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A new specimen of Chasmosaurus belli (Ornithischia: Ceratopsidae), a revision of the genus, and the utility of postcrania in the taxonomy and systematics of ceratopsid dinosaurs

July 2011
Zootaxa 2963(1):1-47

DOI:10.11646/zootaxa.2963.1.1

Authors:

Susannah C R Maidment

Natural History Museum, London

Paul M. Barrett

Natural History Museum, London

A previously undescribed chasmosaurine specimen excavated in 1919-1920 by William Cutler from the Dinosaur Park Formation of Alberta, Canada is referable to Chasmosaurus belli. The specimen comprises an almost complete skull in which, uniquely among Chasmosaurus, the cranial elements are disarticulated, allowing detailed examination of their morphology for the first time. The complete braincase is present and allows comparison with the braincase of other ceratopsians. The specimen also preserves an uncrushed and undistorted postcranium, including cervical, dorsal and sacral vertebrae and limb elements. The vertebral column of Chasmosaurus has never previously been described in detail, and NHMUK R4948 affords the opportunity to examine it because of the unparalleled state of vertebral preservation. A proliferation of new chasmosaurine genera has recently been described; many of them differ from each other only in details of frill and epiparietal morphology. Several of these are based on specimens previously referred to Chasmosaurus. As a result, the characters that distinguish Chasmosaurus from other Campanian chasmosaurines are unclear. However, the genus Chasmosaurus and species within the genus are diagnosable and valid based on unique combinations of characters and frill morphology. Detailed examination of the postcranial morphology of a variety of centrosaurines and chasmosaurines has highlighted previously undescribed synapomorphies for the two major ceratopsid clades, concentrated in the pectoral girdle and forelimb. Inconsistencies in the vertebral formula of specimens referred to Chasmosaurus belli suggests that the postcrania of ceratopsids may vary between species and genera far more than previously thought, and that postcranial characters should be incorporated into phylogenetic and taxonomic studies.

Skull, braincase and lower jaw measurements, NHMUK R4948. Numbers in brackets in the second column corre- spond to measurements in Godfrey and Holmes (1995) for easy comparison.

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Accepted by R. Benson: 23 May 2011; published: 12 Jul. 2011

ZOOTAXA

ISSN 1175-5326 (print edition)

ISSN 1175-5334 (online edition)

Zootaxa 2963: 1–47 (2011)

www.mapress.com/zootaxa/Article

A new specimen of Chasmosaurus belli (Ornithischia: Ceratopsidae),

a revision of the genus, and the utility of postcrania in the taxonomy

and systematics of ceratopsid dinosaurs

SUSANNAH C. R. MAIDMENT1 & PAUL M. BARRETT2

Department of Palaeontology, Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom.

E-mail: 1s.maidment@nhm.ac.uk; 2p.barrett@nhm.ac.uk

Table of contents

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

Systematic palaeontology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Ceratopsia Marsh, 1888. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Neoceratopsia Sereno, 1986 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Ceratopsidae Marsh, 1888. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Chasmosaurinae Lambe, 1915. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Chasmosaurus Lambe, 1914a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

Chasmosaurus belli Lambe, 1902. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Chasmosaurus russelli Sternberg, 1940 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44

Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Abstract

A previously undescribed chasmosaurine specimen excavated in 1919–1920 by William Cutler from the Dinosaur Park

Formation of Alberta, Canada is referable to Chasmosaurus belli. The specimen comprises an almost complete skull in

which, uniquely among Chasmosaurus, the cranial elements are disarticulated, allowing detailed examination of their

morphology for the first time. The complete braincase is present and allows comparison with the braincase of other cer-

atopsians. The specimen also preserves an uncrushed and undistorted postcranium, including cervical, dorsal and sacral

vertebrae and limb elements. The vertebral column of Chasmosaurus has never previously been described in detail, and

NHMUK R4948 affords the opportunity to examine it because of the unparalleled state of vertebral preservation. A pro-

liferation of new chasmosaurine genera has recently been described; many of them differ from each other only in details

of frill and epiparietal morphology. Several of these are based on specimens previously referred to Chasmosaurus. As a

result, the characters that distinguish Chasmosaurus from other Campanian chasmosaurines are unclear. However, the ge-

nus Chasmosaurus and species within the genus are diagnosable and valid based on unique combinations of characters

and frill morphology. Detailed examination of the postcranial morphology of a variety of centrosaurines and chasmosau-

rines has highlighted previously undescribed synapomorphies for the two major ceratopsid clades, concentrated in the pec-

toral girdle and forelimb. Inconsistencies in the vertebral formula of specimens referred to Chasmosaurus belli suggests

that the postcrania of ceratopsids may vary between species and genera far more than previously thought, and that post-

cranial characters should be incorporated into phylogenetic and taxonomic studies.

Key words: Chasmosaurinae, Dinosaur Park Formation, Upper Campanian

MAIDMENT & BARRETT

Introduction

Chasmosaurus Lambe 1914a is a member of Chasmosaurinae, a clade of quadrupedal herbivorous dinosaurs

known exclusively from western North America. They represent part of a diverse and successful Campanian and

Maastrichtian radiation of horned and frilled dinosaurs, the Ceratopsidae (Dodson et al. 2004).

NHMUK R4948 is a previously undescribed individual referable to Chasmosaurus belli Lambe 1902. Unusu-

ally for a specimen of Chasmosaurus, the skull is disarticulated but most of the elements are represented, offering a

rare opportunity to examine the morphology of individual skull elements in multiple views. For example, in most

ceratopsid skulls the braincase is inaccessible due to the presence of other cranial elements or the design of

museum mounts: however, the braincase of NHMUK R4948 is detached from the rest of the skull, allowing its

anatomy to be described in detail. Furthermore, NHMUK R4948 preserves a large amount of well preserved and

undistorted postcranial material, including cervical, dorsal and sacral vertebrae, partial pectoral and pelvic girdle

material, and partial fore- and hind limbs, and represents, to our knowledge, some of the best preserved Chasmo-

saurus postcrania known. Although other specimens of Chasmosaurus also include postcranial material (e.g. ROM

843, 839; CMN 2245, CMN 2280) it is either not as complete (ROM 839; CMN 2280) or it is not as well preserved

(ROM 843; CMN 2245). Perhaps surprisingly, given the large amount of Chasmosaurus material in North Ameri-

can museum collections, the postcrania of Chasmosaurus has never previously been described in detail (although

elements of the postcranium were briefly described in Mallon and Holmes [2006]). We therefore present a detailed

account of the morphology of all postcranial elements preserved.

The specimen was collected from what is now known as quarry 78 in the Dinosaur Park Formation (Tanke

2010) by William E. Cutler, a Canadian fossil collector, in 1919–1920. In a letter dated April 5th 1921, Cutler wrote

to Arthur Smith Woodward, the Keeper of Geology at the British Museum (Natural History) (now the Natural His-

tory Museum, London) to enquire whether he would be interested in purchasing a collection of dinosaurian remains

made during this field season. Cutler asked for $2000 for the collections, which included “…a partial Eo-Ceratop-

sian [sic] skeleton (so far as I know, the only skeleton of this extent) with a finely preserved but disarticulated

skull…”. The purchase was evidently not made, because Cutler wrote again to Smith Woodward in 1923, again

requesting purchase of the skeleton, this time for just £125, “…less than the outlay of the obtaining this specimen

and I do not believe that there is as good a skull and remains anywhere; Ottawa, I believe has the only other

remains. The skull is disarticulated.” (NHMUK archive file DF100/105/6; Tanke 2010). On this occasion Smith

Woodward was able to purchase the specimen.

Chasmosaurus. The genus Chasmosaurus was described by Lambe (1902) for specimens from the Dinosaur

Park Formation of the Red Deer River district, Alberta, Canada, which were excavated between 1897 and 1901.

One specimen, excavated in 1898 from a quarry below the mouth of Berry Creek, Steveville (Lull 1933), was orig-

inally named Monoclonius belli (Lambe 1902); however Lambe later referred it to a new genus, Protorosaurus

(Lambe 1914b). Finding that name occupied, Lambe (1914a) renamed the genus Chasmosaurus. Another speci-

men, originally called Monoclonius canadensis (Lambe 1902) was later made the type of a new genus, Eoceratops

(Lambe 1915). Hatcher considered all of the Belly River ‘Monoclonius’ species referable to the taxon ‘Ceratops’

(Hatcher et al. 1907), but later authors did not agree, and generally accepted Chasmosaurus and Eoceratops as

valid species (e.g. Sternberg 1925; Brown 1933; Lull 1933). These were synonymised, however, by Lehman

(1989), who considered that there were four valid species of Chasmosaurus: C. belli, C. russelli, C. canadensis and

C. mariscalensis, the last being known from the late Campanian Aguja Formation of Texas (Lehman 1989). God-

frey and Holmes (1995) synonymised C. canadensis with C. belli, while Lucas et al. (2006) removed C. marisca-

lensis from the genus Chasmosaurus and renamed it Agujaceratops. Holmes et al. (2001) described a new species,

C. irvinensis, also from the Dinosaur Park Formation of Alberta; however, Sampson et al. (2010) removed C. irvin-

ensis from the genus Chasmosaurus, renaming it Vagaceratops. Longrich (2010) removed a referred specimen of

C. russelli from the genus, renaming it Mojoceratops. Two species of Chasmosaurus are therefore currently recog-

nised: C. belli and C. russelli, both from the Dinosaur Park Formation of Alberta. Chasmosaurine species appear to

be stratigraphically separated within the Dinosaur Park Formation, with C. russelli coming from the lowest beds,

C. belli coming from the middle and upper beds, and Vagaceratops coming from the very uppermost Dinosaur Park

Formation (Godfrey & Holmes 1995; Ryan & Evans 2005).

Chasmosaurine research has undergone something of a renaissance recently, with nine genera being described

in 2010 and 2011 (‘Mojoceratops perifania’ [Longrich 2010]; Utahceratops gettyi, Kosmoceratops richardsoni,

A NEW SPECIMEN OF CHASMOSAURUS BELLI

Vagaceratops irvinensis [Sampson et al. 2010]; Coahuilaceratops magnacuerna [Loewen et al. 2010]; Medusacer-

atops lokii [Ryan et al. 2010], Tatankaceratops sacrisonorum [Ott & Larson 2010]; Ojoceratops fowleri [Sullivan

& Lucas 2010]; and Titanoceratops ouranos [Longrich 2011]), doubling the generic diversity of chasmosaurines in

the Campanian. These genera, known almost exclusively from skull material (although Vagaceratops also pre-

serves a complete, articulated postcranium: CMN 41357), are extremely similar to Chasmosaurus in many

respects, differing subtly from it and each other in the morphology of the frill epi-ossifications. The proliferation of

new chasmosaurine taxa, and the fact that three of the recently described genera represent specimens previously

referred to Chasmosaurus (Agujaceratops, ‘Mojoceratops’ and Vagaceratops), means that many of the features

previously used to diagnose Chasmosaurus are now known from a diversity of chasmosaurines, and a re-examina-

tion of the genus is therefore warranted.

Usage of postcrania in ceratopsid taxonomy. Although most ceratopsid remains in museum collections com-

prise partial skulls and horn cores, many specimens with postcrania are known, and the postcrania are frequently

well preserved, reasonably complete, and often found fully articulated (e.g. Chasmosaurus belli, ROM 843; CMN

2245; Chasmosaurus russelli, CMN 2280; Vagaceratops irvinensis, CMN 41357; Styracosaurus albertensis, CMN

344, Holmes et al. 2005; ‘Anchiceratops longirostris’ CMN 8547, Mallon & Holmes 2010; Triceratops, Hatcher et

al. 1907; pachyrhinosaur sp. indet. TMP 2002.76.01). In addition, a number of paucispecific ceratopsid bone beds,

which include large amounts of ceratopsid postcrania are also known (e.g. Centrosaurus [Ryan et al. 2001; Eberth

et al. 2010]; Pachyrhinosaurus [Currie et al. 2008]; Agujaceratops [Lehman 1989]). However, since the definitive

description of Triceratops by Hatcher et al. (1907) many authors have entirely neglected the ceratopsid postcra-

nium from a descriptive point of view (although see Wiman [1930], Lehman [1989] and Mallon and Holmes

[2010] for notable exceptions) and study has instead focused on forelimb stance and function (e.g. Sterberg 1927;

Erikson 1966; Alexander 1991; Paul & Christiansen 2000; Rega et al. 2010).

Chinnery (2004) conducted a morphometric study of shape variation among ceratopsid appendicular elements

and concluded that there was variation between centrosaurines and chasmosaurines, but did not discuss any poten-

tial differences between the genera within these clades. This appears to have been interpreted by ceratopsian work-

ers to mean that ceratopsid postcrania is taxonomically uninformative; however, most taxonomically important

information comes not from quantitative measurements and ratios of limb elements but rather from the identifica-

tion of suites of distinct features— autapomorphies and synapomorphies—that are identified by examination of the

elements in question and not necessarily captured by measurement data. The conclusions of Chinnery (2004)

should not, therefore, be used to discount postcrania as taxonomically uninformative. Furthermore, Chinnery

(2004) did not investigate shape change in the axial skeleton, and the taxonomic utility of vertebral features in cer-

atopsids remains unexplored.

There is no a priori reason to consider that postcrania are less taxonomically informative or carry less phyloge-

netic signal than crania; indeed, recent phylogenetic studies on other ornithischian groups that encompass both cra-

nial and postcranial data have resulted in better resolution and stronger support for particular phylogenetic

hypotheses than those based on cranial characters alone (e.g. Maidment et al. 2008; Thompson et al. in press). The

postcranium of NHMUK R4948 is excellently preserved, and offers an opportunity to investigate postcranial varia-

tion both within and between genera and species in chasmosaurine ceratopsids.

Institutional Abbreviations

AMNH, American Museum of Natural History, New York, USA; CMN, Canadian Museum of Nature, Ottawa,

Canada; IVPP, Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, People’s Republic of China;

NHMUK, Natural History Museum, London, UK; ROM, Royal Ontario Museum, Toronto, Canada; TMP, Royal

Tyrrell Museum of Paleontology, Drumheller, Alberta, Canada; UALVP, University of Alberta, Edmonton, Can-

ada; YPM, Peabody Museum, Yale University, New Haven, Connecticut, USA.

Systematic palaeontology

Ceratopsia Marsh, 1888

Neoceratopsia Sereno, 1986

MAIDMENT & BARRETT

Ceratopsidae Marsh, 1888

Chasmosaurinae Lambe, 1915

Phylogenetic definition. All ceratopsids more closely related to Triceratops than to Pachyrhinosaurus (Sereno,

1998; Sereno favoured the name Ceratopsinae for this clade, but we follow the majority of other authors and all

recent works in preferring the name Chasmosaurinae).

Amended diagnosis. Modified from Lehman (1989): large ceratopsian dinosaurs with long, low facial region

(preorbital length/height ratio = 1.4 to 3.0); inter-premaxillary fossae present; premaxilla and predentary with hori-

zontal or poorly developed lateral cutting flange; nasal horn core, if present, small and formed in part by a separate

ossification (epinasal); postfrontal foramen present; frontoparietal fontanelle walled mostly by the postorbital

bones; frontal bones reduced; prefrontal bones small; cranial frill long (0.94 to 1.70 basal length of skull, except in

Triceratops); triangular squamosal bones (length/height ratio = 2.0 to 3.5); prominent longitudinal channel in ven-

tral surface of sacrum; triangular acromial process of the scapula arises about half way along the scapula blade;

deep triceps fossa on the caudolateral deltopectoral crest of the humerus; foramen on the caudomedial humerus

located dorsal to the apex of the deltopectoral crest; strongly curved ischium.

Chasmosaurus Lambe, 1914a

Type species. Chasmosaurus belli Lambe, 1902.

Amended diagnosis. Chasmosaurus is diagnosed based on the following combination of characters: (1) Premaxil-

lary flange along entire anterior margin of external naris; (2) supraorbital horns, when present, curve posteriorly

along their length; (3) frill broadens posteriorly to form triangular shield with maximum width more than twice the

skull width at orbits; (4) medial margin of squamosal, where it articulates with the lateral bar of the parietal,

straight; (5) parietal fenestrae large, occupying most of the parietal, and being rounded or anteroposteriorly longer

than transversely wide; (6) epiparietals triangular in shape and project posteriorly or dorsally but do not curve ante-

riorly. Characters 1–3 after Forster et al. (1993). All of these features are seen in other chasmosaurines and do not,

therefore, represent autapomorphies, but this combination of features appears to be unique to Chasmosaurus. See

discussion for more details.

Chasmosaurus belli Lambe, 1902

Monoclonius belli Lambe 1902: 59

Monoclonius canadensis Lambe 1902: 63

Ceratops belli Hatcher et al. 1907: 97

Ceratops canadensis Hatcher et al. 1907: 97

Protorosaurus belli Lambe 1914: 131

Chasmosaurus belli Lambe 1914: 149

Eoceratops canadensis Lambe 1915: 2

Chasmosaurus kaiseni Brown 1933: 2

Chasmosaurus brevirostris Lull 1933: 94

Chasmosaurus canadensis Lehman 1989: 139

Amended diagnosis. Taxon displaying the combination of characters unique to the genus Chasmosaurus along

with the following features: (1) parietal posterior bar bearing no median emargination and is nearly straight so that

it forms a ‘T’ shape with the parietal median bar; (2) lateral pair of epiparietals large and triangular; others, when

preserved, are smaller (after Godfrey & Holmes 1995). Both characters are autapomorphic for C. belli within Chas-

mosaurus.

Holotype. CMN 491, a partial parietal. Although fragmentary, the holotype is diagnostic based on the combi-

nation of generic character 4, and specific character 1, a combination not observed in any other chasmosaurine.

Distribution. Middle and upper beds of the Dinosaur Park Formation, Alberta, Canada (Ryan & Evans 2005).

A NEW SPECIMEN OF CHASMOSAURUS BELLI

Referred specimens. CMN 2245; AMNH 5402; ROM 843; YPM 2016; NHMUK R4948 (after Ryan & Evans

2005). The NHMUK specimen is referred to Chasmosaurus because it possesses characters 1, 3, 4 and 5 from the

diagnosis of Chasmosaurus (above); it is referred to C. belli because it possesses character 1 from the diagnosis of

C. belli (above).

Specimens removed from C. belli. ROM 839 was referred to C. belli by Ryan and Evans (2005) and Longrich

(2010), but is not diagnosable to species level based on the amended diagnosis presented here and represents Chas-

mosaurus sp.

Chasmosaurus russelli Sternberg, 1940

Mojoceratops perifania Longrich, 2010: 683.

Amended diagnosis. Taxon displaying the combination of characters unique to the genus Chasmosaurus along

with the following features: (1) parietal posterior bar bearing a median emargination and is broadly arched either

side so that it forms an ‘M’ shape with the parietal median bar; (2) each side of the posterior parietal bar bears three

roughly equally sized epiparietals (after Godfrey & Holmes, 1995). Both characters are autapomorphic for C. rus-

selli within Chasmosaurus.

Holotype. CMN 8800, comprising a partial skull lacking the lower jaw and part of the rostral, part of the jugals

from both sides, part of the right quadrate, squamosal, and parietal (Sternberg 1940).

Distribution. Lower beds of the Dinosaur Park Formation, Alberta, Canada (Ryan & Evans 2005).

Referred specimens. AMNH 5656; CMN 2280, 41933; TMP 1983.25.01

Description of NHMUK R4948. Skull. The skulls of ceratopsid dinosaurs are often found articulated with the

individual bones fused together and sutures between the elements entirely obliterated. The skull of NHMUK

R4948 was disarticulated when discovered, and it has not been reconstructed, presenting the rare opportunity to

examine the morphology of a number individual skull bones from multiple views. This lack of fusion, together

with several postcranial characters (see below), suggests that the specimen was not osteologically mature at the

time of death. Skull, lower jaw and braincase measurements are given in Table 1.

Rostral. The rostral is a single median element fused anteriorly to the premaxilla forming a beak-like tip to the

snout, and its presence constitutes a ceratopsian synapomorphy (e.g. Sereno 1986, 1999). In NHMUK R4948 the

element is preserved in articulation with the premaxilla (Fig. 1), but the sutures between them are clear. In lateral

view the element has an elongate dorsal process that contacts the anterodorsal premaxilla along a flattened ven-

trally facing facet, and an elongate posterior process (broken on the right side, but better preserved on the left) that

extends along the ventral margin of the premaxilla (Fig. 1D). The ventral margin of the rostral is concave upwards

in lateral view, as in all ceratopsids (Godfrey & Holmes 1995). The surface of the rostral is rugose, pitted and

grooved, suggestive of a horny covering in life. In ventral view, the rostral is deeply concave and drawn to a poste-

rior point on the midline where it intervenes for a short distance between the premaxillae.

Premaxilla. The premaxillae appear to be fused on the midline but the dorsal half of the left element is not pre-

served and has been reconstructed (Fig. 1). The dorsal process of the premaxilla is thickened transversely and the

surface is rugose, as in other specimens of Chasmosaurus (ROM 843, 839; CMN 2280; TMP 1981.19.175) and

Vagaceratops (CMN 41357). At the dorsal end of the process a flat facet is present laterally for the nasal (Fig. 1B);

the suture between the two elements interdigitated so that the nasal overlapped the premaxilla laterally but a tongue

from the fused premaxillae extended ventrally between the two lateral processes of the nasals on the midline (in

contrast to the situation described in Agujaceratops [Forster et al. 1993; Godfrey & Holmes, 1995], but similar to

that seen in other specimens of Chasmosaurus [e.g. ROM 839; CMN 2280; UALVP 40] and Vagaceratops [CMN

41357]). The premaxilla forms the anterior margin of the external naris. The snout was transversely narrow in this

area and the left and right premaxillae closely approach each other forming a shallow premaxillary fossa (Fig. 1B;

Godfrey & Holmes 1995). Anteriorly, the fossa is pierced by a large fenestra, the edges of which are broken and

have been reinforced with plaster (Fig. 1B). A smaller foramen pierces the fossa just ventral to the larger foramen

on the left side (Fig. 1D), but this area is covered with plaster on the right. A similar foramen was also observed in

ROM 839 (Chasmosaurus sp.) and is present in Agujaceratops and other ceratopsids (Lehman 1989). A thin flange

that arises from the ventromedial premaxillary palate extends posteriorly into the external naris (Fig. 1B), as in

Chasmosaurus (Forster et al. 1993) and Agujaceratops (Lehman 1989; Forster et al. 1993). A similar flange is

present in Utahceratops and Kosmoceratops but it is less developed and does not extend along the entire anterior

MAIDMENT & BARRETT

margin of the external naris (Sampson et al. 2010). The ventral margin of the premaxilla is edentulous, a feature

characteristic of all ceratopsids (e.g. Sereno 1986, 1999), and transversely expanded relative to the premaxillary

body above it. Anteriorly, the ventral margin bears a flattened facet laterally and a deep groove ventrally, both for

the articulation of the rostral (Fig. 1B). A similar lateral facet can be seen in UALVP 40 (Chasmosaurus sp.). The

transversely thickened margin extends posteriorly to form a process that extends under the external naris, forming

its ventral margin. Posteriorly the process turns dorsally and there is a grooved and ridged facet for the maxilla ven-

trally (Fig. 1D). A flattened facet is present dorsally for the nasal (Fig. 1B). The distal end of the process is broken

off on both sides. In ventral view the ventral margin of the premaxilla curves medially to form a rudimentary pre-

maxillary palate, but it does not meet its counterpart on the midline. This represents an unusual state in ceratopsids,

but the space between the premaxillae in ventral view is infilled with plaster, and it may be that the medial margins

are broken. The palate is pierced by two foramina, the anterior of which is larger and extends forwards as a shallow

canal towards the rostral suture.

TABLE 1. Skull, braincase and lower jaw measurements, NHMUK R4948. Numbers in brackets in the second column corre-

spond to measurements in Godfrey and Holmes (1995) for easy comparison.

Element Measurement taken Dimension (cm)

Rostral Dorsoventral height 22

Rostral Max. anteroposterior length 15

Left premaxilla Anteroposterior length, as preserved 32

Right premaxilla Dorsoventral height 28.5

Left maxilla Anteroposterior length, as preserved 37

Right maxilla Anteroposterior length, as preserved 36.5

Nasal horncore Height (5) 15.5

Nasal horncore Anteroposterior length at base 14

Nasal horncore Circumference at base 35.5

Right jugal Orbital margin to jugal posteroventral tip (9) 28.5

Right jugal Orbital margin to lateral temporal fenestra margin (10) 12

Right epijugal Height 5

Right epijugal Anteroposterior length at base 6.5

Right supraorbital horncore Anteroposterior length at base (2) 10

Right supraorbital horncore Height (1) 5.5

Orbit Dorsoventral height (13) 13.5

Orbit Anteroposterior length (11) 10

Right quadratojugal Dorsoventral height 17.5

Left quadratojugal Dorsoventral height 17.5

Right quadrate Dorsoventral height 29.5

Left quadrate Dorsoventral height 29.5

Right squamosal Dorsoventral height to jugal notch (14) 22

Right squamosal Max. dorsoventral height (15) 36

Right squamosal Anteroposterior length, as preserved 90

Parietal Median bar length, as preserved 86

Parietal Parietal fenestra transverse width (25) 49

Foramen magnum Transverse width 3.1

Foramen magnum Dorsoventral height 3.4

Occipital condyle Transverse width 6.5

Occipital condyle Dorsoventral height 6.7

Right lower jaw Transverse width, posterior view 14

Left lower jaw Transverse width, posterior view 14

A NEW SPECIMEN OF CHASMOSAURUS BELLI

FIGURE 1. Rostral and premaxillae of NHMUK R4948, Chasmosaurus belli in A–B, right lateral, C–D, left lateral, and E–F,

dorsal view. Abbreviations: pm dp, premaxillary dorsal process; pm f, premaxillary fenestra; pm fl, premaxillary flange

extending into external naris; pm-m f, maxillary facet on premaxilla; pm-n f, nasal facet on premaxilla; pm sf, small foramen

ventral to premaxillary fenestra on premaxilla; r, rostral; r dp, dorsal process of rostral; r pp, posterior process of rostral. Diag-

onal lines indicate broken bone. Scale bars equal to 20 cm.

Maxilla. Both maxillae are preserved (Fig. 2). The maxilla is roughly triangular in lateral view. The anterior-

most portion of the maxilla is reconstructed on both sides, but a groove is present anterodorsally on the left maxilla,

into which the nasomaxillary process of the premaxilla would have fitted (Fig. 2G). The lateral surface of the max-

illa is flat anteriorly, but moving posteriorly a sharp ridge arises that extends posterodorsally resulting in medial

offset of the tooth row (Fig. 2C, G), as in other specimens of Chasmosaurus (ROM 843, 839; UALVP 40; TMP

1981.19.175) and other chasmosaurines (e.g. Agujaceratops, Lehman 1989; Utahceratops, Kosmoceratops, Samp-

son et al. 2010; Triceratops, Hatcher et al. 1907). Dorsal to this ridge the lateral surface of the maxilla is rotated to

MAIDMENT & BARRETT

FIGURE 2. Maxillae of NHMUK R4948, Chasmosaurus belli. A–D, right maxilla in A, C, lateral, and B, D, medial view; E–

H, left maxilla in E, G, lateral, and F, H, medial view. Abbreviations: aof, antorbital fossa; m-ecpt f, ectopterygoid facet on

maxilla; m-la-j f, lacrimal and jugal facets on maxilla; m mf, medial foramen on maxilla; m-n f, nasal facet on maxilla; m-pm

f, premaxillary facet on maxilla; m-pt f, pterygoid facet on maxilla; m r, maxillary ridge. Diagonal lines indicate broken bone.

Scale bars equal to 20 cm.

face dorsolaterally. The facet for the nasal is a dorsally facing surface that forms the apex of the maxilla. The nasal

would have overlapped the maxilla dorsolaterally (Fig. 2C). The ridge that extends across the maxilla, offsetting

the tooth row medially, ends posteriorly in a fluted and grooved facet for the lacrimal and jugal (Fig. 2C); between

the lacrimal–jugal facet and the nasal facet is a shallow groove marking the position of the small antorbital fenestra

(Fig. 2C), which is similar to that observed in ROM 839 (Chasmosaurus sp.). Ventral to the ridge the surface of the

maxilla curves concavely towards the tooth row and is irregularly pierced with foramina (Fig. 2C, G), as in other

specimens of Chasmosaurus (e.g. ROM 843; ROM 839) and other chasmosaurines (e.g. Agujaceratops, Lehman

1989; Triceratops, Hatcher et al. 1907). Below the ridge, the posterior margin of the maxilla describes an arc, con-

cave anteriorly, adjacent to which the coronoid process of the lower jaw and its associated musculature would have

projected when the skull and lower jaws were in articulation. The posteroventral process of the maxilla bears a

shallowly concave facet dorsolaterally that may have been for the ectopterygoid (Fig. 2G; Godfrey & Holmes

1995). The tooth row dominates the maxilla in medial view. No teeth are preserved, but 28 alveoli are present in

both maxillae; two additional sockets are reconstructed anteriorly on the right, while three additional sockets are

A NEW SPECIMEN OF CHASMOSAURUS BELLI

reconstructed on the left. Twenty-seven teeth are present in TMP 1981.19.175 (Chasmosaurus sp.), and tooth count

is known to vary ontogenetically in chasmosaurines (Forster et al. 1993). Anteriorly, the medial surface of the max-

illa is gently concave dorsal to the tooth row (Fig. 2H). Posteriorly, a large foramen pierces the medial side of the

maxilla and posterior to this a thin plate of bone projects dorsally (Fig. 2H). Dorsal to the foramen the thin plate of

bone forms the ventral margin of the antorbital fenestra. Posteroventrally, just dorsal to the tooth row, is a fluted,

ridged and grooved facet for the pterygoid (Fig. 2H).

Nasal. The nasals are firmly fused to each other on the midline (Fig. 3). Anteriorly a short, transversely com-

pressed process forms the articular surface for the premaxilla, which the nasal overlapped laterally (Fig. 3B).

Immediately posterior to the premaxillary facet the nasal horn core rises dorsally. A very prominent groove extends

transversely around the front of the horn core (Fig. 3D), fading on the lateral surface, and this may indicate the

junction with the epinasal. That the suture between the epinasal and nasals is still visible may indicate that

NHMUK R4948 was not fully osteologically mature at time of death (Horner & Goodwin 2006). A very prominent

suture is also visible between the nasals in ventral view. The horn core is relatively short (15.5 cm from the dorsal

margin of the external naris). It is oval in transverse cross-section with its long axis anteroposterior at its base (Fig.

3E, F; in some specimens of Chasmosaurus the horn core is rounded at the base, but this seems to be intraspecifi-

cally variable: Godfrey & Holmes 1995), flattened on top and projects dorsally (in some specimens the horn core

projects posterodorsally, another feature that is apparently intraspecifically variable: Godfrey & Holmes 1995).

The morphology of the nasal horn core is rather different from that of Kosmoceratops and Agujaceratops, in which

the horns are transversely compressed (Forster et al. 1993; Sampson et al. 2010). Its surface is rugose and pitted in

NHMUK R4948, suggestive of a horny covering in life (Fig. 3). A ridge extends up the horn core posteriorly, but

disappears before the tip. Ventral to the horn core, the nasal describes an arc forming the posterior margin of the

external naris in lateral view, as in other ceratopsids (Longrich 2010). Ventrally there is a tongue-and-groove joint

for articulation with the premaxilla (Fig. 3B, D), as in CMN 1254 (Chasmosaurus sp., Lambe 1915) and Vagacer-

atops (CMN 41357), although this has been partly reconstructed on both sides. Part of the posteroventral nasal has

also been reconstructed, and the articular surface for the prefrontal and frontal is not preserved.

Circumorbital region. The bones of the circumorbital region, including the lacrimal, jugal, postorbital and

supraorbital are fused together on the right side (Fig. 4; on the left only the jugal and part of the postorbital are pre-

served: Fig. 5). The orbit is circular. Anteroventrally the lacrimal presumably forms the margin of the orbit,

although sutures between the lacrimal and other elements cannot be seen. Medially the boundary between the lacri-

mal and the jugal appears to be defined by a very prominent ridge that bears a grooved facet for the maxilla (Figs

4D, 5H). At least one supraorbital element likely formed the anterior and dorsal margins of the orbit (Forster 1996).

In ROM 843 (C. belli), ROM 839 and TMP 1981.19.175 a deep groove is present dorsally above the orbit that sep-

arates two areas of rugosity, plausibly suggesting a suture between two supraorbital elements, as in a variety of

other ornithischians (Maidment & Porro 2010). No such groove is observable in NHMUK R4948, however,

although this area is heavily repaired with plaster. Anterior to the orbit the anterior supraorbital (palpebral of God-

frey & Holmes 1995) is rugose, bearing a large number of horizontally extending grooves and ridges (Fig. 4C), as

seen in other specimens of Chasmosaurus (ROM 843, 839; CMN 2245, 2280; UALVP 40; TMP 1981.19.175) and

in some specimens of Agujaceratops (Lehman 1989), Kosmoceratops and Utahceratops (Sampson et al. 2010).

The horn core is located anterodorsal to the orbit and projects anteriorly (Fig. 4). It is oval in cross-section at its

base, very short (5.5 cm tall from the dorsal margin of the orbit), and flattened on top. Medially it is partially recon-

structed. Supraorbital horn size is variable in specimens referred to Chasmosaurus (Lull 1933; Godfrey & Holmes

1995) and other ceratopsids, such as Agujaceratops (Lehman 1989). The postorbital forms the posterodorsal mar-

gin of the orbit. It is formed of two distinct surfaces in lateral view: one surface faces dorsally and formed the skull

roof posterior to the orbit, while one surface faces laterally and formed the posterior margin of the orbit (Fig. 5A–

D). Anteriorly, the left element bears a concave groove above the orbit for the posterior supraorbital (a neomorphic

element: Maidment & Porro 2010; Fig. 5C). Posterior to this the orbital margin is slightly thickened and rugose.

The medial edge of the dorsally facing surface extends posteromedially in a dorsoventrally deep, straight, flattened

facet for the frontal, and ends in a medially facing concave surface that may have contributed to the frontoparietal

fontanelle (Fig. 5D). A deep, triangular pit below this surface indicates the facet for the laterosphenoid (Fig. 5D), as

seen in Agujaceratops (Lehman 1989). The posteromedial surface is broken on both sides, but posterolaterally

there is a fluted and grooved interdigitating series of facets for the squamosal and parietal, and it is clear that

these bones and the postorbital overlapped each other along this complicated suture (Fig. 4C), as in CMN 1254

MAIDMENT & BARRETT

FIGURE 3. Nasals of NHMUK R4948, Chasmosaurus belli in A–B, right lateral, C–D, left lateral, and E–F, dorsal view.

Abbreviations: nhc, nasal horn core; n-pm f, premaxillary facet on nasal; n-pm p, premaxillary process of nasal. Diagonal

lines indicate broken bone. Scale bars equal to 20 cm.

A NEW SPECIMEN OF CHASMOSAURUS BELLI

FIGURE 4. Right circumorbital region of NHMUK R4948, Chasmosaurus belli in A, C lateral, and B, D, medial view. Abbre-

viations: aso, anterior supraorbital; epj, epijugal; j, jugal; j-ma f, maxillary facet on jugal; j-qj f, quadratojugal facet on jugal;

la-j r, ridge between lacrimal and jugal; ltf, lateral temporal fenestra; orb, orbit; po-p f, parietal facet on postorbital; po-sq f,

squamosal facet on postorbital; sohc, supraorbital horn core. Diagonal lines indicate broken bone. Scale bar equal to 20 cm.

(Chasmosaurus sp., Lambe 1915). The suture between the postorbital and jugal cannot be seen, but presumably

extended from the lateral temporal fenestra to the posterior margin of the orbit, as in other ornithischians. The jugal

forms the ventral margin of the orbit and a series of radial grooves extend across the lateral surface in this area (Fig.

4C). The posteroventral process of the jugal extends posterior to the orbit, as in other chasmosaurines (e.g. Agujac-

eratops, Forster et al. 1993; Kosmoceratops, Utahceratops; Sampson et al. 2010; Vagaceratops, Holmes et al.

2001). The ventral margin of the process describes a smooth, dorsally concave curve; the posterior surface of the

jugal forms the anterior margin of the lateral temporal fenestra. A pyramidal epijugal is situated at the distal end of

the posterior process (Figs 4C, 5G), as in other specimens of Chasmosaurus (e.g. CMN 2245, Lambe 1914a;

AMNH 5401, Brown 1933; ROM 843; TMP 1981.19.175) and the suture between it and the jugal is clear in both

lateral and medial view. It is 5 cm tall and 6.5 cm wide anteroposteriorly at its base. Its surface is pitted and rugose

and it projects laterally. In medial view, ventral to the orbit, the jugal bears a smooth oval facet for the maxilla with

a ridge extending posterodorsally across it. Immediately posterodorsal to the facet on the left side is a small fora-

men with a canal opening towards the maxillary facet (Fig. 5H). The distal end of the posterior process of the jugal

bears a two-pronged facet in medial view for the quadratojugal, which was overlapped by the jugal. A deep groove

extends up the centre of this facet (Figs 4D, 5H).

MAIDMENT & BARRETT

Quadrotojugal. Both quadratojugals are preserved: the right is almost complete while the left is incomplete

posteromedially and has been reconstructed (Fig. 6). In lateral view the quadratojugal is roughly triangular with the

apex pointing ventrally. The posterodorsal margin forms a portion of the ventral margin of the lateral temporal

fenestra, a feature present in CMN 1254 (Chasmosaurus sp., Lambe 1915) and UALVP 40 (Chasmosaurus sp.),

which are both juveniles. In some Chasmosaurus specimens, however the squamosal overlaps the top of the quad-

rate and quadratojugal in lateral view, contacting the jugal and excluding the quadratojugal from the margin of the

lateral temporal fenestra (Lambe 1914a; Godfrey & Holmes 1995; CMN 2280; CMN 2245; ROM 839). Several

lines of evidence, such as the lack of fusion of some skull elements, a visible epinasal suture, lack of fusion of the

ilia to the sacrum and visible neurocentral sutures on dorsal vertebrae (see below) suggest NHMUK R4948 was not

osteologically mature at the time of death and the contribution of the quadratojugal to the margin of the lateral tem-

poral fenestra may well vary ontogenetically. A well-developed ridge extends from the dorsal surface ventrally and

projects strongly laterally; it reaches an apex ventrally (Fig. 6D). Anterior to this ridge is a facet for the posterior

process of the jugal; it is similar in morphology to the poorly preserved quadratojugal of Vagaceratops (CMN

41357) and that of Triceratops (Hatcher et al. 1907). The facet is deeply grooved and large, occupying half the

quadratojugal; the apex of the ridge apparently helped to support the epijugal ossification: it is rugose and contrib-

utes posterolaterally to the epijugal when the elements are articulated (Fig. 6D, F). Posterior to the jugal facet and

ridge the surface of the quadratojugal is smooth. The posterior margin is transversely thick and bears a slightly con-

cave facet for the quadrate (Fig. 6E). This facet rotates from facing wholly posteriorly more dorsally to facing

medially on the ventral quadratojugal. In this area the facet is very rugose and lumpy, as it is in Vagaceratops

(CMN 41357). In medial view there is a flattened oval facet dorsally for the squamosal, indicating that at least part

of the squamosal underlapped the quadratojugal (Fig. 6E).

Quadrate. Both quadrates are preserved but have been repaired with plaster (Fig. 7). The quadrate is antero-

posteriorly compressed and rectangular in lateral outline with the long axis trending dorsoventrally. Medially the

pterygoid process is short dorsoventrally and incomplete on both sides; in posterior view a ridge extends ventrally

down the medial surface of the quadrate and curves medially along the pterygoid process, marking the facet for the

pterygoid (Fig. 7F, H), as in Vagaceratops (CMN 41357). The lateral surface of the quadrate is the anteroposteri-

orly broadest part of the element. It is composed of three surfaces. The quadratojugal facet occupies the ventral

third of the lateral surface, as in Agujaceratops (Lehman 1989) and Vagaceratops (CMN 41357). Ventrally it is

rugose, as is the corresponding surface on the quadratojugal, and moving dorsally it becomes smoother and rotates

onto the anterior surface of the bone. Dorsal to this facet, which is defined laterally by a ridge trending posteroven-

trally, the middle part of the lateral surface would be visible when articulating with other skull elements in lateral

view. Dorsally, again separated by a ridge, is a flattened facet for the squamosal (Fig. 7E). Distally, the articular

condyle of the quadrate is anteroposteriorly broad. In posterior view, a series of striations and low rugosities posi-

tioned dorsolaterally may indicate facets for the paroccipital processes (Fig. 7F, H). Similar features were also

observed in Vagaceratops (CMN 41357).

Squamosal. Both squamosals are preserved. They are shaped like elongate scalene triangles with the apex

pointing posteriorly (Fig. 8). Anteriorly the left element preserves a fluted and grooved facet for the postorbital,

which apparently overlapped the squamosal along much of the length of the contact (Fig. 8F), as in Agujaceratops

(Lehman 1989) and other ceratopsids. Medially, an anterodorsally trending ridge offsets part of the postorbital facet

laterally relative to the rest of the medial surface, forming an articular facet for the paroccipital process (Fig. 8D). A

second facet is present ventrally, probably for the head of the quadrate. The part of the squamosal that contributes

to the lateral temporal fenestra is not preserved on either side. Ventral to the postorbital facet, the squamosal arcs

posteroventrally. The lateral surface of the squamosal is flat anteriorly and becomes concave posteriorly, as in other

specimens referred to Chasmosaurus (ROM 843, 839; CMN 2245, 2280), and bears numerous pits and grooves

(Fig. 8B). The medial margin of the squamosal, where it articulates with the parietal, is slightly transversely thick-

ened. A large foramen pierces the surface of the left element, but this is not present on the right side; similar asym-

metry is seen in ROM 843 and ROM 839 (Chasmosaurus; Godfrey & Holmes 1995), Utahceratops (Sampson et

al. 2010) and other ceratopsids (Tanke & Farke 2007). Medially the squamosal is gently convex. A groove extends

all the way along the margin medially (Fig. 8F) marking the facet for the parietal and suggesting the lateral parietal

bar was complete, a feature that, although thought to be diagnositic of Chasmosaurus belli by Godfrey and Holmes

(1995), is also present in other chasmosaurines (e.g. Kosmoceratops [Sampson et al. 2010]; Vagaceratops [Holmes

et al. 2001]; Torosaurus [Hatcher et al. 1907]), some specimens of Chasmosaurus russelli (CMN 2280), and is

A NEW SPECIMEN OF CHASMOSAURUS BELLI

FIGURE 5. Left postorbital and jugal of R4948, Chasmosaurus belli. A–D, postorbital in A, C, lateral and B, D, medial view;

E–H, jugal in E, G, lateral and F, H, medial view. Abbreviations: epj, epijugal; fpf, margin of the frontoparietal fontanelle; j,

jugal; j-ma f, maxillary facet on jugal; j-qj f, quadratojugal facet on jugal; la-j r, ridge between lacrimal and jugal; orb, orbit;

po-f f, frontal facet on postorbital; po-lsp f, laterosphenoid facet on postorbital; po-pso f, posterior supraorbital facet on postor-

bital. Diagonal lines indicate broken bone. Scale bars equal to 20 cm.

MAIDMENT & BARRETT

FIGURE 6. Quadratojugals of NHMUK R4948, Chasmosaurus belli. A–F, right quadratojugal in A, D, lateral, B, E, medial

and C, F, posterior view. Abbreviations: ltf m, margin of the lateral temporal fenestra; qj-epj f, epijugal facet on quadratojugal;

qj-j f, jugal facet on quadratojugal; qj-q f, quadrate facet on quadratojugal; qj r, ridge on quadratojugal; qj-sq f, squamosal

facet on quadratojugal. Scale bar equal to 5 cm.

A NEW SPECIMEN OF CHASMOSAURUS BELLI

FIGURE 7. Quadrates of NHMUK R4948, Chasmosaurus belli. A–B, E–F, right quadrate in A, E, anterior and B, F, posterior

view; C–D, G–H, left quadrate in C, G, anterior and D, H, posterior view. Abbreviations: q-poc f, paroccipital process facet on

quadrate; q-pt f, pterygoid facet on quadrate; q-pt p, pterygoid process of quadrate; q-qj f, quadrotojugal facet on quadrate; q-

sq f, squamosal facet on quadrate. Scale bar equal to 5 cm.

known to vary within individuals in Pentaceratops (Lehman 1989). The ventral margin of the squamosal bears a

series of fused pyramidal episquamosals with oval bases. On the right side seven are preserved, while on the left

there are six, although there is space for one more. Sutures between episquamosals and the squamosals are very

clear, suggesting one may not have been entirely fused and has been lost from the left side. Episquamosal number

is known to vary between six and ten in specimens of Chasmosaurus (Lull 1933; Godfrey & Holmes 1995; Farke

2011). The episquamosals are generally asymmetrical, with the apex nearer to their anterior margin than their pos-

terior margin. The fourth episquamosal on the right side has a double apex (Fig. 8B), and in medial view a groove

separates the peaks, suggesting that this episquamosal was originally formed from two ossifications that have

coalesced. This condition has not, to our knowledge, been reported before in ceratopsids.

Parietal. The parietal is preserved in six pieces that fit together and represent all parts of the element (Fig. 9).

Anteromedially the parietal forms a transversely broad, dorsally convex ridged and grooved platform that extended

anteriorly to form the posterior margin of the frontoparietal fontanelle (Fig. 9B). Laterally, the sides of this plat-

form are smooth and concave and form the medial margins of the supratemporal fenestrae, which were confluent

with the parietal fenestrae, as in other specimens of Chasmosaurus and other ceratopsids (Farke 2010). Ventrally,

MAIDMENT & BARRETT

this part of the parietal bears three rounded fossae. The median bar is complete but in three pieces, and as preserved

is 86 cm long anteroposteriorly. It is roughly triangular in cross-section with the apex pointing ventrally and the tri-

angle base forming a flat dorsally-facing surface that bears a series of longitudinal striations. Laterally the sides of

the median bar bear irregular grooves and ridges that are asymmetric on either side. The posterior parietal bar lies

at right angles to the median bar and there is no ‘U’-shaped emargination where the two meet (Fig. 9; Fig. 10), in

contrast to Agujaceratops (Lehman 1989), Chasmosaurus russelli (Fig. 10D; CMN 2280) and Utahceratops

(Sampson et al. 2010), but similar to other specimens of Chasmosaurus belli including the holotype (CMN 491;

Lambe 1902), AMNH 5401 (Brown 1933), ROM 843 (Fig. 10A) and CMN 2245 (Fig. 10B), Vagaceratops (Hol-

mes et al. 2001), Torosaurus (Hatcher et al. 1907) and Kosmoceratops (Sampson et al. 2010). The dorsal surface of

the junction between the bars is crossed with sinuous grooves that probably represent blood vessel channels (Fig.

9B). The posterior bar, which is completely preserved on the left side, is rounded in cross-section but ventrally

bears a thin anteriorly directed flange that is reconstructed and repaired with plaster along much of its length; how

much of this feature is real is difficult to determine. The posterior bar of ROM 843 (C. belli) is also rounded in

cross-section (Fig. 10A), as is that of Agujaceratops (Lehman 1989), and TMP 1983.25.1 (C. russelli; Fig. 10E)

but that of CMN 2245 (C. belli; Fig. 10B) is ‘C’-shaped, being strongly concave anteriorly, and this suggests the

shape of the posterior bar is variable in Chasmosaurus and should not be used as a diagnostic feature of the genus

(contra Longrich 2010). Epiparietals are not fused to the posterior bar and are not preserved, but the fusion of ossi-

fications to the parietal may vary ontogenetically in Chasmosaurus (Lehman 1989) as they do in Triceratops

(Horner & Goodwin 2006). The internal surface of the corner of the posterior bar and lateral bar is flattened, while

the external surface, which forms the posterolateral corner of the frill, bears a facet for an epiparietal that was not

fused and has not been preserved. The lateral bar is compressed dorsolaterally-ventromedially. Laterally it bears an

elongate facet for the squamosal (Fig. 9B, D), while medially there is a distinct groove below a low ridge. This

ridge is better developed in CMN 2245 (C. belli), in which the lateral bar is triangular in cross-section with the

apex pointing medially. The middle section of the lateral bar is not preserved in NHMUK R4948, but anteriorly the

lateral bar flares medially as a thin flange to form the anterolateral corner of the parietal fenestra. The surface bears

a large number of blood vessel grooves, a feature present in other Chasmosaurus specimens (Lull 1933; ROM 843;

CMN 2280) and is broken medially.

Braincase. The braincase is complete and, rarely for chasmosaurines, is disarticulated from the rest of the skull

(Figs 11, 12).

Individual braincase elements are fused and the sutures between them have been obliterated.

The paroccipital process is presumably formed by the fused exoccipital and opisthotic, and as in many adult

reptiles, no suture is visible between them (Romer 1956). In posterior view (Figs 11E, 12A), NHMUK R4948 has

an elongate paroccipital process that projects posterolaterally. It is deep dorsoventrally and flares distally; although

it is incomplete distally on both sides, it does not appear to flare to the same degree as it does in the centrosaurine

Diabloceratops (Kirkland & Deblieux 2010: fig. 8.8). The dorsal part of the paroccipital process is gently exca-

vated producing a shallow, posterodorsally facing sulcus, which probably served as an insertion area for the m. rec-

tus capitis posterior (Fig. 12A; Tsuihiji 2010). As the dorsal margins of the paroccipital processes are poorly

preserved, it cannot be determined if posttemporal foramina were present or absent. The morphology of this area is

similar to that seen in other Chasmosaurus specimens (ROM 839; CMN 2245; UALVP 40; TMP 1981.19.175),

Centrosaurus (Dodson et al. 2004), Diabloceratops (Kirkland & Deblieux 2010) and Triceratops (Hatcher et al.

1907). The anterior and distal parts of the paroccipital process are probably formed by the opisthotic (Romer 1956).

The anterior surface of the paroccipital process bears a number of fine transverse ridges and striations. At the distal

end of the left paroccipital process a diagonal ridge extending dorsomedially–ventrolaterally is present and this

may represent a facet for articulation of the quadrate (Figs 11D, 12C).

Ventral to the paroccipital process, a deeply concave fossa is present on each side of the occipital condyle. A

second, slightly smaller fossa positioned lateral to this large fossa is preserved on the left side of the condyle; this is

one of several asymmetries in the braincase and is probably preservational in origin (Fig. 12A). The larger fossa

probably surrounded the exits for the vagus (X), accessory (XI) and hypoglossal nerves (XII), as it does in Tricer-

atops (Forster 1996), Agujaceratops (Lehman 1989), Pentaceratops (Lehman 1993), and Pachyrhinosaurus (Wit-

mer & Ridgely 2008), although the actual foramina are not visible due to the presence of matrix. Primitively in

dinosaurs, cranial nerves IX to XI exited the braincase via the metotic foramen (Sampson & Witmer 2007), which

represents the remains of the embryonic metotic fissure in reptiles and is located between the otic capsule and the

occipital pillar of the embryological chondrocranium, which ossifies to form the opisthotic (Starck 1979). How-

A NEW SPECIMEN OF CHASMOSAURUS BELLI

ever, in neotheropods, the vagus canal, which minimally transmitted the vagus and accessory nerves, was diverted

posteriorly to open on to the occiput in conjunction with the hypoglossal nerve (Sampson & Witmer 2007). This

derived condition, which is not present in non-ceratopsid neoceratopsians (e.g. Forster 1996; Makovicky 2001)

appears to have occurred convergently in ceratopsids (Forster 1996; Witmer & Ridgely 2008) and thus represents a

ceratopsid synapomorphy.

FIGURE 8. Squamosals of NHMUK R4948, Chasmosaurus belli. A–D, right squamosal in A–B, lateral and C–D, medial

view; E–F, left squamosal in medial view. Because of the delicate condition of the left squamosal, it could not be turned for

photography in lateral view at the time of writing. Abbreviations: episq, episquamosals; sq-pa f, parietal facet on the squa-

mosal; sq-po s, suture with the postorbital; sq-poc f, paroccipital process facet on the squamosal; sq-q f, quadrate facet on the

squamosal. Hatching indicates broken bone. Scale bar equals 20 cm.

MAIDMENT & BARRETT

FIGURE 9. Parietal of NHMUK R4948, Chasmosaurus belli, which is preserved in six parts. A–B, dorsal view; C–D, ventral

view. Abbreviations: lb, lateral bar; mb, median bar; mp, median platform; pb, posterior bar; sq f, facet for the squamosal.

Hatching indicates broken bone. Scale bar equals 20 cm.

A NEW SPECIMEN OF CHASMOSAURUS BELLI

FIGURE 10. Comparison of parietal posterior bar and eqiparietal morphology in specimens referred to Chasmosaurus. A–C,

Chasmosaurus belli; D–E, Chasmosaurus russelli. A, ROM 843 in dorsal view; B, CMN 2245 in dorsolateral view; C,

NHMUK R4948 in dorsal view; D, CMN 2280 in dorsal view; E, TMP 1983.25.01 (the holotype of ‘Mojoceratops’) in dorsal

view. Not to scale.

In adult ceratopsids the exoccipitals meet dorsally above the foramen magnum, excluding the supraoccipital

from its margin (Hatcher et al. 1907: fig. 6; Goodwin et al. 2006). In NHMUK R4948 these sutures cannot be seen,

and they were not observed in other Chasmosaurus specimens (ROM 839; CMN 2245; UALVP 40; TMP

1981.19.175). The foramen magnum is deeper dorsoventrally (3.4 cm) than it is wide transversely (3.1 cm) and it is

angled posterodorsally so that it is not clearly visible in posterior view (Fig. 11A). In articulated specimens, this

appears to be because the occipital condyle is angled slightly ventrally relative to the horizontal axis of the skull

(ROM 839; CMN 2245; Diabloceratops, Kirkland & Deblieux 2010). In Triceratops (Hatcher et al. 1907: fig. 6;

Forster 1996) Agujaceratops (Lehman 1989: fig. 6), Centrosaurus (Dodson et al. 2004: fig. 23.4), Diabloceratops

(Kirkland & Deblieux 2010) and Chasmosaurus sp. (UALVP 40; TMP 1981.19.175) the ventral margin of the

supraoccipital articulates with the exoccipitals, forming a vertical and slightly posteriorly inclined wall. These taxa

also possess a prominent ridge separating two fossae that were probably occupied by a venous sinus (Tshihiji

2010). The ridge extends ventrally down the midline of the supraoccipital. The dorsal margin of the occiput is bro-

ken in NHMUK R4948 (Fig. 11A), but it differs from the aforementioned taxa in being angled anterodorsally and

in lacking a prominent midline ridge. In Diabloceratops, the exoccipitals form a thin, caudally-extending shelf

which projects over the dorsal margin of the foramen magnum (Kirkland & Deblieux 2010); this feature is not

present in NHMUK R4948.

The occipital condyle is composed of the exoccipitals laterally and the basioccipital ventrally in ceratopsids

(Hatcher et al. 1907: fig. 7; Lehman 1989: fig. 6; Goodwin et al. 2006: fig. 9) but no sutures can be identified in

this area in NHMUK R4948. The condyle is larger than the foramen magnum (6.7 cm tall dorsoventrally; 6.5 cm

wide transversely), has a circular outline in posterior view, and a short neck that curves down to the basal tubera,

narrowing in width slightly as it does so. The basal tubera are separated in posterior view by a shallow notch. The

basal tubera are extremely large in comparison with other ornithischians, suggesting enlarged nuchal musculature

(m. longissimus capitis, pars transversalis cervicis and m. iliocostalis capitis, Tsuihiji 2010) and are transversely

broad plates in posterior view. In lateral view, they expand strongly anteroposteriorly towards their distal ends and

project ventrally. In ventral view the distal ends of the tubera have an oval outline, with the long axis of this oval

orientated transversely; a small foramen opens between them and comparison with crocodiles suggests this is for

the basilar artery (Fig. 12B, Hopson 1979).

In lateral view (Figs 11C, D; 12C, D), a large foramen is present at the base of the paroccipital process immedi-

ately anterior to the basal tubera. This represents the fenestra ovalis, which would have received the footplate of the

stapes, and it may also have transmitted the glossopharangeal nerve (IX; Sampson & Witmer 2007; Witmer & Rid-

MAIDMENT & BARRETT

gely 2008). Anterior to the fenestra ovalis another large foramen pierces the braincase and is identified as the

trigeminal foramen, transmitting the maxillary (V2) and mandibular (V3) parts of the trigeminal nerve (V). In birds

V2&3 exit the braincase via separate foramina (Hartwig 1993), but in dinosaurs the foramina are coalesced, as they

are in crocodiles (Hopson 1979; Starck 1979). The trigeminal foramen is located within the prootic and its anterior

boundary is formed by the laterosphenoid (Starck 1979). The fenestra ovalis and trigeminal foramen are separated

by a sharp ridge of bone, which is often termed the crista prootica (e.g. Forster 1996). This ridge arises from the

posteroventral margin of the trigeminal foramen, extends dorsally to a point level with the dorsal margin of the

foramen and then turns posteriorly, to extend dorsal to the fenestra ovalis. The ridge continues posteriorly, extend-

ing on to the anterior surface of the paroccipital process, fading out approximately one-third of the way along the

process (Fig. 12C, D).

FIGURE 11. Braincase of NHMUK R4948, Chasmosaurus belli in A, dorsal, B, ventral, C, right lateral, D, left lateral and E,

posterior view. Scale bar equals 10 cm.

Anterior to the basal tubera the basisphenoid expands ventrally to form the basipterygoid processes, which are

separated from each other by a deep fossa (Fig. 12B). The right process is broken, but the left is complete. It is tri-

A NEW SPECIMEN OF CHASMOSAURUS BELLI

angular in lateral view with the apex tapering ventrally, but in anterior view it expands slightly transversely. A

small foramen positioned ventral to the trigeminal foramen in the concavity formed between the basal tubera and

basipterygoid process is present on the left side of the braincase (its presence on the right cannot be established

externally due to breakage). A shallow groove extends from it posteriorly towards the basal tubera and it probably

represents the entrance for the internal carotid artery (Sampson & Witmer 2007; Witmer & Ridgely 2008). A simi-

lar feature in the same location was also interpreted as the foramen for the internal carotid in Diabloceratops (Kirk-

land & Deblieux 2010).

FIGURE 12. Interpretive drawings of the braincase of NHMUK R4948, Chasmosaurus belli in A, posterior, B, ventral, C, left

lateral and D, right lateral view. Abbreviations: II, foramen for exit of optic nerve; III, foramen for exit of oculomotor nerve;

IV, foramen for exit of trochlear nerve; V1, foramen for exit of trigeminal nerve, ophthalmic branch; V2&3, foramen for exit of

trigeminal nerve, maxillary and mandibular branches; X–XII, foramen for exit of vagus, accessory and hypoglossal nerves;

aob, antotic buttress; ba, foramen for basilar artery, bt, basal tuber; bv, foramen for blood vessel; bpt p, basipterygoid process;

crp, crista prootica; dep, preservational depression; fo, fenestra ovalis; ica, internal carotid artery; oc, occipital condyle; poc,

paroccipital process; poc-q f, facet for quadrate on paroccipital process; sul, sulcus. Hatching indicates broken bone. Scale bar

equal to 10 cm.

In other dinosaurs the foramen for the facial nerve (VII) pierces the braincase in the region between, or slightly

ventral to, fenestra ovalis and the trigeminal foramen and a small facial foramen has been identified in all ceratop-

sians whose braincases have been studied (Hay 1909; Brown & Schlaikjer 1940; Marya ska & Osmólska 1975;

Lehman 1989, 1993, 1996; Forster 1996; Chinnery & Weishampel 1998; Makovicky 2001; Witmer & Ridgely

2008; Kirkland & Deblieux 2010). However, this opening cannot be identified in NHMUK R4948.

Anterior to the trigeminal foramen, the lateral wall of the braincase is pierced by numerous small foramina

(Fig. 12C, D). Several are only present on the right side of NHMUK R4948, but this asymmetry is probably preser-

vational. A ridge extending dorsally along the laterosphenoid probably corresponds to the structure termed the

antotoic buttress by Godfrey and Holmes (1995) and the laterosphenoid buttress by Kirkland & Deblieux (2010). It

is pierced ventrally by a foramen opening anteriorly that probably represents the exit for the ophthalmic branch of

MAIDMENT & BARRETT

the trigeminal nerve (V1). A similar structure in the same location was identified as V1 in Diabloceratops (Kirkland

& Deblieux 2010). Ventromedial to the V1 foramen a second small foramen is present. Previous workers have iden-

tified this as the opening for the oculomotor nerve in other ceratopsian braincases (III; Brown & Schlaiker 1940;

Lehman 1989, 1996; Makovicky 2001). These foramina mark the anterior extent of the basisphenoid and its suture

with the orbitosphenoid above and parasphenoid below (Norman 1986). Further anteriorly, three small foramina lie

adjacent to each other. Previous work has suggested that the foramen anterodorsal to the exit of cranial nerve III is

the exit for the trochlear nerve (IV; Hay 1909; Brown & Schlaikjer 1940; Lehman 1989, 1996; Forster 1996; Mak-

ovicky 2001; Dodson et al. 2004) while the opening anterior to that for cranial nerve III (which also lies closest to

the midline) is the exit for the optic nerve (II; Hay 1909; Brown & Schlaikjer 1940; Lehman 1989, 1996; Forster

1996; Makovicky 2001; Dodson et al. 2004), which lies on the suture between the parasphenoid below and orbito-

sphenoid above (Norman 1986). The dorsalmost foramen in this area is located within the orbitosphenoid and prob-

ably represents a blood vessel canal, possibly the orbitocerebral vein (Witmer & Ridgely 2008). Ventral to these

foramina the braincase is broken and has been reconstructed with plaster, potentially filling the space that would

have marked the exit for the olfactory tracts. The interpretation of these cranial foramina differs slightly from the

interpretation of the braincase of the centrosaurine Diabloceratops by Kirkland and Deblieux (2010), in which the

foramen for cranial nerve III lies anterior and dorsal to V1, and corresponds to the foramen here interpreted as the

exit for cranial nerve II. The opening for cranial nerve II in Diabloceratops is interpreted as the opening for IV,

while the opening for IV in Diabloceratops is interpreted as a blood vessel pit herein. Our interpretation of brain-

case foramina is more similar to other work on ceratopsian braincase anatomy (Hay 1909; Brown & Schlaikjer

1940; Makovicky 2001; Witmer & Ridgely 2008).

In dorsal view (Fig. 11A), the supraoccipital and posterior part of the frontals have been broken, but anteriorly

there is a large concave fossa present between the laterosphenoids, presumably lying within the remnants of the

broken frontals, and this probably represents part of the supracranial sinus, a feature present in many ceratopsids

(Farke 2006; 2010).

Lower jaw. Predentary. The predentary is arrow-head shaped in dorsal view. Its dorsal surface is deeply con-

cave, and the lateral margins (triturating surfaces) are transversely broad, orientated horizontally and flat to slightly

concave, joining anteriorly in a point that is curved dorsally in lateral view (Fig. 13). Posteroventrally the preden-

tary is also drawn into a midline point, and in posterior view two deeply concave facets extend from the poster-

oventral midline point to the dorsal surface for articulation with the dentaries. Ventrally the surface of the

predentary is convex, pitted and grooved, suggestive of a horny covering in life. It is extremely similar to the pre-

dentaries of Triceratops and Agujaceratops (Hatcher et al. 1907; Lehman 1989) in all respects. A distinct groove

extends anteroposteriorly down the midline ventrally.

FIGURE 13. Predentary of NHMUK R4948, Chasmosaurus belli in A, dorsal, B, ventral and C, right lateral view. Scale bar

equal to 10 cm.

Posterior lower jaw elements. The posterior elements of the lower jaw, including the surangular, articular and

prearticular are preserved on both sides and are fused together; sutures are visible in places (Figs 14, 15). Addition-

ally the coronoid process of the left dentary is present (Fig. 14K, L). Godfrey and Holmes (1995) suggested that co-

ossification of the posterior jaw elements never occurred in Chasmosaurus, however, this is clearly not the case in

NHMUK R4948, where these elements are in articulation, have not been displaced and are fused together. In lateral

view (Figs 14B, 15B) the surangular is rectangular, with the long axis angled obliquely anterodorsally; it is similar

to that of Triceratops (Hatcher et al. 1907). The surface is rugose and posterolaterally it bears striations and small

A NEW SPECIMEN OF CHASMOSAURUS BELLI

lateral tumescenses. The angular would have been located ventral to the surangular, as in Triceratops (Hatcher et

al. 1907) and ventrally, the surangular bears a deeply concave facet into which the angular would have articulated,

wrapping underneath the posterior lower jaw (Fig. 14B, 15B). Anterolaterally there is an oval facet for articulation

with the dentary (Fig. 14B), also observed in CMN 2245 (C. belli). This differs from the condition in Vagaceratops,

where the dentary appears to articulate along a blunt, anteriorly-facing facet (CMN 41357). The anterior parts of

both surangulars are broken. On the right a large foramen extends posteriorly from the margin of the adductor fossa

into the body of the surangular; this area is damaged on the left side and infilled with plaster. In posterior view

(Figs 14F, 15J), the surangular extends medially as a dorsoventally thin process to articulate with the prearticular,

as in Vagaceratops (CMN 41357). Two small foramina are present posterolaterally; foramina in similar locations

were illustrated in Triceratops by Hatcher et al. (1907) and are present in Vagaceratops (CMN 41357).

FIGURE 14. Preserved left lower jaw elements of NHMUK R4948, Chasmosaurus belli. A–J, posterior part of the left lower

jaw in A–B, lateral, C–D, medial, E–F, posterior, G–H, dorsal and I–J, ventral view. K–L, left coronoid process in K, lateral

and L, medial view. Abbreviations: add, adductor fossa; ar, articular; for, foramen; gle, glenoid fossa; par, prearticular; sa,

surangular; sa-a f, facet for angular on surangular; sa-d f, facet for dentary on surangular. Hatching indicates broken bone.

Scale bars equal to 5 cm.

The prearticular forms the posteromedial and medial portions of the posterior part of the lower jaw (Figs 14D,

15D). Posteromedially the prearticular contacts the surangular, and in ventral view (Figs 14J, 15H) a suture can be

traced extending anteriorly along the ventromedial surface. A triangular wedge of the articular is visible between

the prearticular and surangular in ventral view. Posterodorsally the prearticular is deeply concave, where it forms

the posteromedial part of the glenoid for articulation with the quadrate. Anteriorly the cup-like articular surface

gives way to a transversely compressed, dorsoventrally thin lamina that extends forwards and is broken on both

sides.

The articular forms approximately half of the articular surface for the quadrate and is reniform in dorsal view

(Figs 14H, 15F). It is concave medially, where it overlies the prearticular, while laterally it becomes convex, over-

lying the surangular. The articular appears to extend ventrally between the surangular and prearticular, although it

is excluded from the posterior surface of the lower jaw by contact of these elements. In ventral view the articular

MAIDMENT & BARRETT

forms a triangular wedge between the surangular and prearticular, so that the apex of the triangle points posteriorly,

and the base of the triangle forms the smooth, slightly concave surface of the adductor fossa.

Axial skeleton. Although the presacral axial skeleton is preserved in three specimens of Chasmosaurus (ROM

843, CMN 2245, CMN 2280), it has not previously been described in detail (although it was briefly described in

Mallon & Holmes 2006). The cervicals and dorsals of NHMUK R4948 are the least distorted of any Chasmosaurus

specimen and are uncrushed. Dimensions of the cervical and dorsal vertebrae are given in Table 2.

TABLE 2. Measurements of free cervical and dorsal vertebrae, NHMUK R4948..

Cervical vertebrae. The first three cervical vertebrae are fused together to form the cervical bar or syncervical,

a feature that constitutes a neoceratopsian synapomorphy (Dodson et al. 2004; Campione & Holmes 2006; Tsuihiji

and Makovicky 2007). In NHMUK R4948 the atlas, axis and cervical three are clearly differentiated from each

other by rugose sutures (Fig. 16). The atlas is longer than wide and rounded in transverse section, with a deeply

concave anterior facet for the occipital condyle, as in Triceratops (Hatcher et al. 1907) and Centrosaurus (ROM

767). The anterior rim is smooth, although it is finished with plaster on the left side. The lateral sides of the atlas

are smooth except where they rise to rugose tumescences about half way along the length of the element: these are

rounded, situated dorsally on the intercentrum and represent the articular facet for the single-headed atlas rib,

which is unpreserved. The suture with the axis is expanded transversely and rugose laterally; there is no evidence

of the atlas centrum (odontoid process) and it probably fused to the axis early in ontogeny. The atlantal neural

arches are broken on both sides.

The axis forms the second fused element in the cervical bar. It is similar in length anteroposteriorly to the atlas

and the lateral sides of the centrum are smooth. Ventrally a very slight ridge is present extending anteroposteriorly,

a feature also observed in ROM 843 (Chasmosaurus belli). In left lateral view a small parapophysis projects later-

ally from the anterior part of the lateral centrum, as in Triceratops (Hatcher et al. 1907); on the right side this area

is broken. Posteriorly the centrum expands transversely along the suture with cervical three and is rugose. As in all

ceratopsians, the neural arch of the axis is very large (Campione & Holmes 2006; Tsuihiji & Mackovicky 2007). It

is broken along the anterior edge, and comprises two transversely thin sheets of bone that converge above the neu-

ral canal to form an elongate, posteriorly inclined neural spine that is fused to the anterior surface of the neural arch

of cervical three, forming an elongate plate that presumably served as an anchorage point for some of the muscula-

ture necessary for the support of the large ceratopsid head (Hatcher et al. 1907; Romer 1956; Campione & Holmes

2006; Tsuihiji 2010). The end of the neural spine is rounded dorsally and a cleft separates it from the dorsal end of

the spine of cervical three. Posteroventrally a foramen separates the axis neural arch from the neural arch pedicle of

cervical three; this is broken around its edges. A foramen in present in the same location in ROM 843, CMN 2280

(Campione & Holmes 2006: fig. 3B, C), Triceratops (Hatcher et al. 1907), Styracosaurus (CMN 344) and Centro-

Element Length of centrum (cm) Width across anterior articular surface (cm)

Cervical 4 6.7 11.2

Cervical 5 5.5 11.7

Cervical 6 6.0 11.2

Cervical 7 5.8 10.5

Cervical 8 6.0 10.9

Dorsal 1 5.9 9.8

Dorsal 2 6.4 9.5

Dorsal 3 6.5 9

Dorsal 4 6.4 8.9

Dorsal 5 5.9 8.8

Dorsal 6 5.9 9.7

Dorsal 7 5.9 9.2

Dorsal 8 5.9 9.4

Dorsal 9 6.6 9.2

A NEW SPECIMEN OF CHASMOSAURUS BELLI

saurus (CMN 344). In left lateral view a small diapophysis projects laterally on a sturdy transverse process from

the side of the neural arch; this area is broken on the right side.

FIGURE 15. Preserved right lower jaw elements of NHMUK R4948, Chasmosaurus belli in A–B, lateral, C–D, medial, E–F,

dorsal, G–H, ventral and I–J, posterior view. Abbreviations: add, adductor fossa; ar, articular; for, foramen; gle, glenoid fossa;

par, prearticular; sa, surangular; sa-a f, facet for angular on surangular. Hatching indicates broken bone. Scale bar equals 5.

The centrum of cervical three, the final element in the ceratopsid cervical bar (Tsuihiji & Mackovicky 2007), is

approximately the same length as the atlas and axis. The posterior centrum facet is flat, the lateral surface is

smooth, and ventrally a very slight ridge is present extending anteroposteriorly. A small, rounded parapophysis is

located anterodorsally on the lateral surface of the centrum; it is supported by a bulge that continues onto the poste-

rolateral surface of the axis, similar to Triceratops (Hatcher et al. 1907). The anterior surface of the neural arch and

neural spine of cervical three is coalesced with those of the axis and prezygapophyses, and sutures have been

largely obliterated, as in Triceratops (Hatcher et al. 1907); in contrast, the postzygapophyses of cervical three

extend posteriorly from just dorsal to the neural canal, face ventrolaterally, and are broadly separated, as in Centro-

saurus (ROM 767). The diapophysis, which is smaller than the parapophysis, is located posterodorsal to the latter

MAIDMENT & BARRETT

and situated on a short transverse process that projects ventrally and slightly posteriorly. A foramen pierces the

neural arch ventrally at the base of the diapophysis and appears to extend dorsomedially in left lateral view; this

feature is not present on the right side because the diapophysis has been covered with plaster in this area. The neu-

ral spine is short and stout, being broader transversely than it is anteroposteriorly.

A further five cervical vertebrae are preserved, bringing the total number of cervicals to eight, and based on

their articulations with each other, the morphology and sizes of the anterior dorsals, and comparisons with CMN

2245 (Chasmosaurus belli), this probably represents the complete cervical column (Fig. 17). However, no quarry

map exists and the sequence of the vertebrae assumed herein is based on parapophysis location, height of the neural

spines and matching of similarly sized articular surfaces. Cervical vertebrae are distinguished from dorsal vertebrae

on the basis of parapophyseal position: cervicals bear a parapophysis located on the centrum or neurocentral suture,

whereas in dorsal vertebrae the parapophysis is located on the neural arch.

FIGURE 16. Syncervical of NHMUK R4948, Chasmosaurus belli in A, right lateral and B, left lateral view. Abbreviations:

III, cervical three; III dia, diapophysis of cervical three; III ns, neural spine of cervical three; III para, parapophysis of cervi-

cal three; at, atlas; at rf, atlas rib facet; ax, axis; ax dia, diapophysis of axis; ax na, neural arch of axis; ax ns, neural spine of

axis; ax para, parapophysis of axis. Scale bar equals 20 cm.

The centra of cervicals four to eight are amphiplatyan, transversely wider than they are anteroposteriorly long,

and laterally bear several small foramina. Foramina are also observed piercing the sides of the centra in ‘Anchicer-

atops’ (CMN 8547). Brown (1917) noted that the cervical centra of Centrosaurus become progressively shorter

more posteriorly along the column; in contrast, the lengths of the centra in NHMUK R4948 remain subequal. Cer-

vicals four, five and six bear a flattened ridge ventrally that extends between the anterior and posterior centrum fac-

ets; in cervicals seven and eight the ridge is less well defined. The parapophysis of cervicals four to six is located

on the anterior half of the lateral centrum and slightly closer to the neurocentral suture than the ventral margin, as in

Triceratops (Hatcher et al. 1907). This process is rounded, concave, faces posterolaterally and is slightly raised

from the lateral surface. Striations extending anterodorsally are present above the parapophysis in cervical four. In

cervicals seven and eight the parapophyses are located more dorsally on the centrum than in the other cervicals, and

in cervical eight they are oval in shape, with the long axis angled anteroventrally, and are larger than in the other

cervicals.

The neural arches of cervicals four to eight exhibit variable preservation. Cervical seven is present as a cen-

trum only; however an isolated partial neural arch and spine that may belong to this cervical is present. The height

and angle of the neural spine are congruent with the interpretation that this is the neural arch of cervical seven.

In all cervicals the neural canal is circular or tear-drop shaped in outline and is approximately as wide as it is

tall. The neural arch in cervicals five to eight leans slightly anteriorly, a feature also seen in other specimens of

Chasmosaurus (CMN 2245, ROM 843). The prezygapophyses are located immediately dorsal to the neural canal

A NEW SPECIMEN OF CHASMOSAURUS BELLI

and are widely separated, with ovate articular surfaces that face dorsomedially. A ridge extends anteriorly from the

anterior margin of the neural spine, lying between the prezgyapophyses, and prominent depressions are present

either side of this ridge, as is also the case in Triceratops (Hatcher et al. 1907: fig. 51). The postzygapophyses are

broadly separated in posterior view and have articular surfaces that are oriented ventrolaterally. These surfaces are

reniform in outline in cervical four but oval in cervicals six and eight.

In cervical four, the diapophysis, which is preserved completely on the left side, is positioned on a short trans-

verse process that extends laterally and slightly ventrally. In contrast, the fourth cervical of Triceratops has trans-

verse processes that extend dorsolaterally (Hatcher et al. 1907). Cervicals five and eight of NHMUK R4948, the

only other cervicals in which they are preserved, have transverse processes that extend dorsolaterally. By contrast,

in Centrosaurus (ROM 767) these processes extend more strongly laterally. In cervical eight of NHMUK R4948

the transverse processes are longer and more robust than they are in cervical five, and bear ovate diapophyses with

flat to slightly concave articular surfaces. The base of the transverse process is pierced by a large foramen in cervi-

cals four and six, but this feature is absent in cervicals five and eight; the area is not preserved in cervical seven. A

similar foramen is present in cervical five of Chasmosaurus belli (CMN 2245), and in cervicals four and five of

Styracosaurus (CMN 344), but no such features were observed in C. russelli (CMN 2280). The neural spine is

completely preserved in cervicals four, seven and eight, and it projects dorsally, as it does in CMN 2245, CMN

2280, Triceratops (Hatcher et al. 1907),‘Anchiceratops’ (CMN 8547) and Styracosaurus (CMN 344). In cervical

four the spine broadens transversely towards its apex and the aforementioned ridge that extends forward between

the prezygapophyses extends approximately halfway up the spine before splitting to give way to a flattened antero-

dorsal surface. In Triceratops, the top of the neural spine of cervical four is also broader transversely than it is

anteroposteriorly (Hatcher et al. 1907). The summit of the neural spine in cervicals seven and eight of NHMUK

R4948 is not expanded transversely at the top, but is bifurcated by a groove posteriorly so that it is arrow-head

shaped in cross-section with the apex pointing anteriorly.

Dorsal vertebrae. Seven dorsal vertebrae comprising centra and parts of the neural arch are present, along with

two additional centra and five isolated partial neural spines (Figs 18, 19). Four of these appear to be anteriorly posi-

tioned and probably represent dorsals one to four based on the height of the neural arch, the angle of the transverse

processes and the size of the neural spine relative to that on the last cervical vertebra (Fig. 18). Other dorsals (here

termed dorsals five to seven) are more posterior dorsals based on neural spine and zygapophysis morphology,

although it is not possible to determine which vertebrae they represent (Fig. 19). This suggests that the middle dor-

sals were not preserved: comparisons with other Chasmosaurus specimens suggest that around four dorsal verte-

brae are missing (CMN 2245; ROM 843).

The centra of all dorsals are amphiplatyan, wider than long, and the lateral sides are smooth and generally lack

foramina, except for dorsal four, which bears two small nutrient foramina on its right side. The lateral sides are not

deeply excavated, in contrast to those of Centrosaurus (ROM 1426; Lull 1933). Ventrally, a flattened ridge extends

from the anterior to the posterior articular surface in dorsal one. In dorsals two to seven the anterior articular sur-

face is slightly larger than the posterior surface and both articular surfaces extend ventrally under the centrum as

rugosities, producing strong, thickened rims to the centra, which increasingly approach each other in the more pos-

terior regions of the dorsal column, a feature that also occurs in Agujaceratops (Lehman 1989: fig.13), but is not

apparent in Centrosaurus (Lull 1933). The neurocentral suture, obliterated on the cervicals and dorsals one and

two, is clear on dorsals three to seven, suggesting fusion of the neural arches to the centra may have proceeded pos-

teriorly during ontogeny, and that the animal was not fully osteologically mature at the time of death (Irmis 2007).

The neural canal of all dorsals is rounded, except for that of dorsal one, which is oval, being taller than wide.

The prezygapophyses of dorsals one to four face dorsomedially and their bases are separated from each other by a

groove that extends to the top of the neural canal. This is similar to the condition in Triceratops (Hatcher et al.

1907: fig. 52), but contrasts with that in Centrosaurus (Lull 1933) and Styracosaurus (CMN 344), in which the

bases of the prezygapophyses meet ventrally. This groove becomes more prominent in the posterior dorsals, in

which the prezygapophyseal articular surfaces rotate to face entirely dorsally. Accordingly, the postzygapophyses

face ventrolaterally in dorsals one to four, but entirely ventrally in dorsals five to seven, a feature also present in

Agujaceratops (Lehman 1989), ‘Anchiceratops’ (Mallon and Holmes 2010) and Triceratops (Hatcher et al. 1907:

fig. 52). A ridge extends ventrally from the postzygapophyses, along the midline to the top of the neural canal. The

zygapophyses of Chasmosaurus belli (ROM 843) are rather different from those of NHMUK R4948: they are

fused to each other ventrally forming a continuous, concave (prezygapophyses) or convex (postzygapophyses) sur-

face for articulation with the preceding or following vertebra, as in Centrosaurus (Lull 1933). It is possible that this

MAIDMENT & BARRETT

FIGURE 17. Cervical vertebrae four to eight of NHMUK R4948, Chasmosaurus belli. A–C, cervical four; D–F, cervical five;

G–I, cervical six; J–L, cervical seven; M–O, and cervical eight; shown in A, D, G, J, M, anterior, B, E, H, K, N, posterior and

C, F, I, L, O, right lateral view. Scale bar equals 5 cm.

A NEW SPECIMEN OF CHASMOSAURUS BELLI

FIGURE 18. Dorsal vertebrae one to four of NHMUK R4948, Chasmosaurus belli. A–C, dorsal one; D–F, dorsal two; G–I,

dorsal three; J–L, and dorsal four; shown in A, D, G, J, anterior, B, E, H, K, posterior and C, F, I, L, right lateral view. Scale

bar equals 5 cm.

MAIDMENT & BARRETT

FIGURE 19. Posterior dorsal vertebrae of NHMUK R4948, Chasmosaurus belli in A, D, G, anterior, B, E, H, posterior and C,

F, I, right lateral view. These vertebrae are termed dorsals five to seven in the text, but their exact location in the dorsal verte-

bral column is unknown. Scale bar equals 5 cm.

A NEW SPECIMEN OF CHASMOSAURUS BELLI

feature is subject to ontogenetic variation, and this warrants further investigation. Additionally, in all of the dorsals

of the latter two taxa, regardless of their position in the axial column, the prezygapophyses face dorsomedially,

while the postzygapophyses face ventrolaterally.

In dorsal one the parapophysis, an oval, concave facet, is located below the base of the transverse process,

level with the neural canal. In dorsals two to four, the parapophysis is located more dorsally, and is present as a

rounded, deeply concave facet situated on a robust, laterally projecting stalk that arises from the transverse process

approximately level with the prezygapophyses. In dorsal six, the only posterior dorsal in which the parapophysis is

preserved, it is a smaller, circular facet located on the anteroventral transverse process below the diapophysis and

dorsal to the prezygapophysis. In several dorsals of ROM 843, the capitulum of the rib is fused to the parapophysis;

this may be a pathological or ontogenetic feature and is not seen in NHMUK R4948.

In NHMUK R4948 the diapophysis is located at the distal end of the dorsolaterally projecting transverse pro-

cess; in dorsals one to three the cross section of the transverse process is shaped like an inverted ‘L’. The diapoph-

ysis is expanded anteroposteriorly, rounded, and angles ventrolaterally, as in Triceratops (Hatcher et al. 1907). In

dorsal four and dorsal six, the only posterior dorsal in which the transverse process is preserved, the transverse pro-

cess is ‘T’ shaped in cross section, an anterior ridge having been developed. The diapophysis is not as expanded in

dorsal four as it is in dorsals one to three; in the posterior dorsals it is not preserved. The neural spine is preserved

completely only in dorsal four; however, the base of the spine is preserved in dorsals three, five and six. In dorsal

four the neural spine is blade-shaped, strongly transversely compressed, tapers dorsally and is oriented slightly pos-

teriorly. In the posterior dorsals the neural spine is much broader anteroposteriorly (as in Triceratops [Hatcher et al.

1907], ‘Anchiceratops’ [CMN 8547] and Centrosaurus [ROM 767]) although it remains compressed transversely,

and appears to have projected more strongly dorsally. Mallon and Holmes (2006) suggested that the neural spines

of the anterior dorsals of CMN 2245 (C. belli) projected more strongly posteriorly than the posterior dorsal neural

spines, a feature not observed in CMN 2280 (C. russelli). Our observations of NHMUK R4948 support the sugges-

tion that the anterior neural spines projected more posteriorly than the posterior neural spines in C. belli, and this

may prove to be a specific difference, although more specimens are needed to confirm this.

Sacral vertebrae. The centra of six vertebrae are fused together to form the sacral rod, which appears to com-

prise two dorsosacrals and four sacrals (Fig. 20; dorsosacrals are those that bear ribs similar in morphology to dor-

sal ribs, while the four true sacrals, homologous to the four sacrals of basal ornithischians, bear sacral ribs: see

below). In contrast, nine vertebrae are fused to form the sacral rod in CMN 2245 (one dorsosacral, four sacrals and

four caudosacrals) and eleven are fused in ROM 843 (three dorsosacrals, four sacrals and four caudosacrals). Leh-

man (1989) reported ten vertebrae in the sacral rod in Agujaceratops (three dorsosacrals, four sacrals and three cau-

dosacrals), and there are also ten in Triceratops (Hatcher et al. 1907: two dorsosacrals, four sacrals and four

caudosacrals). In NHMUK R4948, the anteriormost vertebra fused to the sacral rod, the second dorsosacral, bears

prezygapophyses that face dorsally and are identical in morphology to those of the posterior dorsals. The dor-

sosacral vertebrae bear laterally-projecting transverse processes that are comparable in anteroposterior width to

those of the dorsals. No evidence for parapophyses is visible on the lateral sides of the vertebrae, suggesting that

they either bore single-headed ribs or more likely that the transverse processes contacted the preacetabular process

of the ilium. Their neural spines are strongly inclined posteriorly, in contrast to those of Triceratops, which extend

dorsally (Hatcher et al. 1907: fig. 54), and are not fused to each other or to those of the other vertebrae in the sacral

rod. The posterior four vertebrae in the sacral rod bear sacral ribs and are probably homologous to the four sacral

vertebrae present in primitive ornithischians (Butler et al. 2008). Foramina pierce the fused neural arches between

the third and fourth vertebrae fused into the rod (sacrals one and two) and the fourth and fifth vertebrae fused into

the rod (sacrals two and three). Ventrally, all of the vertebrae in the rod bear a deep groove that extends along the

centrum anteroposteriorly, a feature present in chasmosaurines but developed to a much lesser extent in centrosau-

rines (Lehman 1989). The neural spines of vertebrae three to six (sacrals one to four) are coalesced into a trans-

versely compressed sheet and sutures between them have been obliterated. No ossified tendons are preserved. The

posterior centrum facet of the final vertebra in the rod, sacral four, is rugose and unfinished and suggests an addi-

tional vertebra, a caudosacral, may have contributed to the sacral rod but was not fused at the time of death. Since

other specimens of Chasmosaurus (CMN 2245; ROM 843) bear four caudosacrals, it is likely that several addi-

tional vertebrae would have fused into the sacral rod during ontogeny, and the unfused state of these vertebrae pro-

vides further evidence that the animal was not osteologically mature at the time of death. The sacral ribs of the

third, fourth and fifth vertebrae in the sacral rod (sacrals one to three) are dorsoventrally deep and anteroposteriorly

MAIDMENT & BARRETT

compressed, and slightly hour-glass shaped in cross section. There are two distinct articular surfaces, one dorsal

and one ventral, homologous with the diapophysis and parapophysis of dorsal vertebrae, respectively. Both of these

articular surfaces would have contacted the medial surface of the ilium. The ventral articular surfaces of sacrals one

to three are coalesced into one anteroposteriorly elongate surface, while the dorsal articular surfaces remain distinct

from each other and do not fuse, as in Triceratops (Hatcher et al. 1907: fig. 54) and Pentaceratops (Wiman 1930:

pl.5). The rib of the posteriormost vertebra fused to the sacral rod, sacral four, does not bear distinct dorsal and ven-

tral articular surfaces for the ilium; instead these coalesce and are joined to the ventral articular surfaces of the

other sacral ribs, resulting in the rib angling anterodorsally, a feature also observed in Triceratops and Pentacer-

atops.

Ribs. Many dorsal rib fragments are preserved, but these are broken into small pieces and no complete rib

remains. Anterior dorsal ribs are ‘Y’-shaped, with the tuberculum and capitulum held on elongate processes at right

angles to each other. The tuberculum is anteroposteriorly expanded and oval in outline, while the capitulum, which

sits on the longer of the two branches of the ‘Y’, is not expanded relative to the shaft and is also oval in outline.

Proximally, the rib shaft is anteroposteriorly compressed and oval in cross-section; more distally it becomes trian-

gular in cross-section with the apex pointing anteriorly. The process bearing the tuberculum in the more posterior

dorsal ribs is much shorter proximodistally than it is in the anterior ribs, while the process for the capitulum is

much longer. The tuberculum is not significantly expanded anteroposteriorly, whereas the tuberculum is larger than

in anterior ribs. The proximal shaft is transversely compressed and its anterior surface is concave so that it is ‘C’

shaped in cross-section. More distally, the shaft is triangular in cross-section but the apex points posteriorly, in con-

trast to the situation in the anterior dorsal ribs (Fig. 21).

FIGURE 20. Sacral vertebrae of NHMUK R4948, Chasmosaurus belli in A, dorsal, B, right lateral and C, left lateral view.

Abbreviations: ds1, first dorsosacral vertebra; ds2, second dorsosacral vertebra; s1, first sacral vertebra; s2, second sacral ver-

tebra; s3, third sacral vertebra; s4, fourth sacral vertebra. Scale bar equals 10 cm.

Appendicular skeleton. Elements of the pectoral girdle, forelimb, pelvic girdle and hind limb are well pre-

served in NHMUK R4948; unfortunately no manus or pes material was recovered. Dimensions of the appendicular

skeleton are given in Table 3.

Coracoid. Both coracoids are well preserved (Fig. 22A–D). They were not fused to the scapula, in contrast with the

situation in other specimens of Chasmosaurus (ROM 843; ROM 839; CMN 2245; CMN 2280) and most other cer-

atopsids (Dodson et al. 2004), probably because the specimen was not osteologically mature at the time of death.

The coracoid is gently convex laterally, gently concave medially, and the bone surface is smooth. Proximal to the

sutural surface for the scapula the dorsal margin of the coracoid is rugose and thickened, representing the inferred

origin of the m. supracoracoideus (Maidment and Barrett unpublished data); a similar roughened area was observed

in Styracosaurus (CMN 344) and an unnamed pachyrhinosaur (TMP 2002.76.01). The coracoid foramen is fully

enclosed on the lateral surface; medially it opens onto the sutural surface for the scapula. The glenoid is deeply

concave and faces posteroventrally. A prominent sternal process projects from the anteroventral surface well below

the level of the glenoid, as in ROM 843, CMN 2280 and other ceratopsids (Dodson et al. 2004).

A NEW SPECIMEN OF CHASMOSAURUS BELLI

TABLE 3. Postcranial measurements, NHMUK R4948.

FIGURE 21. Examples of the dorsal ribs of NHMUK R4948, Chasmosaurus belli, in A–B, anterior and C–D, posterior view.

Location of ribs on the dorsal column unknown. Scale bar equals 20 cm.

Scapula. Only a small portion of the proximal plate and the distal end of the left scapula are preserved (Fig.

22E–G). The sutural surface for the coracoid is rugose, unfinished and transversely compressed dorsally; it thick-

ens ventrally close to the glenoid. The dorsal margin of the scapula is drawn into a small, poorly defined acromial

process that rises gently anteriorly as in all ceratopsids (Triceratops, NHMUK R3886-8, Hatcher et al. 1907: fig.

64; ‘Anchiceratops’, CMN 8547; Styracosaurus, CMN 344; Centrosaurus, ROM 767, 1426; pachyrhinosaur sp.

Element Measurement taken Dimension (cm)

Left coracoid Dorsoventral height 32.0

Right coracoid Dorsoventral height 33.5

Left humerus Length 59.0

Left humerus Midshaft circumference 25.5

Right humerus Length 59.5

Right humerus Midshaft circumference 25.0

Left ulna Length 44.5

Right ulna Length 46.0

Right femur Length 78.0

Right femur Midshaft circumference 34.5

Right tibia Length 58.5

MAIDMENT & BARRETT

indet., TMP 2002.76.01; in the centrosaurines examined the acromial process appears to be shorter, occupies less

of the scapula shaft, and is less well developed than in the chasmosaurines examined). The dorsal margin of the

acromial process is folded over laterally to form a flattened apex in lateral view just posterior to the coracoid suture

for inferred attachment of the m. deltoideus clavicularis (Maidment & Barrett unpublished data), as in other speci-

mens of Chasmosaurus (CMN 2280, ROM 839), Styracosaurus (CMN 344), Triceratops (Hatcher et al. 1907: fig.

64) and an unnamed pachyrhinosaur (TMP 2002.76.01). The glenoid is thickened transversely relative to the rest of

the proximal plate. It is pentagonal in cross-section with the apex pointing ventrally, and it faces anteroventrally.

Posterior to the glenoid on the ventral surface are rugosities and a shallow depression, probably indicating the ori-

gin of the m. triceps longus (Maidment and Barrett, unpublished data). Similar features are seen in the same loca-

tion in other specimens of Chasmosaurus (ROM 839; ROM 843, CMN 2245; CMN 2280) and in other ceratopsids

(Triceratops NHMUK R3886-8, Hatcher et al. 1907; ‘Anchiceratops’, CMN 8547; Styracosaurus, CMN 344; Cen-

trosaurus, ROM 767, 1426; pachyrhinosaur sp. indet., TMP 2002.76.01). In medial view a shallow canal extends

from the coracoid suture posteriorly and would have joined the coracoid foramen when the elements were in artic-

ulation, as in CMN 2245. Posterior to this a small foramen pierces the medial surface. The small portion of the dis-

tal end of the scapula suggests that the scapula blade was not significantly flared posteriorly, as is the case in other

specimens (CMN 2280; ROM 839) and other ceratopsids (Triceratops, NHMUK R3886-8; ‘Anchiceratops’, CMN

8547; Styracosaurus, CMN 344; Centrosaurus ROM 767). It is rugose and unfinished, suggestive of a cartilagi-

nous suprascapula.

FIGURE 22. Preserved pectoral and pelvic girdle elements of NHMUK R4948, Chasmosaurus belli. A–D, coracoid in A, right

lateral, B, right medial, C, left lateral and D, left medial view. E–G, proximal plate of left scapula in E, lateral, F, medial and G,

anterior view. H–K, partial right pubis in H, lateral, I, medial, J, dorsal and K, ventral view. The anterior portion of the prepu-

bis is preserved separately and shown in its approximate location with respect to the rest of the pubis in J and K. Abbreviations:

ace, acetabular part of the pubis; acr, acromial process; can, canal; cor s, surface for coracoid; gle, glenoid; pop, postpubis;

prp, prepubis; scc, area of attachment of the m. supracoracoideus; sp, sternal process. Scale bar equals 10 cm.

A NEW SPECIMEN OF CHASMOSAURUS BELLI

FIGURE 23. Humeri of NHMUK R4948, Chasmosaurus belli. A–D, right humerus in A, anterior, B, posterior, C, lateral and

D, medial view. E–J, left humerus in E, anterior, F, posterior, G, lateral, H, medial, I, dorsal and J, ventral view. In I and J,

anterior is towards the top of the figure. Abbreviations: dpc, deltopectoral crest; g, groove separating area of attachment of m.

pectoralis from m. deltoideus clavicularis and scapularis; hd, humeral head; n, notch on dorsal surface separating medial tuber-

osity; str, striations; tf, triceps fossa; see text for details. Scale bar equals 10 cm for A–H and 5 cm for I and J.

MAIDMENT & BARRETT

Humerus. Both humeri are uncrushed and quite well preserved (Fig. 23). In anterior view, the proximal end of

the humerus is rectangular in outline. The medial tuberosity is distinguished from the dorsal surface of the element

by a notch, which is also present in other well preserved Chasmosaurus specimens (ROM 843; ROM 839) and

developed to a greater degree in Triceratops (Hatcher et al. 1907: fig. 65). The deltopectoral crest is small and proj-

ects anterolaterally. Its anterolateral surface is incomplete on both humeri, but appears to be straight in lateral view,

as in other chasmosaurines (e.g. Chasmosaurus, CMN 2280; CMN 2245; ROM 839; ‘Anchiceratops’, CMN 8547,

Triceratops, Hatcher et al. 1907: fig. 66) but in contrast to the condition in centrosaurines (e.g. Styracosaurus,

CMN 344; Centrosaurus, ROM 767; pachyrhinosaur sp. indet., TMP 2002.76.01) in which it is concave upwards

in lateral view. The apex, which points anteriorly, is well preserved on both sides in NHMUK R4948 and it forms a

flattened, dorsoventrally elongate surface that probably formed the insertion of the m. pectoralis (Maidment & Bar-

rett unpublished data). It is similar in morphology to that of other specimens of Chasmosaurus (ROM 843; ROM

839), Styracosaurus (CMN 344), Centrosaurus (ROM 1426) and an unnamed pachyrhinosaur (TMP 2002.76.01).

The apex of the deltopectoral crest reaches approximately midlength, and below it the shaft constricts rapidly

before flaring for the distal condyles, which are rugose and unfinished in appearance, suggestive of a thick cartilag-

inous cap. The humeral head is restricted to the posterior surface, as is the case in all quadrupedal ornithischians

(SCRM pers. obs., 2009–2010). It is distinct, rounded, and rugose and projects posteriorly. The posterior surface of

the medial tuberosity bears some vertical striations. The posterolateral surface of the deltopectoral crest is strongly

striated for the inferred insertion of the deltoid musculature, a feature seen in many ceratopsids (e.g. ‘Anchicer-

atops’, CMN 8547; Styracosaurus, CMN 344; Centrosaurus, ROM 767, 1426; pachyrhinosaur sp. indet., TMP

2002.76.01; Vagaceratops, CMN 41357; Tricerat ops, Hatcher et al. 1907) and other specimens of Chasmosaurus

(CMN 2280, CMN 2245; ROM 839; ROM 843); the area of insertion of the m. pectoralis on the apex of the delto-

pectoral crest is clearly distinguished from the insertion of the deltoids by a deep groove, also observed on ROM

839, CMN 2280 and Triceratops (Hatcher et al. 1907: fig. 66) but not on the more poorly preserved humeri of

ROM 843. The posterior surface of the humerus lateral to the head bears a deep fossa, a feature observed on other

ceratopsid humeri (Triceratops, NHMUK R3886-8, Hatcher et al. 1907: fig. 66; ‘Anchiceratops’, CMN 8547;

Styracosaurus, CMN 344; Centrosaurus, ROM 767; pachyrhinosaur sp. indet., TMP 2002.76.01; Vagaceratops,

CMN 41357). The fossa probably represents the origin of m. triceps brevis (Maidment & Barrett unpublished data;

contra Lehman 1989) and is much better developed in chasmosaurines than in centrosaurines. In many ceratopsid

humeri, a foramen pierces the posteromedial humerus on the proximal half of the element (e.g. CMN 2280; CMN

2245; ROM 843; Styracosaurus, CMN 344; Centrosaurus, ROM 767; pachyrhinosaur sp. indet., TMP 2002.76.01;

Vagaceratops, CMN 41357, Triceratops, Hatcher et al. 1907: fig. 66); this may correspond to the insertion of the

m. latissimus dorsi. In NHMUK R4948 the posterior shaft is patched with plaster on both sides and the foramen

cannot be seen. In chasmosaurines (e.g. Chasmosaurus, CMN 2280, 2245; ROM 843, Triceratops, Hatcher et al.

1907: fig. 66) the foramen is dorsal to the apex of the deltopectoral crest, whereas in centrosaurines (Styracosaurus,

CMN 344; Centrosaurus, ROM 767; pachyrhinosaur sp. indet., TMP 2002.76.01) it is located approximately level

with the apex and more medially.

Ulna. Both ulnae are present (Fig. 24A–L), although the olecranon process is eroded on the right ulna, and part

of the shaft is reconstructed. On the left ulna, the olecranon process is large, rounded in cross-section and tapers

dorsally, as in ROM 843 and other ceratopsids (e.g. ‘Anchiceratops’, CMN 8547; Centrosaurus, ROM 1426; Styra-

cosaurus, CMN 344; pachyrhinosaur sp. indet., TMP 2002.76.01; Vagaceratops, CMN 41357; Agujaceratops,

Lehman, 1989; Triceratops, Hatcher et al. 1907). A well-developed anterolateral process is present, as in all qua-

drupedal ornithischians (SCRM pers. obs., 2009–2010). It forms a right angle to the medial process, which is larger

and has a flattened anterior surface against which the posterior surface of the proximal radius articulated, compar-

ing favourably with ROM 843 and ROM 839. The distal end is not expanded relative to the shaft, and it is ringed in

vertical striations, which are also observed in ‘Anchiceratops’ (CMN 8547), Styracosaurus (CMN 344) and Cent-

rosaurus (ROM 767, 1426). A large roughened scar on the anteromedial surface of the distal end marks the articu-

lar facet for the distal end of the radius, as in ROM 839 and other ceratopsids (e.g. ‘Anchiceratops’, CMN 8547;

Centrosaurus, ROM 767, 1426; Styracosaurus, CMN 344; Triceratops, Hatcher et al. 1907: fig. 67). The presence

of a large anterolateral process of the ulna results in the radius being located anteromedial to the ulna rather than

wholly anteriorly, as it is in basal, bipedal ornithischians, and this makes pronation of the manus possible (Bonnan

2003).

A NEW SPECIMEN OF CHASMOSAURUS BELLI

FIGURE 24. Ulnae and radius of NHMUK R4948, Chasmosaurus belli. A–F, right ulna in A, anterior, B, posterior, C, lateral,

D, medial, E, dorsal and F, ventral view. G–L, left ulna in G, anterior, H, posterior, I, lateral J, medial, K, dorsal and L, ventral

view. M–P, right radius in M, anterior, N, posterior, O, dorsal and P, ventral view. The radius is preserved in three parts that

have been approximately positioned relative to each other. Abbreviations: al p, anterolateral process; m p, medial process; o p,

olecranon process; r f, radial facet; u f, ulnar facet. Scale bar equals 10 cm for A–D, G–J and M–N, and 5 cm for E–F, K–L

and O–P.

Radius. Only the proximal and distal ends of the right radius are preserved (Fig 24M–P). The proximal end,

which was expanded transversely and anteroposteriorly relative to the shaft, is flat dorsally. It is oval in cross-sec-

tion with the long axis oriented transversely, as in Chasmosaurus belli (ROM 843), Chasmosaurus sp. (ROM 839)

MAIDMENT & BARRETT

and other ceratopsids (Centrosaurus; ROM 767, 1426; Styracosaurus, CMN 344; pachyrhinosaur sp. indet., TMP

2002.76.01; Agujaceratops, Lehman, 1989); the posterior surface is flattened for articulation with the medial pro-

cess of the ulna. The distal end is also expanded relative to the shaft. It is expanded more medially than it is later-

ally in anterior view, and it extends further ventrally on the medial side than it does on the lateral side. A small boss

is present on the posterolateral surface for articulation with the distal ulna, a feature also seen in ROM 843, ROM

839 and other ceratopsids (e.g. ‘Anchiceratops’, CMN 8547; Centrosaurus, ROM 1426; Styracosaurus, CMN 344;

pachyrhinosaur sp. indet., TMP 2002.76.01); although the two elements articulated they were clearly not tightly

associated with each other and rotation of the distal end of the radius around the ulna was probably possible, allow-

ing some degree of pronatory and supinatory rotation at the wrist.

Pubis. A partial right pubis is the only pelvic element preserved (Fig. 22H–K). The acetabular region of the

pubis is broader transversely than it is deep dorsoventrally. The acetabulum is cup-shaped, concave and faces dor-

solaterally. The anteromedial corner of the acetabular rim is triangular in shape, rugose and unfinished, and repre-

sents the articular surface for the pubic peduncle of the ilium. Posteriorly the acetabular rim angles posteriorly and

is rugose for articulation with the ischium; these features are also observed in ROM 843, the only other Chasmo-

saurus specimen to preserve this portion of the pubis. The postpubis has almost completely broken off and is not

preserved, except for a small portion proximal to the acetabular region of the pubis. It is flattened dorsoventrally

and slightly concave dorsally, as in Vagaceratops (CMN 41357) and Triceratops (Hatcher et al. 1907). The prepu-

bis is elongate, dorsoventrally flattened and transversely as broad as the acetabular part of the pubis, as in other cer-

atopsids (Triceratops, NHMUK R3886-8, Hatcher et al. 1907; pachyrhinosaur sp. indet., TMP 2002.76.01;

Vagaceratops, CMN 41357; Pentaceratops, Wiman 1930: pl. 6). The anterior margin of the prepubis is broken. It is

greatly expanded dorsoventrally relative to the rest of the prepubis, and is also expanded medially, so that the

medial surface of the prepubis is concave upward when viewed from above at the anterior end, a feature observed

in other specimens of Chasmosaurus (CMN 2245; ROM 843) and other ceratopsids (Triceratops, NHMUK R3886-

8, Hatcher et al. 1907; Vagaceratops, CMN 41357, Pentaceratops, Wiman 1930; pl. 6). This medial expansion may

have contacted the posterior dorsal ribs (Sternberg 1927; Lehman 1989).

Femur. The right femur is preserved but it is anteroposteriorly crushed and the medullary cavity has collapsed

(Fig. 25). The femoral head is separated from both the shaft and greater trochanter by a distinct neck, as in all neor-

nithischians. It is slightly flattened posteriorly and bears several ventrally-trending striations. The head is separated

from the greater trochanter by a saddle-shaped depression. The greater trochanter projects dorsally to approxi-

mately the same level as the head, a feature common to most neornithischians. Laterally, the greater trochanter is

flattened, broad and slightly striated along its dorsal margin. The anterior trochanter appears to be fused to the ante-

rior side of the greater trochanter, as in ROM 843 and all ceratopsids (Dodson et al. 2004), although the cleft

between the two in lateral view is filled with plaster. The anterior trochanter can be clearly distinguished from the

greater trochanter because it projects further laterally and does not project as far dorsally, as in Triceratops

(Hatcher et al. 1907: pl. 14). The shaft is poorly preserved and crushed. The fourth trochanter is present as an

obliquely-trending ridge in posterior view, as in ROM 843 and other ceratopsids (Styracosaurus, CMN 344; pachy-

rhinosaur sp. indet., TMP 2002.76.01; Triceratops, Hatcher et al. 1907: pl. 14); its surface is flat to concave. Medi-

ally it is fringed by a series of small horizontal striations, probably for the m. caudofemoralis longus (Maidment

and Barrett unpublished data). In posterior view, the medial distal condyle is larger than the lateral one; the lateral

condyle is divided into a posterior and a lateral surface, separated by a groove in lateral view, as in all neornithis-

chians.

Tibia. The right tibia is present, but the shaft is crushed and the distal end is poorly preserved (Fig. 26A–D).

Proximally, the tibia is in good condition and broader anteroposteriorly than it is transversely. The cnemial crest is

transversely compressed. It projects further dorsally than any other part of the proximal tibia, is slightly concave

laterally and flat medially, and is similar in morphology to ROM 839 Chasmosaurus sp. (ROM 839), C. belli

(ROM 843) and Styracosaurus (CMN 344). The proximodorsal part is covered in plaster. The rounded fibula con-

dyle projects strongly laterally and is rugose: many grooves and canals cross this surface and are suggestive of a

thick cartilaginous cap; it is similar in morphology to that of C. belli (ROM 843) and Triceratops (Hatcher et al.

1907: pl. 16). Posterior to the fibula condyle the proximal end is transversely broad and flattened dorsally. The

bone surface is rugose and unfinished in this area. The distal end is also broader anteroposteriorly than it is trans-

versely, in contrast to the condition in other ornithischians. Since the distal end is very crushed and poorly pre-

served, it is likely that it has rotated around to lie in this orientation as a result of post-mortem deformation. The

posterior surface of the distal end now faces laterally. It is crushed but gently convex. The anterior surface, which

A NEW SPECIMEN OF CHASMOSAURUS BELLI

now faces medially, bears two distinct surfaces separated by a groove, as in Triceratops (Hatcher et al. 1907: pl.

16). The fibula would have articulated with the lateralmost of these surfaces, which projects further ventrally than

the medial surface, and is slightly striated (as in ROM 843). The calcaneum would have articulated ventrally, and

the surface for it is convex. The facet for the astragalus, in contrast, is flattened.

FIGURE 25. Right femur of NHMUK R4948, Chasmosaurus belli, in A, anterior, B, posterior, C, lateral, D, medial, E, dorsal

and F, ventral view. Abbreviations: 4t, fourth trochanter; at, anterior trochanter; gt, greater trochanter; hd, femoral head. Scale

bar equals 20 cm for A–D, 15 cm for E–F.

FIGURE 26. Right tibia and fibula of NHMUK R4948, Chasmosaurus belli. A–D, tibia in A, lateral, B, medial, C, dorsal and

D, ventral view. E–F, fibula in E, lateral and F, medial view. Abbreviations: cc, cnemial crest; fc, fibular condyle; ifb, attach-

ment area for m. iliofibularis. Scale bars equal 10 cm.

Fibula. The right fibula is slender and elongate (Fig. 26E–F). Its proximal end is transversely compressed

while the distal end is anteroposteriorly compressed, as in Centrosaurus (Brown 1917; Lull 1933). The distal end is

expanded more than the proximal end, which is slightly broken anteriorly. The shaft is flattened on its medial sur-

face proximally and it bears a ridge on its lateral surface about one third of the way from the proximal end that

probably represents the insertion of m. iliofibularis (Dilkes 2000). About half way down the shaft, the posterior sur-

face bears a rugose, lumpy muscle scar, probably for the m. peroneus brevis (Dilkes 2000).

MAIDMENT & BARRETT

Discussion

The proliferation of new chasmosaurine taxa—Kosmoceratops, Utahceratops, Vagaceratops (Sampson et al.

2010), ‘Mojoceratops’ (Longrich 2010), Coahuilaceratops (Loewen et al. 2010), Ojoceratops (Sullivan & Lucas

2010), Medusaceratops (Ryan et al. 2010), Tatankoceratops (Ott & Larson 2010) and Titanoceratops (Longrich

2011)—warrants re-examination of the generic and specific characters that differentiate Chasmosaurus from other

genera, especially since three chasmosaurine genera, ‘Mojoceratops’, Vagaceratops and Agujaceratops, are based

on material previously referred to Chasmosaurus.

Status of ‘Mojoceratops perifania’ . Longrich (2010) named ‘Mojoceratops perifania’ based on a skull previ-

ously referred to Chasmosaurus russelli. Longrich (2010) diagnosed ‘Mojoceratops’ as follows: (1) lateral rami of

the parietal posterior bar bearing a prominent sulcus on their anterior surface; (2) lateral rami of the parietal poste-

rior bar with a thickened anterodorsal edge, bearing node-like swellings; (3) parietal epoccipital 1 bearing a medial

accessory process; (4) lateral rami of the parietal posterior bar anteroposteriorly narrow and dorsoventrally thick-

ened, giving them a rod-like shape; (5) a strongly notched caudal margin of the parietals, with the lateral rami

diverging at an angle of no more than 105 degrees; (6) strongly arched lateral rami of the parietal posterior bar, giv-

ing the posterior bar a distinctive ‘m’ shape, and extending the parietals well beyond the squamosals; (7) parietal

epoccipitals project caudally from the parietal; (8) parietosquamosal frill erect, long axis of the parietal forming an

angle of about 45 degrees with the horizontal; (9) parietal fenestrae anteriorly extended towards the supratemporal

fossae to a degree not seen in Chasmosaurus; (10) triangular postfrontal fontantelle with strong transverse expan-

sion; (11) prominent supraorbital horns, length exceeding 200% of basal diameter; (12) supraorbital horns oriented

dorsolaterally, being inclined away from the vertical plane by 45 degrees in anterior view; (13) epijugal ossification

prominent and subconical. Characters 1–3 were said to be autapomorphies of ‘Mojoceratops’. However, examina-

tion of the holotype specimen (TMP 1983.25.01) and other chasmosaurine material shows that these features are

extremely subtle and can be attributed to intraspecific variation. Character (1) refers to the shape of the posterior

parietal bar in cross section, which is variable among specimens in Chasmosaurus (see parietal description, above).

Characters (2) and (3) relate to extremely subtle variations in the shape of the posterior parietal bar and epiparietals

(See Fig. 10), could not be observed during direct examination of the specimen in the case of (2) and are subject to

a wide range of variation among other specimens in the case of (3). These features also do not seem to be present in

referred specimens (TMP 1999.55.282; AMNH 5656; Longrich, 2010, figs 4, 6). None of these features represents

a robust autapomorphy.

Characters 4 and perhaps 9 were said to be derived characters unique to ‘Mojoceratops’ and Agujaceratops.

However, character (4) is variable in specimens examined (e.g. ROM 843, CMN 2245, CMN 2280) and in a variety

of other chasmosaurines (e.g. Sampson et al. 2010), while character (9) is difficult to operationalize and requires

quantification. The remaining characters were said to distinguish ‘Mojoceratops’ from Chasmosaurus, however,

characters (5) and (6) are also present in Chasmosaurus russelli (e.g. CMN 2280), characters (7), (12) and (13) are

present in all Chasmosaurus specimens, as well as being present in a variety of other chasmosaurine taxa in the

case of (12) (e.g. Utahceratops, Kosmoceratops, Sampson et al. 2010) and requiring quantification in the case of

(13). Characters (8) and (10) are strongly dependent on preservation and thus are highly variable between speci-

mens. Character (11), which is absent in the holotype of ‘Mojoceratops’, is subject to large variation in individuals

referred to Chasmosaurus, and previously proposed to be intraspecifically variable in Chasmosaurus russelli (God-

frey & Holmes 1995). Characters (9) and (11) perhaps offer the best evidence for differentiation between ‘Mojocer-

atops’ and Chasmosaurus, but since they are both related to relative prominence of skull ornamentation and likely

to be highly variable between individuals due to differences in ontogenetic stage and sex, we do not consider them

to represent robust autopomorphies in the absence of other unique characters or combinations of characters. We

therefore find no compelling reason to consider the holotype of ‘Mojoceratops’ to be anything other than an indi-

vidual of Chasmosaurus russelli and consider ‘Mojoceratops perifania’ a junior subjective synonym of the former.

Diagnosis of Chasmosaurus. Forster et al. (1993) diagnosed Chasmosaurus using the following characters:

(1) premaxillary flange along anterior margin of external naris; (2) supraorbital horn cores curve posteriorly; (3)

strap-like posterior border of parietal fenestra with transverse dimension at least twice that of the proximodistal

width; and (4) frill broadens posteriorly to form triangular shield with maximum width more than twice the skull

width at orbits. None of these characters are autapomorphic for Chasmosaurus because they are also present in

Agujaceratops and Vagaceratops, genera based on specimens considered to be Chasmosaurus by Forster et al.

A NEW SPECIMEN OF CHASMOSAURUS BELLI

(1993). However, characters 1, 2 and 4 are incorporated into the amended diagnosis as part of a unique character

combination. Character 3 is difficult to understand in the light of Chasmosaurus anatomy.

Three additional characters have been added to the diagnosis and, as part of a unique combination with the

above characters, serve to distinguish Chasmosaurus from other chasmosaurine taxa. (1) Medial surface of the

squamosal, where it articulates with the lateral bar of the parietal, straight. In Ojoceratops (Sullivan & Lucas 2010:

fig. 11.2), Agujaceratops (Lehman 1989: fig. 8) and Kosmoceratops (Sampson et al. 2010: fig. 6) the dorsal surface

of the squamosal along which the parietal articulates is strongly upwardly concave in lateral view, so that the squa-

mosals are lunate in shape rather than triangular. Triangular squamosals are also present in Vagaceratops (Holmes

et al. 2001), Utahceratops (Sampson et al. 2010: fig. 3) and other chasmosaurines in which they are preserved, so

this character is not an autapomorphy of Chasmosaurus. (2) Parietal fenestrae large, occupying most of the parietal,

and being rounded or anteroposteriorly longer than transversely wide. Parietal fenestrae are much smaller than they

are in Chasmosaurus in some chasmosaurine taxa, such as Vagaceratops (Holmes et al. 2001) and Kosmoceratops

(Sampson et al. 2010). However, they are large in Agujaceratops (Lehman 1989), Utahceratops (Sampson et al.

2010) and Pentaceratops (Lehman 1993), so this character does not constitute a Chasmosaurus autapomorphy.

Finally, (3) epiparietals triangular in shape and project posteriorly or dorsally but do not curve anteriorly. In many

chasmosaurine genera, at least the medial epiparietals curve strongly anteriorly e.g. Pentaceratops (Lehman 1993),

but in some taxa such as Vagaceratops (Holmes et al. 2001), and Kosmoceratops (Sampson et al. 2010), all of the

epiparietals curve forward. In Chasmosaurus and Utahceratops (Sampson et al. 2010), none of the epiparietals

curve anteriorly. Because this feature is present in both Utahceratops and Chasmosaurus, it is not an autapomorphy

of Chasmosaurus.

Diagnosis of Chasmosaurus belli. Chasmosaurus belli is diagnosable on the basis of autapomorphies unique

to C. belli within the genus Chasmosaurus. Longrich (2010) diagnosed Chasmosaurus belli as follows: Chasmo-

saurus exhibiting the following combination of characters: (1) lateral ramus of parietal caudal bar straight in dorsal

view; (2) lateral rami of parietal caudal bar strongly divergent, separated by an angle of 140o–180o; (3) three or four

pairs of parietal epoccipitals; (4) medial parietal epoccipitals coalesced and forming a low, ridge-like structure; (5)

lateral pair of parietal epoccipitals large and subtriangular; and (6) orbital horns reduced, their length being no

more than 100% basal diameter. Godfrey and Holmes (1995) diagnosed C. belli using the following characters: (7)

parietal frill with nearly straight transverse posterior bars; (8) parietal bears one large triangular epoccipital on its

posterolateral corner; (9) other parietal epoccipitals variable in number and degree of ossification with the parietal,

but always much smaller; and (10) lateral bar of the parietal completely encloses the parietal fenestra.

Characters (1), (2) and (7) apparently refer to the same feature and are included in the amended diagnosis.

Characters (3), (4), (5), (8) and (9) are difficult to operationalize because epiparietals are very often not fused to the

parietals in specimens of Chasmosaurus (e.g. ROM 843; NHMUK R4948; CMN 2245), although characters (5)

and (8), which refer to the same feature, do appear to distinguish C. belli from C. russelli, so have been maintained

as an autapomorphy of C. belli within Chasmosaurus. Characters (6) and (10) are present in a large number of

chasmosaurines and are known to be variable within and between species (Lehman 1989; see squamosal descrip-

tion, above).

Diagnosis of Chasmosaurus russelli. Longrich (2010) diagnosed C. russelli as follows. Chasmosaurus dis-

playing the following combination of characters: (1) lateral rami of posterior parietal bar weakly arched in dorsal

view; (2) well-developed posterior emargination of the frill, with an angle between the lateral rami of 120 degrees;

(3) three broad, moderately elongate parietal epoccipitals. Godfrey and Holmes (1995) diagnosed C. russelli as fol-

lows: (4) Posterior margin of parietal frill broadly arched on either side of median emargination; (5) each side bears

three low, roughly equal sized parietal epoccipitals; (6) the lateral ramus of the parietal is reduced and does not

completely encircle the fenestra in all but one specimen, permitting the squamosal to form part of its lateral border.

Character (1), which appears to be a consequence of character (2), is formulated as a single character (4) by God-

frey and Holmes (1995) and is encorporated into the amended diagnosis as an autapomorphy of C. russelli within

Chasmosaurus. Character (3) is also better formulated by Godfrey and Holmes (1995) as character (5) and has been

included in the amended diagnosis. Character (6) is variable among specimens of C. russelli (Godfrey & Holmes,

1995) and is therefore not included in the amended diagnosis herein.

Use of postcrania in ceratopsid taxonomy. Ceratopsid taxonomy is based almost exclusively on variation in

frill morphology, and a collecting bias for skulls means that the ceratopsid postcranial skeleton is routinely over-

looked in descriptions of new taxa. For example, the holotype of Vagaceratops irvinensis (CMN 41357) comprises

MAIDMENT & BARRETT

a complete, articulated postcranium that has not been described to date, although the skull was described in 2001

(Holmes et al. 2001; the forelimb has been included in some functional studies: Thompson & Holmes 2007; Rega

et al. 2010). Phylogenetic studies of ceratopsians are routinely dominated by skull characters (e.g. Dodson et al.

2004, 85% skull characters; Sampson et al. 2010, 85% skull characters; Longrich 2010, 82% skull characters), and

postcranial characters are usually used only to discriminate between basal ceratopsians and ceratopsids, rather than

between ingroup clades. Because postcrania are rarely described or figured, those postcranial characters that have

been proposed are extremely difficult to operationalize and verify. Likewise, potential new autapomorphies or syn-

apomorphies based on postcrania are almost impossible to confirm from the existing literature on ceratopsians.

Nevertheless, examination of a range of ceratopsid postcranial skeletons as part of a wider study investigating mus-

culature in ornithischians has revealed a number of previously unrecognised postcranial features that may prove to

be synapomorphies for Ceratopsidae, Chasmosaurinae and Centrosaurinae. Furthermore, postcranial features

apparently unique to particular specimens may be autapomorphic and warrant further investigation.

TABLE 4. Ceratopsian specimens examined.

Taxon Specimen number

Psittacosaurus sinensis IVPP V738

Psittacosaurus sinensis IVPP V740-741

Psittacosaurus sp. IVPP V120888

Psittacosaurus sp. (six individuals) IVPP V14341

Yinlong downsi IVPP V14530

Yinlong downsi IVPP WCW-06A-38

Archaeoceratops oshimai IVPP V11114

Archaeoceratops oshimai IVPP V11115

Protoceratops andrewsi IVPP unregistered

Protoceratops andrewsi AMNH 6424

Protoceratops andrewsi AMNH 6466

Leptoceratops gracilis CMN 8889

Chasmosaurus belli NHMUK R4948

Chasmosaurus belli ROM 843

Chasmosaurus belli CMN 2245

Chasmosaurus russelli CMN 2280

Chasmosaurus russelli TMP 1983.25.01

Chasmosaurus sp. TMP 1981.19.175

Chasmosaurus sp. UALVP 40

Chasmosaurus sp. ROM 839

Vagaceratops irvinensis CMN 41357

Vagaceratops irvinensis TMP 1987.45.01

‘Anchiceratops longirostris' CMN 8547

Triceratops prorsus NHMUK R3886-8

Centrosaurus apertus ROM 767

Centrosaurus apertus ROM 1426

Styracosaurus albertensis CMN 344

Pachyrhinosaur sp. TMP 2002.76.01

A NEW SPECIMEN OF CHASMOSAURUS BELLI

In addition to the postcranial characteristics of ceratopsids listed by Dodson et al. (2004), Sampson et al.

(2010) and Longrich (2010), the humeri of all ceratopsids examined (Table 4) bore a triceps fossa posterolaterally

on the deltopectoral crest (Fig. 23), and a foramen, possibly representing a scar for the m. latissimus dorsi on the

posteromedial humerus. In the centrosaurine taxa examined, the triceps fossa was shallow and poorly defined, and

the latissimus foramen was located level with the apex of the deltopectoral crest. In lateral view, the deltopectoral

crest was concave upwards. The acromial process of the scapula, which is triangular in shape in ceratopsids, arose

on the proximal part of the scapula and was in general poorly developed. These features differ in all chasmosaurine

taxa examined. The triceps fossa was much more clearly defined and deeper, while the latissimus foramen was

located proximal to the apex of the deltopectoral crest. The deltopectoral crest was straight in lateral view, and the

acromial process of the scapula was larger, occupying more of the blade. In addition, a prominent groove was

observed under the sacral rod in chasmosaurines, a feature apparently less well pronounced in centrosaurines (Leh-

man 1989).

The axial skeleton of Chasmosaurus. Dodson et al. (2004) stated that ceratopsids had 10 cervical, 12 dorsal

and 10 sacral vertebrae. The presacral axial skeleton of three specimens of Chasmosaurus, CMN 2245, ROM 843

(C. belli) and CMN 2280 (C. russelli) is completely known but has not been described in detail (although see Mal-

lon & Holmes 2006 for a brief description of some elements of CMN 2254 and CMN 2280). The presacral verte-

bral formula appears to be rather more variable than indicated by Dodson et al. (2004): ROM 843 has eight

cervicals, 13 dorsals, and three dorsosacrals fused to the sacral rod; CMN 2245 has eight cervicals, 13 dorsals, and

one dorsosacral fused to the sacral rod; NHMUK R4948 has eight cervicals, a dorsal column of at least nine verte-

brae and two dorsosacrals. These specimens are all considered referable to C. belli. CMN 2280, the only specimen

referable to C. russelli that preserves postcrania, has eight cervicals, 10 dorsals and an unknown number of dor-

sosacrals. If it is assumed that the four sacral vertebrae that bear sacral ribs (the true sacrals) are homologous in

each specimen, ROM 843 clearly possesses two more presacral vertebrae (24) than CMN 2245 (22). It is possible

that two vertebrae were not recovered during the excavation of CMN 2245, but Sternberg (1927: 69) reported that

the specimen was found in articulation, consisting of “…skull and jaws complete, column complete and articulated

to the fourth sacral…”. It is extremely unlikely that presacral vertebral counts vary among individuals to the degree

seen in Chasmosaurus belli, or with ontogeny, and it is not unreasonable to suggest that this difference is of taxo-

nomic importance, suggesting that CMN 2245 and ROM 843 are different species, if not different genera.

Examination of a range of other ceratopsid taxa suggests that presacral vertebral numbers are far more variable

than previously realised. Centrosaurus apertus had 24 presacrals (Brown 1917), while Styracosaurus albertensis

(CMN 344) had at least 23. Twenty-three presacrals are also present in Triceratops (Hatcher et al. 1907) and Pen-

taceratops (Wiman 1930). ‘Anchiceratops’ had 23 presacral vertebrae, not including dorsosacrals, the exact num-

ber of which cannot be determined (J. C. Mallon, pers. comm. 2011).

Conclusion

NHMUK R4948 is referable to Chasmosaurus belli and is unique among specimens of Chasmosaurus because it

preserves an almost complete, disarticulated skull, allowing an examination of cranial elements in multiple views

for the first time. The disarticulated and well preserved braincase is the first to be described in detail for Chasmo-

saurus and allows identification of cranial foramina and comparisons with other ceratopsians to be made. Associ-

ated postcranial elements are also preserved, including the best preserved vertebrae in any Chasmosaurus

specimen, and uncrushed limb elements.

Recent descriptions of new chasmosaurine genera have resulted in a doubling of the generic diversity of chas-

mosaurines in the Campanian. Many of these genera differ from each other only by characteristics of frill morphol-

ogy and number and shape of parietal and squamosal epiossifications. Several specimens previously considered to

be Chasmosaurus have been removed from the genus and designated as new genera. As a result, the features that

distinguish Chasmosaurus from other Campanian chasmosaurines have become confused and unclear. However,

the genus Chasmosaurus is diagnosable based on a unique combination of characters, while species of the genus

are differentiated by the degree of medial emargination of the posterior parietal bar, and characteristics of the epi-

parietals, when preserved. No features are identified that reliably distinguish between ‘Mojoceratops’ and Chasmo-

saurus russelli, so the former is considered a junior subjective synonym of the latter.

MAIDMENT & BARRETT

Although ceratopsian taxonomy is so strongly biased toward skull characteristics, it is possible that further

autopomorphies might be present in the postcranial skeleton, which needs to be documented in more detail. Here,

we demonstrate that postcranial material is potentially useful in ceratopsid taxonomy, and that postcranial charac-

ters might help to distinguish between competing taxonomic hypotheses. New phylogenetics software such as TNT

allows the coding of continuous data in phylogenetic analyses, and quantitative characters are increasingly becom-

ing used in cladistic analyses of fossil vertebrates (e.g. Maidment et al. 2008; Upchurch, 2009; Ketchum & Benson

2010). Information derived from postcranial quantitative data analyses will also allow ontogenetic trends to be bet-

ter understood. While it would be premature and unwise to entirely revise the taxonomy of Chasmosaurus based on

vertebral number, given that most specimens are based only upon skulls, the case outlined above demonstrates that

some caution may be necessary with respect to the utility of variation in frill morphology for taxonomy. We hope

that this contribution will encourage ceratopsid workers to pay more attention to the postcranial skeleton, so that

discrete qualitative and continuous quantitative characters can be used in taxonomic and phylogenetic studies on

ceratopsids, and that existing postcranial material in museum collections can be reappraised more rigorously.

Acknowledgements

We thank C. Collins (NHMUK) for conserving the specimen; P. Hurst (NHMUK) for photography, and S. Wills for

assistance with cleaning and re-housing the specimen. The following people allowed access to specimens in their

care and hospitality during collections visits: D. C. Evans, K. Seymour, and B. Iwama (ROM), M. Currie, K. Shep-

herd, A. Macdonald, and C. Kennedy (CMN) and D. Henderson (TMP). Thanks to J. C. Mallon (University of Cal-

gary), D. H. Tanke (Royal Tyrrell Museum) and C. Brown (University of Toronto) for ceratopsian-based

discussion. Reviewers J. C. Mallon (University of Calgary) and A. A. Farke (Raymond Alf Museum of Paleontol-

ogy) and Editor R. B. J. Benson (University of Cambridge) provided detailed comments that greatly improved this

manuscript. SCRM is funded by Natural Environment Research Council grant number NE/G001898/1 awarded to

PMB.

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Transitional evolutionary forms and stratigraphic trends in chasmosaurine ceratopsid dinosaurs : evidence from the Campanian of New Mexico

Preprint

Full-text available

Nov 2019

Three new chasmosaurines from the Kirtland Formation (~75.0 - 73.4 Ma), New Mexico, form morphological and stratigraphic intermediates between Pentaceratops (~74.7 - 75Ma, Fruitland Formation, New Mexico) and Anchiceratops (~72 - 71Ma, Horseshoe Canyon Formation, Alberta). The new specimens exhibit gradual enclosure of the parietal embayment that characterizes Pentaceratops, providing support for the phylogenetic hypothesis that Pentaceratops and Anchiceratops are closely related. This stepwise change of morphologic characters observed in chasmosaurine taxa that do not overlap stratigraphically is supportive of evolution by anagenesis. Recently published hypotheses that place Pentaceratops and Anchiceratops into separate clades are not supported. This phylogenetic relationship demonstrates unrestricted movement of large-bodied taxa between hitherto purported northern and southern provinces in the Late Campanian, weakening support for the hypothesis of extreme faunal provincialism in the Late Cretaceous Western Interior.

A new chasmosaurine ceratopsid from the Upper Cretaceous (Campanian) Farmington Member of the Kirtland Formation, New Mexico

Article

Full-text available

Aug 2022

A nearly complete skull of a new ceratopsid dinosaur, Bisticeratops froeseorum, is described from the Farmington Member of the Kirtland Formation (late Campanian, Upper Cretaceous) of New Mexico. Bisticeratops is distinguished by several diagnostic cranial characters, including those of the premaxilla (stepped dorsal margin), maxilla (short jugal process lacking the ventral pocket-like fossa), jugal (short maxillary process of the jugal), and palpebral ornamentation (short with moderate ornamentation). It differs from other known chasmosaurines, especially from stratigraphically older species in the same geographic region, Pentaceratops sternbergi and Titanoceratops ouranos, by a strongly reduced jugal process of the maxilla and an unusual maxilla/jugal contact, which forms a shallow, triangular-shaped lateroposteriorly concave sulcus. A phylogenetic analysis recovers Bisticeratops froeseorum as sister species to the unnamed Almond Formation chasmosaurine and as a member of a potentially new southern clade of chasmosaurines, outside the Triceratopsini, and distinct from other southern Laramidian chasmosaurines such as Pentaceratops. The dinosaur fauna of the Farmington Member is comparatively poorly understood, especially compared to stratigraphically older faunas in the San Juan Basin. Therefore, the new, presumably rare species Bisticeratops froeseorum, together with several recently named and described chasmosaurines such as Navajoceratops sullivani, Sierraceratops turneri, and Terminocavus sealeyi, add to the diversity and disparity of chasmosaurines and provides further support for latitudinal variation in the ceratopsid fauna during the Late Cretaceous interval in the Western Interior Basin of North America.

Sierraceratops turneri, a new chasmosaurine ceratopsid from the Hall Lake Formation (Upper Cretaceous) of south-central New Mexico

Article

Sep 2021
CRETACEOUS RES

The horned dinosaurs (Ceratopsidae) were a diverse family of herbivorous dinosaurs originating in the Late Cretaceous in western North America (Laramidia). As one of the most species-rich dinosaur groups, their diversity and distribution are important to understanding Cretaceous dinosaur evolution. Ceratopsids have previously been hypothesized to have high levels of endemism despite inhabiting a relatively small land mass with few barriers to dispersal. Here, we document a new chasmosaurine ceratopsid, Sierraceratops turneri gen. et sp. nov., from the Upper Cretaceous (latest Campanian–Maastrichtian) Hall Lake Formation of south-central New Mexico, consistent with the hypothesis that southern Laramidia supported an endemic dinosaur fauna. Sierraceratops is distinguished by its relatively short, robust, and mediolaterally compressed postorbital horns; a flattened medial ridge on the posterior end of the pterygoid; a jugal with pronounced anterior flanges; a long pyramid-shaped epijugal horncore; a D-shaped cross section of the median parietal bar; and a squamosal with a pointed tip and low episquamosal ossifications. Phylogenetic analysis recovers Sierraceratops as sister to Bravoceratops and Coahuilaceratops, part of a clade endemic to the southwestern United States and Mexico. Sierraceratops adds to the diversity and disparity of the Chasmosaurinae in the Late Cretaceous and provides additional evidence for Laramidian endemism. Together with Sierraceratops, the Hall Lake Formation dinosaur fauna suggests that the latest Cretaceous of southern Laramidia was characterized by endemic clades and distinct community structures.

A Hadrosauroid Vertebra from the Upper Cretaceous Izumi Group, Kagawa Prefecture, Japan

Article

Jul 2024
Paleontol Res

Of the four main Japanese islands, Late Cretaceous dinosaur fossils have been discovered in Hokkaido, Honshu, and Kyushu. Here, we report the first Late Cretaceous dinosaur from the remaining main island Shikoku, an isolated dorsal vertebra from the upper Campanian Hiketa Formation (Izumi Group) in Sanuki, Kagawa Prefecture. The vertebra is incomplete, comprising a robust centrum with a subrectangular profile that is generally characteristic of dinosaurs. Histological examination of the centrum reveals moder- ately packed trabecular bone and the complete absence of pneumatic structures, which precludes referral of the specimen to Saurischia or Pterosauria. Instead, we interpret it as a hadrosauriform ornithischian based on the slightly expanded anterior articular surface of the centrum; heart-shaped outline of the intervertebral surface, resulting from its dorsally wide and ventrally narrow shape; ventral keel; and neural canal partially embed- ded into the centrum. As the ventral positioning of the neural canal is common to Bactrosaurus and higher taxa within Hadrosauriformes, we tentatively refer the specimen to Hadrosauroidea. This discovery provides addi- tional evidence that hadrosauriforms had dispersed into present-day Japan by the Campanian and highlights the potential of the Hiketa Formation to provide additional evidence to improve our understanding of the dino saur diversity at the extreme eastern continental margin of Eurasia.

Lokiceratops rangiformis gen. et sp. nov. (Ceratopsidae: Centrosaurinae) from the Campanian Judith River Formation of Montana reveals rapid regional radiations and extreme endemism within centrosaurine dinosaurs

Article

Jun 2024

The Late Cretaceous of western North America supported diverse dinosaur assemblages, though understanding patterns of dinosaur diversity, evolution, and extinction has been historically limited by unequal geographic and temporal sampling. In particular, the existence and extent of faunal endemism along the eastern coastal plain of Laramidia continues to generate debate, and finer scale regional patterns remain elusive. Here, we report a new centrosaurine ceratopsid, Lokiceratops rangiformis , from the lower portion of the McClelland Ferry Member of the Judith River Formation in the Kennedy Coulee region along the Canada-USA border. Dinosaurs from the same small geographic region, and from nearby, stratigraphically equivalent horizons of the lower Oldman Formation in Canada, reveal unprecedented ceratopsid richness, with four sympatric centrosaurine taxa and one chasmosaurine taxon. Phylogenetic results show that Lokiceratops , together with Albertaceratops and Medusaceratops , was part of a clade restricted to a small portion of northern Laramidia approximately 78 million years ago. This group, Albertaceratopsini, was one of multiple centrosaurine clades to undergo geographically restricted radiations, with Nasutuceratopsini restricted to the south and Centrosaurini and Pachyrostra restricted to the north. High regional endemism in centrosaurs is associated with, and may have been driven by, high speciation rates and diversity, with competition between dinosaurs limiting their geographic range. High speciation rates may in turn have been driven in part by sexual selection or latitudinally uneven climatic and floral gradients. The high endemism seen in centrosaurines and other dinosaurs implies that dinosaur diversity is underestimated and contrasts with the large geographic ranges seen in most extant mammalian megafauna.

Exploring the ceratopsid growth record: A comprehensive osteohistological analysis of Triceratops (Ornithischia: Ceratopsidae) and its implications for growth and ontogeny

Article

Oct 2023
CRETACEOUS RES

Furcatoceratops elucidans, a new centrosaurine (Ornithischia: Ceratopsidae) from the upper Campanian Judith River Formation, Montana, USA

Article

Jul 2023
CRETACEOUS RES

Postcranial description of Wendiceratops pinhornensis and a taphonomic analysis of the oldest monodominant ceratopsid bonebed

Article

Aug 2022

The early centrosaurine ceratopsid, Wendiceratops pinhornensis, was discovered in Alberta, Canada in a medium density monodominant bonebed from the Oldman Formation (mid-Campanian, ~79 Ma). The bonebed contains abundant, well-preserved, adult-sized and some juvenile-sized postcranial material, allowing for the first description of a number of elements of the postcrania of this basal centrosaurine ceratopsid. The postcranial elements described are generally consistent with postcrania described for more derived centrosaurine taxa. However the rectangular-shaped distal terminus of the ischium previously considered to be an apomorphy of Wendiceratops. is shown to also be present in Medusaceratops, and thus may be a synapomorphy of basal centrsaurines. The bonebed represents a lag deposit within a mudstone-bearing overbank facies and contains individuals from multiple age classes. It contains over 95% ceratopsid remains, with all identifiable elements referable to Wendiceratops. The elements are completely disarticulated, but have undergone little weathering or abrasion (both Stage 0), although the ends of long bones and processes capped by cartilage in life frequently exhibit evidence of wet rot and breakage by hydrological reworking after decomposition. The taphonomy of the bonebed is consist with other monodominant centrosaurine bonebeds that have been interpreted as mass death assemblages preserving evidence of gregarious (herding) behavior. At approximately 79 million years old, the Wendiceratops bonebed is approximately two million years older than other ceratopsid bonebeds indicating that this bonebed is the oldest documented evidence of herding behavior in a ceratopsid.

Transitional evolutionary forms in chasmosaurine ceratopsid dinosaurs: evidence from the Campanian of New Mexico

Article

Full-text available

Jun 2020

Three new chasmosaurines from the Kirtland Formation (~75.0–73.4 Ma), New Mexico, form morphological and stratigraphic intermediates between Pentaceratops (~74.7–75 Ma, Fruitland Formation, New Mexico) and Anchiceratops (~72–71 Ma, Horseshoe Canyon Formation, Alberta). The new specimens exhibit gradual enclosure of the parietal embayment that characterizes Pentaceratops , providing support for the phylogenetic hypothesis that Pentaceratops and Anchiceratops are closely related. This stepwise change of morphologic characters observed in chasmosaurine taxa that do not overlap stratigraphically is supportive of evolution by anagenesis. Recently published hypotheses that place Pentaceratops and Anchiceratops into separate clades are not supported. This phylogenetic relationship demonstrates unrestricted movement of large-bodied taxa between hitherto purported northern and southern provinces in the late Campanian, weakening support for the hypothesis of extreme faunal provincialism in the Late Cretaceous Western Interior.

A paleontologia de Pokémon como ferramenta para a divulgação científica

Article

Full-text available

Dec 2019

The similarity of some morphological characteristics between living beings, mainly animals, and the Pokémon, was one of the formulas for the great success, since 1995, of the famous Pocket Monsters. They were created with the purpose of being collected, thus conferring a range of structures and flashy colorings such as horns, claws, stripes throughout the body, exotic appearance and other characteristics commonly found in animals that, although they belong to a fictitious environment, partially obey the natural and biological laws of the real world. Fossils, uncommon for much of the public, also bring a wide variety of forms that, when compared to the species found today, instills curiosity about palaeodiversity. In the world of Pokémon, the fossils are represented by two groups, the invertebrates with eight taxa, and the vertebrates with 13. About the invertebrates analyzed, a greater variety of taxonomic groups representing different geological periods were identified. This way, the morphological and systematic comparisons help and popularize the interest in paleontology through fossils highlighted in Pokémon, which can be used as a tool for scientific dissemination, promoting greater accessibility of content inside and outside academic environments.

The smallest known triceratops skull: new observations on ceratopsid cranial anatomy and ontogeny

Article

Full-text available

Mar 2006

The discovery of the smallest Triceratops skull (UCMP 154452) provides a new ontogenetic end member for the earliest stage of ceratopsid (Centrosaurinae plus Chasmosaurinae) cranial development. The lack of co-ossification among the parietal, squamosals, postorbitals, quadratojugal arch, and the braincase preserves sutural contacts and bone surfaces that later become obscured in adults. The ability to document the early development and morphology of the horns and frill in Triceratops allows a reevaluation of their functional roles. UCMP 154452 shows that the cranial ornamentation of the frill and the postorbital horns were not restricted to adults, but began at an early age in this species. This evidence supports the hypothesis that the function of ceratopsid horns and frills was potentially important for visual communication and species recognition because in this young form it could not have functioned in sexual display. Although some features of UCMP 154452 anticipate or mimic the adult character states, some braincase characters recapitulate the juvenile and adult stages of more basal neoceratopsians.

Bone resorption, bone lesions, and extracranial fenestrae in ceratopsid dinosaurs: A preliminary assessment

Chapter

Jan 2006

The normal ceratopsid dinosaur skull possesses two parietal fenestrae, but some specimens exhibit extra fenestrae within the parietal and squamosal bones. Previous authors have interpreted these fenestrae as either trauma-related pathology or a nontraumatic, random character. A survey of chasmosaurine ceratopsid skulls shows that squamosal fenestrae in this subfamily are regular in their shape, relative size, and placement. No skulls display any evidence that squamosal fenestrae are due to disease or traumatic injury (except the Diceratops hatcheri type). Squamosal fenestrae are now reported in centrosaurine ceratopsids. Squamosal fenestrae in centrosaurines tend to be irregular in their placement and are accompanied by irregular, pathological bone texture. Two different mechanisms are proposed for the formation of extra fenestrae: nonpathological bone resorption, and pathological osteolytic processes as the result of unknown bone disease. Squamosal fenestrae in many chasmosaurine ceratopsids center on the thinnest portion of the squamosal, suggesting that the fenestrae simply removed structurally unnecessary bone from the frill. Specimens of Cen-trosaurus, Styracosaurus, and cf. Pachyrhinosaurus from Alberta, Canada, suggest that squamosal fenestrae in centrosaurines originated as a small, circular pitted lesion. With continued growth, this lesion may have punched through the squamosal, creating a new fenestra. Similar lesions have been observed throughout the skull in Triceratops and Torosaurus. Their etiology is unknown. Additionally, pitting affects the tips of postorbital horn cores in mature specimens of several centrosaurine taxa, suggesting bone resorption related to advanced age or other factors.

A new species of Chasmosaurus (Dinosauria: Ceratopsia) from the Dinosaur Park Formation of Southern Alberta

Article

Jan 2001
CAN J EARTH SCI

Chasmosaurus irvinensis (sp. nov.) is distinguished from other species of this genus by the possession of a broad snout, absence of a brow horn (the position of which is occupied by a pit or rugosities suggestive of bone resorption), broadly rounded and open jugal notch, subrectangular squamosal, straight posterior parietal bar bearing 10 epoccipitals, eight of which are flattened, strongly curved anterodorsally, and nearly indistinguishably coossified to their neighbours, and small, transversely oriented parietal fenestrae restricted to the posterior portion of the frill. This species, restricted to the upper part of the Dinosaur Park Formation, is significantly younger than the other recognized Canadian Chasmosaurus species, C. belli and C. russelli. Phylogenetic analysis shows that C. irvinensis is most closely related to the other Canadian Chasmosaurus species and more distantly related to Chasmosaurus mariscalensis from Texas.

The anatomy and homologies of the ceratopsid syncervical

Article

Dec 2006

Morphometric analysis of evolutionary trends in the ceratopsian postcranial skeleton

Article

Sep 2004

Brenda Chinnery

The cranial anatomy of ceratopsian (“horned”) dinosaurs is well understood, but the postcranial skeleton has been largely ignored in previous studies of phylogeny, evolution, and function. In order to study morphological differences among ceratopsian postcranial elements and to compare evolutionary patterns, multivariate (Principal Components Analysis) and bivariate methods were used to analyze linear measurement data, and the shape methods Resistant-Fit Theta-Rho Analysis (RFTRA), Least-Squares Theta-Rho Analysis (LSTRA), and Euclidean Distance Matrix Analysis (EDMA) were applied to biological landmark data. Results of the analyses show that size is the primary change through ceratopsian skeleton evolution. Elements display positive allometry, and increasing structural support is evident, especially in the radius and fibula. Phylogenetic distribution of ceratopsian postcrania agrees with the skull material included in recent cladistic analyses. Psittacosaurus elements are in many ways derived relative to those of non-ceratopsid neoceratopsians, and evidence suggests that Psittacosaurus was bipedal, while non-ceratopsid neoceratopsians were not, except maybe for Udanoceratops. With increasing body size, neoceratopsian limbs bowed laterally. The variety of methods allows for unbiased interpretation of results, provides more information than any one method, and provides controls for each other. However, sample sizes are not ideal, and all results should be treated with caution at this time.

The central nervous system of birds: A study of functional morphology

Article