Fig 1.
Regional map of Chasmosaurus belli, Chasmosaurus russelli, Chasmosaurus sp., and Vagaceratops specimens.
(1) AMNH 5402, CMN 0491, CMN 2245, NHMUK R4948, ROM 843, and YPM 2016; (2) AMNH 5656, CMN 2280, and TMP 1999.055.0292; (3) AMNH 5401, CMN 1254, CMN 8801, CMN 34829, CMN 34832, ROM 839, TMP 1979.011.0147, TMP 1981.019.0175, TMP 1993.082.0001, and UALVP 40; (4) TMP 1987.045.0001; (5) TMP 2009.034.0009; (6) TMP 1997.132.0002; (7) CMN 41357; (8) TMP 2011.053.0046; (9) TMP 1998.102.0008; (10) CMN 8800; (11) CMN 8802; and (12) CMN 8803. Chasmosaurus belli (triangle), C. russelli (inverted triangles), Chasmosaurus sp. (diamonds), and Vagaceratops (circles); DPP = Dinosaur Provincial Park. [planned for page width].
Fig 2.
Parameters of cranial measurements used in this study.
(A) lateral view, and (B) dorsal view (modified from [3]: Fig 5). Asterisks denote parameters used in principal component analysis. [planned for column width].
Fig 3.
Chasmosaurus and Vagaceratops frills.
Chasmosaurus: (A) CMN 8800 (Chasmosaurus russelli holotype), (B) CMN 8803, (C) TMP 1999.055.0292, (D) TMP 1997.132.0002, (E) AMNH 5656, (F) CMN 2280, (G) TMP 1983.025.0001 (Mojoceratops perifania holotype), (H) ROM 843 (cast), (I) CMN 2245, (J) CMN 0491 (Chasmosaurus belli holotype), (K) NHMUK R4948 ([7]: Fig 9), (L) TMP 2008.012.0001, (M) YPM 2016, and (N) AMNH 5402. Vagaceratops: (O) TMP 2009.034.0009, (P) TMP 1998.102.0008, (Q) TMP 1987.045.0001, and (R) CMN 41357 (V. irvinensis holotype; cast). Rectangular brackets delimit size of epiossifications; numbers in brackets above frill denote posterior embayment angle. The posterior margin ‘K’ and ‘L’ are not labelled, as this region is either too difficult to interpret (‘K’) or insufficiently preserved (‘L’). In both ‘C’ and ‘D’, the real right fragment is reflected on the left to help reconstruct the frill. Chasmosaurus belli (triangle), C. russelli (inverted triangles), Chasmosaurus sp. (diamond), and V. irvinensis (circles). Plaster reconstruction = grey. [two pages, each planned for page width].
Fig 4.
Stratigraphic positions of chasmosaurine specimens from the Dinosaur Park Formation.
Specimens above the regional disconformity (0 m) separating the Dinosaur Park and Oldman formations (error bars ±5 m). Specimens are shown on right in ascending stratigraphic order, in dorsal and lateral views. CMN 41357 was collected either at the base of or within the Lethbridge Coal Zone (LCZ), and TMP 1998.102.0008 was collected somewhere within the LCZ, as indicated by the vertical dashed lines. DPFZ = Dinosaur Park Faunal Zone ([15, 16]). Plaster reconstruction = grey. [planned for page width].
Fig 5.
Specimen-based phylogenetic analysis of Chasmosaurus and Vagaceratops specimens, using 153 cranial and postcranial characters.
Strict consensus trees of: (A) Chasmosaurus, Vagaceratops, and other taxa included in Campbell [22] (5410 most parsimonious trees, tree length (TL) = 293 steps, consistency index (CI) = 0.61, retention index (RI) = 0.76); (B) same taxa as ‘A’, but excluding Bravoceratops and Eotriceratops (sensu [48]) (TL = 282 steps, CI = 0.63, RI = 0.77); (C) same taxa as ‘B’, but excluding Judiceratops and CMN 1254, the latter of which is the most fragmentary of those specimens missing the species-specific posterior frill region (TL = 279 steps, CI = 0.63, RI = 0.77); (D) same taxa as ‘C’, but excluding AMNH 5401, ROM 839, TMP 1981.019.0175, and UALVP 40, which are also missing the posterior frill region (TL = 276 steps, CI = 0.64, RI = 0.76; 50% majority rule consensus tree on right). Bootstrap replicate frequency and Bremer support (bold) values are shown below each node; only Bootstrap values of 50% or higher are given. Chasmosaurus belli (triangles), C. russelli (inverted triangles), Chasmosaurus sp. (diamonds), and Vagaceratops specimens (circles). [planned for page width].
Fig 6.
Principal component analysis (PCA 1) of Chasmosaurus and Vagaceratops.
PCA of 18 specimens of Chasmosaurus belli (triangles; n = 5), C. russelli (inverted triangles; n = 4), Chasmosaurus sp. (diamonds; n = 7), and Vagaceratops irvinensis (circles; n = 2): (A) PC1 vs. PC2 (52.5% of variance), (B) PC2 vs. PC3 (35.4% of variance), (C) PC3 vs. PC4 (27.6% of variance), and (D) PC4 vs. PC5 (18.3% of variance). [planned for page width].
Fig 7.
Principal component analysis (PCA 2) of Chasmosaurus and Vagaceratops, controlling for ontogenetic differences.
PCA of 18 specimens of Chasmosaurus belli (triangles; n = 5), Chasmosaurus russelli (inverted triangles; n = 4), Chasmosaurus sp. (diamonds; n = 7), and Vagaceratops irvinensis (circles; n = 2): (A) PC1 vs. PC2 (77.2% of variance); (B) PC2 vs. PC3 (17.2% of variance); and (C) PC3 vs. PC4 (12.9% of variance). [planned for column width].
Fig 8.
Ontogenetic transformation series for Chasmosaurus specimens.
Strict consensus of 24 most parsimonious trees (TL = 40 steps, CI = 0.65, RI = 0.81) using 18 cranial characters. Bootstrap replicate frequency is shown above each node (only Bootstrap values of 50% or higher are given); Bremer values are shown above each node, in italics. Characters and associated states (shown in brackets) are shown on left and are mapped at their earliest occurence on the tree. These character state changes represent an inferred sequence of development; however, due to variable timing of character changes amongst specimens, this sequence is an approximation. Below each specimen is the previous taxonomic designation; state reversals are listed below. In box to the right of each specimen, rostral-to-epijugal length (top, bold, in mm; parameter 16, Fig 2) and squamosal length (bottom, in mm; parameter 19, Fig 2) are given for skull size reference, where preserved. Although TMP 1998.128.0001 was not included in the analysis, its basal position on the tree is indicated by a dashed line, inferred based on its small size and possession of immature character states (12(0), 13(0), and 14(0)). Boxes at bottom delimit age classes (see text for definitions); numbers below each box represent rostral-to-epijugal lengths (in mm) for each age class (est. = estimated). [planned for page width].
Fig 9.
Ontogenetic changes in squamosal of Chasmosaurus.
Increase in length/width ratio (character 12), changing outline of lateral margin (character 13), articulation (character 14) and remodeling (character 15) of episquamosals: (A) TMP 1998.128.0001 (flipped), (B) CMN 1254, (C) AMNH 5656, (D) AMNH 5401, (E) NHMUK R4948 (courtesy of J. Mallon), and (F) CMN 8800. Blank arrows = unadorned episquamosal loci; solid arrows = articulated episquamosals; solid arrows with asterisks = remodeled episquamosals. Chasmosaurus belli (triangle), Chasmosaurus russelli (inverted triangles) and Chasmosaurus sp. (diamonds). [planned for page width].
Fig 10.
Ontogenetic changes in skull roof of Chasmosaurus.
Articulation between: premaxillae (character 5), premaxilla-nasal (character 6), nasals (character 7), nasal-frontal (character 8), frontals (character 9), and frontal-postorbital (character 10): (A–B) CMN 1254, (C–D) UALVP 40, (E–F) AMNH 5402, (G–H) AMNH 5401 (courtesy of J. Mallon), and (I–J) CMN 2280. Solid lines = open sutures; dotted lines = closed sutures; plaster reconstruction = grey. Chasmosaurus belli (triangle), Chasmosaurus russelli (inverted triangle), and Chasmosaurus sp. specimens (diamonds). [planned for page width].
Fig 11.
Ontogenetic changes in nasal horncore of Chasmosaurus.
Articulation of epinasal with nasals (character 2) and subsequent resorption of nasal horncore (character 3): (A) epinasal disarticulated (CMN 1254; flipped), (B) epinasal articulated with suture open (CMN 2245), (C) epinasal articulated with suture closed, and (D) (YPM 2016) and (E) (CMN 8800) horncore partly resorbed. Arrows = confirmed or inferred epinasals; arrows with asterisks = resorbed surfaces; dashed lines = confirmed or inferred sutural contacts; plaster reconstruction = grey. Chasmosaurus belli (triangles), Chasmosaurus russelli (inverted triangle), and Chasmosaurus sp. specimens (diamond). [planned for column width].
Fig 12.
Ontogenetic changes in parietal of Chasmosaurus.
Thinning of lateral bar (character 16), articulation (character 17) and reorientation (character 18) of epiparietals (character 18): (A) CMN 1254, (B) AMNH 5656, (C) TMP 1983.025.0001, and (D) CMN 2280 (flipped). Blank triangles = unadorned epiparietal loci; solid triangles = articulated epiparietals; long triangles = epiparietals (or loci) oriented posteriorly in the plane of the frill, and short triangles = epiparietals oriented anterodorsally. Lines represent extent of lateral bars. Chasmosaurus russelli (inverted triangles) and Chasmosaurus sp. (diamond). [planned for column width].
Fig 13.
Schematic of an idealized chasmosaurine snout ([11]: Fig 8, modified).
Centrosaurine features (i.e., not present in chasmosaurines) are indicated by asterisks (*) ([35]: fig 16.1). [planned for column width].
Fig 14.
Ontogenetic changes in rostral of Chasmosaurus.
Articulation of rostral with premaxillae (character 1): (A) rostral separate and missing (UALVP 40); (B) rostral articulated, but dorsal suture open (AMNH 5402); and (C) rostral articulated with suture closed (YPM 2016). Arrows = rostra; dashed lines = sutural contacts; plaster reconstruction = grey. Chasmosaurus belli (triangles) and Chasmosaurus sp. specimens (diamond). [planned for page width].
Fig 15.
Ontogenetic changes in epijugal of Chasmosaurus.
Articulation of epijugal with jugal and quadratojugal (character 11): (A) epijugal disarticulated (UALVP 40), (B) epijugal articulated with open suture (ROM 839) and (C) epijugal articulated with closed suture (TMP 1981.019.0175). Arrows = epijugals; dashed lines = sutural contacts. Chasmosaurus sp. (diamonds). [planned for column width].
Fig 16.
Frill of CMN 2245 (Chasmosaurus belli).
Frill in: (A) dorsal, (B) anterior, and (C) posterior views. Brackets delimit size of epiossifications; dashed lines = parietal-squamosal contacts. [planned for column width].
Fig 17.
Ontogenetic changes in postorbital horncores of Chasmosaurus.
Resorption of horncores (character 4): (A) (UALVP 40) and (B) (AMNH 5401; flipped), horncore complete; (C) horncore partly resorbed (TMP 1981.019.0175; flipped); and (D) horncore resorbed to base (CMN 8800). Arrows with asterisks = resorbed surfaces; plaster reconstruction = grey. Chasmosaurus russelli (inverted triangle) and Chasmosaurus sp. (diamonds). [planned for column width].
Fig 18.
Scatter plots showing Chasmosaurus postorbital horncore size over skull size.
Horncore length and basal circumference (parameters 1 and 4, Fig 2, respectively) used as proxies for horncore size; rostral-to-epijugal length and squamosal length (parameters 16 and 19, Fig 2, respectively) used as proxies for skull size. Rostral-to-epijugal length vs. horncore length (A) and basal circumference (B); and squamosal length vs. horncore length (C) and basal circumference (D). Chasmosaurus belli (triangles), Chasmosaurus russelli (inverted triangles), and Chasmosaurus sp. specimens (diamonds). [planned for page width].
Fig 19.
Ontogenetic development of postorbital horncores of Dinosaur Park Formation chasmosaurine skulls.
Horncores arranged by ontogenetic stage; age classes and node numbers on left correspond to those given in the ontogenetic tree (Fig 8). Proposed “long horncore” (left) and “short horncore” (right) ontogenetic trajectories. Arrows = resorbed postorbital horncores; plaster reconstruction = grey. Image of ROM 843 courtesy of J. Mallon; image of NHMUK R4948 modified from Maidment & Barrett ([7]: Fig 4); images of CMN 1254, NHMUK R4948, ROM 839, and TMP 1981.019.0175 flipped. [planned for page width].
Fig 20.
Skull of CMN 8801 (Chasmosaurus sp.).
Skull in (A) right lateral view. Snout in (B) right lateral view; brackets and arrows delimit extent of breakage along the triangular process and septal flange of the premaxillae. Skull roof in (C) dorsal view; corner brackets delimit region shown in (D) and (E). Dashed line in ‘E’ represents the extent of the frontoparietal fontanelle, which is infilled with sediment. [planned for page width].
Fig 21.
Frill of YPM 2016 (Chasmosaurus belli).
Frill in: (A) dorsal view, (B) dorsal view of right half, (C) posterior view of right posterior parietal bar, and (D) posterior view of medial portion of right posterior bar. Brackets delimit size of epiossifications; dashed line = parietal-squamosal contact; plaster reconstruction = grey. [planned for page width].
Fig 22.
Frill of AMNH 5402 (Chasmosaurus belli).
Frill in: (A) dorsal, (B) dorsal (left side), (C) oblique dorsal (left side), (D) posterior (left side), and (E) dorsal (right side) views. Brackets delimit size of epiossifications; dashed line = parietal-squamosal contact; arrows = inferred epiparietal loci; plaster reconstruction = grey. [planned for column width].