
the shale member, the lower red conglomerate, the brown
conglomerate, the upper conglomerate, and the rhyolite tuff
members (Drewes, 1968, 1971a, 1971b). The material described
here and other vertebrate fossils (Table 1) were recovered from
the shale member, which records the abrupt onset of deposition
on an unconformable surface developed on the underlying,
Albian-age Turney Ranch Formation (Heckert et al., 2003).
The shale member is composed largely of mudrocks and silty
142
FIGURE 1. Crittendenceratops krzyzanowskii gen. et sp. nov.,
skeletal reconstruction, elements represented in the material
collected from the bonebed are indicated in gray.
FIGURE 2. Skeletal reconstruction of the referred specimen
of Crittendenceratops krzyzanowskii gen. et sp. nov., elements
represented in the material collected from the bonebed are
indicated in gray.
mudrocks, which are interbedded with subordinate siltstone
and sandstone (Heckert et al., 2003). Fossils found in the shale
member include bivalve and gastropod mollusks, which are
relatively common in the formation (Heckert et al., 2003).
The Salero Formation volcanic rocks that overlie the Fort
Crittenden Formation have been dated radiometrically to 70-74
Ma (Bikerman and Damon, 1966; Drewes, 1971a; Hayes and
Drewes, 1978; Inman, 1987). The volcanic rocks below the
Fort Crittenden yield a biotite K/Ar age of 75 Ma (Hayes, 1986,
1987). These ages suggest a late Campanian age for the Fort
Crittenden Formation (Heckert et al., 2003; Lucas and Heckert,
2005)
The Fort Crittenden Formation correlates with the Ringbone
Formation of southwestern New Mexico (Hayes, 1970a, 1970b;
Lawton et al., 1993; Lucas et al., 1995, 2000; Basabilvazo,
2000; Lucas and Heckert, 2005). Both formations are similar
lithologically and have similar vertebrate fossils (Lucas et al.,
1990, 1995; Anderson et al., 1998; Lucas and Heckert, 2005).
The Hidalgo Formation, which overlies the Ringbone Formation,
has been radioisotopically dated to 70.5 and 71.4 Ma (Lawton et
al., 1993). This further conrms the age of the Fort Crittenden
and the Ringbone formations as late Campanian (Lawton et al.,
1993; Lucas and Heckert, 2005).
MATERIAL AND METHODS
The holotype material was recovered from Adobe Canyon
in 2000 by the late Stan Krzyzanowski. The referred material
was collected by ASDM volunteers in the mid 1990’s from a
single site at Adobe Canyon. The type specimens described here
were prepared by SGD. All measurements of the specimens
were taken using a standard metric ruler. PAUP: Phylogenetic
Analysis Using Parsimony (Swofford, 2018) was used for the
phylogenetic analyses. To assess the systematic position of
Crittendenceratops krzyzanowskii, we coded it into the character
dataset generated by Evans and Ryan (2015) (Appendix1). Tree
statistics are the consistency index (CI), and rescaled consistency
index (RCI).
Nomenclatural Acts
The electronic edition of this article conforms to the
requirements of the amended International Code of Zoological
Nomenclature, and hence the new names contained herein
are available under that Code from the electronic edition of
this article. This published work and the nomenclatural acts it
contains, have been registered in ZooBank, the online registration
system for the ICZN. The ZooBank LSIDs (Life Science
Identiers) can be resolved and the associated information
viewed through any standard web browser by appending the
LSID to the prex “http://zoobank.org/.” The LSID for this
publication is: urn:lsid:zoobank.org:pub:0E856D22-94ED-
471A-BF42-98F2DB9FBFE4. The electronic edition of this
work was published in a journal with an ISSN, and has been
archived and is available from the following digital repositories:
LOCKSS (http://www.lockss.org); PubMed Central (http://
www.ncbi.nlm.nih.gov/pmc).
SYSTEMATIC PALEONTOLOGY
ORNITHISCHIA Seeley, 1888
CERATOPSIA Marsh, 1890
NEOCERATOPSIA Sereno, 1986
CERATOPSIDAE Marsh, 1888
CENTROSAURINAE Lambe, 1915
NASUTOCERATOPSINI Ryan,
Holmes, Mallon, Loewen, and Evans, 2017
Crittendenceratops, new genus
urn:lsid:zoobank.org:act:984E919F-464A-4E91-B3F8-
E419E6509441
Etymology: Derived from “Crittenden” referring to the
Fort Crittenden Formation, the stratum from which the specimen
came; “ceratops,” meaning a “horned-face” in Latinized Greek.
Diagnosis: As for type species, by monotypy.
Crittendenceratops krzyzanowskii, new species
Figs. 4-12
urn:lsid:zoobank.org:act:C9E5D1B1-8BDA-46A9-8225-
24372F7791FE
143
TABLE 1. Vertebrate fauna of the late Campanian Fort
Crittenden Formation, southeastern Arizona (data from McCord
et al., 2001; Heckert et al., 2003; D’Emic et al., 2010; Molnar,
pers. comm., 2010)
Chondrichthyes
Elasmobranchii
Rhinobatidae
Myledaphus bipartitus
Osteichthyes
Actinopterygii
Neopterygii
Holostei
Lepisosteidae
Lepisosteus occidentalis
Amiidae
Genus and species indeterminate
Vidalamiinae
Melvius sp.
Teleostei
Pachyrhizodontidae
cf. Pachyrhizodus sp.
Palaeolabridae
Palaeolabrus montanensis
Reptilia
Chelonia
Cryptodira
Adocidae
Adocus sp.
Trionychiidae
Trionyx s1
Plastomoneus sp.
Helopanolia distincia
Genus and species indeterminate
Squamata
Lacertilia
Teiidae
Polyglyphanodontinae
Genus and species indeterminate
Crocodylia
Eusuchia
Alligatoridae
Genus and species indeterminate
Family indeterminate
Genus and species indeterminate
Dinosauria
Ornithischia
Ornithopoda
Hadrosauridae
Genus and species indeterminate
Ceratopsia
Ceratopsidae
Centrosaurinae
Nasutoceratopsini
Crittendenceratops krzyzanowskii
gen. et sp. nov.
Saurischia
Theropoda
Tyrannosauridae
Genus and species indeterminate
Dromaeosauridae
Genus and species indeterminate 1
Genus and species indeterminate 2
Family indeterminate
Genus and species indeterminate
FIGURE 3. Generalized stratigraphic section of the lower Fort
Crittenden Formation in Adobe Canyon, Arizona, showing
the stratigraphic location of tetrapod localities (modied from
Heckert et al., 2003). Inset maps show the location of Adobe
Canyon in Santa Cruz County, Arizona.
Etymology: The specic epithet honors the late Stan
Krzyzanowski, who discovered and collected the specimen.
Diagnosis: Centrosaurine ceratopsid characterized by the
following unique combination of characters: forward-curving,
hook-like anges located along the dorsomedial margin of the
parietal lateroposterior ramus; extensive epiparietals located
along the lateroposterior margin of the parietal ramus; parietal
ramus dorsoventrally thick; dorsal surface of the parietal ramus
contains deep elongate fossa; posteroventrolateral concavity
pronounced and extensively rugose; squamosal dorsal ridge
short, pronounced and located in close proximity to dorsolateral
margin of the bone.
Holotype: NMMNH P-34906, incomplete right parietal
and nearly complete left squamosal.
Referred specimens: ASDM 380, posterior end of the
right dentary; ASDM, 884, 1133, and 1138, teeth, ASDM 1935,
mid-parietal bar; ASDM 1975, left squamosal; ASDM 1981,
epiparietal locus.
Type locality: Adobe Canyon, Santa Rita Mountains,
Santa Cruz County, Arizona (NMMNH locality 4669). Exact
coordinates on le at the New Mexico Museum of Natural
144
FIGURE 4. Holotype right parietal of Crittendenceratops krzyzanowskii gen. et sp. nov., A, dorsal view; B, ventral view; C,
posterior view; D, ventral view of the posterior portion of the parietal ramus; E, lateral view. Abbreviations: d, dorsal ange; gr,
groove; m, medial ange of the lateral parietal ramus; P, epiparietal locus; pcon, posterior concavity; PF, parietal fenestra; plvcov,
posterolateroventral convexity point; pvs, posteroventral surface; rdg, ridge.
History and Science, Albuquerque.
Horizon and age: The specimens were recovered from
late Campanian shale beds (~73 Ma) of the lower part (“shale
member”) of the Fort Crittenden Formation (Heckert et al.,
2003).
DESCRIPTION
Parietal: The holotype (NMMNH P-34906) right parietal is
incompletely preserved (Fig. 4). It is 2.5 cm thick dorsoventrally
and 20 cm long along the lateral margin. The lateral and dorsal
margins of the preserved parietal form a semicircular outline
in dorsal and ventral views. As preserved, the parietal has four
well-developed epiparietal loci, which are completely fused to
the bone. However, it is likely that the more complete parietal
had at least six epiparietal loci on the right and the left sides. The
epiparietal loci are present along the lateral and caudal margins
of the preserved parietal. They are located at the dorsal surface
of the lateral and caudal margins of the parietal and are not
uniform in size. This unusual location of the epiparietal loci and
the dorsoventral thickness of the parietal results in the formation
of an extensive caudal concavity, which is most pronounced
along the dorsal surface of the caudal portion of the parietal.
Some of the epiparietal loci are triangular, whereas others are
rectangular. The dorsal surface at the apices of each preserved
epiparietal locus is strongly sculpted and convex, whereas more
ventrally the epiparietal loci are concave. The sculpted surface of
the epiparietal loci is formed by the short and elongate grooves
and ridges.
The concave base of each epiparietal locus merges with a
deep and elongate groove that extends along the dorsal surface
of the preserved parietal.
There is a pronounced, ange-like structure on the
dorsomedial margin of the parietal that slightly overhangs
the parietal fenestra. The ange-like structure is incomplete,
and most of its dorsal surface is missing. The function of the
ange-like structure is unknown. The bone surface of the ventral
side of the parietal is strongly rugose and dorsoventrally deep.
The rugosity is more prominent along the ventral surface of
the parietal. In ventral view, the lateral and dorsal margins of
the parietal meet at an 110° angle. The point at which these
two margins meet is strongly convex, rugose and is identied
here as the posterolateroventral convexity of the parietal. The
lateral margin of the parietal, especially the portion of the bone
at the broken end, is slightly twisted medially. There is a low,
distinctive ridge that extends along the ventromedial margin
of the parietal that is rugose and visible in dorsal and ventral
aspects.
The fragments of the parietal of the referred specimen
consist of the mid-parietal bar (ASDM 1935) and an isolated
right lateral epiparietal locus (ASDM 1981) (Fig. 5). The dorsal
surface of the mid-parietal bar is convex and is covered with
densely packed ne grooves and ridges. The ventral surface is
slightly concave. The bone is dorsoventrally thick and appears
transversely wide, similar to that of Wendiceratops peterhewsi
(Evans and Ryan, 2015).
The isolated right epiparietal locus is rectangular-shaped
145
FIGURE 5. Referred cranial elements to Crittendenceratops krzyzanowskii gen. et sp. nov., ASDM 1935 mid-parietal bar in A,
dorsal and B, ventral views; ASDM 1981 right epiparietal locus in C, dorsal and D, ventral views.
146
FIGURE 6. Holotype left squamosal of Crittendenceratops
krzyzanowskii gen. et sp. nov., NMMNH P-34906 A, dorsal;
and B, ventral views. Abbreviations: em, embayment; eop,
exoccipital contact; for, foramen; fos, fossa; dgs, dorsal groove
of squamosal; dr, dorsal ridge; dsp, dorsal squamosal process;
lvr, lateroventral ridge; otn, otic notch; qc, quadrate contact;
qjc, quadratojugal contact; pac, parietal contact; poc, postorbital
contact; pog, paraoccipital groove; pvgr (1, 2), posteroventral
groove; rdg, ridge; SU, squamosal undulation.
FIGURE 7. Left squamosal of Crittendenceratops krzyzanowskii gen. et sp. nov., A, anterior; B, posterior; C, medial; and D, lateral
views. Abbreviations: eop, exoccipital contact; fos, fossa; dr, dorsal ridge; dsp, dorsal squamosal process; lvr, lateroventral ridge;
gr, groove; qc, quadrate contact; qjc, quadratojugal contact; pac, parietal contact; pmes; posteromedial elliptic contact surface;
poc, postorbital contact; pog, paraoccipital groove; pt, pit.
and is approximately 5.5 cm wide and 4.2 cm long. The dorsal
surface of the epiparietal locus is rugose with several circular
pores. The ventral margin of the epiparietal locus has a diagonal
rugose contact suture for the squamosal articulation.
Squamosal: The holotype (NMMNH P-34906) left
squamosal is well preserved and nearly complete, missing only
the anterior portion (Figs. 6-8). Overall length of the preserved
squamosal is 25 cm, whereas the maximum mediolateral width
is 19 cm. The squamosal has the “stepped” squamosal-parietal
contact, a feature characteristic of all centrosaurines (Ryan,
2007). However, among centrosaurines the “stepped” squamosal
parietal contact in Avaceratops is weakly developed.
The squamosal has a subrectangular shape. The posterior
margin of the squamosal is well-preserved, with six undulation-
like structures, which are identied here as the squamosal
undulation, and are abbreviated as SU (Fig. 6). The rst two
undulations (SU1 and SU2) have ragged posterior margins, each
formed by four small and closely spaced triangular serration-
like features. The rst undulation (SU1) is 4 cm long, whereas
the second undulation (SU2) is 6 cm long. Undulations two
(SU2) and three (SU3) are separated by a low embayment that
is approximately 1.5 cm long. The third undulation (SU3) has
the same length as the second undulation (SU2); however, its
posterior margin is not ragged, but convex. Undulations three
(SU3) and four (SU4) are also separated by a low embayment
that is approximately 1 cm long. Undulation four (SU4) is 3.3
cm long and has a convex caudal margin. Undulations four
(SU4) and ve (S5) are also separated by an embayment.
However, here the embayment is more pronounced than the
embayment between undulations two (SU2) and three (SU3)
and three (SU3) and four (SU4). Undulation ve (SU5) is 3 cm
long and has a convex posterior margin. Undulations ve (SU5)
and six (SU6) are separated by a low and short embayment that
is approximately 0.5 cm long.
The dorsal surface of the squamosal has a distinct, well-
developed ridge that extends for nearly half of the length of the
squamosal (Fig. 6). The ridge is pronounced and strongly convex
at the anterior end of the squamosal (its point of origin). As the
ridge extends posteriorly, it slopes towards the lateral margin
of the squamosal at a low angle. The ridge parallels the lateral
margin of the squamosal and nearly merges with it, terminating
7.3 cm from undulation six (SU6). The ridge has gentle, sloping
sides. The characteristic position of the ridge in the squamosal
is identied here as an autapomorphy of Crittendenceratops.
147
FIGURE 8. Holotype left squamosal of Crittendenceratops krzyzanowskii gen. et sp. nov., in dorsal view, showing the morphology
and position of the foramina. A, anterior foramina in dorsal; B, closeup of the anterior foramina in dorsal view; C, closeup of the
anterior foramina in ventral view; D, posterior foramen; E, closeup of the posterior foramen. Abbreviations: for, foramen; rdg,
ridge.
A single, ovoid-shaped, bump-like process is located at the
posterior end of the ridge. This bump-like process is identied
here as the dorsal process of the squamosal. The process is
pronounced and has a rugose dorsal surface and is visible in
anterior, dorsal, lateral, medial, and posterior aspects (Figs. 6-8).
The postquadrate embayment (otic notch) is elongate and
broad, and lies anterior to a sharp posterolateral angle facing the
convex corner of the squamosal (Fig. 6).
The dorsal surface of the squamosal has three distinct
neurovascular foramina (Figs. 6, 8). The two anterior foramina
are located on the lateral side of the dorsal ridge. The foramina
are aligned and approximately 0.2 cm apart from each other. The
third foramen is located at the terminal end of the dorsal ridge.
The anteroventral surface of the squamosal is divided
by two vertical ridges that parallel each other and dene two
sulci, one for the contact with the exoccipital and the other for
the contact with the quadrate (Figs. 6-7). The contact for the
exoccipital is represented by a triangular-shaped concavity. The
contact for the quadrate is distinctly elongate and narrower than
the contact for the exoccipital. There is a deep paraoccipital
sulcus that separates these two contacts from one another.
Directly posterior to the exoccipital contact, quadrate
contact and the paraoccipital groove are striated muscle scars.
These muscle scars probably correspond to the m. adductor
mandibulae posterior for movement of the jaws during feeding.
Directly posterior to the quadrate contact, the lateroventral
margin of the squamosal has a low ridge that is 4.5 cm long
(Figs. 6-7). The ridge emerges from the base of the quadrate
contact, extends along the lateroventral margin of the squamosal
and tapers into the bone posteroventrally. The bone is smooth
ventral to this ridge in the postquadrate embayment (otic notch).
There is a shallow fossa that separates the ridge from the lateral
margin of the squamosal. Directly posterior to the ridge the bone
surface of the squamosal is smooth and convex. A distinctive
low ridge extends near the lateral margin of the squamosal. The
ridge originates approximately at the level of the “stepped”
squamosal-parietal contact and continues posteriorly toward the
undulation (SU6) margin. At the level of the posterior corner
of the squamosal and undulation six (SU6), the ridge begins to
curve gently, continues to ascend medially and then terminates
between undulation one (SU1) and the posterior margin of the
parietal contact. The ridge is not uniform from the point of origin
to its terminal end. It lies closer to the posterior margin of the
squamosal at the level of undulations one (SU1) and two (SU2).
The surface texture near the posterior margin of the squamosal is
smooth, whereas the convex surface of the undulations possesses
a distinct surface texturing.
There are two distinct, elongated shallow grooves, which
are located on the ventral surface at the posterior end of the
squamosal. The grooves parallel each other and extend from the
posterior margin of undulation six (SU6).
The medial side of the squamosal preserves the contact
for the parietal posteriorly. The contact surface is concave and
contains several shallow grooves, pits and ridges. The contact
surface for the parietal has a characteristic elliptical-shaped
surface that is approximately 3.5 cm long. In medial view,
148
FIGURE 9. ASDM 1975, left squamosal referred to
Crittendenceratops krzyzanowskii gen. et sp. nov., in A, dorsal
and B, ventral views. Abbreviations: dr, dorsal ridge; dsp,
dorsal squamosal process; otn, otic notch; qjc, quadratojugal
contact; rdg, ridge; SU, squamosal undulation.
FIGURE 10. ASDM 1980, left squamosal referred to
Crittendenceratops krzyzanowskii gen. et sp. nov., A, dorsal
view and B, closeup of the dorsal squamosal process.
missing a large portion of the medial end and a portion of the
anterior end (Fig. 9). The length of the preserved squamosal is
39 cm. The squamosal has a subrectangular shape. The posterior
margin of the squamosal is not well preserved, and only three
undulation-like structures are present, which are identied here as
SU4, SU5 and SU6. The undulation SU4 is broken in the middle
and is missing a portion of its posterior margin. The undulations
SU5 and SU6 are complete, but are not as strongly inated as the
undulations in the holotype squamosal of Crittendenceratops
krzyzanowskii. Here they are low and slightly more elongated.
However, the undulation SU6 exhibits some ination, and in
overall morphology it closely resembles the undulation SU6 in
the holotype specimen of C. krzyzanowskii. The posterior margin
of the squamosal is not well preserved; therefore, it is difcult to
determine if the undulations were separated by the characteristic
embayment, as in the holotype specimen of C. krzyzanowskii.
The dorsal surface of the squamosal has a low dorsal ridge.
The ridge is convex at the anterior end of the squamosal (point
of its origin). And, as the ridge extends posteriorly, it slopes
towards the lateral margin of the squamosal at a low angle. The
ridge parallels the lateral margin of the squamosal and nearly
merges with it, terminating 18.5 cm from undulation six (SU6).
The ridge has gentle, sloping sides, similar to the dorsal ridge
in the holotype specimen of Crittendenceratops krzyzanowskii.
A single, ovoid-shaped dorsal process of the squamosal is
preserved on the dorsal surface of the dorsal squamosal ridge.
The process is pronounced and has a rugose dorsal surface and is
visible in anterior, dorsal, lateral, medial and posterior aspects.
It is situated at the posterior end of the dorsal ridge and seems
to overhang the lateral margin of the squamosal (Fig. 10). The
postquadrate embayment (otic notch) is broad and elongated.
It lies anterior to a low posterolateral angle facing the convex
corner of the squamosal (Fig. 9).
The ventral surface is not well preserved. There are several
elongated grooves and ridges that extend through the surface;
however, some of these ridges and grooves are most likely
the result of weathering and are not morphological features.
However, there is a single ridge that underlies the squamosal
undulations, a feature that is also present in the holotype
specimen of Crittendenceratops krzyzanowskii (Fig. 6). The
quadratojugal contact surface is broad, but is incomplete,
missing its distal end.
Dentary: The referred right dentary (ASDM 380) is
incomplete (Fig. 11). It preserves a portion of the posterior end.
The lateral side of the dentary preserves two low ridges, which
are separated by a shallow groove. The ridges and the groove
mark the base of the coronoid process. The ridges are gently
FIGURE 11. ASDM 308, posterior part of right dentary referred
to Crittendenceratops krzyzanowskii gen. et sp. nov., in A,
lateral, B, medial, C, dorsal, D, ventral views. Abbreviations:
alv, alveoli; rdg, ridge.
between the terminal end of the elliptical-shaped contact surface
and undulation one (SU1) is a deep sinuous fossa. This fossa
extends on the medial surface of the squamosal and nearly
parallels the ventral margin of the parietal contact surface.
The anterodorsal portion of the squamosal from the
“stepped” parietal contact is convex, whereas the posterodorsal
portion from the “stepped” parietal contact is angled, so that
the surface in this region of the squamosal is concave. This
characteristic shape of the squamosal is best seen in medial and
lateral views (Fig. 7).
The referred left squamosal (ASDM 1975) is incomplete,
149
curved posterodorsally. There is a shallow fossa that separates
the base of the coronoid process from the body of the dentary.
The lingual side of the dentary preserves several empty alveoli.
The alveoli are narrow and dorsoventrally deep, a typical
ceratopsian morphology (e.g., Penkalski and Dodson, 1999;
Evans and Ryan, 2015).
Teeth: Three isolated teeth (ASDM 884, 1133, 1138) are
preserved (Fig. 12). These are not well preserved, but, they have
typical ceratopsid size and morphology (e.g., Evans and Ryan,
2015). Some of the morphological features identied in these
teeth, include the following: cingulum, denticles, mesial and
distal lobes and primary and secondary ridges. The teeth are leaf
shaped, as in other ceratopsians (e.g., Evans and Ryan, 2015).
And, as in other ceratopsians the upper portion of the tooth is
separated from the root by a raised ridge called the cingulum
(e.g., Tanoue et al., 2009). The cingulum is well preserved in
all three teeth. The lingual enameled side in each tooth has a
prominent longitudinal ridge, which is called the primary ridge
(e.g., Tanoue et al., 2009; Evans and Ryan, 2015). In some
teeth the primary ridge is offset either mesially or distally from
the central plane of the tooth. It divides the lingual side of the
tooth into distal and mesial lobes. The margins of the two lobes
contain small, papillae-like denticles (e.g., Tanoue et al., 2009).
Each tooth has two secondary longitudinal ridges on the lingual
enameled side, which nearly parallel the primary ridge. There
are no subsidiary ridges between the primary and secondary
ridges, and the lingual, enameled side of the tooth is not
ornamented. In contrast, the teeth of derived ceratopsians (e.g.,
Centrosaurus and Wendiceratops) have ne subsidiary ridges,
which are aligned subparallel to the primary ridge (e.g., Evans
and Ryan, 2015).
All the teeth are missing the root. Therefore, it is unclear
if the teeth were double-rooted as are the teeth of derived
ceratopsids (e.g., Evans and Ryan, 2015; Tanoue et al., 2009).
PHYLOGENETIC ANALYSIS
Crittendenceratops krzyzanowskii is coded in the
phylogenetic analysis of Evans and Ryan (2015). The data
matrix was analyzed in Tree statistics. Consistency index (CI)
and rescaled consistency index (RCI), and Bremer support
values were calculated using PAUP (Swofford, 2018). We
report a “plurality rules” consensus tree also showing four
clades that are the best supported but below 50% of the most
parsimonious trees as would be shown in a 50% majority rule
tree (Fig. 13). The phylogenetic analysis resulted in 4845 most-
parsimonious trees (tree length of 289 steps, 116 informative +
2 constant + 7 parsimony uninformative [no effort was made
to exclude uninformative characters] 104 binary, 21 multistate
CI (consistency index) = 0.5190, retention index and rescaled
consistency index (RCI) = 0.3684). All multistate characters
ordered. Multiple states for a taxon were treated as uncertainty.
Tree search used tree-bisection-reconnection on a starting tree
determined by random addition using 10 replicates. Bootstrap
analysis was conducted using 420 bootstrap replicates with
full heuristic search as in the initial analysis, but with only
one random addition sequence per replicate. Upper numbers
in bold on branches indicate branch representation percentage
among the MPTs. Lower numbers in italics on branches indicate
bootstrap proportion or support value.
Crittendenceratops is nested well within Natsuoceratopsini
and is recovered here as a tentative sister taxon to the Malta taxon.
However, due to low MPT percentages, the interrelationship
of Nasutoceratopsini is not fully resolved at this time. In our
analysis, the newly erected clade Eucentrosaura includes
Centrosaurini (sensu Maiorino et al., 2015 and Ryan et al., 2017)
such as Centrosaurus, Coronosaurus, Rubeosaurus, Spinops,
Styracosaurus, and Xenoceratops members of Pachyostora
(sensu Fiorillo and Tykoski, 2012) such as Achelousaurus,
Einiosaurus, and three species of the genus Pachyrhinosaurus,
P. canadensis, P. lakustai, and P. perotorum. In the analysis
of Sampson et al. (2013) and Lund et al. (2016a, 2016b), taxa
such as Sinoceratops, Wendiceratops, and Xenoceratops were
recovered in Pachyrhinosaurini. Furthermore, in our analysis
Albertaceratops, Machairoceratops, Medusaceratops, and
Xenoceratops are not recovered in a polytomy. The overall
morphology of the plurality rules tree is most similar to that of
the strict consensus tree of Chiba et al. (2018).
DISCUSSION
Relationships of Crittendenceratops krzyzanowskii
Crittendenceratops krzyzanowskii is recovered as a member
of the stem-based clade Nasutoceratopsini Ryan et al. 2017,
which includes taxa more closely related to Avaceratops +
Nasutoceratops than to Centrosaurus apertus. Furthermore,
C. krzyzanowskii is the rst described ceratopsian from the
late Campanian Fort Crittenden Formation of Arizona and
represents one of the youngest known nasutoceratopsins.
Members of the Nasutoceratopsini clade can be differentiated
from other centrosaurine ceratopsians based on the following
morphological features: the lack of the prominent epimarginal
ornamentation in the frills, the lack of median embayment of the
posterior parietal ramus, and the possession of a median scallop
to support the epiparietal locus P0 (Ryan et al., 2017). In contrast,
the Centrosaurini clade of Ryan et al. (2017), which includes taxa
more closely related to Centrosaurus than to Pachyrhinosaurus,
is characterized by extensively ornate parietosquamosal frills,
prominent nasal horncores and short supraorbital horncores.
Additionally, some members of the Centrosaurini clade (e.g.,
Centrosaurus apertus) have a long overhanging epiparietal
locus (P1). Although nasutoceratopsins have less ornate frills,
C. krzyzanowskii is the rst member of the clade with complex
parietal ornamentation (Fig. 14). The epiparietal loci in C.
krzyzanowskii are all fused to the parietal ramus. The dorsal
surface of each locus is strongly convex, whereas the ventral
surface close to the parietal fenestra is concave.
Unlike other nasutoceratopsins (e.g., Avaceratops,
Nasutoceratops, “Malta new taxon,” GPDM 63, and the
Oldman Formation taxon, CMN 8804) Crittendenceratops
has a thick parietal, which becomes only slightly thinner at
its proximal end towards the contact with the squamosal.
Although the parietal of Crittendenceratops is incomplete, there
is no clear evidence that this element possessed the median
embayment, a feature that is present and well-developed in
some of the advanced centrosaurine (e.g., Achelousaurus,
Einiosaurus, and Styracosaurus) and chasmosaurine ceratopsids
(e.g., Arrhinoceratops, Chasmosaurus, Pentaceratops, and
FIGURE 12. Referred isolated teeth to Crittendenceratops
krzyzanowskii gen. et sp. nov., A, ASDM 883, B, ASDM 1133,
C, ASDM 1138 in lingual view.
150
FIGURE 13. Phylogenetic relationships of Crittendenceratops krzyzanowskii gen. et sp. nov. within Ceratopsidae. “Plurality rules”
tree of 4845 most parsimonious trees (tree length = 289; CI = 0.5190; RCI = 0.3684) recovered in the phylogenetic analysis. See
text for details.
151
FIGURE 14. Reconstructions and comparison of nasutoceratopsin parietals-frills, A, Avaceratops lammersi (modied from
Penkalski and Dodson, 1999); B, Crittendenceratops krzyzanowskii, C1, CMN 8804 in dorsal and C2, CMN 8804 in ventral views;
D, Nasutoceratops titusi.
Spiclypeus), but absent in members of the Triceratopsini clade
(e.g., Ojoceratops, Regaliceratops, Torosaurus, and Triceratops).
In chasmosaurines (e.g., Chasmosaurus, Pentaceratops, and
Spiclypeus), the median embayment of the parietal is formed
by the caudolateral orientation of the posterior portion of
parietal ramus. In contrast, in centrosaurine ceratopsids the
median parietal embayment is formed by the modication of
epiparietals on both sides of the posterior midline (Ryan et al.,
2017). Avaceratops lammersi and Nasutoceratops titusi have
epiparietal locus P0 instead of the median parietal embayment
(Ryan et al., 2017).
As shown in the description, Crittendenceratops has well-
developed parietal fenestrae. Similarly, well-developed parietal
fenestrae are present in Nasutoceratops titusi (e.g., Lund, 2010;
Sampson et al., 2013; Lund et al., 2016). Penkalski and Dodson
(1999) stated that specimens ANSP 15800 and MOR 692, referred
to Avaceratops lammersi, lack parietal fenestrae. However, both
specimens are known from incomplete parietals. Therefore, it is
difcult to determine if A. lammersi had a fenestrated frill (Ryan
et al., 2017). Ryan et al. (2017) suggested that the indeterminate
Oldman Formation nasutoceratopsin (CMN 8804), had small,
anteriorly positioned fenestrae. However, the parietals of CMN
8804 are incomplete, which makes it difcult to determine the
presence of the parietal fenestrae.
One of the characteristic morphological features of the
squamosal of Crittendenceratops krzyzanowskii is the dorsal
squamosal ridge with a single dorsal squamosal process.
Sampson et al. (2013) suggested that the dorsal squamosal ridge
is an autapomorphy of Nasutoceratops. However, this feature
is present in a basal centrosaurine, the Menefee Formation new
taxon (NMMNH P-25052), and in other basal centrosaurines such
as Diabloceratops and Wendiceratops, and is also present in the
nasutoceratopsins Avaceratops, “Malta new taxon,” GPDM 63,
and Yehuecauhceratops. In contrast, the ridge is less developed
in more advanced centrosaurines such as Centrosaurus and
Styracosaurus. Therefore, the dorsal squamosal ridge is now
considered a symplesiomorphy of basal centrosaurines (Ryan et
al., 2017). However, among the nasutoceratopsins the position
152
FIGURE 15. Comparison of nasutoceratopsin squamosals in left dorsal view. A, Avaceratops lammersi; B, Crittendenceratops
krzyzanowskii; C, Nasutoceratops titusi. D, Yehuecauhceratops mudei, showing the position and the overall morphology of the
dorsal squamosal ridge and the position of the dorsal squamosal process. Abbreviations: dr, dorsal squamosal ridge; dsp, dorsal
squamosal process.
FIGURE 17. Squamosal of Centrosaurus apertus, TMP1995.401.0007, showing the position of the dorsal squamosal process and
the dorsal squamosal ridge. Abbreviation: dr, dorsal squamosal ridge; dsp, dorsal squamosal process.
153
FIGURE 16. Squamosals of basal centrosaurine ceratopsians in left dorsal view showing the position of dorsal ridges. A, the
Menefee Formation new taxon, NMMNH P-25052; B, Wendiceratops pinhornensis, TMP 2011.051.0009 (right squamosal
reversed). Abbreviations: dsb, dorsal squamosal process; pdr, primary dorsal ridge of the squamosal; sdr, second dorsal ridge of
the squamosal; tdr, third dorsal ridge of the squamosal.
154
FIGURE 18. Squamosals of centrosaurine ceratopsians in right dorsal view. A, Achelousaurus horneri (left reversed); B,
Albertaceratops nesmoi (left reversed); C, Coronosaurus brinkmani; D, Einiosaurus procurvicornis, showing the position of the
dorsal squamosal ridge and the dorsal squamosal process. Note: A. horneri and E. procurvicornis do not have the dorsal squamosal
process and the dorsal ridge in these taxa is weakly developed.
and the overall morphology differ. For example, in Avaceratops
and Nasutoceratops the anteriormost portion of the ridge lies
close to the medial margin of the parietal contact and slopes
gently posterolaterally; whereas, in Crittendenceratops and
Yehuecauhceratops the ridge lies close to the lateral margin of
the squamosal (Fig. 15).
In Crittendenceratops, Avaceratops, Nasutoceratops and
Yehuecauhceratops the dorsal squamosal ridge is pronounced
(Fig. 15). However, in Crittendenceratops the ridge is short,
whereas in Avaceratops, Nasutoceratops, and Yehuecauhceratops
the ridge extends throughout most of the length of the squamosal.
Among the centrosaurines, the Menefee Formation new taxon
(NMMNH P-25052) is the only taxon in which the squamosal
has three distinct dorsal ridges, whereas most other taxa have
only one dorsal ridge; the exception is Wendiceratops, with two
dorsal ridges (Fig. 16).
The dorsal squamosal process located on the dorsal
squamosal ridge in Crittendenceratops is another characteristic
morphological feature. Overall morphology and placement of
the ridge is most similar to that of Yehuecauhceratops (Fig. 15).
In both taxa the dorsal squamosal process is located near the
terminal end of the dorsal squamosal ridge. In Crittendenceratops
the dorsal squamosal process is farther away with respect to the
quadratojugal contact; whereas in Yehuecauhceratops the dorsal
squamosal process is closer to the quadratojugal contact and
to the otic notch. In Nasutoceratops the position of the dorsal
squamosal process is most similar to that of Yehuecauhceratops
(Fig. 15). The dorsal squamosal process is also present in
Centrosaurus apertus (Fig. 17), whereas in some other taxa,
such as Achelousaurus and Einiosaurus (Fig. 18A–D), the ridge
is weakly developed, and in Albertaceratops and Coronosaurus
(Fig. 18B–C) the ridge is formed by the coalescence of three
distinctive, low dorsal squamosal processes. In Coronosaurus
there are four dorsal squamosal processes; however, the fourth
dorsal squamosal process is not a part of the dorsal squamosal
ridge (Fig. 18C). Interestingly, Avaceratops has four dorsal
squamosal processes that form the dorsal squamosal ridge (Fig.
15A). Similarly, the right squamosal of the Oldman Formation
taxon (CMN 8804) preserves three dorsal squamosal processes
on the dorsal squamosal ridge. The overall morphology and the
position closely resemble that of TMP 1965.23.26, referred to
Centrosaurus (Fig. 19). However, based on overall morphology,
TMP 1965.23.26 more closely resembles a nasutoceratopsin
than Centrosaurus.
Another distinctive morphological feature in the squamosal
of Crittendenceratops krzyzanowskii is a low ridge on the
ventral surface that extends along the lateral and posterior
margins of the squamosal. A similar ridge is present in
basal and advanced centrosaurine taxa (e.g., Centrosaurus,
Diabloceratops, Einiosaurus, and the Menefee Formation new
taxon) and is absent in pachyrhinosaurins and nasutoceratopsins
(e.g., Pachyrhinosaurus and Yehuecauhceratops) (Fig. 20). In
155
FIGURE 19. Squamosals of centrosaurine ceratopsians in right dorsal view. A, “Centrosaurus,” TMP1965.23.26; B, the Oldman
Formation taxon, CMN 8804, showing a series of dorsal squamosal processes on the dorsal squamosal ridge. Abbreviations: dsp,
dorsal squamosal process; otn, otic notch; qjc, quadratojugal contact.
156
FIGURE 20. Squamosals of centrosaurine ceratopsians in left medial view. A, Centrosaurus apertus; B, Diabloceratops eatoni;
C, Einiosaurus procurvicornis; D, the Menefee Formation new taxon, NMMNH P-25053; E, Pachyrhinosaurus lakustai; F,
Yehuecauhceratops mudei, showing the position and the overall morphology of the posteroventral ridge. Note: the ridge is absent in
P. lakustai and Y. mudei. Abbreviation: rdg, ridge.
157
FIGURE 21. Life reconstruction of Crittendenceratops krzyzanowskii gen. et sp. nov., by Sergey Krasovskiy.
Crittendenceratops, the ridge is not uniform from the point of its
origin, which is at the level of the “stepped” squamosal-parietal
contact to its terminal end at the squamosal undulation (SU6)
margin. In Centrosaurus the ridge also originates at the level
of the “stepped” squamosal-parietal contact and does not reach
the medial margin of the squamosal, but instead it terminates at
the level of episquamosal four (S4). The ridge is not uniform
throughout its length; however, the bone surface around the
ridge is smooth. In Einiosaurus the overall morphology of the
ridge is most similar to that of Centrosaurus. However, the ridge
in Einiosaurus has a more uniform outline, and its point of origin
is nearly at the posterior margin of the quadratojugal contact,
whereas its terminal end is at the level of episquamosal one (S1).
Furthermore, the terminal end of the ridge in Einiosaurus
does not reach the medial margin of the squamosal and is
approximately 3.5 cm from it. In Diabloceratops and in the
Menefee Formation new taxon, the ridge is pronounced and
well developed. In both taxa the ridge also originates at the
level of the “stepped” squamosal-parietal contact. However, in
Diabloceratops the ridge is directly posterior to and contacts the
quadratojugal contact, whereas in the Menefee Formation new
taxon, the ridge is approximately 4.5 cm from the quadratojugal
contact. In Diabloceratops the ridge reaches the posteromedial
margin of the squamosal, whereas in the Menefee Formation
new taxon, the ridge terminates at the level of episquamosal
two (S2). Furthermore, the outline of the ridge in the Menefee
Formation new taxon is more uniform than in Diabloceratops.
The squamosal of Crittendenceratops can be further
differentiated from other centrosaurines on the basis of
the swollen appearance of the episquamosal loci and the
presence of two elongate, but shallow grooves located in the
posteroventral corner of the squamosal. Finally, the well-
developed ornamentation of the parietosquamosal frill sets
Crittendenceratops krzyzanowskii apart from all known
centrosaurine ceratopsid taxa and in particular from other known
nasutoceratopsins (Figs. 14, 21).
CENTROSAURINE EVOLUTION IN NORTH AMERICA
Since the discovery over a century ago of the rst skeletal
remains of North American ceratopsian dinosaurs (e.g.,
Centrosaurus, Chasmosaurus, Styracosaurus, Torosaurus,
and Triceratops), the speculation about their place of origin
has continued (Ryan et al., 2017). However, during the past
decade the discoveries of several new taxa shed new light about
the origin of the Centrosaurinae clade in southern Laramidia,
including the following taxa: the Menefee Formation new
taxon (NMMNH P-25052) of northwestern New Mexico (83
Ma) and Diabloceratops eatoni (80 Ma) from the Wahweap
Formation of southern Utah (Kirkland and DeBlieux, 2010).
The chasmosaurine Judiceratops tigris (Longrich, 2013) from
the lower Judith River Formation, Montana (79 Ma), provides
evidence for the oldest occurrences of the Chasmosaurinae
clade in northern Laramidia. The oldest recognized member of
the Nasutoceratopsini clade is Avaceratops lammersi (Dodson,
1986), from the lower Judith River Formation, Montana (78 Ma);
whereas the oldest member of the Pachyrhinosaurini clade is an
indeterminate pachyrhinosaurine ceratopsian (TMP2001.79.1)
from the upper Dinosaur Park Formation, Alberta (75.1 Ma),
which point to the northern Laramidia origin of these clades
(Ryan et al., 2010).
We did not include the Menefee Formation new taxon in
our phylogenetic analysis. However, based on its stratigraphic
158
position and temporal occurrence and also on several primitive
morphological characters, it represents the oldest record
of centrosaurines in North America, and is basal to both
nasutoceratopsins and centrosaurins. The Menefee Formation
new taxon has a pronounced dorsal squamosal ridge, a feature
that it shares with all nasutoceratopsins and with some advanced
centrosaurines (Fig. 16). This ridge is formed by the coalescence
of three dorsal squamosal processes. The position of one of
these processes (dsp3) in the Menefee Formation new taxon is
similar to that of nasutoceratopsins (e.g., Crittendenceratops,
Nasutoceratops, and Yehuecauhceratops). Although the
Menefee Formation new taxon is not a nasutoceratopsin, the
various morphological features it shares with the members of
this clade suggest that the origin of Nasutoceratopsini was in
southern Laramidia and not in northern Laramidia. Furthermore,
the Menefee Formation new taxon is most likely a common
ancestor of Centrosaurinae and Nasutoceratopsini. However,
extensive sampling of various Late Cretaceous localities,
especially in the southern part of western North America, and the
recovery of new specimens are needed for better understanding
of the origin, evolution, and paleobiogeographic distribution of
nasutoceratopsins and other ceratopsian groups.
CONCLUSIONS
Crittendenceratops krzyzanowskii is a new genus
and species that represents the youngest current record of
nasutoceratopsins in North America. The identity of a new
member of the Nasutoceratopsini clade in southern Laramidia
lls in the evolutionary gap between the slightly older
Yehuecauhceratops and the nasutoceratopsins known from the
late Campanian in northwestern North America. Furthermore,
Crittendenceratops and Yehuecauhceratops add new information
to the paleobiogeographic distribution of nasutoceratopsins
during the Cretaceous.
ACKNOWLEDGMENTS
We thank the late Stan Krzyzanowski for the discovery of the
type material of Crittendenceratops krzyzanowskii. Furthermore,
we thank Andrew Farke, Steven E. Jasinski, and Héctor Rivera-
Sylva for sharing photographs of various specimens. We thank
Anna Domitrovic and Robert Scarborough for their help at
ASDM. JPH thanks Robert McCord, Gavin McCullough and
Ralph Molnar for their conversations and notes on the Fort
Crittenden Formation. We thank the reviewers Andy Farke
and Jonathan Wagner for helpful and constructive comments.
SGD thanks Jonathan Wagner for great help with the cladistic
analysis. Lastly we thank Sergey Krasovskiy for a beautiful life
reconstruction of Crittendenceratops krzyzanowskii.
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APPENDIX 1
List of characters used in the phylogenetic analysis of
Crittendenceratops krzyzanowskii based on the data presented
by Evans and Ryan (2015). Some characters from the original
dataset were combined, but no character information was
discarded. Character names are preceded by an alphanumeric
code so they can be tracked through different numbering
schemes. RM followed by a number indicates that the character
is derived from the character of that number in the original
Evans and Ryan (2015) dataset. NC are new characters, and
the number is simply a unique identier. Numbers followed by
a letter indicate that the original character has been atomized
into the lettered characters. All multistate characters were
ordered, and the matrix was constructed specically in the
160
context of character ordering. No attempt was made to remove
autapomorphies or other parsimony-uninformative characters.
Dermal skull roof
1) RM001. Rostral, shape and extent of dorsal and ventral
processes: (0) triangular in lateral view, with short dorsal
and ventral processes; (1) elongate, with deeply concave
caudal margin and hypertrophied dorsal and ventral
processes.
2) RM002. Premaxillary septum, shape: (0) rostrally
elongate; (1) semi-circular.
3) RM003. Premaxillary septum, nasal contribution: (0)
septum formed by premaxilla only; (1) septum formed by
premaxilla and nasal.
4) RM004. Premaxilla, narial strut: (0) absent; (1) present.
5) RM005. Premaxilla, septal fossa: (0) absent; (1) present.
6) RM006. Premaxilla, triangular process: (0) absent; (1)
present.
7) RM007. Premaxilla, recess along ventral portion of
septum: (0) absent; (1) present.
8) RM008. Premaxilla, caudoventral expansion of oral
margin: (0) absent; (1) present.
9) RM009. Premaxilla, ventral extent of caudoventral
oral margin: (0) at or above level of alveolar margin of
maxilla; (1) well below alveolar margin of maxilla.
10) RM010. Caudoventral oral margin, composition of
ventral angle: (0) premaxilla and maxilla; (1) premaxilla
only.
11) RM011. Premaxilla, position of caudal tip of caudoventral
process: (0) inserts into an embayment in the nasal; (1)
inserts between nasal and maxilla.
12 RM012. Premaxilla, distal end of caudoventral process:
(0) single; (1) forked. RM013. Premaxilla–nasal contact
in dorsal view: (0) premaxillae insert between nasal; (1)
nasals insert between premaxillae.
13) RM014. Accessory antorbital fenestra: (1) absent; (0)
present, slight penetration, nasal cavity not visible in
lateral view; (2) present, pronounced penetration of nasal
cavity visible in lateral view.
15) RM016. External antorbital fossa, size: (0) large, 20% or
more length of body of maxilla; (1) greatly reduced or
absent, less than 10% length of body of maxilla.
16) RM017. Maxillary tooth row, position: (0) ventrally
displaced from rostral edentulous portion of maxilla; (1)
at same level as rostral edentulous portion of maxilla.
17) RM018. Maxilla, maxillary cavity: (0) absent; (1) present.
18) RM019. Ectopterygoid, development: (0) well-developed
ectopterygoid/pterygoid complex covers entire dorsal
surface and laps onto lateral surface of caudal ramus of
maxilla; (1) ectopterygoid vestigial.
19) RM020A Nasal, ornamentation length in adult: (0) non-
pronounced; (1) shorter than skull is deep; (2) longer than
skull is deep; (3) very long.
20) RM020B Nasal, orientation of nasal horncore: (0) curved
well caudally; (1) curved slightly caudal to straight; (2)
curved rostrally; (3) wrapped rostrally to approach rostral
tip of skull.
21) RM021. Epinasal ossication on nasal: (0) absent; (1)
present. .
22) RM022. Nasal, narial spine: (0) absent; (1) present.
23) RM025A. Postorbital, presence and length of supraorbital
ornamentation in adult: (0) ornamentation absent; (1)
ornamentation present, short, less than 15% basal skull
length; (2) present, elongate, greater than 35%.
24) RM025B. Postorbital, type of supraorbital ornamentation
in adult: (0) horncore; (1) rugose boss.
25) RM023. Postorbital, extent of cornual sinuses in base of
supraorbital ornamentation: (0) sinus invades frontal and
parietal; (1) sinus enters postorbital.
26) RM024. Postorbital, proportions of supraorbital
ornamentation in subadult to adult: (0) pointed apex,
ornamentation at least as tall as rostrocaudally long; (1)
rounded or blunt apex, ornamentation rostrocaudally
longer than tall.
27) RM026. Postorbital, position of supraorbital
ornamentation: (0) centered rostrodorsal or dorsal to
orbit, narrow base with caudal margin of supraorbital
ornamentation extending to or only slightly behind caudal
margin of orbit; (1) centered caudodorsal to orbit, broad
base with caudal margin of ornamentation extending well
behind caudal margin of orbit.
28) RM027. Postorbital, orientation of base of supraorbital
ornamentation: (0) dorsally directed; (1) dorsolaterally
directed.
29) RM029. Postorbital, curvature of supraorbital horncore
in lateral view: (0) caudally recurved; (1) straight; (2)
rostrally curved.
30) RM030. Postorbital, curvature of supraorbital horncore
in rostral view: (0) medially recurved; (1) straight; (2)
laterally curved.
31) RM031. Prefrontals contact along midline of skull: (0)
absent; (1) present.
32) RM032. Palpebral, shape: (0) rod-like, articulates with
prefrontal only at its base and projects across dorsal orbit,
ligamentous attachment; (1) blocky, fully fused into
dorsal orbital margin, sutural articulation with prefrontal
and frontal.
33) RM033. Palpebral, antorbital buttress: (0) absent; (1)
present.
34) RM034. Palpebral, extent of antorbital buttress: (0)
present along only rostrodorsal portion of orbit; (1)
present along entire rostral portion of orbit.
35) RM035. Jugal, size and orientation of jugal body: (0)
projects strongly caudoventrally, does not extend below
the level of the maxillary tooth row; (1) projects nearly
ventrally, elongated to extend below the level of the
maxillary tooth row.
36) RM036. Jugal infratemporal process: (0) absent; (1)
present, contacts or nearly contacts infratemporal process
of squamosal.
37) RM037. Epijugal attachment scar: (0) large bladelike
triangle with obtuse angle oriented towards quadratojugal;
(1) scar roughly equilateral in shape.
38) RM038. Frontal fontanelle leading into supracranial
cavity complex: (0) absent; (1) present.
39) RM039. Frontal fontanelle, shape: (0) transversely
narrow, slit-like; (1) keyhole shaped, circular, or elongate
oval.
40) RM040. Parietal, rostral extent on dorsum of skull
relative to occipital condyle: (0) rostral end of parietal
located well in front of occipital condyle; (1) rostral end
of parietal lies directly over occipital condyle.
41) RM041. Squamosal, shape of expanded blade: (0)
subrectangular in outline; (1) triangular in outline,
caudally narrowed.
42) RM042. Squamosal, rostromedial lamina forming the
caudolateral oor of supratemporal fenestra: (0) absent;
(1) present.
43) RM043. Squamosal–quadrate contact: (0) socket-like
cotylus on ventrolateral squamosal for ball-like quadrate
head; (1) elongate groove on medial surface of squamosal
to receive lamina of quadrate.
44) RM044. Squamosal, thickened, rounded swelling along
medial margin: (0) absent, lateral surface of squamosal
at to slightly convex; (1) present, lateral surface of
squamosal slightly concave.
161
45) RM098A. Dorsal squamosal ridge: (0) absent; (1) weakly
developed; (2) prominent series of bumps or continuous
raised ridge; (3) pair of prominent ridges.
46) RM098B. Dorsal squamosal ridge, form: (0) ridge; (1)
prominent series of bumps.
47) NC103. Squamosal, number of dorsal ridges: (0) single
ridge is present; (1) primary and secondary ridges are
present, secondary ridge nearly parallels the contact
surface for the parietal.
48) NC102. Squamosal, dorsal ridge, location: (0) extending
along and close to the lateral margin of the squamosal;
(1) extending along the long axis of the squamosal; (2)
extending along and close to the medial margin of the
squamosal. (new character)
49) NC108A. Squamosal, dorsal groove preseence: (0)
absent; (1) present. (new character)
50) NC108B. Squamosal, dorsal groove orientation: (0)
parallels the medial margin of the parietal contact; (1)
parallels the medial margin of the parietal contact, but
does not form a straight line, instead it is bowed medially
or laterally.
51) NC109. Squamosal, dorsoventral groove; (0) absent; (1)
present.
52) NC106A. Squamosal, ventral groove along the
lateroventral and caudoventral margins: (0) absent; (1)
present and shallow; (2) present and deep.
53) NC106B. Squamosal, ventral groove along the
lateroventral and caudoventral margins, shape: (0)
sinuous; (1) smoothly curved.
54) NC104. Squamosal, dorsal squamosal process: (0) absent;
(1) one process present; (2) two process present; (3) three
process present; (4) four processes present.
55) RM045. Parietosquamosal contact, shape in lateral view:
(0) straight; (1) curved, medially concave.
56) RM046. Parietal, concave median embayment on caudal
margin: (0) absent; (1) present.
57) RM047. Parietal, form of concave median embayment:
(0) tightly curved, restricted to center of margin; (1)
broad, entire transverse bar is a V-shaped embayment.
58) RM048. Parietal, rim on medial margin of supratemporal
fenestra: (0) absent; (1) present, well-dened, laterally
projecting rim denes medial margin of fenestra.
59) RM049A. Parietal, median ridge on interfenestral bar: (0)
present and high; (1) present and low; (2) absent.
60) RM049B. Parietal, median knobs: (0) absent; (1) low; (2)
high.
61) RM049C. Parietal, number of median knobs: (0) absent;
(1) row of 1-3 low, undulating rounded knobs; (2) row of
4-6 knobs.
62) RM050. Parietal, rostrocaudal thickness of transverse bar
at narrowest point: (0) narrow and strap-like, less than
10% total parietal length; (1) broad, 20% or more of total
parietal length.
63) RM051. Parietal, median bar, transverse width: (0)
narrow and strap- like, transverse width less than 10%
total parietal length; (1) relatively wide, transverse width
15% or more of total parietal length.
64) NC110A. Parietal, dorsoventral thickness; (0) thin; (1)
thick.
65) NC112A. Parietal, shape of the parietal: (0) rostrocaudally
short, fenestra circular in dorsal and ventral view; (1)
rostrocaually elongate, fenestrae elongate in dorsal and
ventral view; (2) very elongate, forming an elongate frill.
66) NC112B. Parietal, presence of posterolateroventral
convexity: (0) absent; (1) present.
67) NC113. Parietal, dorsomedial ange; (0) absent; (1)
dorsomedial ange present on dorsal surface of parietal,
at to slightly concave; (2) concave dorsomedial ange
present, overhanging the parietal fenestra.
68) NC114.Parietal, rostral marign of frill fenestra; (0)
smoothly curving; (1) one or more angles or narrow slit
directed rostrally, undulating.
Epiossifications
69) RM053. Marginal dermal undulations or distinct
ossications, presence: (0) absent; (1) present on parietal
and squamosal.
70) RM052. Parietosquamosal frill, imbrication of
epiossications: (0) absent; (1) present.
71) NC105A. Uniformity of the episquamosal loci: (0)
episquamosals subequal in size; (1) episquamosals not
subequal in size.
72) NC105B. Pattern of non-uniformally shaped episquamosal
loci: (0) no pattern; (1) episquamosals decrease in size
caudally.
73) RM054. Episquamosal, midlateral, shape: (0) very small;
(1) small and crescentic/ eplisoidal; (2) large, triangular
or elongate.
74) RM055. Episquamosals, number per side: (0) 3–5; (1) six
or more.
New Character This study
Char. 105(?) Char. NC107(?)
Char. 105(-) Char. NC107 (-)
Char. 107(0/3) Char. NC107 (0)
Char. 107(1) Char. NC107 (2)
Char. 107(2) Char. NC107 (1)
75) NC107. Squamosal, embayments along caudal margin
between episquamosal loci: (0) absent; (1) one; (2) two
or more.
76) RM056. Marginal ossication crossing squamosal–
parietal contact: (0) absent; (1) present.
77) NC110B. Parietal, epiparietal ornamentation; (0) small
and present only at the posterior margin of the parietal;
(1) epiparietal ornamentation large and present on lateral
and posterior margins of the parietal.
78) NC111. Parietal, epiparietal loci; (0) bases of caudal
and lateral epiparietals emerge from dorsal margins of
the parietal rami; (1) caudal epiparietal bases on dorsal
surface of parietal, lateral epiparietals extend from
peripheral margin of parietal; (2) all epiparietals extend
from peripheral margin of parietal.
79) RM057. Epiparietals, number per side: (0) three; (1) ve
or more.
80) RM099. Epiparietal, locus P0: (0) absent; (1) present.
81) RM058. Epiparietal locus P1: (0) absent; (1) present.
82) RM100. Epiparietal, shape of locus P1: (0) low D-shaped
process, wider than long; (1) rugose tongue-shaped
process, less than twice as long as wide (2) elongate
attened process or spike, greater than twice as long as
wide.
83) RM101A. Epiparietal, curvature of locus P1: (0) straight;
(1) curved.
84) RM101B. Epiparietal, orientation of curved P1: (0)
laterally curved; (1) dorsally curved;
85) RM059. Epiparietal, shape of locus P2: (0) low D-shaped
process, wider than long; (1) rugose tongue-shaped
process, less than twice as long as wide; (2) elongate
attened process or spike, greater than twice as long as
wide.
86) RM060A. Epiparietal, curvature of locus P2: (0) straight;
(1) curved.
87) RM060B. Epiparietal, orientation of curvature of locus
P2: (0) laterally curved; (1) dorsally curved; (2) medially
curved.
162
88) RM061. Epiparietal, shape of locus P3: (0) low D-shaped
or triangular process; (1) rugose tongue-shaped process,
less than twice as long as wide; (2) elongate attened
process or spike, greater than twice as long as wide.
89) RM062A. Epiparietal, curvature of locus P3: (0) uncurved
or slightly medially curved; (1) curved.
90) RM062B. Epiparietal, orientation of curvature of locus
P3: (0) laterally curved; (1) dorsally curved.
91) RM063. Epiparietal, locus P4 shape: (0) low raised
D-shaped process; (1) elongate spike.
92) RM064. Epiparietal, locus P5: (0) absent; (1) present.
93) RM065. Epiparietal, locus P5 shape: (0) low D-shaped or
triangular process; (1) elongate spike.
94) RM066. Epiparietal, locus P6: (0) absent; (1) present.
95) RM067. Epiparietal, locus P6 shape: (0) low D-shaped or
triangular process; (1) elongate spike.
96) RM068. Epiparietal, locus P7: (0) absent; (1) present; (2)
very large.
Braincase
97) RM069. Supraoccipital, contribution to foramen
magnum: (0) forms dorsal margin of foramen magnum;
(1) eliminated from margin by exoccipital–exoccipital
contact on midline.
Lower jaw
98) RM070. Predentary, dentary processes: (0) ventral
processes much longer than abbreviated dorsal processes;
(1) dorsal and ventral processes elongate and subequal in
length.
99) RM071. Predentary, orientation of triturating surface: (0)
nearly horizontal; (1) inclined steeply laterally.
100) RM072. Dentary lateral ridge conuent with cutting
surface of predentary: (0) present; (1) absent.
101) RM073. Dentary, caudal extent of tooth row: (0) terminates
at the center of coronoid process; (1) terminates caudal to
coronoid process.
Dentition
102) RM074. Teeth, number of roots: (0) one; (1) two.
103) RM075. Teeth, number of alveoli in dentary: (0) fewer
than 20; (1) more than 20.
104) RM076. Teeth, number of replacement teeth per alveolus:
(0) one or two replacement teeth; (1) three or more
replacement teeth.
Axial skeleton
105) RM077. Cervical vertebrae, formation of syncervical: (0)
C1–C3 fused or tightly articulated, atlantal hypocentrum
present as a ventrally placed, wedge-like bone; (1) C1–
C3 rmly fused, atlantal hypocentrum unites with other
elements to form a complete ring.
106) RM078. Axis, neural spine shape and orientation: (0)
bladelike and nearly vertical, overhangs only rostralmost
portion of C3; (1) blade-like morphology lost, spine
steeply angled to reach caudal margin of C3.
107) RM079. Atlantal rib: (0) present; (1) absent; (Sampson et
al., 2010, character 129).
108) RM080. Dorsal vertebrae, shape of centra: (0) relatively
axially elongate; (1) axially shortened.
109) RM081. Sacrum, longitudinal sulcus on ventral surface:
(0) absent; (1) present.
Pectoral girdle and forelimb
110) RM082. Scapula, relative contribution to glenoid fossa:
(0) scapula and coracoid contribute equally; (1) scapula
contributes well over half of the glenoid.
111) RM083. Olecranon process: (0) relatively small; (1)
enlarged (greater than one-third of ulnar length).
112) RM084. Clavicle: (0) present; (1) absent.
113) RM085. Manual and pedal unguals, shape: (0) taper to
distal tip; (1) dorsoventrally attened with blunt and
rounded distal tips.
114) RM086. Manual and pedal penultimate phalanges shape:
(0) length exceeds width; (1) width exceeds length.
Pelvic girdle and hind limb
115) RM087. Ilium, lateral eversion of dorsal margin: (0)
absent; (1) present.
116) RM088. Ilium, relative lengths of pubic and ischial
peduncles: (0) pubic and ischial peduncles long, extend
well below body of ilium approximately the same
distance; (1) ischial peduncle reduced along ventral
aspect, pubic peduncle projects further ventrally than
ischial peduncle.
117) RM089. Pubis, prepubic process: (0) short and
unexpanded distally; (1) elongate, distal end greatly
expanded dorsoventrally.
118) RM090. Pubis, position and length of postpubic rod: (0)
relatively short but extends past ischial peduncle of ilium,
arises ventral to acetabulum and lies along ventral and
ventromedial margin of ischium; (1) very abbreviated,
terminates at level of ischial peduncle, arises medial to
acetabulum, and passes entirely medial to ischium.
119) RM091. Pubis and ischium, morphology of contributions
to acetabulum: (0) pubic acetabular surface faces
caudolaterally, pubis and pubic process of ischium
contribute equally to ventral margin of acetabulum; (1)
pubic acetabular surface faces laterally and forms a partial
medial wall to the acetabulum, pubic process of ischium
elongate and meets pubis close to anterior margin of
acetabulum, ventral portion of pubic acetabular surface
lies medial to pubic ramus of ischium.
120) RM092. Ischium, cross-sectional shape of shaft: (0) thick
and ovoid; (1) laterally compressed and bladelike, tapered
dorsally.
121) RM093. Ischium, orientation of shaft: (0) nearly straight
or slightly decurved; (1) broadly and continuously curved.
122) RM094. Femur, morphology of greater and lesser
trochanters: (0) trochanters distinct and located below the
level of femoral head; (1) trochanters coalesced and level
with femoral head.
123) RM095. Femur, size of fourth trochanter: (0) large and
pendant; (1) small, reduced to low prominence.
124) RM096. Femur–tibia proportion: (0) tibia longer than
femur; (1) femur longer than tibia.Note that values for
this character may be subject to allometry.
125) RM097. Pes, metatarsal proportions: (0) length of MT I
two-thirds the length of MT II; (1) MT I reduced to one-
half or less the length of MT II.
Data Matrix:
Leptoceratops_gracilis
1??0???001000000?0???00----?--000-0000-0000?0---0-00-0
00-000-??000010---------------------------
00000000000000000000000000000
Protoceratops_andrewsi
0??0???000000100000-000----?--000-0000-0010?100?0-00-00
0-000-00000010---------------------------
00000000000000000000000000000
Magnirostris_dodsoni
1??0???00011020000??0010??001?000-0000-
???????????????0????????????1????????????????????????????
00100?0??????????????????????
Bagaceratops_rohdesvenskyi
1??0???000100200000-000-?--?--000-0000-001????010-00-00
0-?00-??000010---------------------------
0010000??????????????????????
163
Turanoceratops_tardabilis
??????????????0000????20??00?2?1?????0?????????????????
?????????????????????????????????????????00????0?????????
????????????
Zuniceratops_christopheri
10000--???010200000-?120000001?1101100-?0?0???010-00-0
???0???100000?0---------------------------
00000000???110?????????01?0??
Chasmosaurus_belli
100111100?010111112110101?00010111111111101110020-
00-0111110-00020011011210012001011012011?0-0-
011011111111111111111111111111
Pentaceratops_sternbergi 100111100?011111111110201
001210111111111101110010-00-0111110-
0002001101121001200101100-00-?0-0-
01101111111111111111111111?111
Diabloceratops_eatoni
01100--101001200?00-0120??0001?110110100011010111102
00010120-1101101101110211110121000-00-
0101001??????1?????????????????????
Albertaceratops_nesmoi
?1?00--?????00101?0-
0?20??0?2??111111??001101000101??401010111101?0011??
10?11210121000-00-0100-0?1101111?????????????????????
Rubeosaurus_ovatus
01??0--1?1??0?????30??100?00???1???????????????????????
101????1011??110-?00?11100-??00-20-
1111?1?????????????????????????????
Styracosaurus_albertensis
01100--111100011113101100000??1111111100011010001010-
101011101101101110-
102112101011110210111111111011111?111101111111101111?
Spinops_sternbergorum
??1?0--??????0????11??100?00???111???10?????1001???0-0?
10120-11?11??1?0-100??1?0121120-
??????????????????????????????????????
Centrosaurus_apertus
01100--11110001111220110000011111111110001101000101
0-101012101101111110-10011110121111000-01010111101111
111111011111111011111
Coronosaurus_brinkmani
011?0--111??0011111101100001121111111100011011???????
?010120-11?????11???0?1??10121110-
110010101111011111?11?1????
111110?111?
Xenoceratops_foremostensis
???????????????????????0????????????????0110????101???0
10?20-110111110???0?11110111120-
????1?1?2?????????????????????????????
Sinoceratops_zhuchengensis
??1??????????21???11??0-------010-???100011010????????00?
121111?????11???0?1??111111112111010????????????????1??
??11?????11??
Einiosaurus_procurvicornis
?11?0--??????011112301111100--010-111100011010001010-
001012101100101110-102111100---01120-
010101111011111?11?1??1?111??1111??
Achelousaurus_horneri
011?0--11110?011110-01111100--?10-1?1100011010001010-
0010100-11001011110102?11100---
01121001010111101111?????????????????????
Pachyrhinosaurus_canadensis
01100--11110?011110-01111?10--?10-111100?11010001010-0
0??1?????0000?110-1?0?11100---
111210010101111011?????1??????????????1??
Pachyrhinosaurus_lakustai
01100--111100111110-01111110--?10-1?1100011010001010
-00101220110000?110-100111100---
111210010101111011111?11?1??11111110111??
Pachyrhinosaurus_perotorum
01?00--111????11?10-0111??10--?10-???1????1???????
????010????11?????1?????????101011??????
0??????????1?1???1???????????0111??
Yehuecauhceratops_mudei
????????????????????????????????????????0?102000??00-
10?????????????1?10100???1?????????????????????????????
?????????????????
Crittendenceratops_krzyzanowskii
????????????????????????????????????????0?1020001002010
?-?20-1?1002?1010012?101?????00-00-0???????????????????
???????????????
Avaceratops_lammersi
?110?--111??0?101?12??????????????101???0?10200210010
400-?011110000?1010002?021110???1??????????0???11111??
1?10?11???????1?11
MOR692
?1????-11110?0111?????101?0120?1101??1??0?1?20021
00102???????110000?1010202?02????????????????????????1
1?????????????????????
Nasutoceratops_titusi
01100--111100010100-01101?0120?110??110001102000100
10100-11111100001100-00010211100-00-00-
010101???????111?1?10??????????????
CMN8804
?1??0??1?1????????????101?0110????111???0?102000?????
1?0-?????1?????10??0?????1??00-???????????????????????
??????????????????
Malta_ceratopsine
????????????????????????????????????????011020????????0
0-????11?????11??{01}0????10100-00-00-
01010??????????????????????????????
Wendiceratops_peterhewsi
?????????????0101?{1 2 3}?0???????????????????011030001
0?100010?20-110110?110-1021101011111121110100-
0?????11????1?10?1?11???11????
Machairoceratops_cronusi
??????????????????0-
??10??0001????111???0?10100010?100010122111???????10
0?0??1?01211??????????????????????1??????????????????
164
Medusaceratops_lokii
01?????1???0???01?0-0110100122?111?111000?101?0????112
010????110110?1110002?121011112101100100-
0?1?01??????1?10???1????0111??
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A partial skull (CMN 8804) of a ceratopsid from the upper unit of the Campanian Oldman Formation of Alberta is the first Canadian example of the newly established Nasutoceratopsini, a new subclade of Centrosaurinae defined as the stem-based clade of centrosaurine ceratopsids more closely related to Nasutoceratops titusi than to Centrosaurus apertus. The new clade is diagnosed, in part, by having a parietosquamosal frill lacking modified epimarginals; a small nasal horncore; large, rostrolaterally directed postorbital horncores; and a relatively short, deep face. Although the CMN 8804 taxon closely resembles Nasutoceratops, its phylogenetic position within Nasutoceratopsini is unresolved. The CMN 8804 taxon would have been contemporaneous with dinosaurs from the lower portion of the Dinosaur Park Formation 200 km to the northwest in Dinosaur Provincial Park. The presence of the CMN 8804 taxon in Alberta, and the approximately contemporaneous Nasutoceratops in Utah, indicates that the nasutoceratopsins pers...
Article
Most horned dinosaur remains recovered from the Aguja Formation in West Texas are referable to the endemic chasmosaurine Agujaceratops mariscalensis. One specimen, however, differs sufficiently to justify its designation as the holotype of a new species, Agujaceratops mavericus sp. nov. This specimen and an isolated postorbital horncore from the same vicinity are stratigraphically the highest found in the Aguja Formation. A well-preserved juvenile specimen exhibits some unique features, and others compatible with A. mavericus, but due to its immature condition cannot be identified with certainty. A parietal referred to A. mariscalensis is the most complete thus far known, and shows that the frill of this taxon is more elaborately ornamented than previously believed, bearing a set of large horn-like spikes at the posterolateral corners. These two species share features of the premaxilla and squamosal, which warrant their inclusion in the same genus. However, characters thought to distinguish the two species vary in a manner similar to that found in other chasmosaurines, where debate persists as to their taxonomic significance. A consensus species concept has yet to be adopted for ceratopsid genera, of which most are monotypic. As a result, the two Agujaceratops species could be interpreted as arbitrary anagenetic stages in a single lineage, end-members in a spectrum of ontogenetic and sex-associated variation in that lineage, or two sympatric lineages that occupied separate niches in the same range. http://zoobank.org/urn:lsid:zoobank.org:pub:1846D524-AC7F-4126-8787-33B26D80CF52