278


Journal of Paleontology 92(2):272–288


12 3 ep 1


ep 1 ep 2 ep 3


ep 2 ep 4


ep 5 ep 3 ep 3


ep 4 ep 5


Figure 4. Comparison of frill ornamentations of (1) Albertaceratops nesmoi in Ryan (2007), (2) previous reconstruction of Medusaceratops lokii frill in Ryan et al. (2010) (gray part represents where the holotype [WDC-DJR-001] corresponds), and (3) new reconstruction of M. lokii frill in this study, mainly based on ROM 73832, ROM 73836, and WDC-DJR-001. Abbreviation: ep, epiparietal.


centrosaurines in that the body exhibits a slight torsion such that its medial portion is located on the dorsal surface of the posterior ramus, but the lateral portion is on the posterior margin (Fig. 3.1–3.3). This epiparietal is proportionally broad and low (114.2 by 15.7mm), but projects forward (Fig. 3.1). Although smaller, it is most similar in morphology and position to the ep 1 of Xenoceratops foremostensis Ryan, Evans, and Shepherd, 2012 (P2 in Ryan et al., 2012) among known centrosaurines. ROM 73836 (Fig. 3.8–3.10).—ROM 73836 is an antero-


lateral segment of the parietal that includes the three lateralmost epiparietals (ep 3–5, also see description of WDC-DJR-001 below) and the squamosal contact of the right lateral ramus. Although all three epiparietals are completely fused, the boundary between the epiparietals and the underlying parietal ramus is clearly delineated (Fig. 3.9). On both dorsal and ventral surfaces, the specimen exhibits the combination of a long-grained texture on the lateral side and adult bone texture on themedial side of the lateral parietal ramus (Fig. 3.10). Note that the long-grained texture is always proximally associated with the mottled texture but not the adult texture in centrosaurines (e.g., Avaceratops, “Brachyceratops,”“Monoclonius,” Coronosaurus brinkmani, Centrosaurus, Styracosaurus, Pachyrhinosaurus) that were examined by Brown et al. (2009). The intriguing mixture of textures on ROM73836may suggest a unique ontogenetic textual transition in Medusaceratops. The squamosal contact is rugose and convex, which is typical of centrosaurines but not known in chasmosaurines (Dodson et al., 2004). The two epiparietals closest to the squamosal contact (ep 4


and 5) have a low and rounded triangular morphology when viewed dorsally, similar to unmodified epiparietals in other centrosaurines. Comparatively, the epiparietal (ep 3) posterior to these has a shorter base and a tall, triangular profile with an acute apex (Fig. 3.9). Ep 3 closely resembles the morphology and proportions of the lateral epiparietals on the holotype of Albertaceratops (TMP 2001.026.0001). All of the epiparietals on ROM 73836 are strongly imbricated (Fig. 3.8), and the


squamosal contact is convex, both of which support a centrosaurine assignment for the Mansfield bonebed material (Dodson et al., 2004). WDC-DJR-001 (holotype, Fig. 2.1–2.4).—Part of the


posterior ramus and all of the lateral ramus of the parietal are preserved on WDC-DJR-001, the holotype of M. lokii. Long- grained bone texture occurs on the lateral side of the lateral ramus, as seen on ROM 73836. The posterior ramus thickness (28.1mm) is also similar to that ofROM73832, the midline bar. Ryan et al. (2010) recognized only three epiparietals on this specimen: from medial to lateral these are; a large, wide-based, and pachyostotic hook; a smaller lobe-shaped process; and a round triangular-shaped epiparietal (Ryan et al., 2010). However, comparisons toROM73832 andROM73836 suggest that WDC-DJR-001 actually possesses two previously uniden- tified epiparietal loci, for a total of five. The additional epiparietals include a diminutive epiparietal


medial to the large pachyostotic hook, which we interpret as ep 1, and an open sutural locus for ep 5. The medialmost epiparietal (ep 1) is represented by a small eminence with a porous texture on the posterodorsal margin of the posterior ramus (Fig. 2.2, 2.3). Although the size of the epiparietal differs from the ep 1 on ROM 73832, the incipient nature and the location of these epiparietals on the holotype and ROM 73832 suggests that they are homologous. Other parietals exhibit the presence of a variably sized epiparietal (ep 1) medial to the enlarged pachyostotic hook (ep 2) (see below for detailed description of WDC-DJR-002, ROM 73837 [Fig. 3.6, 3.7] and TMP 2002.069.0006). The smaller pachyostotic process (ep 3) and the round


triangular-shaped epiparietal (ep 4) are imbricated (Fig. 2.4). The pattern of imbrication indicates that the holotype preserves the left side of the frill, instead of the right side as Ryan et al. (2010) originally described. According to the re-orientation, the large pachyostotic hook (ep 2) slightly flexes ventrally at its base and has a distinct margin of the overgrowth on the ramus ventrally, which is similar to the condition of P1 and 2 of


ep 2


ep 1


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100  |  Page 101  |  Page 102  |  Page 103  |  Page 104  |  Page 105  |  Page 106  |  Page 107  |  Page 108  |  Page 109  |  Page 110  |  Page 111  |  Page 112  |  Page 113  |  Page 114  |  Page 115  |  Page 116  |  Page 117  |  Page 118  |  Page 119  |  Page 120  |  Page 121  |  Page 122  |  Page 123  |  Page 124  |  Page 125  |  Page 126  |  Page 127  |  Page 128  |  Page 129  |  Page 130  |  Page 131  |  Page 132  |  Page 133  |  Page 134  |  Page 135  |  Page 136  |  Page 137  |  Page 138  |  Page 139  |  Page 140  |  Page 141  |  Page 142  |  Page 143  |  Page 144  |  Page 145  |  Page 146  |  Page 147  |  Page 148  |  Page 149  |  Page 150  |  Page 151  |  Page 152  |  Page 153  |  Page 154  |  Page 155  |  Page 156  |  Page 157  |  Page 158  |  Page 159  |  Page 160  |  Page 161  |  Page 162  |  Page 163  |  Page 164  |  Page 165  |  Page 166  |  Page 167  |  Page 168  |  Page 169  |  Page 170  |  Page 171  |  Page 172  |  Page 173  |  Page 174  |  Page 175  |  Page 176  |  Page 177  |  Page 178  |  Page 179  |  Page 180  |  Page 181  |  Page 182  |  Page 183  |  Page 184  |  Page 185  |  Page 186  |  Page 187  |  Page 188  |  Page 189  |  Page 190  |  Page 191  |  Page 192  |  Page 193  |  Page 194  |  Page 195  |  Page 196  |  Page 197  |  Page 198  |  Page 199  |  Page 200  |  Page 201  |  Page 202  |  Page 203  |  Page 204