O’Gorman et al.—A new pliosaurid from Patagonia Both palatines are preserved although with displacement,
the right one almost in vertical position. The right palatine projects anteriorly and participates in the posterior margin of the internal naris (Fig. 3). It has pits and small sulci on the ventral surface. The suborbital fenestra is not well defined (Fig. 2). As in other pliosauroids, the pterygoids form a central plate
with anterior, lateral, and quadrate rami. No anterior inter- pterygoid vacuity is present. The space between the pterygoids is a consequence of breakage during preparation. In palatal view, the contact between the pterygoid and vomer forms a deep interdigitate suture (Fig. 2). Lateral to the central plate the pterygoids form two square lateral rami that contact the ectop- terygoids (Fig. 2.2). Caudally to the central plate, the pterygoids form a posterior interpterygoid vacuity that is longer than wide (110mm long x 40mm wide; Fig. 2). The lateral margin of the posterior interpterygoid vacuity forms sharp convex margins (Fig. 2). The quadrate rami of the pterygoids are relatively long and contact the quadrate posteriorly (Fig. 2). In dorsal view, the quadrate rami form relatively tall walls that enclose the basicranium (Fig. 2). The pterygoids meet each other caud- ally to the posterior interpterygoid vacuity and form a long posterior pterygoid symphysis that totally covers the ventral surface of the basioccipital (Fig. 3). The posterior pterygoid symphysis shows a midline groove following the middle suture (Fig. 3). The posterior pterygoid symphysis is separated from the general palatal surface by a marked step that generates a lateral ridge (Fig. 3). Posterior to the posterior interpterygoid vacuity, the parasphenoid is covered ventrally by the pterygoid (Fig. 3). Only the right ectopterygoid is preserved. It is plate-like with
a concave medial margin. The natural position and exact relation with the pterygoid is unknown due to displacement (Fig. 2). Braincase.—The braincase is partially preserved in its
natural position. The epipterygoids are at both sides of the posterior interpterygoid vacuity, although the left one is better preserved. The epipterygoid is low and is located ante- riomedially to the high walls formed by the pterygoids that enclose the basicranium (Fig. 2). The parasphenoid is a long element that divides the pos-
position, forming the floor of the braincase (Fig. 2). All posterior dorsal and anterior surfaces are rugose, indicating the presence of chondral tissue covering the ossified preserved sector (Figs. 2.1, 5.3). However, the lateral surface and the posterior lateral pro- cesses show smooth bone surfaces. The lateral surfaces of the basisphenoid are anteroposteriorly concave and seem to bear a foramen for the internal carotid, but it is covered by matrix that prevents observation. The anterodorsal area bears a deep
terior interpterygoid vacuity into two portions ventrally cover- ing the basisphenoid and basioccipital (Fig. 3). The anterior limit is affected by breakage, but it shows a cultriform process that becomes thinner and overlaps the pterygoid for a short distance. Posteriorly, the parasphenoid is covered ventrally by the posterior interpterygoid symphysis (Fig. 3). No sharp ventral medial keel is observed but the parasphenoid shows a triangular cross section with the apex facing ventrally. Additionally, there is a small convexity located on the posterior third (Fig. 3). In ventral view, the posterior end shows a small pit limited caudally by the posterior interpterygoid symphysis (Fig. 3). The basisphenoid is a stocky element preserved in its natural
247
transversely elongated depression interpreted as the sella turcica, for reception of the hypophysis (Figs. 2, 5.3). The floorofthis cavity shows a medial keel and lateral depressions, probably the foramina for the internal carotids. A deep medial groove is observed along the dorsal surface of the
basisphenoid.This groove generates the posterior notch in the clivus (basisphenoid body). This notch is observed in other plesiosaurs such as Thalassiodracon hawkinsi Owen, 1840 and Eurycleidus arcuatus Owen, 1840 (O’Keefe, 2001, fig. 4; Benson et al., 2013). Lateral and posterior to the sella turcica, there is a depression on the dorsal surface of the basisphenoid, probably for the anterior process of the prootic (Fig. 5.3). The lateroventral surface of the basisphenoid projects into a pair of basipterygoid processes that contact the pterygoids (Fig. 2). The basisphenoid has two posterolateral wall- like processes that lateroventrally embrace the basioccipital and laterally limit a wide unossified space between the basioccipital and basisphenoid (Figs. 2, 5.3). The basioccipital is visible in dorsal, ventral, and posterior
views (Figs. 2, 3, 4.1, 4.2). In dorsal view, the floor of the neural canal is subtriangular (Fig. 2). The exoccipital facets are strongly laterally inclined (Fig. 2). Each facet is divided into anterior and posterior parts by a slightly narrow bridge (Figs. 2, 5.3). The posterior one probably receives the exoccipital whereas the ante- rior receives the opistothic. The entire anterior surface of the basioccipital shows a lobulate texture, indicating the presence of chondral tissue. The contact between basioccipital and basi- sphenoid is limited to a lateral contact with the posterolateral processes of the basisphenoid (Figs. 2, 5.3). The occipital condyle is formed only by the basioccipital. The condyle is strongly con- vex, with a slight central depression, but without a marked notochordal pit (Fig. 4.1, 4.2). The condyle is not limited by a marked neck, but the entire ventral surface shows a wide and diffuse concave area that limits the condylar articular surface. The basioccipital tubera are ventrolaterally directed, but they do not contact the dorsal surface of the pterygoid of the posterior pterygoid symphysis (Fig. 4.1, 4.2). Indeterminate bones.—Two indeterminate bones are
probably part of the cranium. The largest is located on the left subtemporal fossa and shows a dorsal projection cut by a fracture; the same element is concave in palatal view. Other elements located close to the glenoid cavity seem to be part of the opistothic or prootic, but poor preservation impedes a secure identification (Fig. 2). Mandible.—The mandible is almost complete, missing only
part of the symphysis that includes the first four alveoli for functional teeth of the right side and five of the left (Fig. 4.3–4.5). The anterior sector of the symphysis is wider than high and shows no lateral expansion. In lateral view, the ventral margin of the symphysis shows a marked change of inclination between the third and fourth alveoli (Fig. 4.4). This sector has no ventral keel. The ventral and lateral surfaces are pierced by foramina. Because the medial area of the symphysis is lost, the total number of
part of the symphysis and the coronoid eminences; because the palate is enclosed between the mandibular rami, some parts of the medial surface of the mandibular rami are not visible (Figs. 2, 3). The mandibular symphysis is relatively long, with straight lateral borders. Several teeth are partially preserved, but almost all of them are severely damaged and without enamel. The dentaries are preserved in two parts. One is the anterior
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
